Table of Contents
7.1.1 General 3
7.1.1.1 Scope 3
7.1.1.2 Process Description13 4
7.1.2 Emission Mechanisms And Control2"8 8
7.1.2.1 Fixed Roof Tanks 8
7.1.2.2 Floating Roof Tanks 9
7.1.3 Emission Estimation Procedures 14
7.1.3.1 Routine Losses From Fixed Roof Tanks8"14'22 15
7.1.3.2 Routine Losses From Floating Roof Tanks3"513"17 28
7.1.3.3 Floating Roof Landing Losses21 34
7.1.3.4 Tank Cleaning Emissions23 43
7.1.3.5 Flashing Loss25 51
7.1.3.6 Variable Vapor Space Tanks18 52
7.1.3.7 Pressure Tanks 53
7.1.3.8 Variations Of Emission Estimation Procedures 54
7.1.4 Speciation Methodology22 58
Figure 7.1-1. Typical fixed-roof tank.20 63
Figure 7.1-2. External floating roof tank (pontoon type).20 64
Figure 7.1-3. External floating roof tank (double deck).20 65
Figure 7.1-4. Internal floating roof tank.20 66
Figure 7.1-5. Domed external floating roof tank.20 67
Figure 7.1-6. Vapor-mounted primary seals20 68
Figure 7.1-7. Liquid-mounted and mechanical shoe primary seals.20 69
Figure 7.1-8. Secondary rim seals.20 70
Figure 7.1-9. Deck fittings for floating roof tanks.20 71
Figure 7.1-10. Deck fittings for floating roof tanks.20 72
Figure 7.1-11. Slotted and unslotted guidepoles.20 73
Figure 7.1-12. Ladder well.20 74
75
Figure 7. l-13a. True vapor pressure of crude oils with a Reid vapor pressure of 2 to 15 pounds per square
inch.4 75
Figure 7. l-14a. True vapor pressure of refined petroleum stocks with a Reid vapor pressure of 1 to 20
pounds per square inch.4 76
Figure 7. l-13b. Equation for true vapor pressure of crude oils with a Reid vapor pressure of 2 to 15
pounds per square inch.4 See note at Figure 7. l-13a 77
Figure 7.1-14b. Equation for true vapor pressure of refined petroleum stocks with a Reid vapor pressure
of 1 to 20 pounds per square inch.4 See note at Figure 7. l-14a 77
Figure 7.1-15. Equations to determine vapor pressure constants A and B for refined 77
Figure 7.1-16. Equations to determine vapor pressure Constants A and B for crude oil stocks.22 78
Figure 7.1-17. Equations for the average daily maximum and minimum liquid surface temperatures.8.... 78
Figure 7.1-18. Reserved 79
Figure 7.1-19. Vapor pressure function.4 80
Figure 7.1-20. Bottom conditions for landing loss.20 81
Figure 7.1-21. Ladder-guidepole combination with ladder sleeve.20 81
Figure 7.1-22. Slotted-guidepole with flexible enclosure.20 82
Table 7.1-1. LIST OF ABBREVIATIONS USED IN THE TANK EQUATIONS 83
Table 7.1-2. PROPERTIES (Mv, Ml, Pva, Wl) OF SELECTED PETROLEUM LIQUIDS 85
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Table 7.1-3. PHYSICAL PROPERTIES OF SELECTED PETROCHEMICALS 86
Table 7.1-4. Height of the Liquid Heel and vapor space under a landed floating roof 93
Table 7.1-5. LEL VALUES FOR SELECTED COMPOUNDS 94
Table 7.1-6. PAINT SOLAR ABSORPTANCE 95
Table 7.1-7. METEOROLOGICAL DATA (Tax, Tan, V, I, Pa) FOR SELECTED U.S. LOCATIONS
96
Table 7.1-8. RIM-SEAL LOSS FACTORS, KRa, KRb, and n, FOR FLOATING ROOF TANKS 132
Table 7.1-9. RESERVED 134
Table 7.1-10. AVERAGE CLINGAGE FACTORS, Cs 135
Table 7.1-11. TYPICAL NUMBER OF COLUMNS AS A FUNCTION OF TANK DIAMETER FOR
INTERNAL FLOATING ROOF TANKS WITH COLUMN- SUPPORTED FIXED ROOFS 135
Table 7.1-12. DECK-FITTING LOSS FACTORS, KFa, K^, AND m, AND TYPICAL NUMBER OF
DECK FITTINGS, NFa 136
Table 7.1-13. EXTERNAL FLOATING ROOF TANKS: TYPICAL NUMBER OF VACUUM
BREAKERS, Nvb, AND DECK DRAINS, Nd 139
Table 7.1-14. EXTERNAL FLOATING ROOF TANKS: TYPICAL NUMBER OF ROOF LEGS, Ni
140
Table 7.1-15. INTERNAL FLOATING ROOF TANKS: TYPICAL NUMBER OF DECK LEGS, Ni,
AND STUB DRAINS, Nd 141
Table 7.1-16. DECK SEAM LENGTH FACTORS (SD) FOR TYPICAL DECK CONSTRUCTIONS
FOR INTERNAL FLOATING ROOF TANKS 141
Table 7.1-17. ROOF LANDING LOSSES FOR INTERNAL FLOATING ROOF TANK WITH A
LIQUID HEEL3 142
a Reference 21.Table 7.1-18. ROOF LANDING LOSSES FOR EXTERNAL FLOATING ROOF
TANK WITH A LIQUID HEEL3 142
Table 7.1-19. ROOF LANDING LOSSES FOR ALL DRAIN-DRY TANKS3 144
Table 7.1-20. TANK CLEANING EQUATIONS - VAPOR SPACE PURGE EMISSIONS3 145
Table 7.1-21. TANK CLEANING EQUATIONS - CONTINUED FORCED VENTILATION
EMISSIONS3 146
7.1.5 Sample Calculations 147
7.1.6 Historical Equations 193
7.1.6.1 Average Daily Vapor Pressure Range 193
7.1.6.2 Fixed Roof Tank Working Loss 193
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7.1 Organic Liquid Storage Tanks
7.1.1 General
7.1.1.1 Scope
Section 7.1 presents emissions estimating methodologies for storage tanks of various types and
operating conditions. The methodologies are intended for storage tanks that are properly maintained and
in normal working condition. The methodologies do not address conditions of deteriorated or otherwise
damaged materials of construction, nor do they address operating conditions that differ significantly from
the scenarios described herein.
Sections 7.1.3.1 and 7.1.3.2 present emissions estimating methodologies for routine emissions
from fixed roof tanks and floating roof tanks. The equations for routine emissions were developed to
estimate average annual losses for storage tanks, but provisions for applying the equations to shorter
periods of time are addressed in Section 7.1.3.8.1. The equations for routine emissions are a function of
temperatures that are derived from a theoretical energy transfer model. In order to simplify the
calculations, default values were assigned to certain parameters in the energy transfer equations. The
accuracy of the resultant equations for an individual tank depends upon how closely that tank fits the
assumptions inherent to these default values. The associated uncertainty may be mitigated by using
measured values for the liquid bulk temperature. The equations for routine emissions are not intended to
include emissions from the following events (these are addressed separately):
a) To estimate losses that result from the landing of a floating roof. A separate methodology is
presented for floating roof landing losses in Section 7.1.3.3.
b) To estimate losses that result from cleaning a tank. A separate methodology is presented for
tank cleaning losses in Section 7.1.3.4.
c) To estimate losses from storage tanks containing unstable liquids, such as tanks which have
air or other gases injected into the liquid (sparging), tanks storing liquids at or above their
boiling point (boiling), or tanks storing liquids which contain gases that have the potential to
flash out of solution (flashing). Section 7.1.3.5 presents methodologies for the estimation of
flashing losses, but Section 7.1 does not present methodologies for the estimation of sparging
or boiling losses.
d) To estimate losses from variable vapor space tanks. Variable vapor space tanks are discussed
in Section 7.1.3.6.
e) To estimate losses from equipment leaks associated with pressure tanks designed as closed
systems without emissions to the atmosphere. Pressure tanks are discussed in Section 7.1.3.7.
Section 7.1.3.8 addresses the following additional scenarios that are outside the scope of the
methodologies for routine emissions presented in Sections 7.1.3.1 and 7.1.3.2.
f) Time periods shorter than one year. Certain assumptions in the equations for routine
emissions are based on annual averages, and thus the equations have greater uncertainty for a
period of time less than a year. Section 7.1.3.8.1 addresses application of the equations to
time periods shorter than one year, with the caveat that a one-month time frame is
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Liquid Storage Tanks
7.1-3
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recommended as the shortest time period for which routine emissions should be estimated
using these methodologies.
g) Internal floating roof tanks with closed vent systems. The equations for routine emissions
from internal floating roof tanks assume that the tank has open vents in the fixed roof.
Section 7.1.3.8.2 addresses estimation of emissions when an internal floating roof tank has
closed pressure/vacuum vents.
h) Case-specific liquid surface temperature determination. Several parameters pertaining to
liquid surface temperature are assigned default values for incorporation into the equations for
routine emissions. Section 7.1.3.8.3 presents methodology to account for these parameters as
variables in the estimation of emissions from a particular storage tank at a particular location.
i) Heating cycles in fixed roof tanks. The equations for standing loss from fixed roof tanks are
based on a daily cycle of warming and cooling of the vapor space due to heat exchange
between the vapor space and ambient air through the shell and roof of the tank. This heat
exchange results in daytime expansion and nighttime contraction of vapors in the vapor
space, with each expansion causing some portion of the vapors to be expelled from the vapor
space. A similar cycle of expansion and contraction of the vapors may be driven by cyclic
heating of the bulk liquid. Section 7.1.3.8.4 provides guidance for adapting the equations for
fixed roof tank standing loss to the case of cyclic heating of the bulk liquid.
Section 7.1.4 presents calculations for applying Raoult's Law to calculate the contribution of
individual chemical species to the total emissions.
Section 7.1.5 presents worked examples, with estimated emissions shown to two significant
figures. This level of precision is chosen arbitrarily, and may overstate the accuracy of the loss estimates
given the uncertainty associated with the multiple parameters affecting emissions from storage tanks.
Section 7.1.6 contains equations that have been used historically to obtain approximate values,
but which have been replaced with more accurate equations.
7.1.1.2 Process Description1"3
Storage tanks containing organic liquids can be found in many industries, including
(1) petroleum producing and refining, (2) petrochemical and chemical manufacturing, (3) bulk storage
and transfer operations, and (4) other industries consuming or producing organic liquids.
Six basic types of designs are used for organic liquid storage tanks: fixed roof (vertical and
horizontal), external floating roof, domed external (or covered) floating roof, internal floating roof,
variable vapor space, and pressure (low and high). A brief description of each tank is provided below.
Loss mechanisms associated with each type of tank are described in Section 7.1.2.
The emission estimating equations presented in Section 7.1 were developed by the American
Petroleum Institute (API). API retains the copyright to these equations. API has granted permission for
the nonexclusive; noncommercial distribution of this material to governmental and regulatory agencies.
However, API reserves its rights regarding all commercial duplication and distribution of its material.
Therefore, the material presented in Section 7.1 is available for public use, but the material cannot be sold
7.1-4
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without written permission from the American Petroleum Institute and the U. S. Environmental Protection
Agency.
7.1.1.2.1 Fixed Roof Tanks
A typical vertical fixed roof tank is shown in Figure 7.1-1. This type of tank consists of a
cylindrical steel shell with a permanently affixed roof, which may vary in design from cone- or dome-
shaped to flat. Losses from fixed roof tanks are caused by changes in temperature, pressure, and liquid
level.
Fixed roof tanks are either freely vented or equipped with a pressure/vacuum vent. The latter
allows the tanks to operate at a slight internal pressure or vacuum to prevent the release of vapors during
small changes in temperature, pressure, or liquid level. Fixed roof tanks may have additional vents or
hatches, referred to as emergency vents, to provide increased vent flow capacity in the event of excessive
pressure in the tank. Of current tank designs, the fixed roof tank is the least expensive to construct and is
generally considered the minimum acceptable equipment for storing organic liquids.
Horizontal fixed roof tanks are constructed for both above-ground and underground service and
are usually constructed of steel, steel with a fiberglass overlay, or fiberglass-reinforced polyester.
Horizontal tanks are generally small storage tanks with capacities of less than 40,000 gallons. Horizontal
tanks are constructed such that the length of the tank is not greater than six times the diameter to ensure
structural integrity. Horizontal tanks are usually equipped with pressure-vacuum vents, gauge hatches and
sample wells, and manholes to provide access.
The potential emission sources for above-ground horizontal tanks are the same as those for
vertical fixed roof tanks. Emissions from underground storage tanks are associated mainly with changes
in the liquid level in the tank. Losses due to changes in temperature or barometric pressure are minimal
for underground tanks because the surrounding earth limits the diurnal temperature change, and changes
in the barometric pressure result in only small losses.
7.1.1.2.2 External Floating Roof Tanks
A typical external floating roof tank (EFRT) consists of an open-top cylindrical steel shell
equipped with a roof that floats on the surface of the stored liquid. The floating roof consists of a deck,
deck fittings, and a rim seal system. Floating decks that are currently in use are constructed of welded
steel plate and are most commonly of two general types: pontoon or double-deck. Pontoon-type and
double-deck-type external floating roof tanks are shown in Figures 7.1-2 and 7.1-3, respectively. With all
types of external floating roof tanks, the roof rises and falls with the liquid level in the tank. External
floating decks are equipped with a rim seal system, which is attached to the deck perimeter and contacts
the tank wall. The purpose of the floating roof and rim seal system is to reduce evaporative loss of the
stored liquid. Some annular space remains between the seal system and the tank wall. The seal system
slides against the tank wall as the roof is raised and lowered. The floating deck is also equipped with deck
fittings that penetrate the deck and serve operational functions. The external floating roof design is such
that routine evaporative losses from the stored liquid are limited to losses from the rim seal system and
deck fittings (standing loss) and any liquid on the tank walls that is exposed by the lowering of the liquid
level associated with the withdrawal of liquid (working loss). Because of the open-top configuration of
this tank, wind effects have a significant impact on evaporative losses from this type of tank.
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7.1-5
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7.1.1.2.3 Internal Floating Roof Tanks
An internal floating roof tank (IFRT) has both a permanent fixed roof and a floating roof inside.
There are two basic types of internal floating roof tanks: tanks in which the fixed roof is supported by
vertical columns within the tank, and tanks with a self-supporting fixed roof and no internal support
columns. Fixed roof tanks that have been retrofitted to use a floating roof are typically of the first type.
External floating roof tanks that have been converted to internal floating roof tanks typically have a self-
supporting roof. Newly constructed internal floating roof tanks may be of either type. The deck in internal
floating roof tanks rises and falls with the liquid level and either floats directly on the liquid surface
(contact deck) or rests on pontoons several inches above the liquid surface (noncontact deck). The
majority of aluminum internal floating roofs currently in service have noncontact decks. A typical internal
floating roof tank is shown in Figure 7.1-4.
Contact decks include (1) aluminum sandwich panels that are bolted together, with a honeycomb
aluminum core floating in contact with the liquid; (2) pan steel decks floating in contact with the liquid,
with or without pontoons; and (3) resin-coated, fiberglass reinforced polyester (FRP), buoyant panels
floating in contact with the liquid. Variations on these designs are also available. The majority of internal
contact floating decks currently in service are aluminum sandwich panel-type or pan steel-type. The FRP
decks are less common. The panels of pan steel decks are usually welded together.
Noncontact decks are the most common type currently in use. Typical noncontact decks are
constructed of an aluminum deck and an aluminum grid framework supported above the liquid surface by
tubular aluminum pontoons or some other buoyant structure. The noncontact decks usually have bolted
deck seams.
Installing a floating roof minimizes evaporative losses of the stored liquid. Both contact and
noncontact decks incorporate rim seals and deck fittings for the same purposes previously described for
external floating roof tanks. Evaporative losses from floating roofs may come from deck fittings,
nonwelded deck seams, and the annular space between the deck and tank wall. In addition, these tanks are
freely vented by circulation vents at the top of the fixed roof. The vents minimize the possibility of
organic vapor accumulation in the tank vapor space in concentrations approaching the flammable range.
An internal floating roof tank not freely vented is considered an internal floating roof tank with a closed
vent system. Emission estimation methods for such tanks are addressed in Section 7.1.3.8.2.
7.1.1.2.4 Domed External Floating Roof Tanks
Domed external (or covered) floating roof tanks have the heavier type of deck used in external
floating roof tanks as well as a fixed roof at the top of the shell like internal floating roof tanks. Domed
external floating roof tanks usually result from retrofitting an external floating roof tank with a fixed roof.
This type of tank is very similar to an internal floating roof tank with a welded deck and a self-supporting
fixed roof. A typical domed external floating roof tank is shown in Figure 7.1-5.
As with the internal floating roof tanks, the function of the fixed roof with respect to emissions is
not to act as a vapor barrier, but to block the wind. The estimations of rim seal losses and deck fitting
losses include a loss component that is dependent on wind speed and a loss component that is independent
of wind speed. When a tank is equipped with a fixed roof, the wind-dependent component is zero due to
the blocking of the wind by the fixed roof, leaving only the wind-independent loss component.
7.1-6
Liquid Storage Tanks
06/18
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The type of fixed roof most commonly used is a self-supporting aluminum dome roof, which is of
bolted construction. Like the internal floating roof tanks, these tanks are freely vented by circulation vents
at the top and around the perimeter of the fixed roof. The deck fittings and rim seals, however, are
identical to those on external floating roof tanks. In the event that the floating deck is replaced with the
lighter IFRT-type deck, the tank would then be considered an internal floating roof tank.
The distinction between a domed external floating roof tank and an internal floating roof tank is
primarily for purposes of recognizing differences in the deck fittings when estimating emissions. In
particular, the domed external floating roof deck typically has significantly taller leg sleeves than are
typical of an internal floating roof deck. The longer leg sleeves of the domed external floating roof deck
have lower associated emissions than the shorter leg sleeves of the internal floating roof deck. While a
domed external floating roof tank is distinct from an internal floating roof tank for purposes of estimating
emissions, the domed external floating roof tank would be deemed a type of internal floating roof tank
under air regulations that do not separately specify requirements for a domed external floating roof tank.
7.1.1.2.5 Variable Vapor Space Tanks
Variable vapor space tanks are equipped with expandable vapor reservoirs to accommodate vapor
volume fluctuations attributable to temperature and barometric pressure changes. Although variable vapor
space tanks are sometimes used independently, they are normally connected to the vapor spaces of one or
more fixed roof tanks. The two most common types of variable vapor space tanks are lifter roof tanks and
flexible diaphragm tanks.
Lifter roof tanks have a telescoping roof that fits loosely around the outside of the main tank wall.
The space between the roof and the wall is closed by either a wet seal, which is a trough filled with liquid,
or a dry seal, which uses a flexible coated fabric.
Flexible diaphragm tanks use flexible membranes to provide expandable volume. They may be
either separate gasholder units or integral units mounted atop fixed roof tanks. A variable vapor space
tank that utilizes a flexible diaphragm will emit standing losses to the extent that the flexible diaphragm is
permeable or there is leakage through the seam where the flexible diaphragm is attached to the tank wall.
A variable vapor space tank will emit vapors during tank filling when vapor is displaced by
liquid, if the tank's vapor storage capacity is exceeded.
7.1.1.2.6 Pressure Tanks
Two classes of pressure tanks are in general use: low pressure (2.5 to 15 psig) and high pressure
(higher than 15 psig). Pressure tanks generally are used for storing organic liquids and gases with high
vapor pressures and are found in many sizes and shapes, depending on the operating pressure of the tank.
Low-pressure tanks are equipped with a pressure/vacuum vent that is set to prevent venting loss from
boiling and breathing loss from daily temperature or barometric pressure changes. High-pressure storage
tanks can be operated so that virtually no evaporative or working losses occur. In low-pressure tanks,
working losses can occur with atmospheric venting of the tank during filling operations. Vapor losses
from low-pressure tanks storing non-boiling liquids are estimated in the same manner as for fixed roof
tanks, with the vent set pressure accounted for in both the standing and working loss equations.
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7.1-7
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7.1.2 Emission Mechanisms And Control2"8
Emissions from the storage of organic liquids occur because of evaporative loss of the liquid
during its storage and as a result of changes in the liquid level. The emission mechanisms vary with tank
design, as does the relative contribution of each type of emission mechanism. Emissions from fixed roof
tanks are a result of evaporative losses during storage (known as breathing losses or standing losses) and
evaporative losses during filling operations (known as working losses). External and internal floating roof
tanks are emission sources because of evaporative losses that occur during standing storage and
withdrawal of liquid from the tank. Standing losses are a result of evaporative losses through rim seals,
deck fittings, and/or deck seams. The loss mechanisms for routine emissions from fixed roof and external
and internal floating roof tanks are described in more detail in this section.
7.1.2.1 Fixed Roof Tanks
The two significant types of routine emissions from fixed roof tanks are standing and working
losses. The standing loss mechanism for a fixed roof tank is known as breathing, which is the expulsion
of vapor from a tank through vapor expansion and contraction that results from changes in temperature
and barometric pressure. This loss occurs without any liquid level change in the tank. The emissions
estimating methodology presented in Section 7.1 assumes the barometric pressure to be constant, and
standing losses from fixed roof tanks are attributed only to changes in temperature. As vapors expand in
the vapor space due to warming, the pressure of the vapor space increases and expels vapors from the
tank through the vent(s) on the fixed roof. If the venting is of a type that is closed in the absence of
pressure, such as a weighted-pallet pressure-vacuum vent, then vapors are assumed to not be expelled
until the pressure in the vapor space exceeds the set pressure of the vent.
The evaporative loss from filling is called working loss. Emissions due to filling operations are
the result of an increase in the liquid level in the tank. As the liquid level increases, the pressure inside the
vapor space increases and vapors are expelled from the tank through the vent(s) on the fixed roof as
described above for standing loss. No emissions are attributed to emptying, in that the increasing size of
the vapor space during emptying is assumed to exceed the rate at which evaporation increases the volume
of vapors. That is, it would be expected that flow through the vents during emptying would be into the
tank, and thus there are no emissions actually occurring during emptying of a fixed roof tank.
A third type of emissions from fixed roof tanks is commonly referred to as flashing losses. This
emission type is not an evaporative loss, but rather involves entrained gases bubbling out of solution
when a liquid stream experiences a pressure drop upon introduction into a storage tank. As such, it occurs
only in storage tanks that receive pressurized liquid streams containing entrained gases. This scenario is
typical of storage tanks receiving liquids from a separator in oil and gas production operations, but does
not typically occur at downstream facilities. Methodologies for estimating flashing losses are discussed
in Section 7.1.3.5.
Fixed roof tank emissions from standing and working vary as a function of tank capacity, vapor
pressure of the stored liquid, utilization rate of the tank, and atmospheric conditions at the tank location.
Several methods are used to control emissions from fixed roof tanks. Emissions from fixed roof
tanks can be controlled by installing an internal floating roof and seals to minimize evaporation of the
7.1-8
Liquid Storage Tanks
06/18
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product being stored. The control efficiency of this method ranges from 60 to 99 percent, depending on
the type of roof and seals installed and on the type of organic liquid stored.
Fixed roof tank emissions may also be reduced by increasing the vent set pressure, and routine
emissions may be eliminated if the vent set pressure is higher than the pressure that develops in the vapor
space during normal operations. See Section 7.1.3.7 for a discussion of estimating emissions from
pressure tanks. However, the structural design of most storage tanks would not normally accommodate
internal pressures of the magnitude required to significantly reduce emissions, and thus vent set pressures
should not be altered without consideration of the tank design including all appropriate safety factors.
Subjecting a storage tank to greater pressure or vacuum than that for which the tank was designed could
potentially result in failure of the tank.
Vapor balancing is another means of emission control. Vapor balancing is probably most
common in the filling of tanks at gasoline service stations. As the storage tank is filled, the vapors
expelled from the storage tank are directed to the emptying gasoline tanker truck. The truck then
transports the vapors to a centralized station where a vapor recovery or control system may be used to
control emissions. Vapor balancing can have control efficiencies as high as 90 to 98 percent if the vapors
are subjected to vapor recovery or control. If the truck vents the vapor to the atmosphere instead of to a
recovery or control system, no control is achieved.
Vapor recovery systems collect emissions from storage tanks and convert them to liquid product.
Several vapor recovery procedures may be used, including vapor/liquid absorption, vapor compression,
vapor cooling, vapor/solid adsorption, or a combination of these.
Vapors from fixed roof tanks may also be collected and combusted. There are several types of
units at facilities used to accomplish this, including various types of flares and thermal oxidation units.
7.1.2.2 Floating Roof Tanks
Routine emissions from floating roof tanks are the sum of working losses and standing losses.
The working loss mechanism for a floating roof tank is also known as withdrawal loss, in that it occurs as
the liquid level, and thus the floating roof, is lowered rather than raised. Some liquid remains on the inner
tank wall surface and evaporates. For an internal floating roof tank that has a column supported fixed
roof, some liquid also clings to the columns and evaporates. Evaporative loss occurs until the tank is filled
and the exposed surfaces are again covered. Standing losses from floating roof tanks include rim seal and
deck fitting losses for floating roof tanks with welded decks, and include deck seam losses for
constructions other than welded decks. Both the working and standing loss mechanisms for floating roof
tanks pertain to the accumulation of vapors in the headspace above the floating roof. It is assumed that
vapors in the headspace will eventually be expelled from the tank, but this emissions estimating
methodology does not address the rate or time at which the vapors actually leave the tank.
Rim seal losses can occur through many complex mechanisms, but for external floating roof
tanks, the majority of rim seal vapor losses have been found to be wind induced. No dominant wind loss
mechanism has been identified for internal floating roof or domed external floating roof tank rim seal
losses. Losses can also occur due to permeation of the rim seal material by the vapor or via a wicking
effect of the liquid, but permeation of the rim seal material generally does not occur if the correct seal
fabric is used. Testing has indicated that breathing, solubility, and wicking loss mechanisms are small in
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7.1-9
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comparison to the wind-induced loss. The rim seal factors presented in this section incorporate all types
of losses.
The rim seal system is used to allow the floating roof to rise and fall within the tank as the liquid
level changes. The rim seal system also helps to fill the annular space between the rim and the tank shell
and therefore minimize evaporative losses from this area. A rim seal system may consist of just a primary
seal or a primary and a secondary seal, which is mounted above the primary seal. Examples of primary
and secondary seal configurations are shown in Figures 7.1-6, 7.1-7, and 7.1-8.
The primary seal serves as a vapor conservation device by closing the annular space between the
edge of the floating deck and the tank wall. Three basic types of primary seals are used on floating roofs:
mechanical (metallic) shoe, resilient filled (nonmetallic), and flexible wiper seals. Some primary seals on
external floating roof tanks are protected by a weather shield. Weather shields may be of metallic,
elastomeric, or composite construction and provide the primary seal with longer life by protecting the
primary seal fabric from deterioration due to exposure to weather, debris, and sunlight. Mechanical shoe
seals, resilient filled seals, and wiper seals are discussed below.
A mechanical shoe seal uses a light-gauge metallic band as the sliding contact with the shell of
the tank, as shown in Figure 7.1-7. The band is formed as a series of sheets (shoes) which are joined
together to form a ring, and are held against the tank shell by a mechanical device. The shoes are
normally 3 to 5 feet deep when used on an external floating roof, and are often shorter when used on an
internal floating roof. Expansion and contraction of the ring can be provided for as the ring passes over
shell irregularities or rivets by jointing narrow pieces of fabric into the ring or by crimping the shoes at
intervals. The bottoms of the shoes extend below the liquid surface to confine the rim vapor space
between the shoe and the floating deck.
The rim vapor space, which is bounded by the shoe, the rim of the floating deck, and the liquid
surface, is sealed from the atmosphere by bolting or clamping a coated fabric, called the primary seal
fabric, which extends from the shoe to the rim to form an "envelope". Two locations are used for
attaching the primary seal fabric. The fabric is most commonly attached to the top of the shoe and the rim
of the floating deck. To reduce the rim vapor space, the fabric can be attached to the shoe and the floating
deck rim near the liquid surface. Rim vents can be used to relieve any excess pressure or vacuum in the
vapor space.
A resilient filled seal can be mounted to eliminate the vapor space between the rim seal and liquid
surface (liquid mounted) or to allow a vapor space between the rim seal and the liquid surface (vapor
mounted). Both configurations are shown in Figures 7.1-6 and 7.1-7. Resilient filled seals work because
of the expansion and contraction of a resilient material to maintain contact with the tank shell while
accommodating varying annular rim space widths. These rim seals allow the roof to move up and down
freely, without binding.
Resilient filled seals typically consist of a core of open-cell foam encapsulated in a coated fabric.
The seals are attached to a mounting on the deck perimeter and extend around the deck circumference.
Polyurethane-coated nylon fabric and polyurethane foam are commonly used materials. For emission
control, it is important that the attachment of the seal to the deck and the radial seal joints be vapor-tight
and that the seal be in substantial contact with the tank shell.
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Wiper seals generally consist of a continuous annular blade of flexible material fastened to a
mounting bracket on the deck perimeter that spans the annular rim space and contacts the tank shell. This
type of seal is depicted in Figure 7.1-6. New tanks with wiper seals may have dual wipers, one mounted
above the other. The mounting is such that the blade is flexed, and its elasticity provides a sealing
pressure against the tank shell.
Wiper seals are vapor mounted; a vapor space exists between the liquid stock and the bottom of
the seal. For emission control, it is important that the mounting be vapor-tight, that the seal extend around
the circumference of the deck and that the blade be in substantial contact with the tank shell. Two types of
materials are commonly used to make the wipers. One type consists of a cellular, elastomeric material
tapered in cross section with the thicker portion at the mounting. Rubber is a commonly used material;
urethane and cellular plastic are also available. All radial joints in the blade are joined. The second type of
material that can be used is a foam core wrapped with a coated fabric. Polyurethane on nylon fabric and
polyurethane foam are common materials. The core provides the flexibility and support, while the fabric
provides the vapor barrier and wear surface.
A secondary seal may be used to provide some additional evaporative loss control over that
achieved by the primary seal. Secondary seals can be either flexible wiper seals or resilient filled seals.
For mechanical shoe primary seals, two configurations of secondary seals are available: shoe mounted
and rim mounted, as shown in Figure 7.1-8. Rim mounted secondary seals are more effective in reducing
losses than shoe mounted secondary seals because they cover the entire rim vapor space. For internal
floating roof tanks, the secondary seal is mounted to an extended vertical rim plate, above the primary
seal, as shown in Figure 7.1-8. However, for some floating roof tanks, using a secondary seal further
limits the tank's operating capacity due to the need to keep the seal from interfering with fixed roof rafters
or to keep the secondary seal in contact with the tank shell when the tank is filled.
The deck fitting losses from floating roof tanks can be explained by the same mechanisms as the
rim seal losses. While the relative contribution of each mechanism to the total emissions from a given
deck fitting is not known, emission factors were developed for individual deck fittings by testing, thereby
accounting for the combined effect of all of the mechanisms.
Numerous fittings pass through or are attached to floating roof decks to accommodate structural
support components or allow for operational functions. Internal floating roof deck fittings are typically of
different configuration than those for external floating roof decks. Rather than having tall housings to
avoid rainwater entry, internal floating roof deck fittings tend to have lower profile housings to minimize
the potential for the fitting to contact the fixed roof when the tank is filled. Deck fittings can be a source
of evaporative loss when they require openings in the deck. The most common components that require
openings in the deck are described below.
1. Access hatches. An access hatch is an opening in the deck with a peripheral vertical well that is
large enough to provide passage for workers and materials through the deck for construction or servicing.
Attached to the opening is a removable cover that may be bolted and/or gasketed to reduce evaporative
loss. On internal floating roof tanks with noncontact decks, the well should extend down into the liquid to
seal off the vapor space below the noncontact deck. A typical access hatch is shown in Figure 7.1-9.
2. Gauge-floats. A gauge-float is used to indicate the level of liquid within the tank. The float
rests on the liquid surface and is housed inside a well that is closed by a cover. The cover may be bolted
06/18
Liquid Storage Tanks
7.1-11
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and/or gasketed to reduce evaporation loss. As with other similar deck penetrations, the well extends
down into the liquid on noncontact decks in internal floating roof tanks. A typical gauge-float and well
are shown in Figure 7.1-9.
3. Gauge-hatch/sample ports. A gauge-hatch/sample port consists of a pipe sleeve through the
deck for hand-gauging or sampling of the stored liquid. The gauge-hatch/sample port is usually located
beneath the gauger's platform, which is mounted on top of the tank shell. A cover may be attached to the
top of the opening, and the cover may be equipped with a gasket to reduce evaporative losses. A cord may
be attached to the cover so that the cover can be opened from the platform. Alternatively, the opening
may be covered with a slit-fabric seal. A funnel may be mounted above the opening to guide a sampling
device or gauge stick through the opening. A typical gauge-hatch/sample port is shown in Figure 7.1-9.
4. Rim vents. Rim vents are used on tanks equipped with a seal design that creates a vapor pocket
in the seal and rim area, such as a mechanical shoe seal. A typical rim vent is shown in Figure 7.1-10. The
vent is used to release any excess pressure that is present in the vapor space bounded by the primary-seal
shoe and the floating roof rim and the primary seal fabric and the liquid level. Rim vents usually consist
of weighted pallets that rest over the vent opening.
5. Deck drains. Currently two types of deck drains are in use (closed and open deck drains) to
remove rainwater from the floating deck. Open deck drains can be either flush or overflow drains. Both
types of open deck drains consist of a pipe that extends below the deck to allow the rainwater to drain into
the stored liquid. Only open deck drains are subject to evaporative loss. Flush drains are flush with the
deck surface. Overflow drains are elevated above the deck surface. Typical overflow and flush deck
drains are shown in Figure 7.1-10. Overflow drains are used to limit the maximum amount of rainwater
that can accumulate on the floating deck, providing emergency drainage of rainwater if necessary. Closed
deck drains carry rainwater from the surface of the deck though a flexible hose or some other type of
piping system that runs through the stored liquid prior to exiting the tank. The rainwater does not come in
contact with the liquid, so no evaporative losses result. Overflow drains are usually used in conjunction
with a closed drain system to carry rainwater outside the tank.
6. Deck legs. Deck legs are used to prevent damage to fittings underneath the deck and to allow
for tank cleaning or repair, by holding the deck at a predetermined distance off the tank bottom. These
supports consist of adjustable or fixed legs attached to the floating deck or hangers suspended from the
fixed roof. For adjustable legs or hangers, the load-carrying element may pass through a well or sleeve
into the deck. With noncontact decks, the well should extend into the liquid. Evaporative losses may
occur in the annulus between the deck leg and its sleeve. A typical deck leg is shown in Figure 7.1-10.
7. Unslotted guidepoles and wells. A guidepole is an antirotational device that is fixed to the top
and bottom of the tank, passing through a well in the floating roof. The guidepole is used to prevent
adverse movement of the roof and thus damage to deck fittings and the rim seal system. In some cases, an
unslotted guidepole is used for gauging purposes, but there is a potential for differences in the pressure,
level, and composition of the liquid inside and outside of the guidepole. A typical guidepole and well are
shown in Figure 7.1-11.
8. Slotted (perforated) guidepoles and wells. The function of the slotted guidepole is similar to the
unslotted guidepole but also has additional features. Perforated guidepoles can be either slotted or drilled
hole guidepoles. A typical slotted guidepole and well are shown in Figure 7.1-11. As shown in this figure,
7.1-12
Liquid Storage Tanks
06/18
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the guide pole is slotted to allow stored liquid to enter. The same can be accomplished with drilled holes.
The liquid entering the guidepole has the same composition as the remainder of the stored liquid, and is at
the same liquid level as the liquid in the tank. Representative samples can therefore be collected from the
slotted or drilled hole guidepole. Evaporative loss from the guidepole can be reduced by some
combination of modifying the guidepole or well with the addition of gaskets, sleeves, or enclosures or
placing a float inside the guidepole, as shown in Figures 7.1-11 and 7.1-22. Guidepoles are also referred
to as gauge poles, gauge pipes, or stilling wells.
9. Vacuum breakers. A vacuum breaker equalizes the pressure of the vapor space across the deck
as the deck is either being landed on or floated off its legs. A typical vacuum breaker is shown in
Figure 7.1-10. As depicted in this figure, the vacuum breaker consists of a well with a cover. Attached to
the underside of the cover is a guided leg long enough to contact the tank bottom as the floating deck
approaches. When in contact with the tank bottom, the guided leg mechanically opens the breaker by
lifting the cover off the well; otherwise, the cover closes the well. The closure may be gasketed or
ungasketed. Because the purpose of the vacuum breaker is to allow the free exchange of air and/or vapor,
the well does not extend appreciably below the deck. While vacuum breakers have historically tended to
be of the leg-actuated design described above, they may also be vacuum actuated similar to the
pressure/vacuum vent on a fixed roof tank such that they do not begin to open until the floating roof has
actually landed. In some cases, this is achieved by replacing the rim vent described above with a
pressure/vacuum vent.
Fittings typically used only on internal floating roof tanks include column wells, ladder wells, and
stub drains.
1. Columns and wells. Some fixed-roof designs are normally supported from inside the tank by
means of vertical columns, which necessarily penetrate an internal floating deck. (Some fixed roofs are
entirely self-supporting from the perimeter of the roof and, therefore, have no interior support columns.)
Column wells are similar to unslotted guide pole wells on external floating roofs. Columns are made of
pipe with circular cross sections or of structural shapes with irregular cross sections (built-up). The
number of columns varies with tank diameter, from a minimum of 1 to over 50 for very large diameter
tanks. A typical fixed roof support column and well are shown in Figure 7.1-9.
The columns pass through deck openings via peripheral vertical wells. With noncontact decks,
the well should extend down into the liquid stock. Generally, a closure device exists between the top of
the well and the column. Several proprietary designs exist for this closure, including sliding covers and
fabric sleeves, which must accommodate the movements of the deck relative to the column as the liquid
level changes. A sliding cover rests on the upper rim of the column well (which is normally fixed to the
deck) and bridges the gap or space between the column well and the column. The cover, which has a
cutout, or opening, around the column slides vertically relative to the column as the deck raises and
lowers. At the same time, the cover may slide horizontally relative to the rim of the well to accommodate
out-of-plumbness of the column. A gasket around the rim of the well reduces emissions from this fitting.
A flexible fabric sleeve seal between the rim of the well and the column (with a cutout or opening, to
allow vertical motion of the seal relative to the columns) similarly accommodates limited horizontal
motion of the deck relative to the column.
2. Ladders and wells. Some tanks are equipped with internal ladders that extend from a manhole
in the fixed roof to the tank bottom. The deck opening through which the ladder passes is constructed
06/18
Liquid Storage Tanks
7.1-13
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with similar design details and considerations to deck openings for column wells, as previously discussed.
A typical ladder well is shown in Figure 7.1-12.
Tanks are sometimes equipped with a ladder/guidepole combination, in which one or both legs of
the ladder is a slotted pipe that serves as a guidepole for purposes such as level gauging and sampling. A
ladder/guidepole combination is shown in Figure 7.1-21 with a ladder sleeve to reduce emissions.
3. Stub drains. Bolted internal floating roof decks are typically equipped with stub drains to allow
any stored product that may be on the deck surface to drain back to the underside of the deck. The drains
are attached so that they are flush with the upper deck. Stub drains are approximately 1 inch in diameter
and extend down into the product on noncontact decks. A typical flush stub drain is shown in
Figure 7.1-10. Stub drains may be equipped with floating balls to reduce emissions. The floating ball acts
as a check valve, in that it remains covering the stub drain unless liquid is present to lift it.
Deck seams in internal floating roof tanks are a source of emissions to the extent that these seams
may not be completely vapor tight if the deck is not welded. A weld sealing a deck seam does not have to
be structural (i.e., may be a seal weld) to constitute a welded deck seam for purposes of estimating
emissions, but a deck seam that is bolted or otherwise mechanically fastened and sealed with elastomeric
materials or chemical adhesives is not a welded seam. Generally, the same loss mechanisms for deck
fittings apply to deck seams. The predominant mechanism depends on whether or not the deck is in
contact with the stored liquid. The deck seam loss equation accounts for the effects of all contributing loss
mechanisms.
7.1.3 Emission Estimation Procedures
The following section presents the emission estimation procedures for fixed roof, external
floating roof, domed external floating roof, and internal floating roof tanks. These procedures are valid for
all volatile organic liquids and chemical mixtures. It is important to note that in all the emission
estimation procedures the physical properties of the vapor do not include the noncondensibles in the
atmosphere but only refer to the volatile components of the stored liquid. For example, the vapor-phase
molecular weight is determined from the weighted average of the evaporated components of the stored
liquid, and does not include the contribution of atmospheric gases such as nitrogen and oxygen. To aid in
the emission estimation procedures, a list of variables with their corresponding definitions was developed
and is presented in Table 7.1-1.
The factors presented in AP-42 are those that are currently available and have been reviewed and
approved by the U. S. Environmental Protection Agency. As storage tank equipment vendors design new
floating decks and equipment, new emission factors may be developed based on that equipment. If the
new emission factors are reviewed and approved, the emission factors will be added to AP-42 during the
next update.
The emission estimation procedures outlined in this chapter have been used as the basis for the
development of a software program to estimate emissions from storage tanks. The software program
entitled "TANKS" is available through the U. S. Environmental Protection Agency website. While this
software does not address all of the scenarios described in this chapter, is known to have errors, and is no
longer supported, it is still made available for historical purposes.
7.1-14
Liquid Storage Tanks
06/18
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There are also commercially available storage tank emissions estimation software programs.
Users of these programs are advised to understand the extent of agreement with AP-42 Chapter 7
calculation methodology and assume responsibility of the accuracy of the output as they have not been
reviewed or approved by the EPA.
7.1.3.1 Routine Losses From Fixed Roof Tanks8"14'22
The following equations, provided to estimate standing and working loss emissions, apply to
tanks with vertical cylindrical shells and fixed roofs and to tanks with horizontal cylindrical shells. These
tanks must be substantially liquid- and vapor-tight. The equations are not intended to be used in
estimating losses from tanks which have air or other gases injected into the liquid, or which store unstable
or boiling stocks or mixtures of hydrocarbons or petrochemicals for which the vapor pressure is not
known or cannot be readily predicted. Total routine losses from fixed roof tanks are equal to the sum of
the standing loss and working loss:
where:
Lt = total routine losses, lb/yr
Ls = standing losses, lb/yr, see Equation 1-2
Lw = working losses, lb/yr, see Equation 1-35
7.1.3.1.1 Standing Loss
The standing loss, Ls, for a fixed roof tank refers to the loss of stock vapors as a result of tank
vapor space breathing. Fixed roof tank standing losses can be estimated from Equation 1-2.
where:
Ls = standing loss, lb/yr
Vv = vapor space volume, ft3, see Equation 1-3
Wv = stock vapor density, lb/ft3
Ke = vapor space expansion factor, per day
Ks = vented vapor saturation factor, dimensionless
365 = constant, the number of daily events in a year, (days/year)
Tank Vapor Space Volume. Vv - The tank vapor space volume is calculated using the following equation:
Lt — Ls + Lw
(1-1)
Ls = 365 Vv Wv Ke Ks
(1-2)
(1-3)
where:
Vv = vapor space volume, ft3
D = tank diameter, ft, see Equation 1-14 for horizontal tanks
Hvo = vapor space outage, ft, see Equation 1-16
06/18
Liquid Storage Tanks
7.1-15
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The standing loss equation can be simplified by combining Equation 1-2 with Equation 1-3. The result is
Equation 1-4.
(1-4)
where:
Ls = standing loss, lb/yr
Ke = vapor space expansion factor, per day, see Equation 1-5, 1-12, or 1-13
D = diameter, ft, see Equation 1-14 for horizontal tanks
Hvo = vapor space outage, ft, see Equation 1-16; use He/2 from Equation 1-15 for horizontal
tanks
Ks = vented vapor saturation factor, dimensionless, see Equation 1-21
Wv = stock vapor density, lb/ft3, see Equation 1-22
365 = constant, the number of daily events in a year, (days/year)
Vapor Space Expansion Factor, Ke
The calculation of the vapor space expansion factor, Ke, depends upon the properties of the liquid
in the tank and the breather vent settings, as shown in Equation 1-5. As shown in the equation, Ke is
greater than zero. If Ke is less than zero, standing losses will not occur. In that Ke represents the fraction
of vapors in the vapor space that are expelled by a given increase in temperature, a value of 1 would
indicate that the entire vapor space has been expelled. Thus the value of Ke must be less than 1, in that it
is not physically possible to expel more than 100% of what is present to begin with.
A Tv = average daily vapor temperature range, °R; see Note 1
A Pv = average daily vapor pressure range, psi; see Note 2
A Pb = breather vent pressure setting range, psi; see Note 3
Pa = atmospheric pressure, psia
Pva = vapor pressure at average daily liquid surface temperature, psia; see Notes 1 and 2 for
Equation 1-22
Tla = average daily liquid surface temperature, °R; see Note 3 for Equation 1-22
1. The average daily vapor temperature range, A Tv, refers to the daily temperature range of the
tank vapor space averaged over all of the days in the given period of time, such as one year, and should
not be construed as being applicable to an individual day. The average daily vapor temperature range is
calculated for an uninsulated tank using Equation 1-6.
(1-5)
where:
Notes:
ATV = (l — )ATA +
v \ 2.2 (Hs/D) + 1.9/ A
2.2 (Hs/D) + 1.9.
0.042ocr7 + 0.026(Hs/£>)ocs/
2.2 (Hs/D) + 1.9
(1-6)
where:
7.1-16
Liquid Storage Tanks
06/18
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ATv = average daily vapor temperature range, °R
Hs = tank shell height, ft
D = tank diameter, ft,
ATa = average daily ambient temperature range, °R; see Note 4
oir = tank roof surface solar absorptance, dimensionless; see Table 7.1-6
as = tank shell surface solar absorptance, dimensionless; see Table 7.1-6
I = average daily total insolation factor, Btu/ft2 d; see Table 7.1-7.
API assigns a default value of Hs/D = 0.5 and an assumption of a.i< = as. resulting in the
simplified equation shown below for an uninsulated tank:22
ATV = 0.7 ATa + 0.02 a I (1-7)
where:
a = average tank surface solar absorptance, dimensionless
For purposes of estimating emissions, a storage tank should be deemed insulated only if the roof
and shell are both sufficiently insulated so as to minimize heat exchange with ambient air. If only the
shell is insulated, and not the roof, the temperature equations are independent of Hs/D. Also, there likely
will be sufficient heat exchange through the roof such that Equation 1-7 would be applicable.
A more accurate method of accounting for the average daily vapor temperature range, ATv, in
partially insulated scenarios is given below. When the tank shell is insulated but the tank roof is not, heat
gain to the tank from insolation is almost entirely through the tank roof and thus the liquid surface
temperature is not sensitive to Hs/D.
ATv = 0.6 ATa+ 0.02 aR I (1-8)
In the case of a fully insulated tank maintained at constant temperature, the average daily vapor
temperature range, A Tv, should be taken as zero. This assumption that A Tv is equal to zero addresses
only temperature differentials resulting from the diurnal ambient temperature cycle. In the case of cyclic
heating of the bulk liquid, see Section 7.1.3.8.4.
2. The average daily vapor pressure range, A Pv, refers to the daily vapor pressure range at the
liquid surface temperature averaged over all of the days in the given period of time, such as one year, and
should not be construed as being applicable to an individual day. The average daily vapor pressure range
can be calculated using the following equation:
APv = Pvx-Pvn (1-9)
where:
A Pv = average daily vapor pressure range, psia
Pvx = vapor pressure at the average daily maximum liquid surface temperature, psia; see Note 5
Pvn = vapor pressure at the average daily minimum liquid surface temperature, psia; see Note 5
See Section 7.1.6.1 for a more approximate equation for APv that was used historically, but which
is no longer recommended.
In the case of a fully insulated tank maintained at constant temperature, the average daily vapor
pressure range, A Pv, should be taken as zero, as discussed for the vapor temperature range in Note 1.
06/18
Liquid Storage Tanks
7.1-17
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3. The breather vent pressure setting range, APb, is calculated using the following equation:
A Pb — Pbp - Pbv
(1-10)
where:
A Pb = breather vent pressure setting range, psig
Pbp = breather vent pressure setting, psig
Pbv = breather vent vacuum setting, psig
If specific information on the breather vent pressure setting and vacuum setting is not available,
assume 0.03 psig for Pbp and -0.03 psig for Pbv as typical values. If the fixed roof tank is of bolted or
riveted construction in which the roof or shell plates are not vapor tight, assume that A Pb = 0, even if a
breather vent is used.
4. The average daily ambient temperature range, A Ta, refers to the daily ambient temperature
range averaged over all of the days in the given period of time, such as one year, and should not be
construed as being applicable to an individual day. The average daily ambient temperature range is
calculated using the following equation:
where:
A Ta = average daily ambient temperature range, °R
Tax = average daily maximum ambient temperature, °R
Tan = average daily minimum ambient temperature, °R
Table 7.1-7 gives historical values of Tax and Tan in degrees Fahrenheit for selected cities in the
United States. These values are converted to degrees Rankine by adding 459.7.
5. The vapor pressures associated with the average daily maximum and minimum liquid surface
temperatures, Pvx and Pvn, respectively, are calculated by substituting the corresponding temperatures,
Tlx and Tln, into Equation 1-25 or 1-26 after converting the temperatures to the units indicated for the
respective equation.. If Tlx and Tln are unknown, Figure 7.1-17 can be used to calculate their values. In
the case of a fully insulated tank maintained at constant temperature, the average daily vapor pressure
range, APv, should be taken as zero.
If the liquid stored in the fixed roof tank has a true vapor pressure less than 0.1 psia and the tank
breather vent settings are not greater than ±0.03 psig, Equation 1-12 or Equation 1-13 may be used with
an acceptable loss in accuracy.
If the tank location and tank color and condition are known, Ke may be calculated using the
following equation in lieu of Equation 1-5:
ATa — Tax - Tan
(1-11)
KE = 0.0018 ATv =0.0018 [0.7 (Tax-Tan)+ 0.02 « I]
(1-12)
where:
Ke = vapor space expansion factor, per day
A Tv = average daily vapor temperature range, °R
7.1-18
Liquid Storage Tanks
06/18
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Tax = average daily maximum ambient temperature, °R
Tan = average daily minimum ambient temperature, °R
a = tank surface solar absorptance, dimensionless
I = average daily total insolation on a horizontal surface, Btu/(ft2 day)
0.0018 = constant, (°R)_1
0.7 = constant, dimensionless
0.02 = constant, (°R ft2 day)/Btu
Average daily maximum and minimum ambient temperatures and average daily total insolation
can be determined from historical meteorological data for the location, or may be obtained from historical
meteorological data for a nearby location. Historical meteorological data for selected locations are given
in Table 7.1-7, where values of Tax and Tan are given in degrees Fahrenheit. These values are converted
to degrees Rankine by adding 459.7.
If the tank location is unknown, a value of Ke can be calculated using typical meteorological
conditions for the lower 48 states. The typical value for daily insolation is 1,370 Btu/(ft2 day), the average
daily range of ambient temperature is 21°R, and the tank surface solar absorptance is 0.25 for white paint
in average condition. Substituting these values into Equation 1-12 results in a value of 0.04, as shown in
Equation 1-13.
Ke = 0.04 (1-13)
Diameter
For vertical tanks, the diameter is straightforward. If a user needs to estimate emissions from a
horizontal fixed roof tank, some of the tank parameters can be modified before using the vertical tank
emission estimating equations. First, by assuming that the tank is one-half filled, the surface area of the
liquid in the tank is approximately equal to the length of the tank times the diameter of the tank. Next,
assume that this area represents a circle, i.e., that the liquid is an upright cylinder. Therefore, the effective
diameter, De, is then equal to:
De =
LD
n
4
(1-14)
where:
De = effective tank diameter, ft
L = length of the horizontal tank, ft (for tanks with rounded ends, use the overall length)
D = diameter of a vertical cross-section of the horizontal tank, ft
By assuming the volume of the horizontal tank to be approximately equal to the cross-sectional
area of the tank times the length of the tank, an effective height, He, of an equivalent upright cylinder may
be calculated as:
06/18
Liquid Storage Tanks
7.1-19
-------
He =-D (1-15)
4
De should be used in place of D in Equation 1-4 for calculating the standing loss (or in Equation
1-3, if calculating the tank vapor space volume). One-half of the effective height, He, should be used as
the vapor space outage, Hvo, in these equations. This method yields only a very approximate value for
emissions from horizontal storage tanks. For underground horizontal tanks, assume that no breathing or
standing losses occur (Ls = 0) because the insulating nature of the earth limits the diurnal temperature
change. No modifications to the working loss equation are necessary for either aboveground or
underground horizontal tanks.
Vapor Space Outage
The vapor space outage, Hvo is the height of a cylinder of tank diameter, D, whose volume is
equivalent to the vapor space volume of a fixed roof tank, including the volume under the cone or dome
roof. The vapor space outage, Hvo, is estimated from:
Hvo = Hs - HL + Hr0 (1-16)
where:
Hvo = vapor space outage, ft; use He/2 from Equation 1-15 for horizontal tanks
Hs = tank shell height, ft
Hl = liquid height, ft; typically assumed to be at the half-full level, unless known to be
maintained at some other level
Hro = roof outage, ft; see Note 1 for a cone roof or Note 2 for a dome roof
Notes:
1. For a cone roof, the roof outage, Hro, is calculated as follows:
Hro = 1/3 Hr (1-17)
where:
Hro = roof outage (or shell height equivalent to the volume contained under the roof), ft
Hr = tank roof height, ft
Hr = SrRs (1-18)
where:
Sr = tank cone roof slope, ft/ft; if unknown, a standard value of 0.0625 is used
Rs = tank shell radius, ft
2. For a dome roof, the roof outage, Hro, is calculated as follows:
Hro ~Hr
2 6
Ei
(1-19)
7.1-20
Liquid Storage Tanks
06/18
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where:
Hro = roof outage, ft
Rs = tank shell radius, ft
Hr = tank roof height, ft
Hr = Rr-(r2r-R2s)05 (1-20)
Hr = tank roof height, ft
Rr = tank dome roof radius, ft
Rs = tank shell radius, ft
The value of Rr usually ranges from 0.8D - 1.2D, where D = 2 Rs. If Rr is unknown, the tank diameter is
used in its place. If the tank diameter is used as the value for Rr, Equations 1-19 and 1-20 reduce to
Hro = 0.137 Rs and HR = 0.268 Rs.
Vented Vapor Saturation Factor, Ks
The vented vapor saturation factor, Ks, is calculated using the following equation:
1
Ks ~ 1 + 0.053 PvaHvo (1~21)
where:
Ks = vented vapor saturation factor, dimensionless
Pva = vapor pressure at average daily liquid surface temperature, psia; see Notes 1 and 2 to
Equation 1-22
Hvo = vapor space outage, ft, see Equation 1-16
0.053 = constant, (psia-ft)"1
Stock Vapor Density. Wv - The density of the vapor is calculated using the following equation:
Wv = (1-22)
where:
Wv = vapor density, lb/ft3
Mv = vapor molecular weight, lb/lb-mole; see Note 1
R = the ideal gas constant, 10.731 psia ft3/lb-mole °R
Pva = vapor pressure at average daily liquid surface temperature, psia; see Notes 1 and 2
Tv = average vapor temperature, °R; see Note 6
Notes:
1. The molecular weight of the vapor, Mv, can be determined from Table 7.1-2 and 7.1-3 for
selected petroleum liquids and selected petrochemicals, respectively, or by analyzing vapor samples.
Where mixtures of organic liquids are stored in a tank, Mv can be calculated from the liquid composition.
06/18
Liquid Storage Tanks
7.1-21
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The molecular weight of the vapor. Mv, is equal to the sum of the molecular weight, M,. multiplied by the
vapor mole fraction, y,. for each component. The vapor mole fraction is equal to the partial pressure of
component i divided by the total vapor pressure. The partial pressure of component i is equal to the true
vapor pressure of component i (P) multiplied by the liquid mole fraction, (x,). Therefore,
Mr =2>< y, =2><
vaJ
(1-23)
where:
Pva, total vapor pressure of the stored liquid, by Raoult's Law, is:
PVA = YjPxi (1-24)
For more detailed information, please refer to Section 7.1.4.
2. True vapor pressure is defined in various ways for different purposes within the industry, such
as "bubble point" for transportation specifications, but for purposes of these emissions estimating
methodologies it is the sum of the equilibrium partial pressures exerted by the components of a volatile
organic liquid, as shown in Equation 1-24. True vapor pressure may be determined by ASTM D 2879 (or
ASTM D 6377 for crude oils with a true vapor pressure greater than 3.6 psia) or obtained from standard
reference texts. For certain petroleum liquids, true vapor pressure may be predicted from Reid vapor
pressure, which is the absolute vapor pressure of volatile crude oil and volatile nonviscous petroleum
liquids, as determined by ASTM D 323 or ASTM D 5191.
Vapor pressure is sensitive to the lightest components in a mixture, and the de-gassing step in
ASTM D 2879 can remove lighter fractions from mixtures such as No. 6 fuel oil if it is not done with care
(i.e. at an appropriately low pressure and temperature). In addition, any dewatering of a sample prior to
measuring its vapor pressure must be done using a technique that has been demonstrated to not remove
the lightest organic compounds in the mixture. Alternatives to the method may be developed after
publication of this chapter.
True vapor pressure can be determined for crude oils from Reid vapor pressure using Figures 7.1-
13a and 7. l-13b. However, the nomograph in Figure 7. l-13a and the correlation equation in Figure 7.1-
13b for crude oil are known to have an upward bias, and thus use of ASTM D 6377 is more accurate for
crude oils with a true vapor pressure greater than 3.6 psia. For light refined stocks (gasolines and
naphthas) for which the Reid vapor pressure and distillation slope are known, Figures 7.1-14a and 7.1-
14b can be used. For refined stocks with Reid vapor pressure below the 1 psi applicability limit of Figures
7.1-14a and 7.1-14b, true vapor pressure can be determined using ASTM D 2879. In order to use Figures
7.1-13a, 7.1-13b, 7.1-14a, or 7.1-14b, the stored liquid surface temperature, Tla, must be determined in
degrees Fahrenheit. See Note 3 to determine Tla.
Alternatively, true vapor pressure for selected petroleum liquid stocks, at the stored liquid surface
temperature, can be determined using the following equation:
7.1-22
Liquid Storage Tanks
06/18
-------
B
PVA =exp A
(1-25)
where:
exp = exponential function
A = constant in the vapor pressure equation, dimensionless
B = constant in the vapor pressure equation, °R
Tla = average daily liquid surface temperature, °R; see Note 3
Pva = true vapor pressure, psia
For selected petroleum liquid stocks, physical property data including vapor pressure constants A
and B for use in Equation 1-25 are presented in Table 7.1-2. For refined petroleum stocks with Reid vapor
pressure within the limits specified in the scope of ASTM D 323, the constants A and B can be calculated
from the equations presented in Figure 7.1-15 and the distillation slopes presented in Table 7.1-2. For
crude oil stocks, the constants A and B can be calculated from Reid vapor pressure using the equations
presented in Figure 7.1-16. However, the equations in Figure 7.1-16 are known to have an upward bias,
and thus use of ASTM D 6377 is more accurate. Note that in Equation 1-25, Tla is determined in degrees
Rankine instead of degrees Fahrenheit.
The true vapor pressure of organic liquids at the stored liquid temperature can also be estimated
by Antoine's equation:
log = log 10
A = constant in vapor pressure equation, dimensionless
B = constant in vapor pressure equation, °C
C = constant in vapor pressure equation, °C
Tla = average daily liquid surface temperature, °C
Pva = vapor pressure at average liquid surface temperature, mm Hg
For selected pure chemicals, the values for the constants A, B, and C are listed in Table 7.1-3.
Note that in Equation 1-26, Tla is determined in degrees Celsius instead of degrees Rankine. Also, in
Equation 1-26, Pva is determined in mm of Hg rather than psia (760 mm Hg = 14.7 psia).
3. The average daily liquid surface temperature, Tla, refers to the liquid surface temperature
averaged over all of the days in the given period of time, such as one year, and should not be construed as
being applicable to an individual day. While the accepted methodology is to use the average temperature,
this approach introduces a bias in that the true vapor pressure, Pva, is a non-linear function of
temperature. However, the greater accuracy that would be achieved by accounting for this logarithmic
function is not warranted, given the associated computational burden. The average daily liquid surface
temperature is calculated for an uninsulated fixed roof tank using Equation 1-27.
log PVA = A-
V LA +LS
(1-26)
where:
06/18
Liquid Storage Tanks
7.1-23
-------
4.4(H5/D) + 3.8
0.8
B
0.021 ocR I + 0.013(Hs/D) oc5 /
4.4(H5/D) + 3.8
(1-27)
where:
Tla = average daily liquid surface temperature, °R
Hs = tank shell height, ft
D = tank diameter, ft,
Taa = average daily ambient temperature, °R; see Note 4
Tb = liquid bulk temperature, °R; see Note 5
oir = tank roof surface solar absorptance, dimensionless; see Table 7.1-6
as = tank shell surface solar absorptance, dimensionless; see Table 7.1-6
I = average daily total insolation factor, Btu/(ft2 day); see Table 7.1-7
API assigns a default value of Hs/D = 0.5 and an assumption of a.i< = as. resulting in the
simplified equation shown below for an uninsulated fixed roof tank:22
Equation 1-27 and Equation 1-28 should not be used to estimate liquid surface temperature for
insulated tanks. In the case of fully insulated tanks, the average liquid surface temperature should be
assumed to equal the average liquid bulk temperature (see Note 5). For purposes of estimating emissions,
a storage tank should be deemed insulated only if the roof and shell are both fully insulated so as to
minimize heat exchange with ambient air. If only the shell is insulated, and not the roof, there likely will
be sufficient heat exchange through the roof such that Equation 1-28 would be applicable.
A more accurate method of estimating the average liquid surface temperature, Tla, in partially
insulated fixed roof tanks is given below. When the tank shell is insulated but the tank roof is not, heat
gain to the tank from insolation is almost entirely through the tank roof and thus the liquid surface
temperature is not sensitive to Hs/D.
If Tla is used to calculate Pva from Figures 7.1-13a, 7.1-13b, 7.1-14a, or 7.1-14b, Tla must be
converted from degrees Rankine to degrees Fahrenheit (°F = °R - 459.7). If Tla is used to calculate Pva
from Equation 1-26, Tla must be converted from degrees Rankine to degrees Celsius (°C = [°R -
491.7]/1.8).
4. The average daily ambient temperature, Taa, is calculated using the following equation:
Tla — 0.4Taa + 0.6Tb + 0.005 ot I
(1-28)
where:
a = average tank surface solar absorptance, dimensionless
Tla — 0.3 Taa + 0.7 Tb + 0.005 (XrI
(1-29)
7.1-24
Liquid Storage Tanks
06/18
-------
TAa =1AX^TaN) (1-30)
where:
Taa = average daily ambient temperature, °R
Tax = average daily maximum ambient temperature, °R
Tan = average daily minimum ambient temperature, °R
Table 7.1-7 gives historical values of Tax and Tan in degrees Fahrenheit for selected U.S. cities.
These values are converted to degrees Rankine by adding 459.7.
5. The liquid bulk temperature, Tb, should preferably be based on measurements or estimated
from process knowledge. For uninsulated fixed roof tanks known to be in approximate equilibrium with
ambient air, heat gain to the bulk liquid from insolation is almost entirely through the tank shell; thus the
liquid bulk temperature is not sensitive to Hs/D and may be calculated using the following equation:
TB = Taa+ 0.003 as I (1-31)
where:
Tb = liquid bulk temperature, °R
Taa = average daily ambient temperature, °R, as calculated in Note 4
as = tank shell surface solar absorptance, dimensionless; see Table 7.1-6
I = average daily total insolation factor, Btu/(ft2 day); see Table 7.1-7.
6. The average vapor temperature, Tv, for an uninsulated tank may be calculated using the
following equation:
^ _ [2.2(Hs/D)+1.1]Taa+0.8Tb+0.021ocrI + 0.013(Hs/D)ocsI n
1V ~ 2.2 (Hs/D) + 1.9
where:
Hs = tank shell height, ft
D = tank diameter, ft,
Taa = average daily ambient temperature, °R
Tb = liquid bulk temperature, °R
or = tank roof surface solar absorptance, dimensionless
as = tank shell surface solar absorptance, dimensionless
I = average daily total insolation factor, Btu/(ft2 day).
API assigns a default value of Hs/D = 0.5 and an assumption of ai< = as. resulting in the
simplified equation shown below for an uninsulated tank:22
Tv = 0.7Taa + 0.3Tb + 0.009 al (1-33)
where:
a = average tank surface solar absorptance, dimensionless
When the shell is insulated, but not the roof, the temperature equations are independent of Hs/D.
06/18
Liquid Storage Tanks
7.1-25
-------
Tv — 0.6Taa + 0.4Tb + 0.01 cirI
(1-34)
When the tank shell and roof are fully insulated, the temperatures of the vapor space and the
liquid surface are taken as equal to the temperature of the bulk liquid.
7.1.3.1.2 Working Loss
The fixed roof tank working loss, Lw, refers to the loss of stock vapors as a result of tank filling
operations. Fixed roof tank working losses can be estimated from:
Lw = VqKnKpWvKb
(1-35)
where:
Lw = working loss, lb/yr
Vq = net working loss throughput, ft3/yr, see Note 1
Kn = working loss turnover (saturation) factor, dimensionless
for turnovers > 36, Kn = (180 + N)/6N
for turnovers <36, Kn = 1
N = number of turnovers per year, dimensionless
IHq[ = the annual sum of the increases in liquid level, ft/yr
If IHqi is unknown, it can be estimated from pump utilization records.
Over the course of a year, the sum of increases in liquid level,
IHqi, and the sum of decreases in liquid level, IHqu. will be
approximately the same. Alternatively, IHqi may be
approximated as follows:
5.614 = the conversion of barrels to cubic feet, ft3/bbl
Q = annual net throughput, bbl/yr
Hlx = maximum liquid height, ft
If the maximum liquid height is unknown, for vertical tanks use
one foot less than the shell height and for horizontal tanks use
(7i/4) Dh where Dh is the diameter of the horizontal tank
Hln = minimum liquid height, ft
If the minimum liquid height is unknown, for vertical tanks use 1
and for horizontal tanks use 0
Kp = working loss product factor, dimensionless
for crude oils, Kp = 0.75
for all other organic liquids, Kp = 1
Wv = vapor density, lb/ft3, see Equation 1-22
Kb = vent setting correction factor, dimensionless, see Note 2
for open vents and for a vent setting range up to ± 0.03 psig, Kb = 1
N — IHqi / (Hlx - Hln)
(1-36)
IHqi = (5.614 Q) / ((ti/4) D2)
(1-37)
7.1-26
Liquid Storage Tanks
06/18
-------
1. Networking Loss Throughput.
The net working loss throughput, Vq, is the volume associated with increases in the liquid level, and is
calculated as follows:
VQ = (IHqi)(ti/4) D2
(1-38)
where:
IHq[ = the annual sum of the increases in liquid level, ft/yr
If ZHqi is unknown, ZHqi can be estimated from pump utilization records. Over the course of a
year, the sum of increases in liquid level, EHqi, and the sum of decreases in liquid level, IHqu.
will be approximately the same. Alternatively, Vq may be approximated as follows:
VQ =5.614 Q
(1-39)
where:
5.614 = the conversion of barrels to cubic feet, ft3/bbl
Q = annual net throughput, bbl/yr
Use of gross throughput to approximate the sum of increases in liquid level will
significantly overstate emissions if pumping in and pumping out take place at the same
time.
2. Vent Setting Correction Factor
When the breather vent settings are greater than the typical values of ± 0.03 psig, and the
condition expressed in Equation 1-40 is met, a vent setting correction factor, Kb, must be determined
using Equation 1-41. This value of Kb will be used in Equation 1-35 to calculate working losses.
When:
K,
PBP A
. Pi +Pa
>1.0
(1-40)
Then:
K„ =
Pj+Pa
K
-Pi
VA
N
Pbp +Pa ~Pva
(1-41)
where:
Kb = vent setting correction factor, dimensionless
Pi = pressure of the vapor space at normal operating conditions, psig
Pi is an actual pressure reading (the gauge pressure). If the tank is held at atmospheric
pressure (not held under a vacuum or at a steady pressure) Pi would be 0.
Pa = atmospheric pressure, psia
Kn = working loss turnover (saturation) factor (dimensionless), see Equation 1-35
Pva = vapor pressure at the average daily liquid surface temperature, psia; see Notes 1 and 2 to
06/18
Liquid Storage Tanks
7.1-27
-------
Equation 1-22
Pbp = breather vent pressure setting, psig.
See Section 7.1.6.2 for a more approximate equation for fixed roof tank working loss that was
used historically, but which is no longer recommended.
7.1.3.2 Routine Losses From Floating Roof Tanks3"513"17
Routine floating roof tank emissions are the sum of standing and working losses. Routine losses
from floating roof tanks may be written as:
Lt = Ls + Lw (2-1)
where:
Lt = total routine loss, lb/yr
Ls = standing loss, lb/yr; see Equation 2-2
Lw = working (withdrawal) loss, lb/yr; see Equation 2-19
The equations presented in this subsection apply only to floating roof tanks. The equations are not
intended to be used in the following applications:
1. To estimate losses from unstable or boiling stocks (see Section 7.1.3.5) or from mixtures of
hydrocarbons or petrochemicals for which the vapor pressure is not known or cannot readily be predicted;
2. To estimate losses from floating roof tanks vented only through a pressure/vacuum vent in the
fixed roof (i.e., no open vents) (see Section 7.1.3.8.2);
3. To estimate losses from tanks in which the materials used in the rim seal and/or deck fittings
are either deteriorated or significantly permeated by the stored liquid;
4. To estimate losses that result from the landing of a floating roof (see Section 7.1.3.3); or
5. To estimate losses that result from cleaning atank (see Section 7.1.3.4).
7.1.3.2.1 Standing Loss
Standing losses from floating roof tanks are the sum of rim seal, deck fitting and deck seam
losses, and may be written as:
Ls = Lr + Lf + Ld (2-2)
where:
Ls = standing loss, lb/yr
Lr = rim seal loss, lb/yr; see Equation 2-3
Lf = deck fitting loss, lb/yr; see Equation 2-13
Ld = deck seam loss (internal floating roof tanks only), lb/yr; see Equation 2-18
7.1-28
Liquid Storage Tanks
06/18
-------
Rim Seal Loss - Rim seal loss from floating roof tanks can be estimated using the following equation:
Lr = (KRa + KRb vn)DP* Mv Kc (2-3)
where:
Lr = rim seal loss, lb/yr
KRa = zero wind speed rim seal loss factor, lb-mole/ft»yr; see Table 7.1-8
= wind speed dependent rim seal loss factor, lb-mole/(mph)nft»yr; see Table 7.1-8
v = average ambient wind speed at tank site, mph; see Note 1
n = seal-related wind speed exponent, dimensionless; see Table 7.1-8
P* = vapor pressure function, dimensionless; see Note 2
P* =
rVA
Pa
i + [i _ (Sm
o.5 \ 2 (2-4)
Pa)\
where:
Pva = vapor pressure at average daily liquid surface temperature, psia;
See Note 3 below and Notes 1 and 2 to Equation 1-22
Pa = atmospheric pressure, psia
D = tank diameter, ft
Mv = average vapor molecular weight, lb/lb-mole; see Note 1 to Equation 1-22,
Kc = product factor;
Kc = 0.4 for crude oils;
Kc = 1 for all other organic liquids.
Notes:
1. If the ambient wind speed at the tank site is not available, use wind speed data from the nearest
local weather station or values from Table 7.1-7. If the tank is an internal or domed external floating roof
tank, the value of v is zero.
2. P* can be calculated or read directly from Figure 7.1-19.
3. The average daily liquid surface temperature, Tla, for calculation of vapor pressure, Pva, for
floating roof tanks shall be determined as follows:
For internal and domed external floating roof tanks:
T _ [2.86 (Hs/D)+1.43] TAA +[3.52 (Hs/D)+3.79] TB +0.027ocR/ + 0.017(Hs/£>)ocs/
LA 6.38 (Hs/D) + 5.22 ^ " '
where:
Tla = average daily liquid surface temperature, °R
Hs = tank shell height, ft
D = tank diameter, ft,
Taa = average daily ambient temperature, °R; see Equation 1-30
Tb = liquid bulk temperature, °R; see Note 5 for Equation 1-22
oir = tank roof surface solar absorptance, dimensionless; see Table 7.1-6
as = tank shell surface solar absorptance, dimensionless; see Table 7.1-6
06/18
Liquid Storage Tanks
7.1-29
-------
I = average daily total insolation factor, Btu/(ft2 day); see Table 7.1-7
API assigns a default value of Hs/D = 0.5 and an assumption of a.i< = as. resulting in the
simplified equation shown below for an uninsulated internal or domed external floating roof tank:22
Tla = 0.3 Taa + 0.7 Tb + 0.004 a I (2-6)
where:
a = average tank surface solar absorptance, dimensionless
The average daily liquid surface temperature, Tla, for external floating roof tanks is independent
of Hs/D for a given value of Tb. Different expressions for Tla are given for the two common types of
external floating roof deck. If the type of external floating roof deck is unknown, assume the deck to be
the steel peripheral pontoon type.
For external floating roof tanks with a steel peripheral pontoon deck (single deck center area):
Tla = 0.7 Taa + 0.3 TB + 0.008 aRI (2-7)
where the liquid bulk temperature, Tb, is preferably determined from measurements or estimated
from process knowledge, but otherwise may be estimated as follows:
Tb = Taa + [0.71 aRI + 0.485 (Hs/D) asI] / (170 Hs/D + 57) (2-8)
For default Hs/D = 0.5, when a.i< = as:
Tb = Taa + 0.007 a I (2-9)
For external floating roof tanks with a steel double deck:
Tla = 0.3 Taa + 0.7 Tb + 0.009 aRI (2-10)
where the liquid bulk temperature, Tb, is preferably determined from measurements or estimated
from process knowledge, but otherwise may be estimated as follows:
Tb = Taa + [0.39 aRI + 0.485 (Hs/D) asI] / (170 Hs/D + 45) (2-11)
For default Hs/D = 0.5, when aR = as:
Tb = Taa + 0.005 a I (2-12)
Deck Fitting Loss - Deck fitting losses from floating roof tanks can be estimated by the following
equation:
Lf = FfP*MvKc (2-13)
where:
Lf = the deck fitting loss, lb/yr
Ff = total deck fitting loss factor, lb-mole/yr
Ff = [(NFiKFi) + (NF2KF2) + ... +(NFnfKFnf)] (2-14)
Nf; = number of deck fittings of a particular type (i = 0,l,2,...,nf), dimensionless
where:
7.1-30
Liquid Storage Tanks
06/18
-------
Kfj = deck fitting loss factor for a particular type fitting
(i = 0,l,2,...,nf), lb-mole/yr; see Equation 2-15
nf = total number of different types of fittings, dimensionless
P*, Mv, Kc are as defined for Equation 2-3.
The value of Ff may be calculated by using actual tank-specific data for the number of each
fitting type (Nf) and then multiplying by the fitting loss factor for each fitting (Kf).
The deck fitting loss factor, Kp. for a particular type of fitting, can be estimated by the following
equation:
KFl = KFai + KFbl(Kvv)m' (2-15)
where:
Kf; = loss factor for a particular type of deck fitting, lb-mole/yr
K|.;i = zero wind speed loss factor for a particular type of fitting, lb-mole/yr
Ki h| = wind speed dependent loss factor for a particular type of fitting, lb-molc/(mph)n,,yr
m; = loss factor for a particular type of deck fitting, dimensionless
i = 1, 2, ..., n, dimensionless
Kv = fitting wind speed correction factor, dimensionless; see below
v = average ambient wind speed, mph
For external floating roof tanks, the fitting wind speed correction factor, Kv, is equal to 0.7. For
internal and domed external floating roof tanks, the value of v in Equation 2-15 is zero and the equation
becomes:
YLm = KFai (2-16)
Loss factors K|.;i. K|.-h. and m are provided in Table 7.1-12 for the most common deck fittings used on
floating roof tanks. These factors apply only to typical deck fitting conditions and when the average
ambient wind speed is below 15 miles per hour. Typical numbers of deck fittings for floating roof tanks
are presented in Tables 7.1-11, 7.1-12, 7.1-13, 7.1-14, and 7.1-15.
Loss factors may be estimated for deck fitting configurations that are not listed in Table 7.1-12, at
the zero miles-per-hour wind speed condition (IFRTs and Domed EFRTs), from the following equation:
Km = 0.27(^4fl)°86 (2-17)
Where:
Km = zero-wind-speed loss factor for a particular type of deck fitting, in pound-moles per year.
A n = liquid surface area within a particular type of deck fitting, in square inches. The liquid
surface area is the area inside the deck fitting well or leg sleeve, less any area occupied
by an obstruction in the deck fitting well or leg sleeve (such as a fixed-roof support
column, unslotted guidepole, guidepole float, or deck support leg).
06/18
Liquid Storage Tanks
7.1-31
-------
The coefficient, 0.27, has units of pound-moles per (square inches)0 86-year, and the exponent,
0.86, is dimensionless.
This equation is only applicable when the distance from the liquid surface to the top of the deck
fitting well or leg sleeve is 12 inches or greater. Shorter deck fitting wells or leg sleeves may result in
higher loss rates. There are no similar algorithms available for estimating loss factors for shorter deck
fitting wells or leg sleeves.
This equation is for an uncontrolled deck fitting. Effective deck fitting controls would be
expected to result in lower loss factors than would be estimated by this equation, but there are no
algorithms available for estimating the effectiveness of deck fitting controls.
This equation is for the zero miles-per-hour wind speed condition. There are no algorithms
available for estimating loss factors at non-zero wind speeds (EFRTs).
Deck Seam Loss - Deck seams that are welded are assumed to have no deck seam loss (i.e., Ld = 0). All
external floating roofs are assumed to be of welded construction, and some internal floating roofs are of
welded construction. Internal floating roof tanks with bolted decks may have deck seam losses. Deck
seam loss can be estimated by the following equation:
Ld = KdSdD2P*MvKc (2-18)
where:
Kd = deck seam loss per unit seam length factor, lb-mole/ft-yr
= 0.0 for welded deck
= 0.14 for bolted deck; see Note
Sd = deck seam length factor, ft/ft2
A
deck
where:
Lseam total length of deck seams, ft
tt-D2
Adeck = area of deck, ft2 =
4
D, P*, Mv, and Kc are as defined for Equation 2-3.
If the total length of the deck seam is not known, Table 7.1-16 can be used to determine Sd. For a
deck constructed from continuous metal sheets with a 7-ft spacing between the seams, a value of 0.14
ft/ft2 can be used. A value of 0.33 ft/ft2 can be used for Sd when a deck is constructed from rectangular
panels 5 ft by 7.5 ft. Where tank-specific data concerning width of deck sheets or size of deck panels are
unavailable, a default value for Sd can be assigned. A value of 0.20 ft/ft2 can be assumed to represent the
most common bolted decks currently in use.
Note: Recently vendors of bolted decks have been using various techniques, such as gasketing the deck
seams, in an effort to reduce deck seam losses. However, emission factors are not currently
available in AP-42 that represent the emission reduction, if any, achieved by these techniques.
7.1-32 Liquid Storage Tanks 06/18
-------
Some vendors have developed specific factors for their deck designs; however, use of these
factors is not recommended until approval has been obtained from the governing regulatory
agency or permitting authority. A weld seam does not have to be structural (i.e.. may be seal
welded) to constitute a welded deck seam for purposes of estimating emissions, but a deck seam
that is bolted or otherwise mechanically fastened and sealed with elastomeric materials or
chemical adhesives is not a welded seam.
7.1.3.2.2 Working (withdrawal) Loss
The working loss from floating roof storage tanks, also known as withdrawal loss, can be
estimated using Equation 2-19.
0.943 QCsWl(iiNcFc
L'W ~~ 1 -L +
D \ D J (2-19)
where:
Lw = working (withdrawal) loss, lb/yr
Q = annual net throughput, bbl/yr; see Note l
Cs = shell clingage factor, bbl/l,000 ft2; see Table 7. l-lO
Wl = average organic liquid density, lb/gal; see Note 2
D = tank diameter, ft
0.943 = constant, 1,000 ft3,gal/bbl2
Nc = number of fixed roof support columns, dimensionless; see Note 3
Fc = effective column diameter, ft (column perimeter [ft]/7i); see Note 4
Notes:
1. For tanks in which liquid is pumped in and out at the same time, the use of gross throughput to
estimate working loss would overstate emissions, but the overestimation would not be as significant as for
the working loss of fixed roof tanks. It would be more appropriate to express Q in terms of the sum of the
decreases in liquid level ZHqd. Over the course of a year, the sum of decreases in liquid level, IHqu. and
the sum of increases in liquid level, IHqi. will be approximately the same. The effective annual
throughput, Q, may be calculated in terms of IHqu as follows:
Q = (tt/4) D2 (IHqu/5.6 14) (2-20)
IHqu = the annual sum of the decreases in liquid level, ft/yr
D = tank diameter, ft
5.614 = the conversion of barrels to cubic feet, ft3/bbl
If IHqu is unknown, Q can be taken as the annual net throughput.
2. A listing of the average organic liquid density for select petrochemicals is provided in
Tables 7.1-2 and 7.1-3. KWl is not known for gasoline, an average value of 5.6 lb/gal can be assumed.
3. For a self-supporting fixed roof or an external floating roof tank:
Nc = 0.
For a column-supported fixed roof:
06/18
Liquid Storage Tanks
7.1-33
-------
Nc = use tank-specific information or see Table 7.1-11.
4. Use tank-specific effective column diameter or
Fc = 1.1 for 9-inch by 7-inch built-up columns, 0.7 for 8-inch-diameter pipe
columns, and 1.0 if column construction details are not known
7.1.3.3 Floating Roof Landing Losses21
When using floating roof tanks, the roof floats on the surface of the liquid inside the tank and
reduces evaporative losses during routine operations. However, when the tank is emptied to the point that
the roof lands on deck legs or hangers, there is a period where the roof is not floating and other
mechanisms contribute to emissions. These emissions continue until the tank is refilled to a sufficient
level to again float the roof. Therefore, these emission estimation calculations are applicable each time
there is a landing of the floating roof.
This model does not directly address standing idle losses for partial days, but it would be
reasonable to estimate the emissions for a partial day by estimating the standing idle emissions for a
single day and then pro-rating that estimate by the number of hours that the floating roof was actually
landed. For example, if the floating roof were landed for 6 hours, then the estimated standing idle losses
would be 6/24, or one quarter, of the estimated daily standing idle losses.
The total loss from floating roof tanks during a roof landing is the sum of the standing idle losses
and the filling losses. This relationship may be written in the form of an equation:
where:
Ltl = total losses during roof landing, lb per landing episode
Lsl = standing idle losses during roof landing, lb per landing episode
Lfl = filling losses during roof landing, lb per landing episode
The group of applicable equations to estimate the landing losses differs according to the type of
floating roof tank that is being used. The equations needed to estimate landing losses from internal
floating roof tanks are contained in Table 7.1-17; equations for external floating roof tanks are contained
in Table 7.1-18; and equations for drain-dry floating roof tanks are contained in Table 7.1-19. The
following sections explain these equations in more detail.
7.1.3.3.1 Standing Idle Losses
After the floating roof is landed and the liquid level in the tank continues to drop, a vacuum is
created which could cause the floating roof to collapse. To prevent damage and to equalize the pressure, a
breather vent (vacuum breaker) is actuated. Then, a vapor space is formed between the floating roof and
the liquid. The breather vent may remain open until the roof is again floated, so whenever the roof is
landed, vapor can be lost through this vent as well as through other deck fittings and past the rim seal.
(3-1)
7.1-34
Liquid Storage Tanks
06/18
-------
Even in the case of a self-closing breather vent, the vapor space beneath the floating roof is vented via the
other deck fittings and the rim seal, which is effectively rendered vapor mounted once the liquid level
drops below the bottom of the rim seal. These losses are called "standing idle losses."
The three different mechanisms that contribute to standing idle losses are (1) breathing losses
from vapor space, (2) wind losses, and (3) clingage losses. The specific loss mechanism is dependent on
the type of floating roof tank and the bottom condition.
For internal floating roof tanks with liquid remaining in the bottom (liquid heel), the breathing
losses originate from a discernible level of liquid that remains in the tank. This is typically the case for
internal floating roof tanks with nominally flat bottoms (including those built with a slight upward cone),
due to the flatness of the tank bottom and the position of the withdrawal line. If the remaining liquid
covers the entire bottom of the tank, this is known as a full liquid heel. The liquid evaporates into the
vapor space beneath the landed floating roof and daily changes in ambient temperature cause this vapor
space to breathe in a manner similar to a fixed roof tank. A partial liquid heel may be left in tanks with
sloped bottoms, if the withdrawal of liquid ceases while some free standing liquid remains in a sump or
elsewhere in the bottom of the tank.
For external floating roof tanks, which are not fully shielded from the surrounding atmosphere,
wind action across the landed floating roof can create pressure differentials that cause vapors to flow from
beneath the floating roof. The higher the wind speeds, the more vapor that can be expelled. These are
known as wind losses.
For tanks with a cone-down or shovel bottom, the floor of the tank is sloped to allow for more
thorough emptying of the tank contents, therefore, the amount of liquid remaining may differ significantly
from tanks with flat bottoms (see Figure 7.1-20). When the emptying operation drains the tank bottom,
but leaves a heel of liquid in or near the sump, the tank is considered to have a partial liquid heel. A drain-
dry condition is attained only when all of the standing liquid has been removed, including from the
bottom of the sump. However, due to sludge buildup, irregularity of the tank bottom and roughness of the
inside of the tank, a small layer of liquid can remain clinging to the sloped bottom of a drain-dry tank.
This layer of liquid will create vapor that can result in clingage losses. The amount of vapor produced
within a drain-dry tank is directly related to this clingage. Clingage factors for various tank conditions are
contained in Table 7.1-10. However, the clingage factors given in Table 7.1-10 are for the vertical shell of
the tank, which is wiped by the rim seal each time the tank is emptied. The bottom of the tank is more
nearly horizontal and is not wiped by a rim seal, and thus the clingage factors for a vertical shell would
not be directly applicable. A clingage factor of 0.15 bbl/103ft2 should be used to represent the clingage on
the tank bottom.
Standing Idle Loss for Tanks with a Liquid Heel
A constraint on the standing idle loss is added for floating roof tanks with a liquid heel in that the
total emissions cannot exceed the available stock liquid in the tank. This upper limit, represented as
LsLmax, IS a function of the volume and density of the liquid inside the tank.
AsLmax = (area °f tank) (height of liquid) (density of liquid) (3-2)
06/18
Liquid Storage Tanks
7.1-35
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Assuming that the tank has a circular bottom and adding a volume conversion unit, the equation
can be simplified to Equation 3-3 and Equation 3-4.
= (f)d2 K W, (7.48)
= 5.9 D2 h„ W,
'SL max
'SL max
(3-3)
(3-4)
where:
LsLmax limit on standing idle loss, lb per landing episode
7.48 = volume conversion factor, gal/ft3
D = diameter of the tank, feet
hie = effective height of the stock liquid, feet
Wi = density of the liquid inside the tank, lb/gal
Internal Floating Roof Tank with a Liquid Heel
For internal floating roof tanks with liquid heels, the amount of "standing idle loss" depends on
the amount of vapor within the vapor space under the floating roof. Essentially, the mechanism is
identical to the breathing losses experienced with fixed roof tanks. The mechanism shown in Equation 3-5
is identical to Equation 1-2.
where
Lsl = annual breathing loss from standing idle during roof landing, lb/yr
365 = number of days in a year, days/yr
Vv = volume of the vapor space, ft3
Wv = stock vapor density, lb/ft3
Mv = stock vapor molecular weight, lb/lb-mole
Pva = true vapor pressure of the stock liquid, psia at the temperature beneath the landed
floating roof (given that the tank bottom is in contact with the ground, assume the
temperature to be equal to ground temperature, which is taken as the average ambient
temperature for the month in which the landing occurs, unless a different temperature is
known)
R = ideal gas constant, 10.731 (psia-ft3)/(lb-mole °R)
Tv = average vapor temperature, °R, given that the tank bottom is in contact with the
ground, the temperature is assumed to be equal to ground temperature, which is taken as
the average ambient temperature for the month in which the landing occurs, unless a
different temperature is known
Ke = vapor space expansion factor, per day, calculated from Equation 1-5, 1-12 or 1-13 as
appropriate, with the value of A Pb set equal to zero
Lsl= 365VvWvKeKs
(3-5)
(3-6)
7.1-36
Liquid Storage Tanks
06/18
-------
Ks = saturation factor, dimensionless, calculated from Equation 1-21.
This equation requires adjustment, however, in that floating roof landing episodes are measured
in days rather than years. Assuming that nd equals the number of days that the tank stands idle and
substituting for the stock vapor density according to Equation 3-6, the equation is further simplified to
Equation 3-7.
LSL=ndKE^^MvKs (3-7)
K ly
The term with the highest amount of uncertainty is the saturation of the vapor beneath the landed
floating roof. The factor, Ks, is estimated with the same method used to calculate the saturation factor for
fixed roof tanks in Equation 1 -21. In order to establish limits on the value of Ks, the estimated factor is
assumed to be less than or equal to the saturation factor during filling (S). (For more information see
Filling Losses.)
The bottom of the tank may be flooded with a light distillate material, such as diesel, to reduce
volatility when the original heel is a relatively volatile liquid such as gasoline. This procedure is referred
to as distillate flushing. Testing has shown that, when the characteristics of the liquid heel beneath a
landed floating roof are changed, the characteristics of the vapor space beneath the floating roof will tend
toward equilibrium with the new liquid heel within 24 hours. The values for Ke, Pva, and Mv in Equation
3-7 may, then, be based on the properties of the mixture resulting from distillate flushing the day
following the introduction of the distillate into the tank. Properties of this mixture would be a weighted
average of the properties of the original heel and the properties of the distillate material, proportional to
the remaining quantities of each, [add reference]
External Floating Roof Tank with a Liquid Heel
For external floating roof tanks with a liquid heel, wind affects emission releases from the tanks.
As a starting point, begin with a basic equation based on rim-seal loss. The equation, shown as Equation
3-8, is equivalent to Equation 2-3.
Lrl = (KRa + KRb vn)D P Mv Kc (3-8)
where
Lrl = annual rim seal loss during roof landing, lb/yr
KRa = zero wind speed rim seal loss factor, lb-mole/ft-yr
KRb = wind speed dependent rim seal loss factor, lb-mole/((mph)n-ft-yr))
n = seal-related wind speed loss exponent, dimensionless
(Ka,, KRb, and n are specific to a given configuration of rim seal)
v = average ambient wind speed, mph
D = tank diameter, ft
Mv = stock vapor molecular weight, lb/lb-mole
Kc = product factor, dimensionless
P* = a vapor pressure function, dimensionless
06/18
Liquid Storage Tanks
7.1-37
-------
p*
H-Gsof)
2
(3-9)
where:
Pa = atmospheric pressure, psia
Pva = true vapor pressure of the stock liquid, psia.
Assuming that the stock properties included in the vapor pressure function will adequately
account for differences in liquid product type, Kc is assumed to equal 1. Regardless of the type of rim seal
that is in use, it is effectively rendered a 'vapor-mounted' seal when the liquid level falls such that the rim
seal is no longer in contact with the liquid. The contribution of a secondary seal is neglected in that it is
offset by emissions through the deck fittings. The emissions are therefore based on the case of a welded
tank with an average-fitting vapor-mounted primary seal. According to Table 7.1-8, the values of Kra, Krb,
and n are 6.7, 0.2, and 3.0, respectively. The variables were substituted and the equation was converted
from annual emissions to daily emissions by dividing the equation by 365. A value of 10 mph is assigned
to the wind speed, so that estimated standing idle losses from an external floating roof tank will not be
less than for a typical internal floating roof tank. Lower values for the rim seal loss factors or the wind
speed should not be used. The equation for standing idle loss due to wind can be simplified to Equation 3-
As with internal floating roof tanks with a liquid heel, distillate flushing may be used to reduce
the volatility of the liquid heel and thus the values used for the stock properties. The value for Mv, and for
Pva in the calculation of P*, may be based on the properties of the mixture resulting from distillate
flushing the day following the introduction of the distillate into the tank.
After the wind empties the vapor space above the remaining liquid heel, the liquid will continue
to produce vapor. Thus, this standing idle loss will occur every day that the tank stands idle with liquid
remaining in the tank. This equation is adequate at this time, but could be revised as additional testing is
conducted and studied.
Limit on Standing Idle Losses from Drain-Dry Tanks
When a drain-dry tank has been emptied, the only stock liquid available inside the tank is a thin
layer that clings to the wetted surface of the tank interior (if free-standing liquid remains in or near a
sump, or in puddles on the tank bottom, then the tank should be evaluated as having a partial heel, and not
as drain dry - see Figure 7.1-20). The slope prevents a significant amount of stock liquid from remaining
in the tank so that evaporation is much lower than from tanks with liquid heels. Due to the limited amount
10.
LsLwind — 0.57 nd D P* Mv
(3-10)
where:
LsLwind standing idle loss due to wind, lb per landing episode
nd = number of days that the tank is standing idle, days
D = tank diameter, ft
P* = a vapor pressure function, dimensionless
Mv = stock vapor molecular weight, lb/lb-mole
7.1-38
Liquid Storage Tanks
06/18
-------
of liquid clinging to the interior of the tank, as shown in Figure 7.1-20, there would be no liquid
remaining to replenish vapors once the clingage layer has evaporated. For this model, standing idle loss
due to clingage is a one-time event rather than a daily event, involving only evaporation of the clingage
layer.
The loss due to clingage is proportional to a clingage factor, which varies with the condition of
the inside of the tank. A list of clingage factors are shown in Table 7.1-10. However, the clingage factors
given in Table 7.1-10 are for the vertical shell of the tank, which is wiped by the rim seal each time the
tank is emptied. The bottom of the tank is more nearly horizontal and is not wiped by a rim seal, and thus
the clingage factors for a vertical shell would not be directly applicable to the tank bottom.
The factors are given in terms of barrels per thousand square feet. To convert the loss to pounds,
the density of the liquid and the area of the tank bottom must be taken into account, as shown in Equation
3-11.
where:
Lc =
0.042 =
Cs =
Wi =
Area =
Lc =0.042 CsWj(Area)
clingage loss from the drain-dry tank, lb
conversion factor, 1,000 gal/bbl
clingage factor, bbl/1,000 ft2
density of the liquid, lb/gal
area of the tank bottom, ft2
(3-11)
Area =
r kD2^
(3-12)
Among the conditions shown in Table 7.1-10, the one that best approximates a sludge-lined tank
bottom is gunite-lined, particularly given that the tank bottom is nearly horizontal and is not wiped by a
rim seal. Assuming that gasoline is being stored in the tank, a clingage factor of 0.15 and the area term in
Equation 3-12 were substituted into Equation 3-11, which simplifies to Equation 3-13.
TZ D2
Lsl = 0.0063 Wt —-— (3-13)
The clingage loss should be constrained by an upper limit equal to the filling loss for an internal
floating roof tank with a liquid heel. This is demonstrated in Equation 3-14.
LSLmm=0.60^^Mv (3-14)
K lv
where:
LsLmax = maximum standing idle loss for drain-dry tanks due to clingage, lb
Wi = density of the liquid inside the tank, lb/gal
D = diameter of the tank, feet
Pva = true vapor pressure of the liquid inside the tank, psia
Vv= volume of the vapor space, ft3
R = ideal gas constant, 10.731 psia ft3 /lb-mole °R
06/18
Liquid Storage Tanks
7.1-39
-------
Tv = average temperature of the vapor and liquid below the floating roof, °R (= Taa)
Mv = stock vapor molecular weight, lb/lb-mole
Therefore, the standing idle loss for drain-dry tanks, shown in Equation 3-13, must be less than or
equal to Equation 3-14. This relationship is shown by Equation 3-15.
(3-15)
K ly
7.1.3.3.2 Filling Losses
When a floating roof tank is refilled, there are additional emissions resulting from the roof being
landed. These losses are called "filling losses" and continue until the liquid reaches the level of the
floating roof.
The first contributor to filling losses is called the "arrival" component. These are the vapors that
remain under the floating roof at the end of the standing idle period, but have not been accounted for as
standing idle losses. For example, in the case of a liquid heel evaporation takes place into the vapor space
beneath the landed floating roof. The vapors that are expelled from this vapor space by breathing are
accounted for as standing idle losses, and the vapors that remain upon the commencement of refilling are
deemed the arrival component of filling losses.
The second contributor to filling losses is called the "generated" component. These are the vapors
created by the incoming liquid as it evaporates during the filling operation. Even when filling a
completely clean and gas-free tank, the incoming liquid will generate a certain amount of vapors.
Limit on Filling Loss for Tanks with a Liquid Heel
A constraint on the filling loss is added for floating roof tanks with a liquid heel in that the total emissions
cannot exceed the amount of stock liquid initially left in the tank less the amount attributed to standing
idle loss, plus the vapors generated by incoming liquid upon refilling. This upper limit, represented as
LFLmax, may be determined as follows:
Initial amount of stock liquid = 5.9 D2 hie Wi from Equation 3-4
Amount attributed to standing idle loss = Lsl from the applicable equation above for the
given type of tank
Amount generated by incoming liquid = 0.15 Pva Vv Mv / RTv from Equation 3-18
evaluated for a drain-dry tank, to account for only the generated component of vapors
These components of the upper limit on filling loss for a tank with a liquid heel may be combined into the
following equation:
Lfl - iP-9D2hleWl) — LSL+0.\5^-^^^Mv (3-16)
K lv
7.1-40
Liquid Storage Tanks
06/18
-------
General Equation for Filling Loss
The amount of vapor that is lost during filling is directly related to the volume of the vapor space
and the saturation level of the vapor within the vapor space, as shown in Equation 3-17.
Lfl = filling loss during roof landing, lb
Pva = true vapor pressure of the liquid within the tank, psia
Vv = volume of the vapor space, ft3
R = ideal gas constant, 10.731 psia-ft3/(lb-mole-°R)
Tv = average temperature of the vapor below the floating roof, °R(see Equation 3-6)
Mv = stock vapor molecular weight, lb/lb-mole
CSf = filling saturation correction factor for wind, dimensionless
S = filling saturation factor, dimensionless (0.60 for a full liquid heel; 0.50 for a partial liquid
This equation accounts for the arrival losses and the generated losses. The main concern with this
equation is the estimation of the saturation factor. All other components are based on the ideal gas laws.
Internal Floating Roof Tank with a Liquid Heel
A value of 0.6 for the filling saturation factor, which is used in Section 5.2, Table 5.2-1 for
submerged loading of tank trucks and rail cars, has been demonstrated to be suitable for the case of a full
liquid heel. A value of 0.5 has been demonstrated for the case of a partial liquid heel. In that the landed
floating roof in an internal floating roof tank or a domed external (or covered) floating roof tank is
shielded from wind by the fixed roof, the value of CSf is taken as 1.0.
External Floating Roof Tank with a Liquid Heel
For external floating roof tanks with a liquid heel, the amount of vapor lost during filling will be
less than the amount for internal floating roof tanks because of wind effects. The "arrival" component
will have been partially flushed out of the tank by the wind, so the preceding equation requires
evaluation of the saturation correction factor for wind, Csf. The basic premise of the correction factor is
that the vapors expelled by wind action will not be present in the vapor space when the tank is refilled, so
the amount of saturation is lowered. This is demonstrated in Equation 3-19.
Lfl = (vapor space volume)(vapor concentration)(vapor mol wf)(saturation factor) (3-17)
After substituting for the major terms in Equation 3-17, the equation can be simplified to
Equation 3-18.
(3-18)
where:
heel).
i.f
C-f = 1-
(3-19)
06/18
Liquid Storage Tanks
7.1-41
-------
The equation for the saturation factor can be simplified based on other equations contained in this
section as shown in Equation 3-20 and Equation 3-21.
Cif =1-
r {Equation 3 -10) - {Equation 3-7)^
{Equation 3-1) + {Equation 3-18)
(3-20)
Substituting the indicated equations, with the number of days set equal to 1 and CSf set equal to 1
in Equation 3-18 for the case without wind:
( . / /P„.-V„\ \ \
Csf = 1
(0.57 ¦ 1 ¦ D ¦ P* ¦ Mv) - (l ¦ Ke ¦ (pjfcfL) ¦ Mv ¦ Ks)
^ ¦¦K* ¦ ¦¦M" ¦+ ((^O¦• d ¦¦s))/
(3-21)
where:
Csf = filling saturation correction factor for wind, dimensionless
na = set equal to 1, days
Ke = vapor space expansion factor, per day, calculated from Equation 1-5, 1-12 or 1-13 as
appropriate, with the value of A Pb set equal to zero
Vv = volume of the vapor space, ft3
tD:
Vr =-L"^ (3-22)
hv = height of the vapor space under the floating roof, ft
D = tank diameter, ft
R = ideal gas constant, 10.731 psia ft3 / lb-mole R
Mv = stock vapor molecular weight, lb/lb-mole
Ks = standing idle saturation factor, dimensionless
S = filling saturation factor, dimensionless
P* = vapor pressure function, dimensionless
Wi = stock liquid density, lb/gal
Drain-Dry Tanks
The "arrival" component of filling losses for drain-dry tanks is completely covered by the
"clingage" loss. Once this initial loss occurs, there is no remaining liquid inside the tank. Therefore, any
vapors remaining in the tank prior to introducing the incoming liquid would have already been accounted
for as standing idle loss, and thus saturation of the arrival component for drain-dry tank filling losses is
taken as 0. Similarly, a tank with a full or partial liquid heel for which evaporation of the entire heel has
been accounted for as standing idle loss should be considered to have no arrival component of filling
losses, nor should a tank that has been cleaned. Each of these scenarios is deemed "drain dry" for
purposes of estimating the filling loss.
7.1-42
Liquid Storage Tanks
06/18
-------
However, the "generated" component remains a valid aspect of the model. Therefore, the
saturation factor will be lower for drain-dry tanks than for tanks with a liquid heel due to the lack of an
"arrival" component. And, given the absence of an arrival component of vapors for filling loss, the filling
saturation correction factor for wind is taken as 1.0.
AP-42 Chapter 5, Petroleum Industry, provides emission factors for the loading of gasoline and
crude oil into compartments according to the prior state of the compartment. A drain-dry tank would be
most similar to a tank that was cleaned before filling because a cleaned tank also lacks "arrival" losses.
The emission factor (0.33 lb/1000 gallons) for this kind of tank can be converted to a saturation factor by
assuming a pressure of 8 psia (the same assumption used in the formulation of the emission factor), and
substituting the molecular weight of gasoline (64 lb/lb-mole). The resulting saturation factor is 0.15.
7.1.3.4 Tank Cleaning Emissions23
The methodology presented in this section for estimating emissions associated with tank cleaning
events is expressly for the estimation of vapors that are expelled from the tank during forced ventilation.
These vapors potentially occur whenever forced ventilation of the tank is in operation while volatile
organic material remains in the tank, regardless of whether any tank cleaning is actually taking place.
For purposes of estimating emissions, tank cleaning may be characterized as comprising the steps
listed below.
Prior to commencement of forced ventilation (i.e.. not included in the tank cleaning calculations):
Normal Pumpout: As much stock liquid as possible is pumped out through the tank outlet in the
normal manner (i.e., until the liquid level has dropped below the open end of the outlet line, and
no more liquid moves through the outlet). If the tank has a floating roof, the floating roof will
have landed on its legs and the vacuum breaker vent will have opened, causing air to be drawn
into the space beneath the floating roof. Emissions that occur during normal pumpout are
accounted for as routine emissions for fixed-roof tanks and as floating roof landing losses for
floating roof tanks, and thus the normal pumpout period does not require additional calculations
pertaining to tank cleaning.
Standing Idle: The tank may remain in the condition resulting from normal pumpout for some
period of time until the next step begins. Emissions that occur during this period are accounted
for as routine standing (breathing) loss for fixed roof tanks, and as standing idle loss during a
floating roof landing for floating roof tanks, and thus the standing idle period does not require
additional calculations pertaining to tank cleaning.
During forced ventilation (these are the steps for which additional tank cleaning calculations are
required):
a) Vapor Space Purge: When eductors, fans, or blowers are started up, either at the top of the tank
or at a shell manhole, cleanout fitting or other shell fitting, the first air change is deemed to expel
those vapors that remain from the prior standing idle period. This first air change is
characterized as a purge of vapors from the tank. Emissions associated with subsequent air
06/18
Liquid Storage Tanks
7.1-43
-------
changes are accounted for under continued forced ventilation.
A vapor space purge will occur each time that ventilation commences after a period of standing
idle without forced ventilation.
b) Continued Forced Ventilation: Forced ventilation refers to the removal of vapors from a tank by
means of eductors, fans, or blowers. As long as volatile materials remain in the tank, some
portion of the volatile material will evaporate into the air being moved through the tank by
forced ventilation. The forced ventilation will then expel these vapors from the tank.
If forced ventilation is discontinued, such as during the overnight period, then the tank is
returned to a standing idle condition. A subsequent restarting of forced ventilation will result in
another vapor space purge followed by a period of continued forced ventilation.
After the tank is clean and gas free, even if forced ventilation is continuing (not included in the tank
cleaning calculations):
Remain Clean: Once the tank has been rendered clean and gas free it may remain in the clean
condition for some period of time. While forced ventilation may continue, there would be no
further emissions in that there would be no remaining sources of vapors once the tank has been
cleaned. Thus the period of remaining clean does not require additional calculations pertaining
to tank cleaning.
Refilling: If the tank is subsequently refilled, there will be vapors generated by the incoming
stock which would then be expelled from the tank by the rising liquid level. For a fixed roof
tank, these refilling emissions are accounted for as routine working (filling) losses. For a
floating roof tank, these refilling emissions are calculated in the same manner as for the refilling
after a floating roof landing. In that the tank has been cleaned, the saturation factor for the
refilling should be 0.15, as for a drain dry tank. The refilling losses, then, do not require
additional methodology in this section pertaining to tank cleaning.
The emissions to be accounted for in this section on tank cleaning emissions, then, are those
associated with forced ventilation while volatile material remains in the tank. The equations needed to
estimate emissions resulting from forced ventilation during tank cleaning are contained in Tables 7.1-20
and 7.1-21; equations forthe vapor space purge are contained in Table 7.1-20 and equations for
continued forced ventilation are contained in Table 7.1-21. The following sections explain these
equations in more detail.
LFV = Lp + LCV (4-1)
where:
LFV = total emissions due to forced ventilation during a tank cleaning event, lb
Lp = vapor space purge emissions associated with the first air change following commencement
of forced ventilation, lb
LCV = emissions from continued forced ventilation following the first air change, lb
7.1-44
Liquid Storage Tanks
06/18
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7.1.3.4.1 Vapor Space Purge Emissions
The daily breathing cycle that produces the standing idle emissions causes only a portion of the
vapors in the vapor space to be expelled from the tank. The vapors that remain in the vapor space are not
accounted for in the calculation of standing idle emissions. Commencement of forced ventilation expels
these remaining vapors from the tank. The first air change of the vapor space upon commencing forced
ventilation may be referred to as the vapor space purge, and the emissions may be estimated as follows:
LP = CPva Vv/RTv)MvS (4-2)
where:
Pva = the true vapor pressure of the exposed volatile material in the tank (psia),
3
Vy = volume (ft ) of the vapor space,
R = the ideal gas constant (psia fP per lb-mole °R),
= 10.731 psia ft^ per lb-mole °R,
Tv = the average temperature of the vapor space (°R),
= the average ambient temperature (°R),
My = the stock vapor molecular weight (lb/lb-mole),
S is a saturation factor evaluated as a function of the tank type and heel condition, as
discussed later in this section
The volatility of the remaining materials may be less than the volatility of the previously stored
stock liquid, and thus an appropriate judgment should be made in assigning properties to the residual
material in the tank bottom for purposes of determining values for the true vapor pressure, Pva, and the
stock vapor molecular weight, My.
The bottom of the tank may be flooded with a light distillate material, such as diesel, to facilitate
removal of sludge from the bottom of the tank. This procedure is referred to as distillate flushing. Testing
has shown that, when the characteristics of the liquid heel beneath a landed floating roof are changed, the
characteristics of the vapor space beneath the floating roof will tend toward equilibrium with the new
liquid heel within 24 hours. The values for Pva and Mi-in Equation 4-2 may, then, be based on the
properties of the mixture resulting from distillate flushing the day following the introduction of the
distillate into the tank. Properties of this mixture would be a weighted average of the properties of the
original heel and the properties of the distillate material, proportional to the remaining quantities of
each.24
The vapor space purge comprises the expulsion of one vapor space volume, similar to one
working-loss (filling) cycle of the vapor space. Emissions associated with subsequent air changes are
accounted for as continued forced ventilation emissions.
Fixed Roof Tanks
The volume of the vapor space for estimating working loss from a fixed-roof tank is calculated
from the maximum liquid height to which the tank may be filled. For a vapor space purge, however, the
volume of the vapor space is the entire volume under the tank roof:
06/18
Liquid Storage Tanks
7.1-45
-------
V\7=HvO(nD2/4) (4-3)
where:
Hy() = the fixed-roof tank vapor space outage (ft)
HVO = HS- hi + HRO (4-4)
where:
Hs = the height of the tank shell (ft),
hi = the height of the stock liquid and sludge above the tank bottom at the tank shell (ft), and
HRO = the roof outage (the effective height of the vapor space enclosed by the tank roof, ft)
= Sr D/6 for a cone-shaped roof, where Sr is the roof slope in feet per foot.
The vapor space outage, Hy(). would be slightly greater for the case of a cone-down bottom in a
tank that does not have a full liquid heel. The slope of bottoms tends to be much less than the slope of
roofs, however, and the contribution of the bottom cone to the vapor space outage would be very small
compared to the full shell height.
The saturation factor for filling a fixed-roof tank is given as the turnover factor, K]\J. in Equation
1-35, and defined as:
Kn = (180+ N)/6N
where:
N = number of turnovers per year, dimensionless
It would be advantageous to express this saturation factor in terms of days between turnovers (/'. e.,
days standing idle, nd). The number of days between turnovers may be expressed as follows:
nd = 365 IN
and thus the equation for Kv may be rewritten as:
Kn = (0.5 «d+ 1) / 6 (4-5)
Recognizing that the turnover factor, K]\'. is the saturation factor to be used for calculating filling
losses from a fixed-roof tank, the saturation factor, S, may be substituted for the turnover factor, K]\J.
S = (0.5 «d+ 1) / 6 (4-6)
For periods of less than one day, a value of 1 should be used for the standing idle time, nd. This
effectively imposes a minimum value of 0.25 for the saturation factor, S. Thus a value of 0.25 should be
used for S when the vapor space purge follows a standing idle period that was limited to an overnight
cessation of forced ventilation.
The saturation factor value of 0.5 for an internal floating roof tank with a partial heel, as shown in
Equation 3-18, may be reasonably chosen as an upper bound on the value of S for a fixed roof tank vapor
space purge. It would be expected, for a given diameter of tank and type of liquid heel, that the
accumulated vapors would be less concentrated in the larger vapor space of the fixed roof tank than under
7.1-46
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06/18
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a landed floating roof, and thus a value of 0.5 should be a conservative upper bound for the fixed roof
tank vapor space purge saturation factor.
These limits are expressed as follows:
S > 0.25
(4-7)
(4-8)
S < 0.5
Floating Roof Tanks
The volume of the vapor space for estimating the vapor space purge loss from a floating-roof tank
is limited to the space under the floating roof, in that vapors which escape past the floating roof prior to
the commencement of forced ventilation are separately accounted for as standing idle loss from the
floating roof landing event:
3
Vy = volume (ft ) of the vapor space under the floating roof,
where:
hv = the height (ft) of the vapor space under the floating roof for the given vapor space purge
(see Table 7.1-4)
The saturation factor, S, for the initial vapor space purge is evaluated as specified for the filling
saturation factor for a floating roof landing. This approach is conservative in that filling losses have both
an arrival component, from resident vapors, and a generated component, from vapors generated by
incoming liquid (e.g., 25% of the filling saturation factor for an internal floating-roof tank with a full
liquid heel may be attributable to the incoming liquid - the contribution of the incoming liquid to the vapor
concentration varies with the filling scenario). The vapor space purge does not involve incoming liquid,
however, and therefore would have only the arrival component of vapors. It is conservative, therefore, to
use saturation factors that include allowance for the generated component of vapors.
When forced ventilation is discontinued overnight, then the tank cleaning process will involve a
daily cycle that includes a period of standing idle (overnight) followed by a vapor space purge (when
forced ventilation resumes the next morning). Emissions from overnight standing idle periods are
accounted for in the estimate of the next morning's vapor space purge. In that the overnight standing idle
emissions are taken as zero, there is no accounting for wind-driven losses of vapor from under external
floating roofs. These vapors must then be accounted for with the following morning's vapor space purge.
That is, the neglect of wind driven emissions during the overnight period means that the vapors must be
considered to still be present when estimating the next morning's vapor space purge, and thus there must
be no factoring down of the saturation level for the case of external floating-roof tanks. In other words, f v/
should be taken as 1.0 when the vapor space purge follows a standing idle period that was limited to an
overnight cessation of forced ventilation.
Saturation factor values to be used for floating roof tanks are summarized as follows:
(hv) (kD2/4),
(4-9)
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Liquid Storage Tanks
7.1-47
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Full liquid heel
Internal floating roof tank
S= 0.6
External floating roof tank
S = (0.6 G/), where G/is evaluated as shown in Equation 3-21 with nj set to 1 for the initial
vapor space purge; for subsequent vapor space purges that follow a cessation of forced
ventilation overnight, G/shall be taken as 1.0
Partial liquid heel
Internal floating roof tank
S= 0.5
External floating roof tank
S = (0.5 Csf), where G/is evaluated as shown in Equation 3-21 with nj set to 1 for the initial
vapor space purge; for subsequent vapor space purges that follow a cessation of forced
ventilation overnight, G/ shall be taken as 1.0
If all free flowing liquid has been removed, and only sludge remains, use the saturation factor for
a partial heel, in that there is still volatile material in the tank but not free liquid across the entire bottom.
If the heel condition is drain dry, use a saturation factor value of 0, in that evaporation of the
clingage would have already been accounted for in the estimation of the floating roof landing losses.
7.1.3.4.2 Continued Forced Ventilation Emissions
The calculation of vapor space purge emissions account for the vapors that are expelled by the
first air change of the vapor space upon commencing forced ventilation at the end of a standing idle
period. There may still be volatile materials remaining in the tank, however, that will continue to
evaporate and generate vapors, and these additional vapors are expelled by continued forced ventilation.
Continued forced ventilation emissions are calculated from the average vapor concentration in the
vapor space (which may be reported as a percent of the lower explosive limit, or %LEL), the ventilation
rate, and the length of time during which forced ventilation continues to operate. These parameters are
often known since they may be monitored for safety reasons.
The vapor concentration may be approximated from the reading of an LEL monitor, which is
generally displayed as a percent of the LEL for the gas to which the monitor has been calibrated. LEL
values for selected calibration gases are given in Table 7.1-5. The vapor concentration may also be
approximated from the reading of an organic or toxic vapor analyzer, which may be displayed in parts per
million by volume as the calibration gas.
To determine the vapor concentration from a %LEL reading, the LEL of the calibration gas is
multiplied by the reading from the LEL monitor, after each has been divided by 100 to convert from a
percent to a decimal fraction. This gives a volume concentration (mole fraction) in terms of the calibration
gas. This concentration is corrected by a response factor (RF) to account for the difference in the
sensitivity of the LEL monitor to the actual vapors as compared to its sensitivity to the calibration gas.
When the response factor is unknown, use a value of one (RF = 1.0).
7.1-48
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If the vapor concentration is very low, it may be below the minimum detection level of the LEL
monitor. In this case, it may be reasonable to use half the minimum detection level as the %LEL for
determining the vapor concentration.
In order to estimate the mass of vapors that are expelled from the tank by continued forced
ventilation, the vapor concentration in terms of volume must be converted to vapor density in terms of
mass. In order to convert vapor concentration to density, use the molecular weight of the calibration gas
for the LEL monitor. Uncertainty is reduced if the molecular weight of the calibration gas is similar to the
molecular weight of the stock vapors.
The continued forced ventilation emissions (LCV) estimated by the vapor concentration method
are:
LCV = 60 QvncvtvCv(PaMCG /R TV) (4-10)
where:
60 is the conversion of hours to minutes, min/hr
3
Qv = average ventilation rate during continued forced ventilation, ft /min [Note: The nominal
rated capacity of eductors, fans, or blowers should be factored by the resistance associated
with ductwork or other obstructions in order to estimate the actual air flow rate. Fan
capacity may be governed by a required number of air changes per hour.]
ncv = the duration of continued forced ventilation, days
tv = the daily period of forced ventilation, hr/day [Note: Do not include the initial time for the
vapor space purge. It would be reasonable to neglect the first half hour from each stage of
continued forced ventilation],
( 'V = average vapor concentration by volume during continued forced ventilation,
dimensionless
= (average LEL as displayed) (LEL of the calibration gas) RF
"average LEL as displayed" is the average of the % LEL readings during a given stage of
continued forced ventilation, divided by 100 to convert to a decimal fraction; LEL
readings from the first half hour may be neglected in the determination of an average
value
"LEL of the calibration gas" is the LEL of the gas used to calibrate the LEL monitor,
expressed as a decimal fraction
RF = response factor, dimensionless
= 1.0 if unknown. EPA Method 21 allows usage of a vapor monitoring instrument
without correction for the response factor, as long as the response factor is less
than 10 (40 CFRPart 60 Appendix A-7, Method 21, paragraph 8.1.1.2).
Alternatively, C'V may be obtained from an organic vapor analyzer or toxic vapor
analyzer that displays directly in terms of volume concentration, rather than displaying in
terms of LEL.
Pa = atmospheric pressure at the tank location, psia
MCG = calibration gas molecular weight, lb/lb-mole
R = ideal gas constant
06/18
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7.1-49
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= 10.731 psia-ft^/(lb-mole °R),
TV = average temperature of the vapor below the floating roof, °R
= the average ambient temperature, °R
The vapor concentration (C y) is limited by saturation of the vapor space. This limit may be expressed as:
Cy < PVA/Pa (4-11)
where:
PVA = the true vapor pressure of the exposed volatile material in the tank, psia
The estimate of continued forced ventilation emissions should be compared to an upper limit
equal to the total weight of volatile sludge remaining in the tank. While there is free-standing stock liquid
remaining in the tank, the sludge may conservatively be assumed to consist entirely of stock liquid in
establishing the emissions upper limit. This limit is expressed as follows:
LCV < 5.9D 2 hie Wl (4-12)
where:
D = the tank diameter, feet
hie = the effective height of the stock liquid and sludge for the given stage of continued forced
ventilation, ft (see Table 7.1-4)
Wl = the density of the stock liquid, pounds per gallon
3
the constant, 5.9, has units of gal/ft (the product of the constant term id A and the conversion
factor 7.48 gal/ft3).
Once the free-standing stock liquid has been vacuumed out (or drained out, in the case of a drain-
dry tank), however, much of the remaining sludge consists of relatively non-volatile residue. The upper
limit on emissions from the vacuumed-out condition may assume that 20% of the sludge is volatile. This
limit is expressed as follows:
LCV < (k/4)(1) ft)2 I'e (c/s in )(Wl lb/gal)(ft/12 in.)(7.48 gal/ft3)
LCV < 0.49 Fe D 2 ds Wl (4-13)
where:
l'e = the fraction of the sludge with potential to evaporate (= 0.20 if unknown)
ds = the average depth of sludge, inches
9
the constant, 0.49, has units of gal/(in. ft ), and the other terms are defined as shown above.
7.1-50
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7.1.3.5 Flashing Loss25
The equations in Section 7.1.3.1 for estimating routine emissions from fixed roof tanks do not
address the scenario of a tank storing a liquid which contains gases that have the potential to flash out of
solution. This scenario occurs when a gas-liquid mixture has been under sufficient pressure to maintain
the entrained gases in solution, but the mixture is then subjected to a drop in system pressure such that the
pressure is no longer sufficient to maintain the gases in solution. The gases will then rapidly migrate out
of the liquid, similar to carbon dioxide fizzing out of solution when a carbonated beverage container is
opened. This escape of gases from the mixture is referred to as flashing.
The most common scenario for flashing in the petroleum industry is the storage of crude oil or
condensate in the production field. Even though the produced well stream has typically been processed by
one or more separators prior to produced liquids being deposited into a storage tank, the exit pressure
from the last stage separator may be significantly greater than the pressure in the first storage tank. Thus
the produced liquid stream will experience a pressure drop upon entering the storage tank, and remaining
gases will have the potential to flash out of solution in the tank. This scenario, then, has the potential for
flashing losses in addition to routine standing and working losses.
There are numerous methodologies available for estimating flashing losses, including but not
limited to those discussed below. The accuracy of methods that rely on a site-specific sample is dependent
on how representative the sample is of production from that site, and the accuracy of methods that rely on
process simulation is dependent on how representative the modeling assumptions are of the actual
conditions at the site. The conditions to be determined by sampling or modeling are of the crude oil or
condensate properties at the last stage separator, in the oil compartment before the dump valve.
In addition to evaluating a tank with the potential for flashing losses in accordance with a method
such as those described below, the tank must also be evaluated for routine standing and working losses as
described in Section 7.1.3.1. If vapors are routed to a control device, the control efficiency of the device
should be applied to the flashing loss as well as to the standing and working losses. If vapors are routed to
a compressor for injection into a gas line or process, the control efficiency would be assumed to be 100%
whenever the compressor is on-line.
Laboratory GOR. This method involves collecting a pressurized liquid sample from a point between the
last stage separator and the first storage tank, and then analyzing the sample in a laboratory to determine
the gas-oil ratio (GOR). The sample may be taken from the oil compartment of the last stage separator,
before the dump valve, if there is a sample port available for doing so. It is imperative that the sample be
collected in a pressurized instrument, so as to prevent loss of light ends in the handling of the sample.
Specifications for collecting pressurized samples include the Gas Processors Association (GPA) standard
2174, which describes the use of floating piston cylinders and double valve cylinders.
The pressurized sample is then allowed to flash in the laboratory to ambient conditions, and the
relative volumes of gas and oil are measured to determine the standard cubic feet of flash gas generated
per barrel of crude oil or condensate produced (i.e.. the GOR). This GOR may then be multiplied by the
number of barrels produced from that well site for a given time period in order to determine the volume of
flash gas generated during that time period. The volume of flash gas may be converted to pound-moles,
and the pound-moles may be converted to mass, as shown in the following equation.
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7.1-51
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flash gas (pounds) = (GOR) (production) (1/379.48) (MW)
(5-1)
where:
GOR =
production =
379.48 =
MW =
standard cubic feet (scf) of flash gas per barrel of oil
barrels of oil produced
scf per pound-mole at standard conditions
molecular weight of the flash gas (lb/lb-mole)
Laboratory speciation of the flash gas may be conducted to determine the molecular weight of the
gas, as well as to determine the contribution of individual constituents such as inerts (nitrogen and carbon
dioxide), methane and ethane to arrive at a value of VOC gas per barrel of oil produced.
Computer simulation modeling. The flashing losses for a given storage tank may be predicted from a
computer model that uses complex equations of state to simulate the flashing process at that tank. API
developed a computer model, E&P TANK, for the specific purpose of estimating flashing losses in
production field storage tanks. Commercial process simulation programs may also be applied to estimate
flashing losses. The accuracy achieved by any of these computer programs is improved by use of site-
specific data for the inputs, including properties obtained from laboratory analysis of pressurized liquid
samples, rather than relying on default assumptions.
Vasqucz-Bcggs equation. The Vasquez-Beggs equation is a relatively simple calculation based on an
empirical correlation of the gas-oil ratio (GOR) to the separator temperature, separator pressure, gas
specific gravity, and liquid API gravity. Once the GOR has been predicted from the correlation equation,
flashing losses may be calculated in the same manner as described above for the laboratory GOR method.
As with all methods, the accuracy of the Vasquez-Beggs equation is improved if actual site-specific data
are used to determine values for the required input parameters. In that the Vasquez-Beggs equation is
based on an empirical correlation, it is considered to be invalid outside specified ranges for the input
parameters. For example, the Vasquez-Beggs equation is not suitable if the API gravity is greater than 40
degrees, and thus should not be used for estimating flashing losses from tanks storing condensate. The
Vasquez-Beggs equation is generally considered to be less accurate than the methods described above.
Direct measurement. Direct measurement of emissions at the tank vent would be a preferred approach, if
a reliable means of measurement for both the flash vapors and the amount of liquid produced during the
testing period were employed. Efforts at direct measurement should account for uncertainty in the field
measurements of vapor concentration and flow rate through the vent and in the field measurements of
volume of liquid produced during the test period, as well as variation in emission rates over time.
Uncertainty may be mitigated by use of EPA Method 25 A over an extended period of time.
7.1.3.6 Variable Vapor Space Tanks18
Variable vapor space filling losses result when vapor is displaced by liquid during filling
operations. Since the variable vapor space tank has an expandable vapor storage capacity, this loss is not
as large as the filling loss associated with fixed roof tanks. Loss of vapor occurs when the tank's vapor
storage capacity is exceeded. Equation 6-1 assumes that one-fourth of the expansion capacity is available
at the beginning of each transfer.
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Variable vapor space system filling losses can be estimated from:
Ly = (2.40xlCT2)
where:
M''M(>0-(0-25F2Ar2)] (6-1)
V,
Lv = variable vapor space filling loss, lb/1,000 gal throughput
Mv = molecular weight of vapor in storage tank, lb/lb-mole; see Note 1 to Equation 1-22
Pva = true vapor pressure at the average daily liquid surface temperature, psia; see Notes 1
and 2 to Equation 1-22
Vi = volume of liquid pumped into system, throughput, bbl/yr
V2 = volume expansion capacity of system, bbl; see Note 1
N2 = number of transfers into system, dimensionless; see Note 2
Notes:
1. V2 is the volume expansion capacity of the variable vapor space achieved by roof lifting or
diaphragm flexing.
2. N2 is the number of transfers into the system during the time period that corresponds to a
throughput of Vi.
The accuracy of Equation 6-1 is not documented. Special tank operating conditions may result in
actual losses significantly different from the estimates provided by Equation 6-1. For example, if one or
more tanks with interconnected vapor spaces are filled while others are emptied simultaneously, all or
part of the expelled vapors will be transferred to the tank, or tanks, being emptied. This is called balanced
pumping or vapor balancing. Equation 6-1 does not account for balanced pumping, and will overestimate
losses under this condition. It should also be noted that, although not developed for use with heavier
petroleum liquids such as kerosenes and fuel oils, the equation is recommended for use with heavier
petroleum liquids in the absence of better data.
Variable vapor space tanks that rely on either a flexible diaphragm or a flexible coated fabric seal
will have additional losses to the extent that vapors leak through or past the membrane used for the
diaphragm or seal. The leakage rate through the membrane is a function of the permeability of the fabric
material from which the membrane is manufactured, and a leakage rate past the membrane is a function of
the leak tightness of the seam or seams where the membrane is attached to the tank wall. These leakage
rates depend upon the type of fabric used for the membrane and the manner in which the membrane is
attached to the tank wall.
7.1.3.7 Pressure Tanks
Losses occur during routine operations in low-pressure (2.5 to 15 psig) tanks to the extent that
atmospheric venting occurs. These losses are a function of the vent set pressure, and are accounted for in
the equations for routine fixed roof tank standing and working losses in Section 7.1.3.1. High-pressure
tanks are considered closed systems, with virtually no emissions. Fugitive losses from high-pressure tanks
are estimated as equipment leaks, and are not addressed in the methodology for estimating storage tank
emissions.
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A blanket of nitrogen gas is sometimes maintained in a storage tank for either safety or product
purity purposes, but the presence of the nitrogen gas does not reduce emissions. This is because
hydrocarbons readily evaporate into a nitrogen atmosphere, as evidenced by the fact that ambient air is
approximately 79% nitrogen. However, a nitrogen blanket is sometimes maintained in a closed or
pressurized system. In such a case, while evaporation rates would not be affected by the presence of the
nitrogen blanket, emissions may be reduced as result of the vapor space in the tank being tied to a closed
or pressurized system.
7.1.3.8 Variations Of Emission Estimation Procedures
7.1.3.8.1 Time Periods Shorter Than One Year26
All of the emission estimation procedures presented in Section 7.1.3 can be used to estimate
emissions for shorter time periods by manipulating the inputs to the equations for the time period in
question, with an associated increase in uncertainty when applying the equations to fewer tanks or shorter
time periods. Using actual data, such as the measured liquid temperature and true vapor pressure of the
stored liquid, can reduce the uncertainty in the emissions estimate.
For all of the emission estimation procedures, the true vapor pressure should be calculated from
an average daily liquid surface temperature based on the appropriate temperature and insolation data for
the time period over which the estimate is to be evaluated. For example, emission calculations for the
month of June would be based only on the meteorological data for June. It is important to note that a 1-
month time frame is recommended as the shortest time period for which emissions should be estimated
using these methodologies.
In addition to the temperature and vapor pressure corrections, the constant in the standing loss
equation for fixed roof tanks would need to be revised based on the actual time frame used. The constant,
365, is based on the number of days in a year. To change the equation for a different time period, the
constant should be changed to the appropriate number of days in the time period for which emissions are
being estimated. The only change that would need to be made to the working loss equation for fixed roof
tanks would be to change the throughput per year to the throughput during the time period for which
emissions are being estimated.
Other than changing the meteorological data and the vapor pressure data, the only changes
needed for the floating roof rim seal, deck fitting, and deck seam losses would be to modify the time
frame by dividing the individual losses by the appropriate number of days or months. The only change to
the withdrawal losses would be to change the throughput to the throughput for the time period for which
emissions are being estimated.
The issues that render the equations for routine emissions inappropriate for time periods shorter
than one month include, but are not limited to, the following:
a) Temperature calculations are simplified. There are many parameters involved in a thermal
balance model for a storage tank, some of which are listed below. It has been deemed suitable
to assign default values to several of these parameters when the calculations are applied to a
large population of storage tanks located over a wide geographical area for emissions that
occur over the course of a year. However, actual values for these parameters for an individual
storage tank configuration or location, or for a particular day of the year, may deviate
7.1-54
Liquid Storage Tanks
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significantly from the default values. Section 7.1.3.8.3 presents a more detailed discussion of
parameters affecting thermal balance in a storage tank.
1. The angle of incident solar radiation (i.e., the solar declination).
2. Reflectivity of surrounding surfaces.
3. Height to diameter ratio of the tank.
4. Liquid level.
5. Ambient wind speed.
6. Thermal conductance of the floating roof.
7. Presence of a fixed roof (versus an open top).
b) Changes in the liquid bulk temperature. The parameters which are accounted for as variables
in the equations for routine emissions are evaluated in a manner that does not account for
short-term phenomena. For example, calculations of temperature variables in the equations
for routine emissions are based on the liquid and vapor phases within the tank having
achieved a state of thermal equilibrium. The calculations do not, however, account for how
long it may take for thermal equilibrium to be achieved after there has been a change in the
thermal balance, such as the receipt of a batch of liquid. It is demonstrated in the reference
cited in Section 7.1.3.8.3 that atypical time period for approaching thermal equilibrium may
be approximately nine days, and thus a tank that has received liquid within the prior nine days
would be expected to not be in thermal equilibrium. If measured bulk temperature is used
instead of the estimated bulk temperature when estimating emissions, the time for the liquid
to reach thermal equilibrium becomes unimportant when estimating emissions on a shorter
time-scale.
c) Changes in ambient temperature. As ambient temperature changes, there would be an
associated change in the vapor space temperature and subsequently in the liquid surface
temperature. There would, however, be a time lag between a change in the ambient
temperature and the associated change in the liquid surface temperature. This time lag is
deemed inconsequential for the estimation of annual or monthly emissions, but would be
expected to be more significant for shorter periods of time. Shorter time periods would also
be more significantly influenced by abrupt short-term meteorological phenomena, such as
cooling due to cloud cover or precipitation.
d) Saturation factors. The saturation level of vapors in the headspace of a fixed roof tank is a
similarly time-dependent phenomenon. The equations for routine emissions do not fully
account for the time lag required to achieve saturation equilibrium in response to short-term
fluctuations in the values of applicable parameters.
e) Vapor expansion rate. The calculation of standing loss for a fixed roof tank is based on the
total amount of vapor expansion that is expected to occur between the coolest night time
temperature and the warmest day time temperature. The equation does not, however,
calculate the hourly rate at which the vapor expansion takes place or the distribution of vapor
expansion over the course of a day. This hourly rate would be dependent on several of the
variables noted in (a) above, as well as on whether the tank shell is insulated. As discussed
above in Note 1 following Equation 1-5, a fixed roof tank with an insulated shell but an
06/18
Liquid Storage Tanks
7.1-55
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uninsulated roof would be expected to have sufficient capacity for heat exchange through the
roof such that vapor space expansion would occur. However, the insulated shell may cause
the vapor space expansion to have a different hourly pattern than would be expected in the
case of an uninsulated tank shell.
f) Vent flow capacity. In addition to not calculating the hourly rate of vapor expansion, as
noted above, the calculation of standing loss for a fixed roof tank does not take into account
whether the flow capacity of the tank vents will further limit the hourly rate at which vapors
will be expelled from the tank as a result of daytime vapor expansion.
g) Changes in barometric pressure. The equations for routine emissions consider the barometric
pressure to be a constant for a given location, in that it has been deemed reasonable to use the
average barometric pressure when estimating emissions over the course of a year. However,
short-term changes in barometric pressure could impact short-term vapor expansion rates.
h) Fill rate. The calculation of working loss for a fixed roof tank is based on the total volume of
vapor expelled over the course of a year, which can be thought of as the total number of
tankfiils of vapor displaced. However, the equation does not account for the hourly rate at
which a tank is filled.
i) Standing loss for floating roof tanks. The equations for calculating routine standing losses
from floating roof tanks are based on the rate at which vapors migrate from the liquid below
the floating roof to the tank headspace above the floating roof, and do not account for the rate
at which these vapors may be eventually expelled from the tank.
j) Working loss for floating roof tanks. The calculation of working loss for a floating roof tank
is based on the evaporation of the wetted surface that is left on the inside wall of the tank
after lowering the liquid level. The calculation assumes that the entire film of liquid
evaporates, but it does not account for the hourly rate at which the film of liquid evaporates
or when the vapors are actually expelled from the tank.
k) Vapor space outage. The calculation of standing loss for a fixed roof tank is based on an
assumed vapor space outage corresponding to the average liquid height. However, at any
given point in time the tank may be nearly empty or nearly full, thus resulting in very
different scenarios of vapor space outage. For example, if the vapor space expansion factor is
0.15, that indicates 15% of the vapor space will be expelled by daytime warming, and
expelling 15% of the vapor space when the tank is nearly empty would constitute a far greater
volume than 15% of the vapor space when the tank is nearly full.
1) Vented vapor saturation factor. The saturation factor used in the calculation of standing loss
for a fixed roof tank is similarly dependent on the vapor space outage. Annual emission
estimates are based on the average liquid height, but the calculation would indicate a lower
vapor saturation when the tank is nearly empty and a higher vapor saturation when the tank is
nearly full.
7.1.3.8.2 Internal Floating Roof Tanks with Closed Vent Systems27
The equations for routine emissions from internal floating roof tanks assume the tank has open
vents in the fixed roof. Estimation of emissions when an internal floating roof tank has closed
pressure/vacuum vents is presented in API Technical Report 2569.
7.1-56
Liquid Storage Tanks
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The adjustment to account for the closed pressure/vacuum vents in the estimate of emissions was
found to be significant only for small diameter tanks storing relatively high volatility liquids with
infrequent turnovers. When the volatility of the stored liquid is no greater than that of diesel, then the
adjustment is generally less than 10% regardless of the tank diameter or the number of turnovers. When
the tank diameter is 60 feet or greater and the number of turnovers per year is greater than 18, then the
adjustment is generally less than 10% regardless of the volatility of the stored liquid. Given the high
degree of uncertainty associated with these calculations, and the burden of performing them, it would be
reasonable to apply a default reduction of 5% to account for the use of closed vents on a floating roof tank
in lieu of calculating a reduction specific to the given situation.
7.1.3.8.3 Case-Specific Liquid Surface Temperature Determinations22
Several parameters pertaining to liquid surface temperature are assigned default values for
incorporation into the equations for routine emissions. Methodology to account for selected parameters as
variables in the estimation of emissions from a particular storage tank at a particular location is presented
in API Manual of Petroleum Measurement Standards Chapter 19.4, Annex I.
7.1.3.8.4 Heating Cycles in Fully Insulated Fixed Roof Tanks8
The equations in Section 7.1.3.1.1 for standing loss from fixed roof tanks are based on the daily
cycle of warming and cooling of the vapor space due to heat exchange between the vapor space and
ambient air through the shell and roof of the tank. This heat exchange results in daytime expansion and
nighttime contraction of vapors in the vapor space, with each expansion cycle causing some portion of the
vapors to be expelled from the vapor space. The resulting emissions are referred to as breathing losses.
A similar cycle of expansion and contraction of vapors in the vapor space may be driven by
cyclic heating of the bulk liquid. Even in a fully insulated storage tank, in which there is minimal heat
exchange with ambient air, the temperature in the tank vapor space will cycle through a range if the bulk
liquid is heated periodically. This could occur by occasionally receiving hot stock, which then cools over
time prior to the next receipt of hot stock, or as a result of the tank being heated by some means that is
periodically turned on and off.
For uninsulated tanks or for tanks with an insulated shell but an uninsulated roof, the effect of
bulk liquid heating cycles on standing loss may be neglected because it may be random as to whether
cycles of heating the bulk liquid add to or subtract from the vapor space temperature variation driven by
the diurnal ambient temperature cycle.
For fully insulated storage tanks, however, standing loss may be driven by cyclic heating of the
bulk liquid. The equations for routine fixed roof tank breathing loss may be adapted to the case of cyclic
heating of the bulk liquid, as shown below.
The annual breathing loss is calculated from Equation 1-4:
(1-4)
The variables in this equation should be evaluated for calculating heating cycle breathing losses
06/18
Liquid Storage Tanks
7.1-57
-------
in the same manner as described in Section 7.1.3.1.1 for routine breathing losses, except as noted below.
The constant 365 is the number of days in a year. In that heating cycle breathing is an event that
is a function of the frequency of the heating cycle, rather than being a daily phenomenon, replace the
constant 365 with the number of heating cycles in the given time period.
The vapor space expansion factor Ke is calculated from Equation 1-5:
ATy M>y -APr
ke =jjL+; _P >° d-5)
1 LA r A rVA
In a fully insulated tank, the vapor space temperature and the liquid surface temperature are both
assumed to be equal to the liquid bulk temperature. Thus the vapor temperature range A'/'j- should be
calculated from the actual range of liquid bulk temperature in the tank, rather than using Equation 1-6 or
Equation 1-7. The actual range of liquid bulk temperature may be determined from direct measurements
or estimated from process knowledge.
A.Tv=Tbx-Tbn (8-1)
where:
Tbx = typical maximum liquid bulk temperature in the heating cycle, °R
Tbn = typical minimum liquid bulk temperature in the heating cycle, °R
The vapor pressure range A/V is calculated from Equation 1-9.
APv = Pvx-Pvn (1-9)
where:
Pvx and Pvn are the vapor pressures at Tlx and 7respectively, and:
Tlx = Tbx
Tln = Tbn
Similarly, the average liquid surface temperature Tla should be taken as being equal to actual
average liquid bulk temperature, rather than being calculated from Equation 1-27 or Equation 1-28.
Tla = Tb (8-2)
7.1.4 Speciation Methodology22
In some cases it may be important to know the annual emission rate for a component (e. g., HAP)
of a stored liquid mixture. There are two basic approaches that can be used to estimate emissions for a
single component of a stored liquid mixture. One approach involves calculating the total losses based
upon the known physical properties of the mixture (i. e., gasoline) in the vapor phase and then
determining the individual component losses by multiplying the total loss by the vapor weight fraction of
the desired component. However, the weight fraction of a given component in the vapor phase will vary
with temperature, and thus this approach is valid only at the temperature for which the vapor weight
fraction was determined.
7.1-58
Liquid Storage Tanks
06/18
-------
The second approach is similar to the first approach except that the mixture properties in the
vapor phase are unknown; therefore, the vapor phase mixture properties are first determined based on the
composition of the liquid mixture. This involves application of Raoult's Law, which assumes ideal
behavior on the part of each of the components in the mixture. An assumption of ideal behavior has been
found to be reasonable for most hydrocarbon mixtures. The two approaches outlined above are illustrated
in Case 1 below.
An assumption of ideal behavior may not be appropriate for aqueous mixtures or mixtures
containing alcohols. The molecules of water and alcohols are polar, meaning that the individual molecules
of these substances have an attraction for one another, resulting in behavior that deviates significantly
from ideal assumptions. An illustration of speciation for an aqueous mixture is presented in Case 2 below.
Raoult's Law is also not applied to speciate working (withdrawal) loss from floating roof tanks.
The application of Raoult's Law outlined in this section assumes the fraction of the available liquid that
evaporates is very small compared to the total mass of liquid available, and thus the properties of the
remaining liquid can be assumed to be unaffected by the loss of the evaporated fraction. Floating roof
withdrawal loss, however, involves evaporation of a thin film of liquid from the wetted tank shell as the
liquid level descends. It is assumed that the entire film of liquid evaporates, and thus relative fractions of
individual components in the vapors would be the same as for the liquid.
Case 1 - If the physical properties of the mixture are known (Pva, Mv, Ml and Wl), the total
losses from the tank should be estimated using the procedures described previously for the particular tank
type. The component losses are then determined from either Equation 40-1 or 40-2. For fixed roof tanks,
the emission rate for each individual component can be estimated by:
where:
Lti = emission rate of component i, lb/yr
Zy. = weight fraction of component i in the vapor, lb/lb
Lt = total losses, lb/yr
For floating roof tanks, the emission rate for each individual component can be estimated by:
where:
Lti = emission rate of component i, lb/yr
Zvj = weight fraction of component i in the vapor, lb/lb
Lr = rim seal losses, lb/yr
Lf = deck fitting losses, lb/yr
Ld = deck seam losses, lb/yr
Z[. = weight fraction of component i in the liquid, lb/lb
Lw = working (withdrawal) losses, lb/yr
LTi = (Zv,)(Lt)
(40-1)
LTl = (ZVi)(Lr + Lf + Ld) + (ZLl)(Lw)
(40-2)
06/18
Liquid Storage Tanks
7.1-59
-------
If Equation 40-1 is used in place of Equation 40-2 for floating roof tanks, the value obtained will
be approximately the same value as that achieved with Equation 40-2 because withdrawal losses are
typically minimal for floating roof tanks.
In order to use Equations 40-1 and 40-2, the weight fraction of the desired component in the
liquid and vapor phase is needed. The liquid weight fraction of the desired component is typically known
or can be readily calculated or determined by analysis for most mixtures. In order to calculate the weight
fraction in the vapor phase, Raoult's Law must first be used to determine the partial pressure of the
component. The partial pressure of the component can then be divided by the total vapor pressure of the
mixture to determine the mole fraction of the component in the vapor phase. Raoult's Law states that the
mole fraction of the component in the liquid (x,) multiplied by the vapor pressure of the pure component
(at the average daily liquid surface temperature) (P) is equal to the partial pressure (Pi) of that component:
Pi = (P)(xO (40-3)
where:
Pi = partial pressure of component i, psia
P = vapor pressure of pure component i at the average daily liquid surface temperature, psia
xi = liquid mole fraction, lb-mole/lb-mole
The vapor pressure of each component can be calculated from Antoine's equation or found in
standard references, as shown in Section 7.1.3.1. In order to use Equation 40-3, the liquid mole fraction
must be determined from the liquid weight fraction by:
x =
zlMl a
m4
(40-4)
where:
Xi = liquid mole fraction of component i, lb-mole/lb-mole
Zi. = weight fraction of component i in the liquid, lb/lb
Ml = molecular weight of liquid stock, lb/lb-mole
Mi = molecular weight of component i, lb/lb-mole
The liquid mole fraction and the vapor pressure of the component at the average daily liquid
surface temperature can then be substituted into Equation 40-3 to obtain the partial pressure of the
component. The vapor mole fraction of the component can be determined from the following equation:
Yi = T~L" (40-5)
Pva
where:
yi = vapor mole fraction of component i, lb-mole/lb-mole
Pi = partial pressure of component i, psia
Pva = total vapor pressure of liquid mixture, psia
The weight fractions in the vapor phase are calculated from the mole fractions in the vapor phase.
7.1-60
Liquid Storage Tanks
06/18
-------
ZVl = — (40-6)
Mv
where:
Zvj = vapor weight fraction of component i, lb/lb
yi = vapor mole fraction of component i, lb-mole/lb-mole
Mi = molecular weight of component i, lb/lb-mole
Mv = molecular weight of vapor stock, lb/lb-mole
The liquid and vapor weight fractions of each desired component and the total losses can be
substituted into either Equations 40-1 or 40-2 to estimate the individual component losses.
Case 2 -For special cases, such as wastewater, where the liquid mixture is a dilute aqueous
solution, Henry's Law should be used instead of Raoult's Law in calculating total losses. Henry's Law
states that the mole fraction of the component in the liquid phase multiplied by the Henry's Law constant
for the component in the mixture is equal to the partial pressure (Pi) for that component. For wastewater,
Henry's Law constants are typically provided in the form of atm»m3/g-mole.
Therefore, the appropriate form of Henry's Law equation is:
Pi = (Ha) (G) (40-7)
where:
Pi = partial pressure of component i, atm
Ha = Henry's Law constant for component i, atm»m3/g-mole
Ci = concentration of component i in the wastewater, g-mole/m3; see Note
Section 4.3 of AP-42 presents Henry's Law constants for selected organic liquids. The partial
pressure calculated from Equation 40-7 will need to be converted from atmospheres to psia
(1 atm = 14.7 psia).
Note: Typically wastewater concentrations are given in mg/liter, which is equivalent to g/m3. To
convert the concentrations to g-mole/m3 divide the concentration by the molecular weight of the
component.
The total vapor pressure of the mixture can be calculated from the sum of the partial pressures:
Pva = I Pi (40-8)
where:
Pva = vapor pressure at average daily liquid surface temperature, psia
Pi = partial pressure of component i, psia
This procedure can be used to determine the vapor pressure at any temperature. After computing
the total vapor pressure, the mole fractions in the vapor phase are calculated using Equation 40-5. The
vapor mole fractions are used to calculate the molecular weight of the vapor, Mv. The molecular weight
of the vapor can be calculated by:
06/18
Liquid Storage Tanks
7.1-61
-------
Mv = I Miyi (40-9)
where:
Mv = molecular weight of the vapor, lb/lb-mole
Mi = molecular weight of component i, lb/lb-mole
yi = vapor mole fraction of component i, lb-mole/lb-mole
Another variable that may need to be calculated before estimating the total losses, if it is not
available in a standard reference, is the density of the liquid, Wl. If the density of the liquid is unknown, it
can be estimated based on the liquid weight fractions of each component (see Section 7.1.5, Example 3).
All of the mixture properties are now known (Pva, Mv, and Wl). These values can now be used
with the emission estimation procedures outlined in Section 7.1.3 to estimate total losses. After
calculating the total losses, the component losses can be calculated by using either Equations 40-1 or
40-2. Prior to calculating component losses, Equation 40-6 must be used to determine the vapor weight
fractions of each component.
7.1-62
Liquid Storage Tanks
06/18
-------
Breather vent (open or P/V type)
Float gauge conduit
Tank roof and shell
(not insulated)
Gauge-hatch'
sample well
Roof manhole
No floating roof
Stable (nonboiling)
stock liquid
Figure 7.1-1. Typical fixed-roof tank.2"
06/18
Liquid Storage Tanks
7.1-63
-------
Figure 7.1-2. External floating roof tank (pontoon type}.2®
7.1-64
Liquid Storage Tanks
06/18
-------
Overflow drain
Open top (no fixed roof)
Access hatch
Deck leg
Vacuum breaker'
Rim seal-
(mechanical-shoe)l
Gauge hatch/
sample port
Solid guidepole
(unslotted)
Rim vent ¦
Figure 7.1-3. External floating roof tank (double deck).
20
06/18
Liquid Storage Tanks
7.1-65
-------
¦ Peripheral roof vents
-Fixed-roof center vent
Fixed roof
(column-
supported)
^—Rim seal
(vapor-mounted)
Sample port
Deck leg
Access hatch
lank shell
Figure 7.1-4. Internal floating roof tank.
7.1-66
Liquid Storage Tanks
06/18
-------
Rim vent
Vacuum
Deck leg
(pontoon area)
Deck leg
(center area)
Overflow drain
Tank shell
Gauge float
Solid guiaepoie
(unslotted)
Gauge hatch/
sample port
Access hatch
Fixed-roof center vent
Fixed roof
(self-supporting
aluminum
dome)
Figure 7.1-5. Domed external floating roof tank.20
06/18
Liquid Storage Tanks
7.1-67
-------
N/\ /— Floating roof deck
Resilient-filled seal
(not in contact with the liquid surface)
(see section view beiow)
\y\ r—— Tank shell
Floating roof dock
Liquid surface -
Flexible-wiper seal
(wiper position may vary with the
floating roofs direction of travel)
(see section views below)
Liquid
surface
Elastomeric-coated
fabric envelope
Resilient
foam core
¦ Floating
roof
deck
Rim vapor
space
Liquid
surface
Eiastomeric blade
Floating
roof
deck
Liquid-
surface
Elastomeric-coated
fabric envelope
Foam core
¦ Floating
roof
deck
Figure 7.1-6. Vapor-mounted primary seals20
7.1-68
Liquid Storage Tanks
06/18
-------
Floating roof deck
Resilient-filled seal
(bottom of seal in contact with the liquid surface)
(see section view below)
Weathershield
(not shown above)
Elastomeric-
coated
fabric
envelope.
Liquid—
surface
Resilient core
(foam or liquid-filled)
Floating
roof
deck
Floating roof deck
Primary-seal
fabric
(see section view below)
Metallic
shoe
Rim vapor
space
Liquid —
surface
I
Tank shell
Primary-seal fabric
Floating
roof
deck
Figure 7.1-7. Liquid-mounted and mechanical shoe primary seals.2
06/18
Liquid Storage Tanks
7.1-69
-------
Rim-mounted secondary seal
over
resilient-filled primary seal
Secondary seal
(flexible wiper shown)
Rim extender
Primary seal
(resilient-filled)
Liquid
surface
Rim-mounted secondary seal
over
flexible-wiper primary seal
Secondary seal
(flexible wiper shown)
- Rim extender
Shoe-mounted secondary seal
over
mechanical-shoe primary seal
Primary sea!
(mechanical
shoe)-
Liquid —
surface
•Tank shell
¦
Secondary-seal
(shoe-mounted)
Rim-mounted secondary seal
over
mechanical-shoe primary seal
-Tank shell
Primary seal
(mechanical
shoe)
Liquid—
surface
V .
Secondary-seal
(rim-mounted)
Figure 7.1-8. Secondary rim seals.20
7.1-70
Liquid Storage Tanks
06/18
-------
Removable
cover
Floating
roof
deck
Well
Handle -
(see section view below)
Removable cover'
Gasket ^~l§!
Well '
Liquid—
surface
f
-Bolted
closed
Floating
roof
deck
X
Access Hatch
Floating
roof
deck—
¦ Pipe column
(see section view below)
Pipe column
Liquid -
surface
-Floating
roof
=t deck
(noncontact
type shown)
Fixed-Roof Support Column
Cable -
Removable
cover
Floating
roof
deck
Well
Cable
Gasket -
Well-
(see section view below)
Self- Cord
closing
cover
Pipe
sleeve
through,
the
deck
Gauge-hatch/
sample port—
¦Slit-
fabric
sample port
(internal floating roots only)
(see section view below)
Gauge float Sample Ports
Figure 7.1-9. Deck fittings for floating roof tanks.20
06/18
Liquid Storage Tanks
7.1-71
-------
Screened
cover
Pipe
sleeve
Floating
root
Adjustable
Cf'""
(see section view below)
pinhole
Pin
(noncorttsct
type shown)
Screened
cover
Overflow
(see sectfon view below)
drain
(noncontact
type shown
tlii&s#te)
Deck Leg Rim Vent
Figure 7.1-10. Deck fittings for floating roof tanks.20
Dec*;
Filiating
roof
(see section view below)
Adjustable leg
Lag
pinhole
Pin
Floating
roof
deck
Mechanical
shoe
(see section view below)
Rim vent
7.1-72
Liquid Storage Tanks
06/18
-------
Unslotted (solid) Guidepole
Slotted guidepole -
Roller assembly -
Slots in guidepole
(2 staggered rows
on opposite sides)
Slotted guidepole
Roller assembly-
Sliding cover
Well
¦Slotted guidepole
Roller assembly
Liquid
surface
Pole
sleeve
Slotted (perforated) Guidepole
Figure 7.1-11. Slotted and unslotted guidcpolcs.2"
06/18
Liquid Storage Tanks
7.1-73
-------
Floating
roof
Ladder
Sliding
cover
Gasket
Well
Liquid-
surface
{see section view below)
Sliding
cover
deck
(noncontact
type shown)
Figure 7.1-12. Ladder well.35
7.1-74
Liquid Storage Tanks
06/18
-------
Figure 7. l-13a. True vapor pressure of crude oils with a Reid vapor pressure
of 2 to 15 pounds per square inch.4
The nomograph in Figure 7.1-13a and the correlation equation in Figure 7.1-13b for predicting the true
vapor pressure of crude oil from the Reid vapor pressure are known to have an upward bias. When the
true vapor pressure of a crude oil is greater than 3.6 psia, it may be determined more accurately by means
of direct measurement using ASTM D 6377. A curve of true vapor pressure versus temperature may be
obtained by conducting ASTM D 6377 measurements over a range of temperatures.
06/18
Liquid Storage Tanks
7.1-75
-------
0.20
0.30
040
— 0.50
— 060
0.70
— 0.80
— 090
— 100
2 P- 1.50
— 2.00
ST
&
V)
?
a
Q.
|
:
— 2.50
— 3.00
=- 3.50
4.00
— 5.00^
6.00
7.00
8 00
9.00
— 10.0
— 11.0
L 4"
120-
110 —
100 —
90 —
80—
70-
60-
50 —
40 —
30 —
20—
10-:
Notes:
1. 5 = slope of the ASTM distillation curve at 10 percent evaporated, in degrees
Fahrenheit per percent
= ((°F at 15 percent) - (®F at 5 percent)]/(10 percent).
In the absence of distillation data, the following average values of S may be used:
Motor gasoline—3.0.
Aviation gasoline—2.0.
Light naphtha (RVP of 9-14 pounds per square inch)—3.5.
Naphtha (RVP of 2-8 pounds per square inch)—2.5.
2. The broken line illustrates a sample problem for a gasoline stock (5 = 3.0) with a
Reid vapor pressure of 10 pounds per square inch and a stock temperature of 62.5°F.
5
§
Figure 7.1-14a. True vapor pressure of refined petroleum stocks with a Reid vapor pressure of
1 to 20 pounds per square inch.4
True vapor pressure of refined petroleum stocks that are below the range of the Reid vapor pressure
method may be measured directly using ASTM D 2879. A curve of true vapor pressure versus
temperature may be obtained by conducting ASTM D 2879 measurements over a range of temperatures.
7.1-76
Liquid Storage Tanks
06/18
-------
P = exp
2,799
T +459.6,
-2.227
Iog10 (RVP) -
7,261
T +459.6,
+ 12.82
Where:
P = stock true vapor pressure, in pounds per square inch absolute.
T = stock temperature, in degrees Fahrenheit.
RVP = Reid vapor pressure, in pounds per square inch.
Note:This equation was derived from a regression analysis of points read off Figure 7. l-13a over the full range
of Reid vapor pressures, slopes of the ASTM distillation curve at 10 percent evaporated, and stock
temperatures. In general, the equation yields P values that are within +0.05 pound per square inch
absolute of the values obtained directly from the nomograph.
Figure 7.1-13b. Equation for true vapor pressure of crude oils
with a Reid vapor pressure of 2 to 15 pounds per square inch.4 See note at Figure 7. l-13a.
P = exp
0.7553-
413.0
T +459.6
S log10 (RVP) -
1.854-
1,042
T +459.6
-,0.5
Where:
2,416
T + 459.6,
¦2.013
log10 (RVP) ¦
8,742
T +459.6
+ 15.64
P = stock true vapor pressure, in pounds per square inch absolute.
T = stock temperature, in degrees Fahrenheit.
RVP = Reid vapor pressure, in pounds per square inch.
S = slope of the ASTM distillation curve at 10 percent evaporated, in degrees Fahrenheit per percent.
Note: This equation was derived from a regression analysis of points read off Figure 7.1-14a over the full range of Reid
vapor pressures, slopes of the ASTM distillation curve at 10 percent evaporated, and stock temperatures. In general,
the equation yields P values that are within +0.05 pound per square inch absolute of the values obtained directly
from the nomograph.
Figure 7.1-14b. Equation for true vapor pressure of refined petroleum stocks
with a Reid vapor pressure of 1 to 20 pounds per square inch.4 See note at Figure 7. l-14a.
A = 15.64 - 1.854 S05 - (0.8742-0.3280 S05)ln(RVP)
B = 8,742 - 1,042 S0 5 - (1,049-179.4 S0 5)ln(RVP)
where:
RVP = stock Reid vapor pressure, in pounds per square inch
In = natural logarithm function
S = stock ASTM-D86 distillation slope at 10 volume percent
evaporation (°F/vol %)
Figure 7.1-15. Equations to determine vapor pressure constants A and B for refined
petroleum stocks.22
06/18
Liquid Storage Tanks
7.1-77
-------
A = 12.82 - 0.9672 In (RVP)
B = 7,261 - 1,216 In (RVP)
where:
RVP =Reid vapor pressure, psi
In =natural logarithm function
Figure 7.1-16. Equations to determine vapor pressure Constants A and B for crude oil stocks.22
Average Daily Maximum and Minimum Liquid Surface Temperature, (°R)
Tlx = Tla + 0.25 ATv
Tln = Tla - 0.25 ATv
where:
Tlx = average daily maximum liquid surface temperature, °R
Tla is as defined in Note 3 to Equation 1-22
ATv is as defined in Note 1 to Equation 1-5
Tln = average daily minimum liquid surface temperature, °R
Figure 7.1-17. Equations for the average daily maximum and minimum liquid surface temperatures.8
7.1-78
Liquid Storage Tanks
06/18
-------
Figure 7.1-18. Reserved.
06/18 Liquid Storage Tanks 7.1-79
-------
Notes:
0.4
0.3
0.2
0.1
0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
/-
j -
f-
t
-
I
/ -
/'
r
lllfllllll
E
iiiiiini
-
y
i
— c
-i
-
/
-
/
<
-
/
f
-
/
1/
/
= /
'/p.
"I
1
1
i
i
{i
... i
+ n -
i
(pip.
i
>]">*
i
i
•
1
¦ €
~ n
1.0
0.3
0.2
0.04
0.03
0.02
Stock taie vapor pressure. P (pounds per square inch absolute)
1. Broken line illustrates sample problem for P — 5 4 pounds per square inch absolute.
2. Curve is for atmospheric pressure, equal to 14.7 pounds per square inch absolute.
Figure 7.1-19. Vapor pressure function.4
7.1-80
Liquid Storage Tanks
06/18
-------
n. . . =;
F- - - -IS
c
1
%
D
n- - - -|
= - 1 - -IN
1 1 ill
Full Liquid Heel
(standing liquid
across the entire bottom)
Partial Liquid Heel
(standing liquid only
in or near a sump;
clingage elsewhere)
Drain Dry
(no standing liquid,
only liquid is clingage)
Figure 7.1-20. Bottom conditions for landing loss.
06/18
Liquid Storage Tanks
7.1-81
-------
7.1-82
Liquid Storage Tanks
06/18
-------
Table 7.1-1. LIST OF ABBREVIATIONS USED IN THE TANK EQUATIONS
Variable Description
a tank surface solar absorptance,
dimensionless
n constant, (3.14159)
A constant in vapor pressure equation,
dimensionless
Adeck area of deck, ft2
As liquid surface area within a
particular type of deck fitting,
in2
B constant in vapor pressure equation,
°R or °C
C constant in vapor pressure equation,
°R or °C
Cs shell clingage factor, bbl/1,000 ft2
Csf filling saturation correction factor
for wind, dimensionless
Cv average vapor concentration by
volume during continued forced
ventilation, dimensionless
D tank diameter, ft
De effective tank diameter, ft
ds average depth of sludge, in.
Fc effective column diameter, ft
Fe fraction of sludge with potential to
evaporate, dimensionless
Ff total deck fitting loss factor,
lb-mole/yr
ha deck leg height at the tank shell, ft
Hl liquid height, ft
hie effective liquid height during roof
landing, ft
Hln minimum liquid height, ft
Hlx maximum liquid height, ft
EHqd the annual sum of the decreases in
liquid level, ft/yr
EHqi the annual sum of the increases in
liquid level, ft/yr
Hr tank roof height, ft
Hr0 roof outage, ft
Hs tank shell height, ft
hv vapor space height under landed
floating roof, ft
Variable Description
Hvo vapor space outage, ft
i 1,2, n, dimensionless
I average daily total insolation factor,
Btu/ft-d
Kc product factor for floating roof
tanks, dimensionless
Kd deck seam loss per unit seam length
factor, lb-mole/ft-yr
Ke vapor space expansion factor, per
day
Kfeu zero wind speed loss factor for a
particular type of deck fitting,
lb-mole/yr
KFbi wind speed dependent loss factor
for a particular type of deck
fitting, lb-mole/(mph)myr
Kf; loss factor for a particular type of
deck fitting, lb-mole/yr
Kn turnover factor, dimensionless
Kp working loss product factor for fixed
roof tanks, dimensionless
KRa zero wind speed rim seal loss factor,
lb-molc/ft'yr
KRb wind speed dependent rim seal loss
factor, lb-mole/ (mph)Tt*vr
Ks vented vapor saturation factor,
dimensionless
Kv fitting wind speed correction factor,
dimensionless
L length of tank, ft
Lc clingage factor for drain dry tanks,
lb
Lev continued forced ventilation
emissions, lb/cleaning event
Ld deck seam loss, lb/yr
Lf deck fitting loss, lb/yr
Lfv total tank cleaning emissions due to
forced ventilation, lb/cleaning
event
Lfl filling loss during roof landing,
lb/landing event
Variable Description
Lp
vapor space purge emissions due to
first air change from forced
ventilation, lb/cleaning event
Lr
rim seal loss, lb/yr
Lrl
rim seal loss during roof landing,
lb/landing event
Ls
standing losses, lb/yr
Lseam
total length of deck seam, ft
Lsl
standing loss during roof landing,
lb/landing event
Lt
total routine losses, lb/yr
Li\
emission rate of component i, lb/yr
Ltl
total loss during roof landing,
lb/landing event
Ly
variable vapor space filling loss,
lb/1,000 gal throughput
Lw
working losses, lb/yr
Mcg
molecular weight of calibration gas,
lb/lb-mole
m
loss factor for a particular type of
deck fitting, dimensionless
Mi
molecular weight of component i,
lb/lb-mole
Ml
molecular weight of liquid mixture,
lb/lb-mole
Mv
vapor molecular weight, lb/lb-mole
N
number of turnovers per year,
dimensionless
n
seal-related wind speed exponent,
dimensionless
na
number of days standing idle during
roof landing or prior to forced
ventilation, days
n2
number of transfers into system,
dimensionless
Nc
number of columns, dimensionless
nCv
duration of continued forced
ventilation, days
Nd
number of drains
nf
total number of different types of
fittings, dimensionless
-------
Table 7.1-1 (cont.).
Variable Description
N|.„ zero wind speed loss factor for a
particular type of deck fitting,
lb-mole/yr
NFbi wind speed dependent loss factor for
a particular type of fitting,
lb-mole/ mplV"*yr
NF[ number of deck fittings of a
particular type, dimensionless
Ni number of deck legs
Ntotal total number of moles in mixture,
lb-mole
Nvb
number of vacuum breakers
P
true vapor pressure of component i,
P*
psia
vapor pressure function,
dimensionless
Pa
atmospheric pressure, psi
APb
breather vent pressure setting range,
psig
Pbp
breather vent pressure setting, psig
Pbv
breather vent vacuum setting, psig
Pi
gauge pressure within the vapor
space, psig
Pi
partial pressure of component i, psia
APV
average daily vapor pressure range,
psi
PvA
vapor pressure at average daily
liquid surface temperature, psia
PvN
vapor pressure at the average daily
minimum liquid surface
temperature, psia
Pvx vapor pressure at the average daily
maximum liquid surface
temperature, psia
Q annual net throughput, bbl/yr
Qv average ventilation rate during tank
cleaning, ft3/min
R ideal gas constant,
(10.731 psia*rt7lb-molc*°R)
Rr tank dome roof radius, ft
Rs tank shell radius, ft
S filling saturation factor,
dimensionless
Sb tank cone bottom slope, ft/ft
Sd deck seam length factor, ft/ft2
Sr tank cone roof slope, ft/ft
A Ta average daily ambient temperature
range, °R
Taa average daily ambient temperature,
°R
Tan average daily minimum ambient
temperature, °R
Tax average daily maximum ambient
temperature, °R
Variable Description
Tb liquid bulk temperature, °R
Ten typical minimum liquid bulk
temperature in heating cycles,
°R
Tbx typical maximum liquid bulk
temperature in heating cycles,
°R
Tla average daily liquid surface
temperature, °R
Tv average vapor temperature, °R
tv daily period of forced ventilation
during tank cleaning, hr/day
A Tv average daily vapor temperature
range, °R
v average wind speed, mph
Vi volume of liquid pumped into
system, bbl/yr
V2 volume expansion capacity, bbl
Vq net working loss throughput, ft3/yr
Vlx tank maximum liquid volume, ft
Vv vapor space volume, ft3
Wi liquid density of component i, lb/ft3
Wl average organic liquid density,
lb/gal
Wv vapor density, lb/ft3
X! liquid mole fraction of component i,
lb-mole/lb-mole
yi vapor mole fraction of component i,
lb-mole/lb-mole
Z|, liquid weight fraction of
component i, lb/lb
ZV| vapor weight fraction of
component i, lb/lb
7.1-84 Liquid Storage Tanks 06/18
-------
Table 7.1-2. PROPERTIES (Mv, Ml, Pva, Wl) OF SELECTED PETROLEUM LIQUIDS'
Petroleum Liquid
Mixture
Vapor
Molecular
Weight3
Liquid
Molecular
Weight13
Liquid
Density3
ASTM D86
Distillation
Slope0
Vapor Pressure Equation
Constants11
True Vapor
Pressure
(at 60 °F)
Mv
Ml
Wl
S
A
B
Pva
Ib/lb-mole
Ib/lb-mole
lb/gal
°F/vol %
dimension less
°R
psia
Midcontinent Crude Oil
50
207
7.1
-
Figure 7.1-16
Figure 7.1-16
-
Refined Petroleum Stocks
-
-
-
-
Figure 7.1-15
Figure 7.1-15
-
Motor Gasoline RVP 13
62
92
5.6
3.0
11.644
5043.6
7.0
Motor Gasoline RVP 10
d)
CD
CD
92
5.6
3.0
11.724
5237.3
5.2
Motor Gasoline RVP 7
68
92
5.6
3.0
11.833
5500.6
3.5
Light Naphtha RVP 9-14
-
-
-
3.5
-
-
-
Naphtha RVP 2-8
-
-
-
2.5
-
-
-
Aviation Gasoline
-
-
-
2.0
-
-
-
Jet Naphtha (JP-4)
80
120
6.4
-
11.368
5784.3
1.3
Jet Kerosene (Jet A)
130
162
7.0
-
12.390
8933.0
0.008
No. 2 Fuel Oil (Diesel)
130
188
7.1
-
12.101
8907.0
0.006
No. 6 Fuel Oilf
130
387
7.9
-
10.781
8933.0
0.002
Vacuum Residual Oilg
190
387
7.9
-
10.104
10,475.5
0.00004
a References 10 and 11
b Liquid molecular weights from "Memorandum from Patrick B. Murphy, Radian/RTP to James F. Durham, EPA/CPB
Concerning Petroleum Refinery Liquid HAP and Properties Data, August 10, 1993," as adopted in versions 3.1 and 4.0 of
EPA's TANKS software.
c Reference 4.
d For motor gasolines, see Figure 7.1-15;
for crude oil, see Figure 7.1-16;
for Jet Naphtha, Jet Kerosene, and No. 2 Fuel Oil, see Barnett and Hibbard10;
for No. 6 Fuel Oil.22
e Alternatively, in the absence of measured data, a value of 66 Ib/lb-mole may be assumed for all gasolines, in that the variability
shown as a function of RVP is speculative.
'This is for a blend of Vacuum Residual Oil with a light distillate cutter stock, or similar mixture. Vapor pressure constants given
will result in higher vapor pressure values than shown previously in AP-42 for Residual Oil No. 6.
g This is the straight residue from the bottom of the vacuum distillation column, prior to any further processing or blending.
Properties given for Vacuum Residual Oil are those given for Residual Oil No. 6 previously in AP-42.
06/18
Liquid Storage Tanks
7.1-85
-------
Table 7.1-3. PHYSICAL PROPERTIES OF SELECTED PETROCHEMICALS'
Normal
Chemical
Name
CAS
Registry
No.
Molecular
Weight
Liquid
Density
(lb/gal)
Antoine's Equation13
Boiling
Point
(°F)
True
Constants
Temperature Range0
Vapor
Pressure
at 60 °F
(psia)
A
dimension less
B
(°C)
C
(°C)
Minimum
(°F)
Maximum
(°F)
Acetaldehyde
00075-07-0
44.05
6.5464
12.19
8.063
1,637.1
295.47
32
94
69
Acetic acid
00064-19-7
60.05
8.7277
0.176
7.557
1,642.5
233.39
63
244
244
Acetic anhydride
{acetic acid anhydride}
00108-24-7
102.09
9.03
0.053
7.122
1,427.8
198.04
145
283
282
Acetone
00067-64-1
58.08
6.5577
2.921
7.300
1,312.3
240.71
7
454
133
Acetonitrile
00075-05-8
41.05
6.56
1.090
7.154
1,355.4
235.30
59
192
179
Acrylamide
00079-06-1
71.08
9.36
8.57E-05
11.293
3,939.9
273.16
379
Acrylic acid
{2-propenoic acid}
00079-10-7
72.06
8.77
1.344
5.652
648.6
154.68
68
158
282
Acrylonitrile
{2-propenenitrile}
00107-13-1
53.06
6.73
1.383
6.942
1,255.9
231.30
-60
172
172
Allyl alcohol
00107-18-6
58.08
7.13
0.326
11.658
4,510.2
416.80
70
207
206
Allyl chloride
00107-05-1
76.52
7.83
4.702
5.297
418.4
128.68
55
111
113
{3-chloro-1-propene}
Aniline
00062-53-3
93.13
8.53
0.0058
7.221
1,661.9
199.10
88
363
363
Benzene
00071-43-2
78.11
7.32
1.171
6.906
1,211.0
220.79
46
217
176
Benz[a]anthracene
00056-55-3
228.29
7.92E-10
11.528
5,461
273.15
219
260
820
Benzo[a]pyrene
00050-32-8
252.31
2.29E-11
12.482
6,181
273.15
185
316
923
Benzo[ghi]perylene
00191-24-2
276.33
2.07E-13
11.820
6,580
273.15
391
513
Biphenyl
00092-52-4
154.21
8.68
2.37E-04
7.245
1,998.7
202.73
156
520
489
Butadiene (1,3)
{divinyl}
00106-99-0
54.09
5.1377
30.22
6.873
941.7
240.40
-104
29
24
Butane (n)
00106-97-8
58.12
4.7877
25.67
6.725
909.7
237.00
-108
31
32
Butene (1)
00106-98-9
56.11
4.9177
30.83
7.122
1,099.2
264.89
-108
25
21
Butene (cis-2)
00590-18-1
56.11
5.1477
22.62
6.863
957.1
236.65
-94
73
39
Butene (2-methyl-1)
00563-46-2
70.13
5.43
8.257
6.862
1,047.8
232.06
34
145
88
Butene (trans-2)
00624-64-6
56.11
5.0077
24.97
6.919
982.2
242.38
-97
34
34
Butyl alcohol (n)
{butanol (1)}
00071-36-3
74.12
6.76
0.062
7.421
1,351.6
179.81
73
244
243
Butyl alcohol (tert)
{1,1-dimethyl ethanol}
00075-65-0
74.12
6.58
0.424
7.373
1,174.9
179.23
103
180
180
Butyl chloride (-n)
{1-chloro-butane}
00109-69-3
92.57
7.40
1.255
6.871
1,182.9
218.27
2
173
170
Butyl ether (di-tert)
06163-66-2
130.23
6.39
0.381
6.590
1,157.7
203.05
39
228
224
Carbon disulfide
00075-15-0
76.14
10.54
4.817
6.942
1,168.6
241.53
38
176
115
Carbon tetrachloride
00056-23-5
153.82
13.31
1.431
6.898
1,221.8
227.41
68
172
170
7.1-86
Liquid Storage Tanks
06/18
-------
Normal
CAS
Liquid
Boiling
Chemical
Registry
Molecular
Density
Point
Name
No.
Weight
(lb/gal)
Antoine's Equation13
(°F)
True
Constants
Temperature Range0
Vapor
Pressure
A
B
C
Minimum
Maximum
at 60 °F
dimension less
(°C)
(°C)
(°F)
(°F)
(psia)
Chlorobenzene
00108-90-7
112.56
9.23
0.134
6.986
1,435.7
218.03
144
269
269
Chlorobutane (2)
00078-86-4
92.57
7.27
1.255
6.871
1,182.9
218.27
2
173
170
Chloroform
00067-66-3
119.38
12.38
2.468
7.083
1,233.1
232.20
-73
142
142
Chloroprene
{2-chloro-1,3-butadiene}
00126-99-8
88.54
7.98
2.736
6.291
841.9
187.79
68
140
140
Chlorotoluene (o)
{1 -chloro-2methylbenzene}
00095-49-8
126.58
9.04
0.039
7.363
1,768.1
234.76
42
319
318
Chrysene
{benzo[a]phenanthrene}
00218-01-9
228.29
10.63
1.86E-11
12.320
6,160
273.15
185
374
838
Cresol (m)
{3-methyl-phenol}
00108-39-4
108.14
8.63
0.0013
7.477
1,833.1
196.74
301
394
396
Cresol (o)
{2-methyl-phenol}
00095-48-7
108.14
9.4777
0.0016
6.843
1,391.3
160.18
248
376
376
Cresol (p)
{4-methyl-phenol}
00106-44-5
108.14
8.50104
0.00062
7.016
1,498.6
160.55
262
395
395
Cyclohexane
00110-82-7
84.16
6.4677
1.212
6.845
1,203.5
222.86
68
179
177
Cyclohexanol
00108-93-0
100.16
8.03
0.00090
5.956
111 A
91.11
201
321
320
Cyclohexanone
00108-94-1
98.14
7.91
0.0042
5.978
1,495.5
209.55
193
330
311
Cyclohexene
00110-83-8
82.14
6.77
0.110
5.872
1,221.9
223.17
98
196
181
Cyclopentane
00287-92-3
70.13
6.22
4.171
6.878
1,119.2
230.74
60
122
121
Cyclopentanone
00120-92-3
84.12
7.92
0.130
3.958
376.4
104.65
32
78
266
Cyclopentene
00142-29-0
68.12
6.44
3.264
6.921
1,121.8
223.45
111
Decane (-n)
00124-18-5
142.28
6.09
0.011
3.085
440.6
116.25
-21
99
345
Dibromopropane (1,2)
00078-75-1
201.89
16.13
0.088
7.314
1,667.0
234.85
19
287
286
Dibromopropane (1,3)
00109-64-8
201.89
16.55
0.029
7.309
1,776.7
233.46
49
333
314
Dichloroethane (1,1)
00075-34-3
98.96
9.81
2.863
7.097
1,229.2
233.95
-77
135
135
Dichloroethane (1,2)
00107-06-2
98.96
10.4077
0.961
7.460
1,521.8
248.48
-23
211
182
Dichloroethylene (1,2)
{1,2 dichloroethene}
00540-59-0
96.94
10.76
2.579
7.022
1,205.4
230.60
32
183
141
Dichloroethylene (trans-1,2)
00156-60-5
96.94
10.49
4.333
6.965
1,141.9
231.90
-36
185
118
Dichlorotoluene (3,4)
00095-75-0
161.03
10.49
0.0029
7.344
1,882.5
215.00
32
221
408
Diethoxyethane (1,1)
00105-57-7
118.17
6.89
0.307
7.625
1,574.0
229.47
-10
216
212
Diethoxymethane
00462-95-3
104.15
6.94
0.810
6.986
1,270.2
221.26
32
167
191
Diethyl (n,n) aniline
{N,N-diethylbenzenamine}
00091-66-7
149.23
7.77
0.0031
8.258
2,652.8
277.32
122
425
422
Diethyl ketone
{3-pentanone}
00096-22-0
86.13
6.7677
0.423
5.741
716.2
147.17
97
215
215
Diethyl sulfide
00352-93-2
90.19
6.98
0.749
7.541
1,560.5
246.59
-39
190
197
Diethylamine
06/18
Liquid Storage Tanks
7.1-87
-------
Normal
CAS
Liquid
Boiling
Chemical
Registry
Molecular
Density
Point
Name
No.
Weight
(lb/gal)
Antoine's Equation13
(°F)
True
Constants
Temperature Range0
Vapor
Pressure
A
B
C
Minimum
Maximum
at 60 °F
dimension less
(°C)
(°C)
(°F)
(°F)
(psia)
{N-ethyl ethanamine}
00109-89-7
73.14
5.89
2.712
5.737
559.1
140.18
89
141
132
Diethylbenzene (1,2)
00135-01-3
134.22
7.34
0.0094
6.990
1,577.9
200.55
206
364
361
Diethylbenzene (1,3)
00141-93-5
134.22
7.18
0.010
7.006
1,576.3
201.00
203
360
358
Diethylbenzene (1,4)
00105-05-5
134.22
7.20
0.010
7.001
1,589.3
202.02
206
365
363
Di-isopropyl ether
00108-20-3
102.17
6.04
1.877
6.842
1,135.0
218.23
74
153
155
Dimethoxyethane (1,2)
00110-71-4
90.12
7.25
0.966
6.713
1,260.5
235.83
-55
199
185
Dimethyl formamide (n,n)
00068-12-2
73.09
7.8877
0.040
6.806
1,337.7
190.50
86
194
307
Dimethyl hydrazine (1,1)
00057-14-7
60.10
6.6072
1.896
7.588
1,388.5
232.54
-32
68
146
Dimethyl phthalate
00131-11-3
194.18
9.94
2.25E-08
4.522
700.3
51.42
180
304
540
Dimethylbutane (2,3)
00079-29-8
86.18
5.52
3.064
6.810
1,127.2
228.95
58
138
136
Dimethylcyclopentane (1,1)
01638-26-2
98.19
6.2677
0.932
6.830
1,226.6
222.76
60
192
190
Dimethylpentane (2,2)
00590-35-2
100.20
5.63
1.315
6.815
1,190.3
223.34
60
176
174
Dimethylpentane (2,3)
00565-59-3
100.20
5.80
0.842
6.862
1,242.6
222.34
64
195
194
Dimethylpentane (2,4)
00108-08-7
100.20
5.62
1.221
6.836
1,197.6
222.27
57
178
177
Dimethylpentane (3,3)
00562-49-2
100.20
5.79
1.029
6.831
1,231.0
225.58
56
189
187
Dioxane (1,4)
00123-91-1
88.11
8.63
0.439
7.456
1,570.1
241.85
68
221
214
Dipropyl ether
{di-n-propyl ether}
00111-43-3
102.17
6.23
0.754
6.945
1,254.8
218.82
80
192
194
Dodecane(n)
00112-40-3
170.33
6.25
0.00093
6.981
1,625.9
180.31
259
423
421
Epichlorohydrin
{chloromethyl oxirane}
00106-89-8
92.52
9.85
0.194
8.229
2,086.8
273.16
241
Ethane
00074-84-0
30.07
472
6.813
659.7
256.431
-215
-100
-127
Ethanolamine (mono)
00141-43-5
61.08
8.50
0.002
7.168
1,408.9
157.06
150
340
339
Ethyl acetate
00141-78-6
88.11
7.51
1.135
7.103
1,245.7
217.96
60
168
171
Ethyl acrylate
{ethyl ester 2-propenoic acid}
00140-88-5
100.12
7.71
0.445
7.150
1,366.1
220.47
-21
211
211
Ethyl alcohol
{ethanol}
00064-17-5
46.07
6.59
0.648
8.247
1,670.4
232.96
32
173
173
Ethyl chloride
00075-00-3
64.51
7.4377
16.63
7.037
1,052.8
241.07
-69
55
61
Ethyl ether
{diethyl ether}
00060-29-7
74.12
5.96
6.675
6.897
1,062.6
228.22
-10
132
94
Ethylamine
00075-04-7
45.08
5.6577
14.08
7.405
1,203.8
249.43
62
349
64
Ethylbenzene
00100-41-4
106.17
7.24
0.104
6.950
1,419.3
212.61
134
279
277
Ethylcyclopentane
01640-89-7
98.19
6.40
0.475
6.898
1,305.0
221.40
84
220
218
Ethylene
{ethene}
00074-85-1
28.05
4 -74-155
749
6.748
584.1
254.84
-191
-120
-155
Ethyleneoxide
00075-21-8
44.05
7.3650
17.84
8.722
2,022.8
335.81
32
89
53
Ethylpentane (3)
00617-78-7
100.20
5.83
0.701
6.880
1,254.1
220.15
70
202
200
Fluoranthene
00206-44-0
202.25
10.45
3.96E-08
12.836
5,348.1
273.15
77
230
723
7.1-88 Liquid Storage Tanks 06/18
-------
Normal
Chemical
Name
CAS
Registry
No.
Molecular
Weight
Liquid
Density
(lb/gal)
Antoine's Equation13
Boiling
Point
(°F)
True
Constants
Temperature Range0
Vapor
Pressure
at 60 °F
(psia)
A
dimension less
B
(°C)
C
(°C)
Minimum
(°F)
Maximum
(°F)
Fluorobenzene
00462-06-6
96.10
8.53
0.936
7.237
1,409.8
238.36
0
183
185
Formic acid
00064-18-6
46.03
10.18
0.516
4.876
515.0
133.74
33
93
213
Freon 11
{trichlorofluoromethane}
00075-69-4
137.37
12.48
10.93
6.884
1,043.0
236.88
75
Furan
00110-00-9
68.07
7.94
7.963
6.975
1,060.8
227.73
37
143
89
Furfural
{2-furancarboxaldehyde}
00098-01-1
96.09
9.68
0.018
6.969
1,430.1
188.70
133
321
323
Heneicosane (n)
00629-94-7
296.57
6.61
6.23E-07
8.796
3,571.2
253.20
307
663
679
Heptane (n)
00142-82-5
100.20
5.71
0.541
6.903
1,268.6
216.95
79
211
209
Heptene (1)
00592-76-7
98.19
5.82
0.752
7.093
1,400.7
238.96
32
192
201
Hexadiene (1,5)
00592-42-7
82.14
5.7477
2.890
6.563
1,008.1
214.16
32
138
140
Hexane(n)
00110-54-3
86.18
5.4777
1.913
6.878
1,171.5
224.37
55
157
156
Hexanol (1)
00111-27-3
102.17
6.79
0.005
7.288
1,422.0
165.44
126
315
314
Hexene (1)
00592-41-6
84.16
5.62
2.378
6.866
1,153.0
225.85
61
148
147
Hydrogen cyanide
{hydrocyanic acid}
00074-90-8
27.03
5.74
9.931
7.549
1,340.8
261.56
2
115
79
Isobutane
{methylpropane (2)}
00075-28-5
58.12
4.6077
38.22
6.819
912.1
243.34
-121
11
12
Isobutene
{methylpropene (2)}
00115-11-7
56.11
4.9277
32.18
6.522
799.1
226.54
-70
32
20
Isobutyl alcohol
{2-methyl 1-propanol}
00078-83-1
74.12
6.69
0.096
7.306
1,237.0
171.62
176
240
226
Isooctane
{2,2,4-trimethylpentane}
00540-84-1
114.23
5.7477
0.596
6.812
1,257.8
220.74
76
212
211
Isopentane
{2-methyl butane}
00078-78-4
72.15
5.18
9.426
6.790
1,020.0
233.10
61
83
82
Isopentene
{2-methyl 2-butene}
00513-35-9
70.13
5.53
6.210
6.922
1,098.6
233.26
37
159
100
Isoprene
{2-methyl 1,3-butadiene}
00078-79-5
68.12
5.67
7.446
6.091
706.9
186.10
62
93
93
Isopropyl alcohol
{isopropanol}
00067-63-0
60.10
6.5277
0.443
7.736
1,357.4
197.34
134
193
180
Isopropyl benzene
{cumene}
00098-82-8
120.19
7.19
0.048
6.929
1,455.8
207.20
158
308
305
Isopropylbenzene
(1-methyl-2)
00527-84-4
134.22
7.32
0.017
7.417
1,880.5
236.27
178
355
350
Methacrylonitrile
{2-methyl 2-propenenitrile}
00126-98-7
67.09
6.68
0.886
6.999
1,353.6
238.03
-48
194
194
Methane
00074-82-8
16.04
3.53"260
4567
7.096
516.7
284.37
-262
-117
-260
06/18
Liquid Storage Tanks
7.1-89
-------
Normal
Chemical
Name
CAS
Registry
No.
Molecular
Weight
Liquid
Density
(lb/gal)
Antoine's Equation13
Boiling
Point
(°F)
True
Constants
Temperature Range0
Vapor
Pressure
at 60 °F
(psia)
A
dimension less
B
(°C)
C
(°C)
Minimum
(°F)
Maximum
(°F)
Methyl acetate
{methyl ester acetic acid}
00079-20-9
74.08
7.80
2.703
7.079
1,164.4
220.46
35
133
134
Methyl acrylate
{methyl ester 2-propenoic
00096-33-3
86.09
7.96
1.058
7.198
1,338.7
229.63
-47
176
177
acid}
Methyl alcohol
{methanol}
00067-56-1
32.04
6.61
1.476
8.079
1,581.3
239.65
59
183
148
Methyl ethyl ketone
{2-butanone}
00078-93-3
72.11
6.6877
1.081
6.864
1,150.2
209.25
106
207
176
Methyl isobutyl ketone
00108-10-1
100.16
6.6577
0.219
6.828
1,254.1
201.61
71
241
241
Methyl methacrylate
00080-62-6
100.12
7.88
0.416
8.253
1,945.6
265.58
102
192
213
Methyl propyl ether
00557-17-5
74.12
6.1455
6.017
6.563
903.6
206.46
31
103
102
Methyl styrene (alpha)
00098-83-9
118.18
7.60
0.024
6.924
1,486.9
202.40
329
Methylcyclohexane
00108-87-2
98.19
6.42
0.558
6.823
1,270.8
221.42
27
261
214
Methylcyclopentane
00096-37-7
84.16
6.25
1.738
6.863
1,186.1
226.04
59
163
161
Methyldichlorosilane
20156-50-7
115.03
8.91
5.718
7.028
1,167.8
240.70
34
106
Methylene chloride
00075-09-2
84.93
11.07
5.640
7.412
1,327.0
252.68
-40
104
104
Methylhexane (2)
00591-76-4
100.20
5.66
0.799
6.882
1,240.9
220.10
65
196
194
Methylhexane (3)
00589-34-4
100.20
5.72
0.744
6.874
1,243.8
219.63
68
199
197
Methylpentane (2)
00107-83-5
86.18
5.4377
2.730
6.839
1,135.4
226.57
55
142
142
Methyl-tert-butyl ether
{MTBE}
01634-04-4
88.15
6.18
3.226
6.867
1,116.1
224.74
125
431
131
Morpholine
00110-91-8
87.12
8.35
0.109
7.718
1,745.8
235.00
32
111
263
Naphthalene
00091-20-3
128.17
8.56
0.0024
7.146
1,831.6
211.82
177
354
422
Nitrobenzene
00098-95-3
123.11
10.05
0.0022
7.091
1,727.6
199.71
273
411
412
Nitromethane
00075-52-5
61.04
9.49
0.415
7.281
1,446.2
227.52
132
277
214
Nonadecane(n)
00629-92-5
268.52
6.56
3.64E-07
33.303
28,197
725.94
91
131
624
Nonane (n)
00111-84-2
128.26
5.99
0.037
6.700
1,492.9
217.26
-64
94
303
Octadecane (n)
00593-45-3
254.49
6.4882
6.16E-07
7.207
2,069.0
161.22
346
602
592
Octane (n)
00111-65-9
114.23
5.8377
0.142
8.076
1,936.3
253.01
-70
75
258
Octanol (1)
00111-87-5
130.23
6.9077
0.00061
9.352
2,603.4
224.35
68
176
383
Octene (1)
00111-66-0
112.21
5.97
0.196
6.933
1,353.5
212.76
113
252
251
Pentachloroethane
00076-01-7
202.29
14.02
0.040
6.643
1,342.3
196.51
77
324
324
Pentadiene (1,2)
00591-95-7
68.12
5.78
4.718
6.936
1,125.5
231.88
-76
-19
113
Pentadiene (1,4)
00591-93-5
68.12
5.52
10.06
7.035
1,108.2
241.05
-110
65
79
Pentadiene (2,3)
00591-96-8
68.12
5.80
4.223
7.263
1,256.2
239.57
-76
-15
119
Pentane (n)
00109-66-0
72.15
5.23
6.884
6.864
1,070.6
232.70
24
155
97
Pentene (1)
00109-67-1
70.13
5.35
8.671
6.786
1,014.3
229.78
55
87
88
Pentyne (1)
00627-19-0
68.12
5.76
5.657
6.967
1,092.5
227.18
-47
142
104
7.1-90
Liquid Storage Tanks
06/18
-------
Normal
Chemical
Name
CAS
Registry
No.
Molecular
Weight
Liquid
Density
(lb/gal)
Antoine's Equation13
Boiling
Point
(°F)
True
Constants
Temperature Range0
Vapor
Pressure
at 60 °F
(psia)
A
dimension less
B
(°C)
C
(°C)
Minimum
(°F)
Maximum
(°F)
Phenanthrene
00085-01-8
178.23
8.18
3.37E-06
7.394
2,428.5
202.19
212
302
635
Phenol
00108-95-2
94.11
8.80113
0.003
7.122
1,509.7
174.20
225
359
359
Phosgene
00075-44-5
98.92
11.4577
19.43
7.146
1,072.7
243.30
47
345
46
Picoline (3)
{3-methyl pyridine}
00108-99-6
93.13
7.98
0.064
7.054
1,484.3
211.54
165
364
291
Propane
00074-98-6
44.10
4.1277
111
6.858
819.3
248.73
-45
117
-44
Propanethiol (1)
00107-03-9
76.16
7.02
1.943
6.929
1,183.4
224.63
76
216
154
Propanethiol (2)
00075-33-2
76.16
6.80
3.590
6.877
1,113.9
226.16
51
186
131
Propyl alcohol (n)
{propanol (1)}
00071-23-8
60.10
6.6777
0.218
8.189
1,690.9
221.35
67
207
207
Propyl nitrate (n)
{propyl ester nitric acid}
00627-13-4
105.09
8.80
0.261
6.955
1,294.4
206.70
32
158
231
Propylamine (n)
{1-propanamine}
00107-10-8
59.11
5.99
3.990
6.926
1,044.0
210.84
73
172
120
Propylene
{propene}
00115-07-1
42.08
4.22
132
6.850
795.8
248.27
-161
-53
-54
Propylene glycol (1,2)
{1,2 propanediol}
00057-55-6
76.09
8.65
0.00094
8.208
2,085.9
203.54
368
Propylene oxide
00075-56-9
58.08
7.1732
7.101
6.970
1,065.3
226.28
-100
94
95
Pyridine
00110-86-1
79.10
8.20
0.233
7.038
1,371.4
214.65
153
307
240
Resorcinol
00108-46-3
110.11
10.6177
6.65E-06
8.398
2,687.2
210.99
305
530
532
Styrene
00100-42-5
104.15
7.56
0.066
7.095
1,525.1
216.77
86
293
295
Tetrachloroethane (1,1,1,2)
00630-20-6
167.85
12.86
0.133
6.906
1,370.4
210.25
139
266
271
Tetrachloroethane (1,1,2,2)
00079-34-5
167.85
13.32
0.037
6.091
959.6
149.78
77
266
295
Tetrachloroethylene
00127-18-4
165.83
13.54
0.213
7.056
1,440.8
223.98
82
226
250
Tetrahydrofuran
00109-99-9
72.11
7.42
2.039
6.996
1,202.9
226.33
74
211
151
Toluene
00108-88-3
92.14
7.24
0.331
7.017
1,377.6
222.64
32
122
231
Trichloroethane (1,1,1)
00071-55-6
133.40
11.18
1.650
8.761
2,210.2
308.05
22
62
165
Trichloroethane (1,1,2)
00079-00-5
133.40
12.02
0.245
6.945
1,310.3
208.74
122
237
237
Trichloroethylene
00079-01-6
131.39
12.22
0.817
6.429
974.5
187.34
64
188
189
Trichloropropane (1,2,3)
00096-18-4
147.43
11.59
0.031
7.532
1,818.9
232.52
48
316
313
Tridecane (n)
00629-50-5
184.36
6.31
2.46E-04
7.003
1,689.1
174.28
283
457
453
Trifluoroethane
(1,1,2-trichloro-1,2,2)
00076-13-1
187.37
13.0577
4.376
6.880
1,099.9
227.50
-13
181
118
Trimethylbenzene (1,2,4)
00095-63-6
120.19
7.31
0.020
7.044
1,573.3
208.56
126
388
337
Trimethylchlorosilane
{chlorotrimethylsilane}
00075-77-4
108.64
7.1577
3.068
6.951
1,191.0
235.15
37
132
136
Trimethylpentane (2,2,3)
00564-02-3
114.23
5.7477
0.378
6.825
1,294.9
218.42
230
Trimethylpentane (2,3,3)
00560-21-4
114.23
6.06
0.317
6.844
1,328.1
220.38
238
06/18
Liquid Storage Tanks
7.1-91
-------
Chemical
Name
CAS
Registry
No.
Molecular
Weight
Liquid
Density
(lb/gal)
True
Vapor
Pressure
at 60 °F
(psia)
Antoine's Equation13
Normal
Boiling
Point
(°F)
Constants
Temperature Range0
A
dimension less
B
(°C)
C
(°C)
Minimum
(°F)
Maximum
(°F)
Trimethylpentane (2,3,4)
00565-75-3
114.23
6.00
0.314
7.031
1,420.7
228.53
-59
308
237
Undecane (n)
01120-21-4
156.31
6.18
0.0035
6.977
1,572.5
188.02
220
387
383
Vinyl acetate
{acetic acid ethenyl ester}
Vinylidene chloride
{1,1 -dichloro ethene}
00108-05-4
00075-35-4
86.09
96.94
7.78
10.13
1.396
8.096
7.215
6.983
1,299.1
1,104.7
226.97
237.75
71
-19
162
90
163
88
Xylene (m)
{1,3-dimethyl benzene}
Xylene (o)
{1,2-dimethyl benzene}
Xylene (p)
{1,4-dimethyl benzene}
00108-38-3
00095-47-6
00106-42-3
106.17
106.17
106.17
7.21
7.3550
7.19
0.090
0.071
0.097
7.009
6.999
7.021
1.462.3
1,474.7
1.474.4
215.11
213.69
217.77
82
90
56
331
342
355
283
291
281
NOTE Synonyms are shown in braces {}. Prefixes are shown in parentheses ().
a Reference 22.
b Vapor pressure Pva in psia = (0.019337) 1C
c Use of this equation for temperatures outsi
5 ]
)L (Tu 32)5/9+c J where Tla is the temperature in °F.
de the indicated temperature range may result in loss of accuracy.
7.1-92
Liquid Storage Tanks
06/18
-------
Table 7.1-4. HEIGHT OF THE LIQUID HEEL AND VAPOR SPACE UNDER A LANDED
FLOATING ROOF3
Scenario
Condition
Expression for height of the vapor space (/?,)
General Expression
SIodc convention:
Sb is expressed in ft/ft; positive
for cone down, negative for
cone up.
K = [hd+^p^-hle
Full liauid heel
he [h, 1 6 )
hv =hd-hi
Partial liquid heel
(this condition may occur
after normal pumpout of
a tank with a cone-down
bottom, or be created
during the tank cleaning
process of any tank that
had a full liquid heel after
normal pumpout)
hie = the height that would result
from spreading the available
volatile materials evenly over a
flat tank bottom.
hie =
(volume of heel, ft
[zD2/4)
¦ + clingage
hv
hd +
SrD
^ volume of heel, ft31 ( 0.01 in.
7rZr/4
112 in./ft,
No significant amount of
volatile material
remaining
(drain dry tanks or any
tank after sludge
removal)
kle= 0
hv — I hd +
S„D
Flat bottom
(including slight cone-up
bottoms)
SB= 0
he is evaluated per the applicable
case above.
hv = hd hie {= hd-hi, given Sb = 0}
where:
ha = deck leg height at the tank shell, ft
hi = height of liquid at the tank shell, ft
hie = effective liquid height during roof landing, ft
hv = vapor space height under landed floating roof, ft
Sb = tank cone bottom slope, ft/ft
a Reference 23.
06/18
Liquid Storage Tanks
7.1-93
-------
Table 7.1-5. LEL VALUES FOR SELECTED COMPOUNDS'
LEL
Compound (volume percent in air)
Heptane (C7)
1.05
Hexane (C6)
1.1
Pentane (C5)
1.5
Butane (C4)
1.9
Propane (C3)
2.1
Ethane (C2)
3.0
Methane (CI)
5.0
a Reference 28.
7.1-94
Liquid Storage Tanks
06/18
-------
Table 7.1-6. PAINT SOLAR ABSORPTANCE
Surface Color
Shade or Type
Reflective Condition
(see Note 1)
New
Average
Aged
White
0.17
0.25
0.34
Aluminum
Specular
0.39
0.44
0.49
Aluminum
Diffuse
0.60
0.64
0.68
Beige/Cream
0.35
0.42
0.49
Black
0.97
0.97
0.97
Brown
0.58
0.62
0.67
Gray
Light
0.54
0.58
0.63
Gray
Medium
0.68
0.71
0.74
Green
Dark
0.89
0.90
0.91
Red
Primer
0.89
0.90
0.91
Rust
red iron oxide
0.38
0.44
0.50
Tan
0.43
0.49
0.55
Aluminum
(see Note 2)
mill finish, unpainted
0.10
0.12
0.15
NOTE 1 Reflective condition definitions:
New: For paint, paint still retains the fresh shine of having been recently
applied; for mill-finish aluminum, surface is shiny. This was previously
labeled "Good."
Averaqe: For paint, paint is in qood condition, but the initial shine has
faded; for mill-finish aluminum, surface is oxidized but still bright. The
value given in each case is the average of the New and the Aged values
for that case, and does not represent new data.
Aqed: For paint, paint is noticeably faded and dull: for mill-finish aluminum,
surface is dull. This was previously labeled "Poor."
NOTE 2 This refers to aluminum as the base metal, rather than aluminum-
colored paint.
Notes:
a Reference 22. If specific information is not available, a white shell and roof, with the paint in average
condition, can be assumed to represent the most common or typical tank surface in use. If the tank roof
and shell are painted a different color, a is determined from a = (a r + a s)/2; where a r is the tank
roof paint solar absorptance and (X •<, is the tank shell paint solar absorptance.
06/18
Liquid Storage Tanks
7.1-95
-------
Table 7.1-7. METEOROLOGICAL DATA (Tax, Tan, V, I, Pa) FOR SELECTED U.S. LOCATIONS
Location
Symbol
Units
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
Birmingham, AL
Tan
°F
31.3
34.5
42.3
49.3
57.7
65.1
69.4
68.7
63.0
50.2
41.5
34.9
50.7
Tax
°F
51.6
56.8
66.0
74.7
81.0
87.4
90.0
89.1
83.8
74.7
64.6
55.8
73.0
V
mi/hr
7.6
8.5
8.5
8.1
6.7
5.8
5.6
5.4
6.3
6.0
6.7
7.4
6.9
I
Btu/ft2/day
793
1046
1395
1744
1902
1966
1871
1775
1522
1268
888
729
1395
Pa
lb/in2
14.45
Huntsville, AL
Tan
°F
29.1
32.5
40.8
48.9
57.4
64.9
68.9
67.8
61.5
49.3
40.5
33.1
49.6
Tax
°F
48.2
53.4
62.8
72.5
79.3
86.5
89.1
88.9
82.8
73.0
62.4
52.5
71.1
V
mi/hr
9.2
9.8
10.1
9.4
7.8
6.7
6.3
6.0
6.9
7.4
8.5
9.4
8.1
I
Btu/ft2/day
761
983
1300
1680
1871
1997
1934
1807
1490
1236
856
666
1395
Pa
lb/in2
14.43
Mobile, AL
Tan
°F
39.9
42.6
50.2
57.0
64.4
70.7
73.2
72.9
68.7
57.4
49.1
43.2
57.4
Tax
°F
59.7
63.7
70.9
78.4
84.6
90.0
91.2
90.5
86.9
79.5
70.3
63.0
77.4
V
mi/hr
10.1
10.5
10.5
10.3
8.7
7.6
6.7
6.5
7.6
8.1
9.2
9.8
8.7
I
Btu/ft2/day
856
1110
1395
1712
1871
1871
1775
1649
1490
1332
983
793
1395
Pa
lb/in2
14.65
Montgomery, AL
Tan
°F
35.8
38.8
45.7
52.9
60.8
67.8
71.4
70.9
66.0
53.2
44.6
38.7
54.0
Tax
°F
56.3
60.8
68.5
76.5
82.9
89.4
91.0
90.3
87.1
78.3
68.7
60.3
75.7
V
mi/hr
7.6
8.1
8.3
7.4
6.0
5.6
5.6
5.1
5.8
5.6
6.5
7.4
6.7
I
Btu/ft2/day
856
1110
1427
1807
1966
2029
1934
1807
1554
1332
951
793
1458
Pa
lb/in2
14.66
Anchorage, AK
Tan
°F
8.4
11.5
18.1
28.6
38.8
47.1
51.6
49.5
41.5
28.8
15.1
10.0
29.1
Tax
°F
21.4
25.9
33.1
42.8
54.3
61.5
65.1
63.0
55.2
40.5
27.1
22.5
42.6
V
mi/hr
6.5
6.9
6.7
7.4
8.3
8.5
7.2
6.9
6.7
6.7
6.5
6.3
6.9
I
Btu/ft2/day
95
317
729
1141
1458
1554
1458
1110
698
349
127
63
761
Pa
lb/in2
14.56
Annette, AK
Tan
°F
29.7
32.2
34.0
37.0
42.3
47.8
52.0
52.3
48.0
41.9
34.7
31.5
40.3
Tax
°F
38.8
41.9
44.8
49.5
55.8
60.8
64.6
64.9
60.3
51.8
43.9
39.9
51.4
V
mi/hr
11.0
11.2
9.8
9.8
8.5
8.3
7.6
7.6
8.3
10.7
11.2
10.7
9.4
I
Btu/ft2/day
190
380
698
1110
1490
1585
1554
1268
856
444
222
159
824
Pa
lb/in2
14.63
Barrow, AK
Tan
°F
-19.3
-23.6
-21.1
-9.0
14.4
29.7
33.6
33.3
27.0
00
CO
-6.9
-17.1
4.1
Tax
°F
-7.4
-11.7
-9.0
4.6
24.3
38.3
45.0
42.3
33.8
18.1
3.6
-5.3
14.7
-------
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£
&
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r-K
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CfQ
CD
ft
0
1
vo
o
Location
Symbol
Units
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
V
mi/hr
12.3
11.2
11.4
11.6
11.9
11.9
11.6
12.5
13.4
13.0
12.5
11.6
12.1
I
Btu/ft2/day
0
95
507
1173
1490
1554
1427
824
412
159
0
0
634
Pa
lb/in2
14.74
Bethel, AK
Tan
°F
0.3
-0.8
5.4
15.6
31.6
42.3
47.7
46.2
38.3
23.7
10.9
2.1
21.9
Tax
°F
12.9
12.7
21.0
31.3
48.2
58.8
62.2
59.5
52.0
35.1
22.6
14.7
36.0
V
mi/hr
14.5
15.2
14.1
13.0
11.6
11.2
10.7
11.0
11.6
12.5
13.2
14.3
12.8
I
Btu/ft2/day
127
349
793
1236
1427
1522
1363
1015
698
380
159
63
761
Pa
lb/in2
14.55
Bettles, AK
Tan
°F
-20.4
-18.2
-8.7
9.7
33.4
46.9
49.3
43.9
32.4
12.0
-8.9
-16.8
12.9
Tax
°F
-4.9
0.3
14.4
31.5
52.9
67.5
69.6
62.8
48.9
25.0
5.2
-1.8
30.9
V
mi/hr
6.0
6.3
7.2
7.6
7.6
7.2
6.7
6.0
6.7
6.7
6.0
5.6
6.7
I
Btu/ft2/day
32
190
634
1236
1680
1807
1585
1110
666
254
63
0
761
Pa
lb/in2
14.33
Big Delta, AK
Tan
°F
-11.0
-6.2
2.5
20.5
36.9
47.1
50.7
46.0
35.8
17.8
-1.7
-8.5
19.2
Tax
°F
3.0
10.6
24.4
40.3
56.7
66.4
69.6
64.8
53.2
31.3
12.7
5.4
36.5
V
mi/hr
12.1
10.5
9.2
8.5
8.5
7.8
6.5
7.2
8.5
8.7
10.3
11.6
9.2
I
Btu/ft2/day
63
254
729
1236
1617
1744
1649
1236
761
349
95
32
824
Pa
lb/in2
13.97
Cold Bay, AK
Tan
°F
24.1
22.8
25.0
28.6
34.9
40.8
46.0
47.1
43.2
34.9
29.8
26.6
33.6
Tax
°F
33.1
32.0
34.9
37.9
44.4
50.4
55.0
55.9
52.2
44.2
38.8
35.2
43.0
V
mi/hr
17.9
17.9
17.2
17.9
16.3
15.9
15.7
16.1
16.6
17.0
17.4
17.4
17.0
I
Btu/ft2/day
190
380
698
983
1173
1236
1173
951
698
444
222
127
698
Pa
lb/in2
14.55
Fairbanks, AK
Tan
°F
-18.6
-14.4
-1.7
20.5
37.9
49.5
52.5
47.1
36.1
18.1
-5.6
-14.8
17.2
Tax
°F
-1.7
7.2
23.7
41.0
59.4
70.2
72.3
66.4
54.9
32.0
10.9
1.8
36.5
V
mi/hr
3.4
4.3
5.6
6.9
7.8
7.6
6.9
6.5
6.3
5.6
3.8
3.4
5.6
I
Btu/ft2/day
32
254
729
1268
1617
1775
1617
1173
729
317
95
0
793
Pa
lb/in2
14.42
Gulkana, AK
Tan
°F
-13.9
-7.1
2.7
19.9
32.5
42.3
46.4
42.3
33.4
19.6
-2.6
-10.8
17.1
Tax
°F
2.5
13.6
28.0
41.5
54.9
64.2
68.4
64.8
54.1
35.2
12.7
4.6
37.0
V
mi/hr
3.6
4.9
6.0
7.6
8.3
8.5
7.6
7.8
7.2
6.3
4.0
4.0
6.3
I
Btu/ft2/day
95
317
793
1300
1617
1744
1680
1300
824
380
127
63
856
Pa
lb/in2
13.81
King Salmon, AK
Tan
°F
7.5
6.6
14.2
23.4
34.0
41.4
46.4
46.4
39.7
25.2
15.1
8.2
25.7
-------
0
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vo
00
-Q
£
&
C/3
r-K
o
,P
CfQ
o
FT
O
00
Location
Symbol
Units
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
Tax
°F
22.1
22.8
30.7
39.0
50.9
58.6
63.0
61.3
54.7
39.7
29.7
23.4
41.4
V
mi/hr
11.0
11.4
11.4
11.2
11.2
11.0
10.1
10.5
10.5
10.3
10.5
11.0
10.7
I
Btu/ft2/day
159
380
761
1141
1395
1458
1363
1078
729
444
190
95
761
Pa
lb/in2
14.58
Kodiak, AK
Tan
°F
24.6
25.0
27.0
31.5
37.6
43.5
48.2
48.4
43.3
34.2
28.8
25.2
34.9
Tax
°F
35.1
36.1
38.8
43.7
49.5
55.6
60.4
61.9
56.7
47.1
39.9
36.3
46.8
V
mi/hr
12.3
12.3
11.9
11.6
10.3
9.2
7.6
8.1
9.2
11.0
12.1
12.3
10.5
I
Btu/ft2/day
159
349
729
1110
1363
1458
1427
1205
793
476
222
95
793
Pa
lb/in2
14.55
Kotzebue, AK
Tan
°F
-7.4
-11.9
-8.0
2.3
24.4
37.8
48.6
47.3
37.0
18.1
2.5
-7.4
15.3
Tax
°F
5.5
2.3
8.8
20.3
37.9
49.6
59.2
57.0
46.9
27.7
13.1
5.5
27.9
V
mi/hr
13.9
12.3
11.4
11.9
11.6
12.1
12.5
12.5
13.4
13.2
14.3
14.1
12.8
I
Btu/ft2/day
32
190
666
1300
1744
1744
1522
1046
634
285
63
0
761
Pa
lb/in2
14.66
McGrath, AK
Tan
°F
-17.9
-14.3
-2.9
16.0
34.5
45.1
48.9
45.0
35.4
18.0
-3.6
-14.6
15.8
Tax
°F
0.3
9.0
23.4
37.0
54.5
65.5
68.4
63.5
52.9
31.3
12.4
2.7
35.1
V
mi/hr
3.1
4.5
5.6
6.9
6.9
6.7
6.3
6.3
6.3
5.8
4.0
3.4
5.6
I
Btu/ft2/day
95
317
761
1332
1522
1617
1458
1110
698
349
127
32
793
Pa
lb/in2
14.46
Nome, AK
Tan
°F
-0.8
-4.5
-0.2
9.7
29.1
38.8
45.1
44.1
36.3
22.3
9.3
-0.6
19.0
Tax
°F
14.7
12.2
17.4
25.5
42.1
52.9
57.7
56.1
48.7
33.6
22.5
15.1
33.3
V
mi/hr
11.6
10.3
10.1
10.5
10.3
10.1
10.1
11.0
11.6
11.0
11.4
11.2
10.7
I
Btu/ft2/day
63
254
729
1363
1680
1744
1458
1046
666
317
95
32
793
Pa
lb/in2
14.63
St. Paul Island, AK
Tan
°F
22.5
18.0
19.4
23.9
31.3
37.0
42.4
44.4
40.3
33.6
28.9
24.8
30.6
Tax
°F
30.7
27.0
28.9
32.7
39.4
45.9
49.6
51.1
48.7
42.1
37.0
33.3
38.8
V
mi/hr
19.2
19.9
18.6
17.9
15.2
13.6
12.3
13.6
15.7
17.9
18.8
19.7
16.8
I
Btu/ft2/day
159
380
761
1110
1236
1268
1141
919
698
412
190
127
698
Pa
lb/in2
14.59
Talkeetna, AK
Tan
°F
0.7
3.9
9.9
22.5
33.8
44.4
48.9
45.7
36.7
23.2
7.9
2.8
23.4
Tax
°F
19.2
25.3
33.4
43.3
55.9
64.4
67.6
64.6
55.6
39.4
25.2
19.8
42.8
V
mi/hr
6.5
6.0
6.0
5.6
5.6
5.8
5.4
4.5
4.3
4.7
6.0
6.3
5.6
I
Btu/ft2/day
95
317
729
1300
1522
1585
1490
1141
729
380
127
63
793
Pa
lb/in2
14.45
-------
o
00
-Q
£
&
IT!
r-K
o
l-s
,p
CfQ
CD
ft
0
1
vo
Location
Symbol
Units
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
Yakutat, AK
Tan
°F
18.7
21.0
23.7
29.1
36.5
43.3
47.8
46.6
41.0
34.7
25.2
21.0
32.4
Tax
°F
31.5
35.1
38.1
43.5
50.0
55.6
59.4
59.7
55.2
47.1
37.2
33.1
45.5
V
mi/hr
7.2
6.9
6.7
6.7
7.2
6.9
6.5
6.3
6.7
7.6
6.9
7.2
6.9
I
Btu/ft2/day
127
317
698
1110
1300
1395
1332
1078
698
349
159
95
729
Pa
lb/in2
14.63
Flagstaff, AZ
Tan
°F
15.3
17.8
21.4
26.8
33.3
41.4
50.5
48.9
41.2
30.9
22.5
15.8
30.6
Tax
°F
42.3
45.3
49.3
57.7
67.5
78.3
81.9
79.3
73.2
63.3
51.1
43.3
61.0
V
mi/hr
6.5
6.3
6.9
7.4
7.2
6.7
5.1
4.5
5.1
5.4
6.3
5.8
6.0
I
Btu/ft2/day
983
1268
1617
1997
2283
2441
2029
1871
1712
1395
1046
888
1617
Pa
lb/in2
11.43
Phoenix, AZ
Tan
°F
41.2
44.8
48.7
55.2
63.9
72.9
81.0
79.2
72.9
60.8
48.9
41.7
59.4
Tax
°F
65.8
70.7
75.6
84.6
93.6
103.5
106.0
103.6
98.2
88.2
74.8
66.2
85.8
V
mi/hr
5.6
6.3
7.2
7.6
7.6
7.2
7.6
7.2
6.7
6.3
5.8
5.6
6.7
I
Btu/ft2/day
1015
1363
1744
2251
2536
2663
2410
2251
1934
1554
1141
951
1807
Pa
lb/in2
14.13
Prescott, AZ
Tan
°F
21.9
24.1
28.0
33.4
41.2
49.8
57.9
55.8
48.7
38.1
28.6
22.3
37.6
Tax
°F
50.4
54.0
57.4
64.9
73.9
84.6
88.2
84.9
80.1
71.2
59.5
51.1
68.4
V
mi/hr
6.9
7.8
9.2
9.4
9.6
9.2
7.8
6.9
7.6
7.4
7.4
6.7
8.1
I
Btu/ft2/day
983
1236
1617
2093
2378
2536
2188
1997
1807
1458
1078
888
1680
Pa
lb/in2
12.28
Tucson, AZ
Tan
°F
38.7
41.0
44.6
50.4
57.9
67.8
73.6
72.1
67.5
56.7
45.7
39.7
54.7
Tax
°F
63.9
67.8
72.9
81.1
90.0
99.7
99.3
96.8
93.4
84.4
72.7
64.2
82.2
V
mi/hr
8.5
8.5
8.9
9.6
9.2
9.2
8.9
8.3
8.7
8.5
8.3
8.1
8.7
I
Btu/ft2/day
1078
1395
1775
2251
2505
2568
2251
2124
1902
1585
1205
1015
1807
Pa
lb/in2
13.42
Fort Smith, AR
Tan
°F
25.5
30.2
39.2
48.6
57.7
65.8
70.0
68.7
61.9
48.7
38.5
29.3
48.7
Tax
°F
48.4
53.4
64.0
74.1
80.4
88.0
93.0
92.5
85.3
75.7
62.8
51.3
72.3
V
mi/hr
8.1
8.5
9.4
8.9
7.6
6.5
6.3
6.3
6.7
6.7
7.8
8.3
7.6
I
Btu/ft2/day
824
1078
1395
1712
1902
2061
2093
1902
1522
1236
888
729
1458
Pa
lb/in2
14.52
Little Rock, AR
Tan
°F
29.1
33.3
42.3
50.7
59.0
67.5
71.4
69.8
63.5
50.9
41.5
33.1
51.1
Tax
°F
48.9
54.0
64.0
73.4
81.3
89.2
92.5
91.4
84.6
75.0
62.8
52.5
72.5
V
mi/hr
8.3
8.7
9.2
8.5
7.2
6.7
6.3
6.0
6.3
6.5
7.8
7.8
7.4
I
Btu/ft2/day
793
1046
1363
1680
1934
2061
2029
1871
1522
1236
856
698
1427
-------
o
o
-Q
£
&
IT!
r-K
o
l-s
,p
CfQ
CD
ft
o
00
Location
Symbol
Units
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
Pa
lb/in2
14.62
Areata, CA
Tan
°F
38.8
40.5
41.0
41.5
45.0
48.2
50.2
50.7
48.4
45.5
42.6
39.4
44.2
Tax
°F
54.0
54.9
54.9
56.1
58.5
61.3
63.0
63.3
63.9
61.0
57.6
54.0
58.5
V
mi/hr
6.5
7.2
7.8
7.6
7.6
6.7
6.3
5.4
5.1
5.1
6.3
6.3
6.5
I
Btu/ft2/day
571
793
1141
1585
1839
1902
1871
1585
1395
983
634
507
1236
Pa
lb/in2
14.65
Bakersfield, CA
Tan
°F
38.7
42.6
45.9
50.2
57.4
64.0
69.6
68.5
63.5
54.9
44.8
38.3
53.2
Tax
°F
56.8
63.9
68.9
75.9
84.6
92.5
98.4
96.6
90.1
80.8
66.7
56.5
77.7
V
mi/hr
5.6
6.0
6.7
7.4
8.1
7.8
7.4
6.9
6.5
6.0
5.6
5.6
6.7
I
Btu/ft2/day
729
1046
1490
1966
2346
2568
2536
2283
1871
1395
919
666
1649
Pa
lb/in2
14.47
Daggett, CA
Tan
°F
36.7
41.4
46.0
51.4
59.5
67.5
73.9
72.9
65.7
55.6
44.4
36.7
54.3
Tax
°F
60.6
66.0
70.5
78.1
87.4
97.9
103.8
101.5
93.7
82.8
69.4
60.4
81.0
V
mi/hr
7.8
10.1
13.2
14.1
15.2
14.3
12.3
11.0
10.5
9.4
9.6
8.5
11.4
I
Btu/ft2/day
1015
1332
1744
2219
2505
2663
2536
2314
1997
1554
1141
919
1839
Pa
lb/in2
13.73
Fresno, CA
Tan
°F
37.4
40.5
43.3
47.3
53.8
60.4
65.1
63.9
58.8
50.7
42.4
37.0
50.2
Tax
°F
54.1
61.7
66.6
75.0
84.2
92.7
98.6
96.6
90.1
79.7
64.8
53.8
76.5
V
mi/hr
4.9
5.6
6.7
7.6
8.5
8.5
7.6
6.9
6.3
5.1
4.7
4.7
6.5
I
Btu/ft2/day
666
1015
1490
1997
2378
2568
2536
2283
1871
1363
856
602
1649
Pa
lb/in2
14.56
Long Beach, CA
Tan
°F
45.0
46.9
48.9
51.8
56.3
59.7
63.3
64.8
62.8
57.7
50.4
45.0
54.3
Tax
°F
66.7
67.6
68.0
71.4
73.2
77.0
82.8
84.0
82.0
78.4
72.1
66.9
74.1
V
mi/hr
5.6
6.3
6.9
7.4
7.4
6.9
6.7
6.7
6.3
5.6
5.6
5.1
6.5
I
Btu/ft2/day
888
1141
1490
1902
2029
2124
2314
2124
1712
1332
983
824
1585
Pa
lb/in2
14.71
Los Angeles, CA
Tan
°F
47.8
49.3
50.5
52.9
56.3
59.5
62.8
64.2
63.1
59.2
52.9
47.8
55.6
Tax
°F
65.7
65.8
65.5
67.5
69.1
72.0
75.4
76.6
76.6
74.5
70.3
65.8
70.3
V
mi/hr
6.9
7.6
8.5
8.9
8.7
8.5
8.3
8.3
7.8
7.4
7.2
6.7
7.8
I
Btu/ft2/day
888
1141
1522
1934
2029
2093
2251
2061
1680
1332
1015
824
1554
Pa
lb/in2
14.68
Sacramento, CA
Tan
°F
37.8
41.4
43.2
45.5
50.4
55.2
58.1
57.9
55.8
50.4
43.3
37.8
48.0
Tax
°F
52.7
60.1
64.0
71.1
80.2
87.8
93.2
92.1
87.3
77.9
63.1
52.7
73.6
V
mi/hr
5.6
6.9
7.8
8.1
8.7
8.9
8.5
8.1
6.9
5.6
5.6
5.6
7.2
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£
&
IT!
r-K
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CfQ
CD
ft
Location
Symbol
Units
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
/
Btu/ft2/day
602
951
1363
1871
2283
2505
2505
2219
1807
1268
761
539
1554
Pa
lb/in2
14.72
San Diego, CA
Tan
°F
48.9
50.7
52.9
55.6
59.2
61.9
65.7
67.3
65.7
61.0
54.0
48.7
57.6
Tax
°F
65.8
66.6
66.4
68.4
69.1
71.6
76.3
77.7
77.2
74.7
70.0
66.0
70.9
V
mi/hr
6.0
6.7
7.8
8.3
8.3
8.1
7.8
7.8
7.6
6.9
6.3
5.8
7.4
I
Btu/ft2/day
983
1236
1554
1934
1997
2061
2188
2061
1712
1395
1078
919
1585
Pa
lb/in2
14.71
San Francisco, CA
Tan
°F
41.7
45.0
45.9
47.1
49.6
52.5
54.0
55.0
55.2
51.8
47.1
42.6
48.9
Tax
°F
55.6
59.4
60.8
63.9
66.6
70.3
71.6
72.3
73.6
70.2
62.4
56.1
65.1
V
mi/hr
7.4
8.9
10.7
12.3
13.9
13.9
13.9
12.8
11.2
9.6
8.3
7.8
11.0
I
Btu/ft2/day
698
951
1332
1807
2124
2283
2314
2061
1712
1236
793
634
1490
Pa
lb/in2
14.75
Santa Maria, CA
Tan
°F
38.3
40.5
41.4
42.4
46.4
50.4
52.9
54.0
52.3
48.0
42.3
37.8
45.5
Tax
°F
63.9
64.8
64.2
66.9
67.8
71.1
73.2
74.1
74.8
73.9
68.7
64.2
69.1
V
mi/hr
6.3
7.2
8.3
8.5
8.9
8.3
7.2
6.7
6.3
6.3
6.7
6.3
7.2
I
Btu/ft2/day
888
1173
1554
1966
2219
2346
2378
2156
1775
1395
1015
856
1649
Pa
lb/in2
14.62
Alamosa, CO
Tan
°F
-3.8
4.8
15.8
23.5
32.7
41.0
47.8
45.3
36.7
24.6
12.4
-0.6
23.4
Tax
°F
33.3
39.9
48.7
58.6
68.0
77.7
82.0
79.2
72.7
62.4
47.5
35.4
58.8
V
mi/hr
7.6
7.6
10.5
11.4
10.7
10.1
8.1
7.6
6.0
7.6
8.9
5.8
8.5
I
Btu/ft2/day
951
1268
1649
2029
2251
2441
2283
2061
1775
1427
1046
856
1680
Pa
lb/in2
11.20
Colorado Springs, CO
Tan
°F
16.2
19.2
24.6
33.1
42.1
51.1
57.0
55.2
47.1
36.3
25.0
17.4
35.4
Tax
°F
41.4
44.6
50.0
59.7
68.7
79.0
84.4
81.3
73.6
63.5
50.7
42.3
61.5
V
mi/hr
9.2
9.6
10.5
11.4
10.7
9.6
8.9
8.5
9.2
9.4
9.4
8.9
9.6
I
Btu/ft2/day
793
1078
1427
1807
1966
2188
2124
1902
1617
1268
888
729
1490
Pa
lb/in2
11.76
Boulder, CO
Tan
°F
16.2
20.1
25.9
34.5
43.5
52.3
58.6
56.8
47.7
36.3
25.3
17.4
36.1
Tax
°F
43.2
46.6
52.2
61.9
70.9
81.3
88.2
85.8
76.8
66.4
52.5
44.4
64.2
V
mi/hr
8.3
8.5
9.2
9.8
9.2
8.5
8.1
7.8
7.6
7.6
7.8
8.1
8.5
I
Btu/ft2/day
761
1046
1395
1775
1966
2188
2124
1902
1585
1205
824
666
1458
Pa
lb/in2
12.12
Eagle, CO
Tan
°F
3.7
10.4
19.8
26.4
33.8
40.5
47.1
45.3
37.0
26.8
17.4
6.1
26.2
Tax
°F
33.8
40.6
48.4
58.6
69.1
80.1
86.0
83.3
75.0
63.3
47.1
34.9
60.1
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£
&
IT!
r-K
o
l-s
,p
CfQ
CD
ft
o
00
Location
Symbol
Units
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
V
mi/hr
4.3
4.7
5.8
6.9
6.7
6.0
5.6
5.4
5.6
4.7
4.7
4.0
5.4
I
Btu/ft2/day
761
1046
1395
1775
2029
2283
2188
1934
1617
1236
793
666
1490
Pa
lb/in2
11.63
Grand Junction, CO
Tan
°F
14.5
23.5
31.3
38.5
47.8
57.0
63.9
62.2
52.9
41.5
29.5
18.7
40.1
Tax
°F
35.4
45.3
55.6
65.8
75.9
87.6
93.6
90.5
81.1
67.6
51.4
38.7
65.8
V
mi/hr
5.6
6.5
8.1
9.2
9.4
9.4
9.2
8.7
8.5
7.6
6.7
5.6
7.8
I
Btu/ft2/day
793
1110
1458
1902
2219
2441
2346
2093
1744
1300
856
698
1585
Pa
lb/in2
12.37
Pueblo, CO
Tan
°F
14.2
19.6
26.1
35.8
45.7
54.1
61.2
59.0
50.2
36.7
24.3
15.4
36.9
Tax
°F
45.3
50.7
57.2
67.8
76.5
87.6
93.0
89.8
81.3
70.5
56.8
46.8
68.5
V
mi/hr
8.3
8.7
10.3
11.4
11.0
10.1
9.4
8.7
8.7
8.3
8.3
8.1
9.4
I
Btu/ft2/day
856
1141
1490
1902
2124
2346
2283
2061
1712
1332
919
761
1585
Pa
lb/in2
12.40
Bridgeport, CT
Tan
°F
21.9
23.2
30.9
39.7
50.0
59.2
65.7
65.1
57.6
47.1
38.1
27.7
43.9
Tax
°F
36.0
37.6
46.2
56.7
66.7
75.9
81.7
81.0
74.1
64.0
53.1
41.0
59.5
V
mi/hr
13.2
13.6
13.6
13.2
11.6
10.7
10.3
10.5
11.6
11.9
13.0
13.0
12.3
I
Btu/ft2/day
602
856
1173
1490
1712
1871
1839
1649
1332
983
634
507
1205
Pa
lb/in2
14.74
Hartford, CT
Tan
°F
15.8
18.7
28.0
37.6
47.7
56.8
62.2
60.4
51.8
40.6
32.7
21.4
39.6
Tax
°F
33.3
36.3
46.8
59.9
71.6
80.1
84.9
82.8
74.8
63.7
51.1
37.6
60.3
V
mi/hr
8.5
8.9
9.6
9.8
8.5
7.8
7.4
6.9
6.9
7.4
8.3
8.3
8.3
I
Btu/ft2/day
602
856
1173
1458
1712
1871
1871
1617
1300
951
602
476
1205
Pa
lb/in2
14.65
Wilmington, DE
Tan
°F
22.5
24.8
33.1
41.7
52.2
61.5
67.1
65.8
58.3
45.7
37.0
27.7
44.8
Tax
°F
38.7
41.9
52.2
62.6
72.9
81.3
85.6
84.0
77.7
66.6
55.6
43.9
63.7
V
mi/hr
10.1
10.3
11.4
11.0
9.4
8.5
7.8
7.6
8.1
8.3
9.4
9.6
9.4
I
Btu/ft2/day
634
919
1236
1554
1775
1966
1934
1712
1395
1046
698
539
1300
Pa
lb/in2
14.72
Daytona Beach, FL
Tan
°F
46.9
48.4
54.0
58.6
64.9
70.9
72.5
72.9
72.0
65.1
56.3
49.6
61.0
Tax
°F
68.0
69.4
74.8
80.1
84.6
88.0
89.8
89.1
86.7
81.5
75.6
70.3
79.9
V
mi/hr
8.5
9.2
9.4
9.2
8.5
7.6
7.2
6.7
7.8
8.9
8.3
8.1
8.3
I
Btu/ft2/day
983
1236
1585
1966
2029
1934
1902
1807
1554
1332
1078
919
1522
Pa
lb/in2
14.75
Jacksonville, FL
Tan
°F
40.5
43.3
49.3
54.9
62.1
69.1
72.0
71.8
69.1
59.4
50.2
43.3
57.0
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o
00
-Q
£
&
IT!
r-K
o
l-s
,p
CfQ
CD
ft
o
OJ
Location
Symbol
Units
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
Tax
°F
64.2
66.9
73.0
79.2
84.7
89.2
91.4
90.7
87.3
80.2
73.6
66.7
79.0
V
mi/hr
8.1
8.7
8.7
8.3
7.6
7.2
6.7
6.3
6.9
7.6
7.4
7.4
7.6
I
Btu/ft2/day
919
1173
1490
1871
1934
1902
1839
1712
1458
1268
1015
856
1458
Pa
lb/in2
14.75
Key West, FL
Tan
°F
64.9
65.7
69.1
72.1
76.1
78.4
79.5
79.3
78.4
75.6
71.2
66.7
73.0
Tax
°F
74.8
75.4
78.6
81.7
85.1
87.6
89.1
89.2
88.0
84.4
80.1
76.1
82.6
V
mi/hr
11.6
12.1
12.3
11.9
10.7
10.1
9.6
9.2
9.6
11.6
12.3
11.9
11.2
I
Btu/ft2/day
1173
1395
1744
1997
1997
1934
1934
1839
1649
1458
1205
1078
1617
Pa
lb/in2
14.74
Miami, FL
Tan
°F
59.2
60.4
64.2
67.8
72.1
75.0
76.3
76.6
75.9
72.1
66.7
61.5
69.1
Tax
°F
75.2
76.5
79.2
82.4
85.3
87.6
89.1
89.1
87.8
84.6
80.4
76.6
82.8
V
mi/hr
9.6
10.5
11.0
10.7
9.8
8.5
8.3
8.3
8.5
9.8
10.1
9.6
9.4
I
Btu/ft2/day
1110
1332
1649
1902
1902
1775
1839
1775
1554
1395
1173
1046
1522
Pa
lb/in2
14.75
Tallahassee, FL
Tan
°F
38.1
40.1
46.8
52.2
60.8
68.5
71.1
71.4
68.0
55.9
46.2
40.3
55.0
Tax
°F
63.0
66.4
73.6
80.4
86.4
90.9
91.2
91.0
88.5
81.5
73.0
65.8
79.3
V
mi/hr
6.7
7.4
7.6
7.2
6.5
5.6
5.1
5.1
6.0
6.5
6.3
6.5
6.3
I
Btu/ft2/day
919
1173
1490
1871
1997
1934
1839
1744
1554
1363
1046
856
1490
Pa
lb/in2
14.74
Tampa, FL
Tan
°F
50.0
51.6
56.5
60.8
67.5
72.9
74.5
74.5
72.9
65.1
57.2
52.3
63.0
Tax
°F
69.8
71.4
76.6
81.7
87.3
89.4
90.1
90.1
89.1
84.4
77.7
72.1
81.7
V
mi/hr
8.7
9.2
9.4
9.2
8.7
8.1
7.4
6.9
7.6
8.5
8.5
8.5
8.5
I
Btu/ft2/day
1015
1268
1617
1966
2029
1934
1839
1744
1554
1395
1141
983
1554
Pa
lb/in2
14.76
West Palm Beach, FL
Tan
°F
55.8
56.5
61.2
64.8
69.6
73.0
74.5
75.0
74.7
70.7
64.6
58.6
66.6
Tax
°F
74.5
75.9
78.8
82.0
85.6
88.2
90.0
90.0
88.5
84.9
80.1
75.9
82.9
V
mi/hr
10.3
10.7
11.4
11.0
10.3
8.7
8.3
8.3
8.7
10.7
10.7
10.3
9.8
I
Btu/ft2/day
1046
1268
1585
1871
1902
1807
1871
1775
1522
1332
1078
983
1490
Pa
lb/in2
14.75
Athens, GA
Tan
°F
32.0
34.7
42.1
49.8
58.1
65.8
69.4
68.7
63.0
50.7
42.3
35.1
51.1
Tax
°F
51.6
56.3
65.1
73.4
80.4
87.1
89.6
88.2
82.8
73.6
64.4
55.0
72.3
V
mi/hr
8.5
8.9
8.7
8.3
6.9
6.5
6.3
5.8
6.5
6.7
7.4
8.1
7.4
I
Btu/ft2/day
824
1078
1427
1775
1934
2029
1934
1775
1522
1268
919
761
1427
Pa
lb/in2
14.34
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£
&
in
r-K
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l-s
,p
CfQ
CD
ft
o
00
Location
Symbol
Units
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
Atlanta, GA
Tan
°F
31.5
34.5
42.4
50.2
58.6
66.2
69.4
69.1
63.5
52.0
42.8
35.1
51.3
Tax
°F
50.4
55.0
64.2
72.7
79.5
85.8
88.0
87.1
81.9
72.7
63.3
54.0
71.2
V
mi/hr
9.8
10.3
10.1
9.6
8.5
7.8
7.6
7.2
7.8
8.3
8.7
9.4
8.7
I
Btu/ft2/day
824
1078
1427
1807
1966
2029
1966
1807
1522
1300
919
761
1458
Pa
lb/in2
14.23
Augusta, GA
Tan
°F
32.0
34.7
42.3
48.6
57.6
65.7
70.0
69.1
63.1
50.4
41.5
34.9
50.7
Tax
°F
55.8
60.1
68.7
76.6
83.7
89.2
91.8
90.3
85.6
77.2
68.4
59.5
75.6
V
mi/hr
7.2
7.6
7.8
7.6
6.5
6.3
6.0
5.4
5.6
5.6
6.3
6.7
6.5
I
Btu/ft2/day
824
1110
1427
1807
1934
1997
1934
1744
1522
1300
951
761
1458
Pa
lb/in2
14.69
Columbus, GA
Tan
°F
35.2
37.6
45.1
52.2
61.0
68.4
71.8
71.4
66.4
54.1
45.0
38.1
54.0
Tax
°F
56.1
61.0
69.1
77.4
83.7
90.3
91.8
91.2
86.2
77.5
68.2
59.0
75.9
V
mi/hr
7.4
8.1
7.8
7.6
6.7
6.3
6.0
5.6
6.5
6.7
6.7
6.9
6.7
I
Btu/ft2/day
856
1110
1458
1807
1966
2029
1902
1775
1554
1332
983
793
1458
Pa
lb/in2
14.56
Macon, GA
Tan
°F
34.2
36.9
44.2
50.9
59.4
66.7
70.5
69.8
64.2
51.6
43.2
37.0
52.3
Tax
°F
56.7
60.8
69.4
77.7
84.6
90.1
91.9
91.0
86.4
77.9
68.7
60.3
76.3
V
mi/hr
7.6
8.5
8.5
8.3
7.2
6.9
6.7
6.3
6.5
6.5
6.7
7.4
7.2
I
Btu/ft2/day
856
1110
1458
1807
1966
1997
1902
1775
1522
1300
951
793
1458
Pa
lb/in2
14.58
Savannah, GA
Tan
°F
38.1
41.2
48.4
54.5
63.0
69.3
72.3
72.1
67.8
56.8
48.0
41.0
55.9
Tax
°F
59.7
62.4
70.2
77.5
84.0
88.9
91.0
89.8
85.3
77.5
70.0
62.2
76.5
V
mi/hr
8.5
9.2
9.2
8.7
7.6
7.4
7.2
6.5
7.2
7.4
7.6
7.6
7.8
I
Btu/ft2/day
888
1110
1490
1839
1966
1997
1934
1744
1490
1300
983
824
1458
Pa
lb/in2
14.75
Hilo, HI
Tan
°F
63.7
63.7
64.4
65.5
66.6
67.6
68.5
68.9
68.5
68.2
66.7
64.8
66.4
Tax
°F
79.9
79.9
79.5
79.9
81.1
82.8
82.9
83.7
83.8
83.1
81.3
80.1
81.5
V
mi/hr
7.8
8.1
8.1
8.1
7.8
7.6
7.4
7.2
7.2
7.2
7.4
7.6
7.6
I
Btu/ft2/day
1205
1363
1458
1522
1649
1712
1649
1680
1585
1363
1173
1110
1458
Pa
lb/in2
14.72
Honolulu, HI
Tan
°F
65.7
65.5
67.3
68.7
70.3
72.1
73.6
74.1
73.6
72.3
70.3
66.9
70.0
Tax
°F
80.1
80.4
81.7
82.8
84.7
86.5
87.4
88.7
88.5
86.9
84.0
81.1
84.4
V
mi/hr
9.6
9.6
11.2
11.4
11.4
12.3
12.8
12.1
11.0
10.3
10.3
9.6
11.0
I
Btu/ft2/day
1236
1490
1712
1871
2029
2061
2093
2061
1871
1585
1300
1173
1712
-------
o
00
-Q
£
&
IT!
r-K
o
l-s
,p
CfQ
CD
ft
o
Location
Symbol
Units
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
Pa
lb/in2
14.74
Kahului, HI
Tan
°F
63.7
63.3
64.6
66.0
66.9
69.1
70.5
70.9
69.8
69.3
67.6
65.1
67.3
Tax
°F
79.9
80.1
81.1
82.2
84.2
85.8
86.7
87.6
87.6
86.4
83.7
81.1
83.8
V
mi/hr
11.6
12.1
12.8
14.1
15.0
15.9
16.6
15.9
13.9
12.3
12.8
11.2
13.6
I
Btu/ft2/day
1268
1490
1712
1871
2029
2124
2124
2061
1934
1617
1363
1236
1744
Pa
lb/in2
14.69
Lihue, HI
Tan
°F
65.3
65.1
66.9
68.5
70.3
72.5
73.8
74.1
73.6
72.0
70.3
67.1
70.0
Tax
°F
77.9
78.1
78.4
79.5
81.1
83.1
84.0
84.7
84.7
83.1
80.8
78.6
81.1
V
mi/hr
11.6
11.9
13.2
14.3
13.6
13.6
14.3
13.2
12.1
11.9
12.8
11.6
13.0
I
Btu/ft2/day
1173
1363
1554
1680
1871
1934
1902
1871
1775
1490
1205
1110
1585
Pa
lb/in2
14.68
Boise, ID
Tan
°F
21.6
27.5
31.8
36.7
43.9
52.2
57.7
56.8
48.2
39.0
31.1
22.5
39.0
Tax
°F
36.3
44.2
52.9
61.3
71.1
81.0
90.1
88.2
77.0
64.6
48.7
37.8
62.8
V
mi/hr
7.2
8.5
9.4
9.6
9.4
8.7
8.1
7.8
7.8
7.6
8.1
7.4
8.3
I
Btu/ft2/day
507
793
1205
1680
2061
2283
2410
2093
1617
1078
602
444
1395
Pa
lb/in2
13.28
Pocatello, ID
Tan
°F
14.4
19.8
25.9
32.4
39.6
47.3
53.1
50.9
42.8
33.4
26.1
15.8
33.4
Tax
°F
32.2
38.5
46.8
57.6
67.5
78.1
88.2
86.4
75.0
62.4
45.1
33.6
59.4
V
mi/hr
10.1
10.3
11.0
11.6
10.7
9.6
8.9
8.7
8.9
9.2
10.5
9.6
10.1
I
Btu/ft2/day
539
824
1205
1617
1966
2219
2314
1997
1585
1110
634
476
1363
Pa
lb/in2
12.53
Chicago, IL
Tan
°F
12.9
17.2
28.6
38.7
47.7
57.6
62.6
61.5
54.0
42.3
31.6
19.0
39.6
Tax
°F
28.9
33.4
45.9
58.6
70.2
79.5
83.7
81.9
74.8
63.3
48.4
34.0
58.6
V
mi/hr
11.6
11.4
12.1
11.9
10.3
9.4
8.3
8.1
8.9
10.1
10.7
11.0
10.3
I
Btu/ft2/day
571
824
1110
1458
1807
1997
1934
1712
1332
951
571
476
1236
Pa
lb/in2
14.39
Moline, IL
Tan
°F
11.3
16.0
28.0
39.4
49.8
59.5
64.6
61.9
53.2
41.7
30.7
17.4
39.6
Tax
°F
28.4
33.6
46.8
61.3
72.9
82.6
85.8
83.5
75.9
64.2
48.4
33.4
59.7
V
mi/hr
11.4
10.7
12.3
12.1
10.3
9.4
7.8
7.6
8.3
9.6
10.7
11.0
10.1
I
Btu/ft2/day
602
856
1141
1490
1807
2029
1997
1744
1363
1015
634
507
1268
Pa
lb/in2
14.43
Peoria, IL
Tan
°F
13.3
17.8
29.8
40.8
50.9
60.6
65.5
63.1
55.2
43.2
32.5
19.2
41.0
Tax
°F
29.8
34.9
48.0
62.1
72.9
82.2
85.6
83.1
76.8
64.8
49.8
34.5
60.4
V
mi/hr
11.0
10.7
11.9
11.4
9.6
8.5
7.6
7.4
8.1
9.2
10.5
10.5
9.6
-------
o
On
-Q
£
&
IT!
r-K
o
l-s
,p
CfQ
CD
ft
o
00
Location
Symbol
Units
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
/
Btu/ft2/day
634
888
1141
1522
1839
2029
1997
1744
1395
1015
634
507
1268
Pa
lb/in2
14.40
Rockford, IL
Tan
°F
9.9
14.2
26.1
36.9
47.5
57.4
62.4
60.3
52.0
40.6
29.5
16.2
37.8
Tax
°F
26.6
31.6
43.9
58.5
70.9
80.2
83.8
81.3
74.1
62.2
46.2
31.8
57.6
V
mi/hr
11.2
10.7
12.1
11.9
10.5
9.4
8.3
7.8
8.5
9.6
10.7
10.7
10.1
I
Btu/ft2/day
602
856
1110
1458
1807
1997
1934
1712
1332
951
571
476
1236
Pa
lb/in2
14.36
Springfield, IL
Tan
°F
16.0
20.1
31.6
42.4
52.3
61.9
66.0
63.3
55.9
44.4
34.0
21.9
42.4
Tax
°F
32.5
37.2
50.0
63.9
74.7
83.8
86.9
84.2
78.6
66.7
51.6
37.2
62.2
V
mi/hr
12.3
11.9
13.2
12.5
10.7
9.4
8.3
7.8
8.9
10.3
11.6
12.1
10.7
I
Btu/ft2/day
666
919
1173
1585
1902
2061
2029
1807
1458
1078
698
539
1332
Pa
lb/in2
14.43
Evansville, IN
Tan
°F
21.2
25.0
35.8
45.0
54.1
63.3
67.5
64.9
57.6
44.8
36.5
26.8
45.1
Tax
°F
38.8
43.7
55.9
67.5
76.8
86.2
89.1
87.3
80.8
69.6
55.9
43.5
66.4
V
mi/hr
8.9
8.9
9.6
9.2
7.6
6.9
6.0
5.6
6.0
6.7
8.1
8.5
7.6
I
Btu/ft2/day
666
919
1205
1585
1871
2061
1997
1807
1458
1110
729
571
1332
Pa
lb/in2
14.56
Fort Wayne, IN
Tan
°F
15.3
17.8
28.8
38.5
49.1
59.4
63.1
61.0
54.1
42.4
33.4
21.6
40.5
Tax
°F
30.4
34.0
46.2
59.7
71.2
81.0
84.6
82.2
75.6
63.1
49.1
35.4
59.4
V
mi/hr
11.9
11.0
12.1
11.4
9.8
9.2
8.1
7.6
8.1
9.2
10.5
11.2
10.1
I
Btu/ft2/day
571
824
1110
1458
1775
1966
1934
1680
1363
951
571
444
1236
Pa
lb/in2
14.31
Indianapolis, IN
Tan
°F
17.2
20.8
31.8
41.5
51.6
61.0
65.1
62.8
55.6
43.5
34.2
23.2
42.4
Tax
°F
33.6
38.3
50.9
63.3
73.8
82.8
85.5
83.7
77.5
65.8
52.0
38.5
62.1
V
mi/hr
10.5
10.3
11.4
10.5
9.2
8.3
7.4
6.9
7.6
8.5
9.8
10.3
9.2
I
Btu/ft2/day
634
888
1173
1554
1871
2061
1997
1775
1458
1046
666
507
1300
Pa
lb/in2
14.33
South Bend, IN
Tan
°F
16.2
18.7
29.1
38.7
48.7
58.6
63.0
61.2
53.8
42.8
33.4
22.3
40.5
Tax
°F
30.4
34.2
45.7
58.6
70.0
79.5
82.9
80.8
74.1
62.2
48.6
35.4
58.5
V
mi/hr
11.9
11.2
11.9
11.4
9.8
8.9
8.1
7.6
8.3
9.4
10.7
11.4
10.1
I
Btu/ft2/day
539
793
1078
1458
1775
1966
1902
1680
1300
919
539
444
1205
Pa
lb/in2
14.33
Des Moines, IA
Tan
°F
10.8
15.6
27.7
39.9
51.4
61.2
66.6
63.7
54.5
42.6
29.8
16.2
39.9
Tax
°F
28.0
33.6
46.9
61.9
73.0
82.2
86.7
84.2
75.6
64.2
48.0
32.5
59.7
-------
o
00
-Q
£
&
IT!
r-K
o
l-s
,p
CfQ
CD
ft
o
Location
Symbol
Units
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
V
mi/hr
11.4
11.2
12.3
12.3
10.7
9.8
8.7
8.5
9.2
9.8
10.7
11.0
10.5
I
Btu/ft2/day
634
888
1205
1554
1839
2061
2061
1807
1395
1015
666
539
1300
Pa
lb/in2
14.24
Mason City, IA
Tan
°F
4.3
9.9
22.8
35.6
46.8
56.8
61.5
58.6
49.3
37.9
25.0
10.2
34.9
Tax
°F
22.1
27.5
39.9
57.0
70.5
79.9
83.7
81.0
72.1
60.4
43.0
26.4
55.2
V
mi/hr
13.2
12.3
13.2
13.2
12.1
11.0
8.9
8.5
9.6
11.0
12.1
12.5
11.4
I
Btu/ft2/day
602
856
1173
1490
1839
1997
1997
1744
1363
951
571
476
1268
Pa
lb/in2
14.10
Sioux City, IA
Tan
°F
7.7
13.8
25.7
38.3
50.0
59.5
64.8
62.1
52.0
39.6
26.4
12.7
37.8
Tax
°F
27.7
33.3
45.9
62.2
73.2
82.0
86.5
83.5
74.8
64.0
46.4
30.9
59.2
V
mi/hr
11.6
11.4
12.8
13.2
12.1
10.7
9.4
9.2
9.8
10.5
11.2
11.4
11.2
I
Btu/ft2/day
602
888
1205
1554
1839
2093
2061
1807
1395
1015
634
507
1300
Pa
lb/in2
14.16
Waterloo, IA
Tan
°F
5.4
10.6
25.0
37.0
48.7
57.6
62.2
59.0
50.0
38.5
26.2
11.7
36.0
Tax
°F
23.7
29.5
43.3
59.4
71.6
80.4
83.8
81.5
73.8
61.9
45.1
28.9
56.8
V
mi/hr
11.6
11.2
12.5
12.5
11.0
9.8
8.5
8.5
9.2
10.1
11.2
11.4
10.5
I
Btu/ft2/day
602
856
1141
1490
1807
2029
1997
1744
1363
951
602
476
1268
Pa
lb/in2
14.29
Dodge City, KS
Tan
°F
18.1
22.6
30.4
41.4
52.0
61.9
67.5
65.7
56.7
44.2
31.1
21.2
42.6
Tax
°F
41.5
47.3
56.7
68.0
76.3
87.1
93.0
90.7
81.3
70.7
55.2
43.9
67.6
V
mi/hr
13.2
13.4
15.0
15.0
14.1
13.4
13.0
12.3
13.0
13.0
13.2
13.2
13.4
I
Btu/ft2/day
856
1141
1490
1871
2061
2283
2283
1997
1617
1268
888
761
1554
Pa
lb/in2
13.42
Goodland, KS
Tan
°F
15.3
19.0
25.3
35.2
45.7
55.2
61.3
59.2
50.0
37.6
25.7
17.1
37.2
Tax
°F
41.5
45.3
52.7
63.7
72.3
83.5
89.8
87.3
78.1
66.6
51.6
42.1
64.6
V
mi/hr
12.8
12.5
14.3
14.8
13.6
12.8
12.3
11.4
12.1
11.9
12.1
12.3
12.8
I
Btu/ft2/day
793
1046
1427
1807
1997
2283
2251
1997
1617
1236
856
698
1490
Pa
lb/in2
12.88
Topeka, KS
Tan
°F
16.3
21.7
32.2
42.8
53.2
63.0
67.6
64.9
55.8
43.5
32.0
21.0
42.8
Tax
°F
37.0
42.6
55.0
66.9
75.7
84.2
89.2
87.4
79.7
69.1
54.0
40.5
65.1
V
mi/hr
9.8
10.1
11.9
11.6
10.3
9.4
8.5
8.1
8.3
8.7
9.6
9.4
9.6
I
Btu/ft2/day
729
951
1268
1617
1871
2061
2093
1839
1458
1110
761
602
1363
Pa
lb/in2
14.29
-------
o
00
-Q
£
&
IT!
r-K
o
l-s
,p
CfQ
CD
ft
o
00
Location
Symbol
Units
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
Wichita, KS
Tan
°F
19.2
23.7
33.6
44.4
54.3
64.6
70.0
67.8
59.2
46.6
34.0
23.0
45.0
Tax
°F
39.7
45.9
57.2
68.4
76.8
86.7
92.8
90.7
81.3
70.5
55.2
43.0
67.5
V
mi/hr
12.1
12.3
13.9
13.6
12.1
11.6
11.4
11.0
11.4
11.6
12.1
12.1
12.1
I
Btu/ft2/day
793
1046
1363
1712
1934
2124
2156
1934
1554
1205
824
698
1458
Pa
lb/in2
14.04
Covinqton, KY
Tan
°F
19.6
22.6
33.1
42.3
51.8
60.1
64.8
63.0
56.7
44.2
35.2
25.3
43.2
Tax
°F
36.7
40.8
53.1
64.2
73.9
82.0
85.5
84.0
77.9
66.0
53.2
41.5
63.1
V
mi/hr
10.5
10.1
11.0
10.3
8.5
7.8
6.9
6.9
7.2
8.1
9.4
10.1
8.9
I
Btu/ft2/day
602
856
1141
1522
1807
1966
1902
1744
1427
1046
666
507
1268
Pa
lb/in2
14.30
Lexinqton, KY
Tan
°F
22.5
25.3
35.2
44.2
53.4
61.5
65.7
64.4
57.9
46.0
37.0
27.7
45.1
Tax
°F
39.0
43.5
55.2
65.5
74.3
82.8
85.8
84.9
78.3
67.3
54.9
44.2
64.8
V
mi/hr
9.8
9.8
10.5
9.8
8.3
7.6
6.7
6.7
6.9
7.6
9.2
9.8
8.5
I
Btu/ft2/day
634
888
1173
1554
1807
1966
1902
1744
1395
1078
698
539
1300
Pa
lb/in2
14.24
Louisville, KY
Tan
°F
23.2
26.4
36.1
45.3
54.7
63.0
67.3
65.8
58.6
45.9
37.2
28.6
46.0
Tax
°F
40.3
44.8
56.3
67.3
75.9
83.5
87.1
85.6
80.2
69.3
56.8
45.1
66.0
V
mi/hr
9.4
9.4
10.1
9.6
8.1
7.6
6.7
6.7
6.7
7.4
8.7
9.4
8.3
I
Btu/ft2/day
634
888
1205
1585
1839
1997
1934
1775
1427
1110
698
539
1300
Pa
lb/in2
14.50
Baton Rouqe, LA
Tan
°F
39.6
42.4
50.2
57.9
64.8
70.3
73.2
72.7
68.7
57.0
48.9
42.4
57.4
Tax
°F
59.7
63.7
72.3
79.9
85.6
90.5
91.4
91.0
87.4
80.1
70.9
63.3
78.1
V
mi/hr
8.5
8.9
9.2
8.7
7.6
6.5
5.8
5.4
6.5
6.5
7.6
8.1
7.4
I
Btu/ft2/day
824
1110
1395
1712
1871
1902
1807
1712
1522
1363
951
793
1427
Pa
lb/in2
14.72
Lake Charles, LA
Tan
°F
41.2
44.1
50.7
58.6
65.7
71.6
73.6
73.0
68.5
57.9
50.0
43.5
58.3
Tax
°F
59.7
63.3
70.7
77.9
84.0
89.1
90.9
90.9
86.7
80.2
70.9
63.3
77.4
V
mi/hr
9.8
10.3
10.3
10.1
8.7
7.6
6.5
6.0
7.2
7.6
9.2
9.8
8.5
I
Btu/ft2/day
856
1141
1427
1712
1902
1997
1902
1775
1585
1363
1015
824
1458
Pa
lb/in2
14.74
New Orleans, LA
Tan
°F
41.7
44.4
51.6
58.5
65.1
70.9
73.0
72.9
69.4
58.6
51.1
44.8
58.5
Tax
°F
60.8
64.0
71.6
78.4
84.4
89.2
90.7
90.1
86.5
79.3
71.1
64.2
77.5
V
mi/hr
8.9
9.6
9.4
9.2
8.1
6.7
5.8
5.8
6.9
7.4
8.5
8.9
7.8
I
Btu/ft2/day
856
1141
1427
1744
1934
1934
1807
1744
1554
1363
983
824
1458
-------
o
00
-Q
£
&
IT!
r-K
o
l-s
,p
CfQ
CD
ft
o
vo
Location
Symbol
Units
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
Pa
lb/in2
14.75
Shreveport, LA
Tan
°F
34.9
37.9
45.9
54.1
62.1
69.1
72.3
71.2
66.0
54.3
45.3
37.2
54.1
Tax
°F
55.4
60.6
69.3
77.2
83.1
89.8
93.0
93.0
87.3
78.6
68.0
58.5
76.3
V
mi/hr
8.7
9.4
9.8
9.4
8.3
7.4
6.9
6.5
7.2
7.2
8.5
8.7
8.1
I
Btu/ft2/day
824
1078
1395
1712
1902
2029
2029
1902
1585
1300
951
793
1458
Pa
lb/in2
14.62
Caribou, ME
Tan
°F
-1.7
0.7
14.9
28.9
40.1
49.1
54.5
52.2
43.2
34.3
23.7
5.5
28.8
Tax
°F
19.4
23.0
34.3
46.8
61.7
72.0
76.5
73.6
64.0
52.0
37.6
24.1
48.7
V
mi/hr
11.4
11.2
11.9
11.4
10.7
9.8
9.2
8.5
9.4
10.1
10.5
11.0
10.3
I
Btu/ft2/day
507
824
1205
1458
1649
1807
1775
1522
1141
729
444
380
1141
Pa
lb/in2
14.37
Portland, ME
Tan
°F
11.5
13.5
24.4
34.2
43.3
52.2
58.3
57.0
48.9
38.3
30.4
17.8
35.8
Tax
°F
30.4
33.1
41.4
52.3
63.1
72.7
78.8
77.4
69.3
58.6
46.9
35.1
54.9
V
mi/hr
9.2
9.2
9.8
9.8
9.2
8.5
7.6
7.6
7.8
8.3
8.9
8.7
8.7
I
Btu/ft2/day
602
888
1205
1490
1775
1934
1902
1712
1332
919
571
476
1236
Pa
lb/in2
14.69
Baltimore, MD
Tan
°F
23.4
25.9
34.2
42.4
52.5
61.9
66.7
65.7
58.5
45.9
37.0
28.2
45.1
Tax
°F
40.3
43.7
54.0
64.2
74.1
83.1
87.3
85.5
78.4
67.3
56.5
45.1
64.9
V
mi/hr
9.4
9.8
10.3
10.3
8.7
8.1
7.6
7.6
7.8
8.3
8.9
9.2
8.7
I
Btu/ft2/day
666
919
1236
1554
1775
1966
1902
1680
1395
1046
698
571
1268
Pa
lb/in2
14.68
Boston, MA
Tan
°F
21.6
23.0
31.3
40.3
49.8
59.2
65.1
64.0
56.8
46.9
38.3
26.8
43.5
Tax
°F
35.8
37.6
45.9
55.9
66.6
76.3
81.9
79.9
72.9
62.8
52.2
40.5
59.0
V
mi/hr
13.9
13.6
13.6
13.2
12.3
11.4
11.0
10.7
11.4
12.1
13.0
13.6
12.5
I
Btu/ft2/day
602
856
1173
1490
1775
1934
1934
1712
1363
951
602
476
1236
Pa
lb/in2
14.72
Worchester, MA
Tan
°F
15.1
16.5
25.0
34.7
45.1
54.0
60.1
58.6
50.5
40.5
31.3
20.1
37.6
Tax
°F
30.7
33.1
42.4
54.0
65.8
74.5
79.3
77.4
69.6
59.5
47.5
34.7
55.8
V
mi/hr
11.0
10.7
10.7
10.3
9.2
8.5
7.8
7.6
8.1
8.9
10.1
10.3
9.4
I
Btu/ft2/day
602
888
1205
1490
1744
1902
1871
1649
1332
951
602
476
1236
Pa
lb/in2
14.20
Alpena, Ml
Tan
°F
8.8
8.2
18.0
30.0
39.2
48.0
54.0
52.5
46.2
37.0
28.4
16.5
32.4
Tax
°F
26.4
28.2
37.9
51.6
64.8
74.5
80.2
76.8
68.4
56.8
43.0
30.9
53.2
V
mi/hr
9.2
8.7
9.4
9.4
8.5
7.8
7.4
6.9
7.4
8.1
8.9
8.7
8.5
-------
-Q
£
&
IT!
r-K
o
l-s
,p
CfQ
CD
FT
O
00
Location
Symbol
Units
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
/
Btu/ft2/day
507
793
1173
1490
1807
1966
1934
1617
1205
793
476
380
1173
Pa
lb/in2
14.36
Detroit, Ml
Tan
°F
15.6
17.6
27.0
36.9
47.1
56.3
61.3
59.5
52.5
40.8
32.2
21.4
39.0
Tax
°F
30.4
33.3
44.4
57.7
69.6
79.0
83.3
81.3
73.9
61.5
48.0
35.2
58.1
V
mi/hr
12.1
11.4
11.9
11.6
10.3
9.4
8.5
8.3
8.7
9.8
11.2
11.4
10.3
I
Btu/ft2/day
507
793
1078
1458
1775
1966
1934
1680
1300
888
539
412
1205
Pa
lb/in2
14.39
Flint, Ml
Tan
°F
14.2
15.6
25.5
36.0
45.7
54.7
59.7
57.9
51.1
40.5
32.2
20.7
37.8
Tax
°F
28.8
31.3
42.3
55.9
68.0
76.8
81.5
79.2
71.6
59.7
46.6
33.8
56.3
V
mi/hr
11.4
10.7
11.4
11.0
9.8
8.9
8.1
7.6
8.5
9.4
10.7
11.0
9.8
I
Btu/ft2/day
507
793
1078
1458
1775
1934
1902
1649
1268
856
507
412
1173
Pa
lb/in2
14.33
Grand Rapids, Ml
Tan
°F
14.7
15.8
25.3
35.4
45.7
55.2
60.4
58.5
49.8
39.0
30.2
20.7
37.6
Tax
°F
28.9
31.6
42.8
56.7
69.3
78.6
82.8
80.4
72.0
59.7
45.9
33.4
56.8
V
mi/hr
11.4
10.5
11.4
11.0
9.6
8.9
8.3
7.8
8.3
8.9
10.3
10.7
9.8
I
Btu/ft2/day
507
793
1110
1490
1807
1997
1966
1680
1300
856
507
412
1205
Pa
lb/in2
14.31
Houghton, Ml
Tan
°F
8.4
8.2
18.1
31.6
42.1
50.5
55.4
53.8
46.9
37.6
28.4
15.6
33.1
Tax
°F
25.3
28.0
38.1
52.7
66.0
74.8
79.5
76.5
67.8
55.8
42.1
29.5
53.1
V
mi/hr
10.1
9.2
9.8
10.1
9.2
8.5
7.6
7.4
7.8
8.7
9.6
9.6
8.9
I
Btu/ft2/day
412
698
1110
1458
1744
1902
1902
1585
1141
729
412
349
1141
Pa
lb/in2
14.13
Lansing, Ml
Tan
°F
13.3
14.2
24.4
35.1
45.0
54.5
59.0
56.8
49.8
39.2
30.7
19.2
36.9
Tax
°F
28.6
31.6
42.6
56.7
69.1
78.3
82.6
80.4
72.0
59.4
45.9
33.4
56.7
V
mi/hr
12.1
11.0
11.6
11.4
10.1
9.2
8.1
7.6
8.3
9.2
10.7
11.2
10.1
I
Btu/ft2/day
507
793
1110
1458
1775
1966
1934
1649
1268
856
539
412
1205
Pa
lb/in2
14.29
Muskegon, Ml
Tan
°F
17.8
18.0
25.3
35.4
45.1
54.3
60.3
58.8
51.4
41.5
32.7
23.4
38.7
Tax
°F
28.8
30.7
41.2
54.5
66.6
75.6
80.2
78.1
70.9
59.0
46.0
33.6
55.6
V
mi/hr
12.5
11.4
12.1
11.9
10.1
9.4
8.9
8.7
9.4
10.5
11.9
12.1
10.7
I
Btu/ft2/day
507
761
1110
1490
1871
2029
2029
1712
1300
856
507
380
1205
Pa
lb/in2
14.40
Sault Ste. Marie, Ml
Tan
°F
4.6
4.8
15.3
28.4
38.5
45.5
51.3
51.3
44.2
36.1
25.9
11.8
29.8
Tax
°F
21.0
23.2
32.7
48.0
62.6
70.5
76.3
73.8
65.8
54.3
39.9
26.2
49.6
-------
o
00
-Q
£
&
IT!
r-K
o
l-s
,p
CfQ
CD
ft
Location
Symbol
Units
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
V
mi/hr
9.4
8.7
9.6
9.8
9.2
8.3
7.6
7.4
8.1
8.5
9.4
9.2
8.7
I
Btu/ft2/day
507
824
1236
1522
1807
1934
1902
1585
1110
698
444
380
1173
Pa
lb/in2
14.34
Traverse City, Ml
Tan
°F
13.3
11.1
20.1
31.8
41.0
51.1
57.4
55.9
49.3
39.6
30.6
19.6
35.1
Tax
°F
26.2
28.2
38.5
53.2
66.4
75.9
81.3
78.3
69.6
57.9
43.9
31.3
54.1
V
mi/hr
10.3
9.4
9.4
9.6
8.5
8.3
7.6
7.6
8.1
8.5
9.4
9.6
8.7
I
Btu/ft2/day
476
761
1110
1458
1775
1966
1934
1617
1173
761
444
380
1141
Pa
lb/in2
14.40
Duluth, MN
Tan
°F
-2.2
2.8
15.6
28.9
39.6
48.6
55.0
53.2
44.4
35.1
21.6
4.8
28.9
Tax
°F
16.2
21.7
32.9
48.2
61.9
71.1
77.2
73.9
63.9
52.3
35.2
20.7
47.8
V
mi/hr
11.4
10.7
11.9
11.6
11.0
10.1
8.9
8.9
9.8
10.3
11.0
10.7
10.5
I
Btu/ft2/day
507
824
1205
1522
1775
1902
1934
1617
1173
793
476
380
1173
Pa
lb/in2
13.98
International Falls, MN
Tan
°F
-9.9
-4.0
11.5
27.9
39.6
49.5
54.7
51.6
42.4
32.9
17.1
-2.2
25.9
Tax
°F
11.8
19.2
32.7
50.2
64.6
73.4
78.8
75.6
64.2
51.8
32.7
16.5
47.7
V
mi/hr
8.7
8.5
9.4
9.6
9.2
8.3
7.4
7.6
8.3
8.9
9.2
8.7
8.7
I
Btu/ft2/day
444
761
1173
1522
1744
1839
1839
1554
1110
698
444
349
1141
Pa
lb/in2
14.10
Minneapolis, MN
Tan
°F
2.8
9.1
22.6
36.1
47.7
57.6
63.1
60.3
50.4
38.8
25.2
10.2
35.2
Tax
°F
20.7
26.6
39.2
56.5
69.4
78.8
84.0
80.8
70.7
58.8
41.0
25.5
54.3
V
mi/hr
10.5
10.3
11.4
12.1
10.7
10.3
9.4
9.2
9.6
10.3
10.5
10.3
10.3
I
Btu/ft2/day
571
856
1205
1490
1807
1997
1997
1712
1300
888
539
444
1236
Pa
lb/in2
14.30
Rochester, MN
Tan
°F
2.7
8.1
21.4
34.5
45.5
55.2
60.1
57.6
48.6
37.6
24.4
9.3
33.6
Tax
°F
20.1
26.1
38.1
55.2
68.2
77.7
81.9
78.8
69.8
58.3
40.8
25.0
53.2
V
mi/hr
14.8
14.1
14.8
14.8
13.4
12.8
11.0
11.0
12.1
13.2
13.9
14.1
13.2
I
Btu/ft2/day
571
856
1173
1458
1775
1966
1966
1680
1268
888
539
444
1205
Pa
lb/in2
14.04
Saint Cloud, MN
Tan
°F
-2.4
3.7
17.6
32.0
43.3
52.2
57.6
54.9
45.3
34.3
20.3
5.0
30.4
Tax
°F
18.5
24.8
37.6
55.0
68.4
77.4
82.6
79.3
69.1
57.4
39.0
23.2
52.7
V
mi/hr
10.5
8.3
11.2
10.5
9.8
8.3
7.2
7.4
7.6
8.7
9.4
9.8
9.2
I
Btu/ft2/day
539
856
1205
1490
1775
1966
1997
1712
1268
856
539
412
1205
Pa
lb/in2
14.18
-------
NJ
-Q
£
&
IT!
r-K
o
l-s
,p
CfQ
CD
ft
o
00
Location
Symbol
Units
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
Jackson, MS
Tan
°F
32.7
35.8
44.1
52.0
60.1
67.1
70.5
69.6
63.7
50.4
42.3
36.1
52.0
Tax
°F
55.6
60.1
69.3
77.4
84.0
90.7
92.5
91.9
88.0
79.2
69.3
59.5
76.5
V
mi/hr
8.3
8.5
8.9
8.3
7.2
6.3
5.8
5.6
6.5
6.5
7.6
8.5
7.4
I
Btu/ft2/day
824
1110
1427
1744
1934
2029
1966
1839
1554
1332
951
761
1458
Pa
lb/in2
14.59
Meridian, MS
Tan
°F
33.4
36.7
43.5
50.9
58.8
66.0
70.0
69.3
63.9
50.5
42.4
36.7
51.8
Tax
°F
56.5
61.2
69.6
77.4
83.7
90.0
92.1
91.8
86.9
77.7
68.5
60.1
76.3
V
mi/hr
7.2
7.6
7.8
7.2
5.8
5.1
4.7
4.7
5.4
5.1
6.3
7.2
6.0
I
Btu/ft2/day
824
1078
1395
1712
1871
1966
1871
1775
1522
1300
919
761
1427
Pa
lb/in2
14.60
Columbia, MO
Tan
°F
18.5
22.8
33.1
43.7
53.1
61.2
66.2
63.9
57.0
45.5
34.5
23.2
43.5
Tax
°F
36.7
41.4
53.2
65.7
74.1
82.8
88.5
86.7
78.8
67.6
53.6
40.3
64.0
V
mi/hr
11.2
11.2
12.3
11.9
9.6
8.7
8.3
8.1
8.7
9.8
10.7
11.0
10.1
I
Btu/ft2/day
698
951
1268
1649
1902
2093
2093
1871
1458
1110
729
602
1363
Pa
lb/in2
14.30
Kansas City, MO
Tan
°F
16.7
21.7
32.5
43.9
54.0
63.1
68.2
65.7
56.8
45.7
33.6
21.9
43.7
Tax
°F
34.7
40.6
52.9
65.1
74.3
83.3
88.7
86.4
78.1
67.5
52.5
38.8
63.7
V
mi/hr
11.0
11.0
12.3
12.1
10.3
9.6
9.2
8.9
9.2
10.1
10.7
10.7
10.3
I
Btu/ft2/day
698
951
1236
1617
1871
2061
2093
1839
1458
1141
729
602
1363
Pa
lb/in2
14.27
Springfield, MO
Tan
°F
20.5
25.0
34.3
44.1
53.2
61.9
66.6
64.9
57.7
45.9
35.4
25.3
44.6
Tax
°F
41.7
46.2
57.4
67.8
75.9
84.4
89.6
88.5
80.2
69.8
56.7
45.3
66.9
V
mi/hr
11.0
11.0
12.1
11.2
9.4
8.5
7.6
7.8
8.5
9.4
10.3
10.7
9.8
I
Btu/ft2/day
761
983
1300
1649
1871
2029
2093
1871
1490
1173
793
634
1395
Pa
lb/in2
14.10
St Louis, MO
Tan
°F
20.8
25.2
35.4
46.4
55.9
65.7
70.3
67.8
60.4
48.4
37.8
26.1
46.8
Tax
°F
37.8
42.6
54.7
66.9
76.1
85.3
89.2
87.3
79.9
68.5
54.7
41.7
65.5
V
mi/hr
11.0
10.7
11.9
11.6
9.6
9.2
8.5
8.1
8.5
9.2
10.3
10.7
9.8
I
Btu/ft2/day
698
919
1236
1585
1871
2029
2029
1807
1458
1110
729
571
1332
Pa
lb/in2
14.46
Billings, MT
Tan
°F
13.6
19.4
25.2
34.0
43.3
52.0
58.3
56.7
46.6
37.6
25.5
16.5
35.8
Tax
°F
31.8
38.7
45.9
57.0
66.7
77.5
86.7
84.7
71.6
60.6
44.4
34.3
58.3
V
mi/hr
14.1
12.3
11.2
11.4
10.5
9.6
9.4
9.4
9.8
11.0
11.6
13.2
11.2
I
Btu/ft2/day
539
824
1205
1585
1871
2124
2219
1934
1427
983
602
444
1300
-------
o
00
-Q
£
&
IT!
r-K
o
l-s
,p
CfQ
CD
ft
Location
Symbol
Units
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
Pa
lb/in2
12.92
Cut Bank, MT
Tan
°F
7.3
12.6
18.9
28.2
37.6
45.5
49.5
48.6
39.4
31.3
19.0
10.0
28.9
Tax
°F
27.5
33.8
40.3
52.2
62.2
71.1
79.0
78.1
66.9
56.7
39.7
29.8
53.1
V
mi/hr
14.5
13.4
12.5
13.4
12.3
11.4
10.7
10.3
11.0
12.3
12.3
13.2
12.3
I
Btu/ft2/day
444
698
1110
1554
1871
2093
2188
1839
1332
888
507
349
1236
Pa
lb/in2
12.78
Glasgow, MT
Tan
°F
1.2
7.9
19.0
32.0
42.4
51.3
56.7
55.2
44.1
33.3
18.9
5.5
30.6
Tax
°F
19.9
27.1
39.7
56.5
67.3
77.5
84.7
83.5
70.3
58.6
39.6
25.0
54.1
V
mi/hr
9.8
10.3
11.4
12.1
12.3
11.0
11.0
11.0
11.2
10.5
9.6
10.1
10.7
I
Btu/ft2/day
476
729
1141
1490
1807
2061
2124
1807
1300
856
507
380
1236
Pa
lb/in2
13.53
Great Falls, MT
Tan
°F
11.7
17.2
22.8
31.8
40.8
48.6
53.2
52.2
43.5
35.8
24.3
14.5
33.1
Tax
°F
30.6
37.6
43.7
55.2
65.1
74.7
83.3
81.7
69.6
59.4
43.5
33.1
56.5
V
mi/hr
14.3
13.2
12.1
12.3
11.0
10.3
9.6
9.6
10.5
12.3
13.9
14.3
12.1
I
Btu/ft2/day
444
761
1173
1554
1839
2124
2251
1871
1363
888
539
380
1268
Pa
lb/in2
12.88
Helena, MT
Tan
°F
9.7
16.0
22.3
30.6
39.6
48.4
53.4
51.6
41.0
31.6
20.7
11.1
31.3
Tax
°F
29.7
36.9
44.8
56.1
65.5
75.7
84.9
83.1
69.8
58.5
42.4
31.3
56.7
V
mi/hr
6.9
7.6
8.3
9.2
8.7
8.3
7.8
7.2
7.2
6.9
6.9
6.3
7.6
I
Btu/ft2/day
476
729
1110
1522
1839
2061
2219
1871
1395
919
539
380
1268
Pa
lb/in2
12.78
Kalispell, MT
Tan
°F
12.7
18.1
23.9
31.1
38.5
44.1
47.1
46.2
38.7
29.5
23.7
15.4
30.7
Tax
°F
28.2
35.1
43.3
55.2
64.2
71.4
80.1
79.3
67.6
54.3
38.3
29.8
54.0
V
mi/hr
5.8
5.8
6.9
8.1
7.6
6.9
6.7
6.5
6.5
5.1
5.8
5.1
6.5
I
Btu/ft2/day
380
634
983
1363
1712
1934
2124
1775
1268
793
412
317
1141
Pa
lb/in2
13.23
Lewistown, MT
Tan
°F
54.9
14.2
19.6
28.8
37.2
45.1
49.8
49.1
39.9
31.6
20.5
11.7
29.7
Tax
°F
30.9
36.0
41.4
52.9
62.4
72.0
80.8
80.2
68.2
58.3
43.5
33.6
55.0
V
mi/hr
11.2
10.3
9.6
10.3
9.6
8.5
8.5
8.3
8.5
8.9
9.6
10.3
9.4
I
Btu/ft2/day
476
729
1141
1522
1807
2029
2156
1839
1332
888
539
380
1236
Pa
lb/in2
12.65
Miles City, MT
Tan
°F
6.3
12.9
22.3
33.8
44.6
54.1
60.6
58.5
46.6
35.4
21.7
9.3
34.0
Tax
°F
25.7
33.4
44.2
58.1
69.1
79.9
88.9
86.5
73.0
60.4
42.4
28.9
57.6
V
mi/hr
10.3
10.1
11.0
11.6
11.4
10.3
9.8
9.8
10.1
10.1
9.4
9.8
10.3
-------
-Q
£
&
IT!
r-K
o
l-s
,p
CfQ
CD
FT
O
00
Location
Symbol
Units
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
/
Btu/ft2/day
539
824
1205
1554
1871
2156
2219
1902
1395
951
571
444
1300
Pa
lb/in2
13.37
Missoula, MT
Tan
°F
15.4
20.8
25.0
30.9
37.9
46.0
50.2
49.3
40.5
31.3
24.3
16.3
32.4
Tax
°F
30.0
37.4
46.6
57.6
65.7
73.9
83.5
82.2
70.9
57.0
40.6
30.2
56.3
V
mi/hr
5.4
5.8
6.7
7.8
7.6
7.4
7.4
6.7
6.3
5.1
5.6
4.9
6.5
I
Btu/ft2/day
412
666
1015
1427
1744
1997
2188
1839
1332
856
444
349
1205
Pa
lb/in2
13.13
Grand Island, NE
Tan
°F
11.1
16.3
26.2
38.1
49.5
59.4
64.8
62.1
51.6
39.2
26.2
14.9
38.3
Tax
°F
32.5
38.1
49.3
63.5
73.2
83.7
88.5
85.8
76.3
65.5
48.7
35.8
61.9
V
mi/hr
12.1
11.9
13.4
13.9
12.5
11.6
10.3
10.1
10.7
11.0
11.6
11.6
11.6
I
Btu/ft2/day
698
951
1300
1680
1934
2188
2156
1902
1490
1110
729
602
1395
Pa
lb/in2
13.78
Norfolk, NE
Tan
°F
8.4
14.2
25.0
37.6
49.3
58.6
64.0
61.2
51.1
38.7
25.5
12.7
37.2
Tax
°F
29.7
34.7
46.2
61.5
72.7
82.0
86.7
83.8
75.0
64.0
46.9
32.7
59.7
V
mi/hr
12.5
11.9
13.4
13.6
12.3
11.0
9.8
9.8
10.7
11.2
12.1
12.1
11.6
I
Btu/ft2/day
666
919
1268
1617
1902
2124
2124
1839
1427
1046
698
539
1363
Pa
lb/in2
13.92
North Platte, NE
Tan
°F
8.6
14.4
23.0
34.0
44.6
54.1
60.1
57.6
46.2
33.4
21.4
11.1
34.0
Tax
°F
34.5
40.8
49.8
62.4
71.8
81.7
87.8
86.0
76.6
65.7
49.5
37.2
62.1
V
mi/hr
9.4
9.6
11.6
12.5
11.4
10.1
9.6
9.2
9.6
9.4
9.4
9.2
10.1
I
Btu/ft2/day
698
983
1332
1680
1902
2156
2156
1902
1522
1141
761
602
1395
Pa
lb/in2
13.30
Omaha, NE
Tan
°F
11.1
16.5
27.9
40.3
51.8
61.3
66.6
63.9
54.7
43.0
29.7
16.0
40.3
Tax
°F
29.7
35.1
47.7
62.4
72.9
82.4
86.5
84.0
74.8
64.0
47.7
32.9
60.1
V
mi/hr
10.3
10.3
11.4
11.6
9.8
8.9
8.3
8.1
8.7
9.2
10.1
10.1
9.6
I
Btu/ft2/day
666
919
1236
1585
1871
2124
2093
1807
1427
1046
666
539
1332
Pa
lb/in2
14.16
Scottsbluff, NE
Tan
°F
11.8
16.9
22.1
31.5
41.7
52.7
58.6
55.9
45.7
33.6
22.5
12.9
33.8
Tax
°F
37.9
43.5
50.4
61.3
70.9
82.0
89.8
87.3
77.2
65.5
50.2
39.6
63.0
V
mi/hr
11.4
11.4
12.3
12.8
11.9
10.5
9.4
8.9
9.4
9.6
10.1
10.5
10.5
I
Btu/ft2/day
666
951
1300
1680
1902
2188
2219
1966
1554
1110
729
602
1395
Pa
lb/in2
12.75
Elko, NV
Tan
°F
13.5
19.9
25.0
29.5
36.9
44.6
50.4
48.6
38.8
29.7
22.5
14.0
31.1
Tax
°F
36.7
43.0
50.2
59.2
69.4
80.2
91.0
88.5
78.3
65.8
49.1
37.4
62.4
-------
o
00
-Q
£
&
IT!
r-K
o
l-s
,p
CfQ
CD
ft
Location
Symbol
Units
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
V
mi/hr
5.1
5.8
6.7
7.2
6.9
6.5
6.3
6.0
5.6
5.1
5.4
4.9
6.0
I
Btu/ft2/day
666
919
1268
1680
1997
2251
2346
2093
1712
1205
729
602
1458
Pa
lb/in2
12.26
Ely, NV
Tan
°F
9.3
15.4
20.7
26.1
33.6
40.6
48.0
46.6
37.2
28.2
19.0
10.6
28.0
Tax
°F
39.7
43.5
48.4
57.0
67.3
78.3
87.1
84.4
75.2
63.5
49.3
40.6
61.2
V
mi/hr
9.2
9.4
10.1
10.3
10.3
10.1
10.1
10.1
9.6
9.2
9.2
9.2
9.6
I
Btu/ft2/day
824
1078
1427
1839
2093
2378
2314
2061
1775
1300
888
698
1554
Pa
lb/in2
11.73
Las Vegas, NV
Tan
°F
33.6
38.8
43.9
50.7
60.3
69.4
76.3
74.1
66.2
54.3
42.6
34.0
53.8
Tax
°F
57.4
63.3
68.7
77.5
87.8
100.2
106.0
103.3
94.6
82.0
67.5
57.6
80.4
V
mi/hr
8.1
9.2
11.0
11.4
11.6
11.4
11.0
10.1
9.6
8.5
8.5
7.6
9.8
I
Btu/ft2/day
951
1268
1712
2188
2473
2663
2505
2283
1966
1490
1078
888
1807
Pa
lb/in2
13.60
Reno, NV
Tan
°F
20.7
24.3
29.1
33.3
40.1
46.9
51.3
49.6
41.4
32.9
26.8
19.9
34.7
Tax
°F
45.1
51.6
56.3
63.7
72.9
83.1
91.9
89.6
79.5
68.5
53.8
45.5
66.7
V
mi/hr
5.1
6.3
8.3
8.5
8.5
7.8
7.6
6.9
6.3
5.6
6.0
5.6
6.9
I
Btu/ft2/day
729
1015
1427
1871
2219
2410
2473
2188
1807
1300
824
666
1585
Pa
lb/in2
12.57
Tonopah, NV
Tan
°F
18.1
23.5
27.3
33.1
41.7
50.5
56.5
54.7
46.8
36.9
26.2
19.0
36.1
Tax
°F
43.9
49.3
54.5
63.0
73.0
83.5
91.0
88.3
79.5
68.2
53.2
44.4
66.0
V
mi/hr
8.3
9.2
10.7
11.0
10.3
9.6
8.9
8.5
8.7
8.5
8.5
8.3
9.2
I
Btu/ft2/day
856
1141
1522
1966
2251
2505
2473
2219
1871
1395
951
761
1649
Pa
lb/in2
12.10
Winnemucca, NV
Tan
°F
16.7
22.8
25.2
29.5
37.8
45.9
51.3
48.7
38.8
29.3
23.4
17.1
32.2
Tax
°F
42.1
48.9
55.0
63.0
73.0
83.1
93.0
90.7
80.1
68.2
52.3
42.6
66.0
V
mi/hr
7.2
8.1
8.7
8.9
8.9
8.7
8.5
8.1
8.1
7.6
7.8
7.6
8.3
I
Btu/ft2/day
666
919
1300
1744
2093
2346
2441
2124
1744
1205
729
602
1490
Pa
lb/in2
12.60
Concord, NH
Tan
°F
7.3
10.4
22.1
31.5
41.4
51.3
56.5
54.7
46.0
34.9
27.0
14.4
33.1
Tax
°F
29.8
33.1
42.8
56.3
68.9
77.4
82.4
79.9
71.6
60.6
47.1
34.2
57.0
V
mi/hr
6.7
7.2
7.8
7.8
6.7
6.5
5.6
5.4
5.4
5.6
6.7
6.7
6.7
I
Btu/ft2/day
602
888
1236
1490
1775
1934
1934
1680
1332
919
571
476
1236
Pa
lb/in2
14.55
-------
-Q
£
&
IT!
r-K
o
l-s
,p
CfQ
CD
FT
O
00
Location
Symbol
Units
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
Atlantic City, NJ
Tan
°F
21.4
23.5
31.3
39.4
49.6
58.6
64.8
63.5
55.6
43.7
35.8
26.2
42.8
Tax
°F
40.5
42.4
51.6
60.6
71.2
80.1
84.6
83.3
76.6
66.0
55.8
45.3
63.1
V
mi/hr
10.3
10.7
11.4
11.6
10.1
8.9
8.3
7.8
8.3
8.7
10.3
10.3
9.6
I
Btu/ft2/day
634
888
1236
1554
1775
1934
1871
1680
1395
1046
698
571
1268
Pa
lb/in2
14.72
Newark, NJ
Tan
°F
23.4
25.3
33.4
42.6
53.2
62.8
68.5
67.5
59.9
48.2
39.2
29.1
46.0
Tax
°F
37.8
40.5
50.7
61.9
72.3
82.2
87.1
85.5
77.5
66.7
55.4
43.0
63.3
V
mi/hr
11.0
11.4
12.1
11.6
10.3
9.6
8.9
8.9
9.4
9.4
10.5
10.7
10.3
I
Btu/ft2/day
602
856
1205
1522
1744
1902
1871
1649
1363
1015
634
507
1236
Pa
lb/in2
14.74
Albuquerque, NM
Tan
°F
21.7
26.4
32.2
39.6
48.6
58.3
64.4
62.6
55.2
43.0
31.3
23.2
42.3
Tax
°F
46.8
53.4
61.3
70.9
79.7
90.0
92.5
89.1
81.9
71.1
57.4
47.5
70.2
V
mi/hr
8.3
8.7
10.1
11.0
10.7
10.1
8.9
8.5
8.5
8.1
8.1
7.8
9.2
I
Btu/ft2/day
1015
1332
1712
2156
2441
2568
2378
2188
1871
1490
1110
919
1775
Pa
lb/in2
12.15
Tucumcari, NM
Tan
°F
21.7
25.5
32.5
41.7
50.5
59.5
64.2
62.1
55.0
43.5
33.1
23.4
42.6
Tax
°F
52.9
56.5
64.2
73.0
81.0
89.4
92.7
90.1
82.9
74.7
62.4
53.1
72.7
V
mi/hr
9.6
9.8
11.0
11.4
10.7
10.3
9.6
8.7
9.2
8.9
9.6
9.4
9.8
I
Btu/ft2/day
951
1236
1617
2029
2219
2378
2283
2061
1744
1427
1046
856
1649
Pa
lb/in2
12.73
Albany, NY
Tan
°F
10.9
13.8
24.4
35.1
45.3
54.7
59.5
57.7
49.5
38.7
30.7
18.1
36.7
Tax
°F
30.2
33.3
44.1
57.6
69.6
79.0
84.0
81.3
73.2
61.9
48.7
34.9
58.1
V
mi/hr
9.4
9.8
10.5
10.3
8.7
8.1
7.4
6.9
7.4
7.6
9.2
9.4
8.7
I
Btu/ft2/day
571
824
1141
1490
1744
1902
1934
1649
1300
888
539
444
1205
Pa
lb/in2
14.59
Binghampton, NY
Tan
°F
14.4
15.3
24.6
35.2
46.2
54.7
59.7
57.9
50.5
40.3
31.6
20.3
37.6
Tax
°F
27.9
30.0
40.5
53.4
65.5
73.8
78.6
76.5
68.5
57.4
45.0
32.7
54.1
V
mi/hr
11.2
11.0
11.6
11.4
10.1
9.2
8.3
8.3
8.7
9.6
11.0
11.2
10.1
I
Btu/ft2/day
539
793
1110
1427
1680
1839
1839
1585
1236
856
539
444
1173
Pa
lb/in2
13.88
Buffalo, NY
Tan
°F
17.1
17.4
25.9
36.1
46.9
56.5
61.9
60.1
53.1
42.6
34.0
22.8
39.6
Tax
°F
30.2
31.6
41.7
54.1
66.0
75.4
80.2
77.9
70.9
59.4
47.1
35.2
55.8
V
mi/hr
13.9
12.5
12.3
11.9
10.7
10.3
9.6
9.2
9.4
10.3
11.9
12.5
11.2
I
Btu/ft2/day
507
761
1078
1427
1744
1934
1902
1649
1236
824
507
412
1173
-------
o
00
-Q
£
&
IT!
r-K
o
l-s
,p
CfQ
CD
ft
Location
Symbol
Units
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
Pa
lb/in2
14.37
Massena, NY
Tan
°F
4.3
6.4
19.0
32.5
43.9
52.5
57.7
55.6
47.1
37.0
27.7
11.7
33.1
Tax
°F
24.3
26.4
37.6
52.7
66.6
75.4
80.6
77.5
68.7
56.8
42.8
28.8
53.2
V
mi/hr
9.4
9.2
9.4
9.6
8.5
7.6
6.9
6.5
6.7
8.1
8.9
8.9
8.3
I
Btu/ft2/day
539
824
1173
1458
1744
1902
1934
1617
1236
824
476
412
1173
Pa
lb/in2
14.62
New York, NY
Tan
°F
25.3
27.0
34.9
43.9
53.8
63.0
68.4
67.3
60.1
49.6
41.2
30.7
47.1
Tax
°F
37.6
40.3
50.0
61.2
71.8
80.1
85.3
83.7
76.3
65.3
54.0
42.4
62.2
V
mi/hr
13.6
13.6
13.6
13.0
11.6
11.0
10.5
10.5
11.2
11.4
13.0
13.4
12.3
I
Btu/ft2/day
602
856
1205
1554
1807
1934
1902
1712
1363
1015
634
507
1268
Pa
lb/in2
14.74
Rochester, NY
Tan
°F
16.3
16.5
25.7
36.0
46.2
54.3
59.5
57.7
51.6
41.5
33.3
22.5
38.5
Tax
°F
30.9
32.5
42.6
55.9
67.8
75.7
80.8
78.1
71.8
60.4
47.8
35.8
56.7
V
mi/hr
12.1
11.2
11.2
11.4
9.6
8.9
8.3
8.1
8.3
8.9
10.3
11.0
9.8
I
Btu/ft2/day
507
761
1078
1458
1744
1934
1902
1649
1268
856
507
412
1173
Pa
lb/in2
14.45
Syracuse, NY
Tan
°F
14.2
15.4
25.2
35.4
46.0
53.8
59.0
57.7
51.4
41.2
33.1
21.0
37.8
Tax
°F
30.6
32.5
42.6
55.9
68.4
76.6
81.7
79.0
71.6
60.3
48.0
35.4
56.8
V
mi/hr
10.7
10.7
10.7
10.3
8.9
8.1
7.8
7.6
8.1
8.5
10.1
10.5
9.4
I
Btu/ft2/day
539
793
1110
1458
1744
1934
1902
1649
1268
856
507
412
1173
Pa
lb/in2
14.52
Asheville, NC
Tan
°F
24.8
27.3
35.4
42.6
50.9
58.3
62.8
61.9
55.6
43.5
35.8
28.6
43.9
Tax
°F
46.6
50.0
59.2
67.8
75.0
80.4
82.9
82.0
76.8
68.4
59.4
50.4
66.6
V
mi/hr
9.6
9.6
9.4
9.2
7.2
5.8
5.6
5.4
5.6
6.7
8.3
8.9
7.6
I
Btu/ft2/day
793
1046
1363
1712
1839
1902
1839
1680
1427
1205
856
698
1363
Pa
lb/in2
13.66
Cape Hatteras, NC
Tan
°F
36.7
37.6
43.5
50.7
59.5
67.5
71.8
72.0
67.6
58.3
49.3
41.2
54.7
Tax
°F
52.3
53.4
59.5
66.9
74.5
80.8
84.6
84.7
80.8
72.3
64.8
56.8
69.3
V
mi/hr
11.6
11.9
11.9
11.6
10.5
10.5
9.8
9.4
10.5
11.0
11.0
11.2
11.0
I
Btu/ft2/day
761
1046
1395
1775
1934
2029
1966
1775
1522
1173
888
698
1427
Pa
lb/in2
14.76
Charlotte, NC
Tan
°F
29.7
31.8
39.4
47.5
56.5
65.7
69.6
68.9
63.0
50.5
41.5
32.7
49.6
Tax
°F
48.9
53.1
62.2
71.2
78.3
85.8
88.9
87.6
81.9
72.0
62.6
52.3
70.3
V
mi/hr
7.6
8.1
8.7
8.5
7.6
6.9
6.5
6.3
6.5
6.5
6.9
7.4
7.4
-------
-Q
£
&
IT!
r-K
o
l-s
,p
CfQ
CD
FT
O
00
Location
Symbol
Units
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
/
Btu/ft2/day
793
1046
1395
1744
1902
1997
1934
1775
1490
1236
888
729
1395
Pa
lb/in2
14.37
Greensboro, NC
Tan
°F
26.6
29.3
37.4
45.7
54.7
62.6
66.9
65.8
59.5
47.1
38.5
30.6
47.1
Tax
°F
46.8
50.7
60.3
69.6
77.0
83.7
86.9
85.5
79.9
70.0
60.4
50.5
68.4
V
mi/hr
7.6
8.1
8.5
8.3
7.2
6.7
6.3
6.0
6.3
6.5
7.2
7.6
7.2
I
Btu/ft2/day
761
1015
1363
1712
1902
1997
1934
1744
1458
1173
856
698
1395
Pa
lb/in2
14.30
Raleigh-Durham, NC
Tan
°F
28.8
31.3
38.7
46.2
55.2
63.7
68.2
67.5
61.2
48.4
39.7
32.4
48.4
Tax
°F
48.9
52.5
62.1
71.8
78.6
84.9
88.0
86.7
81.1
71.6
62.6
52.7
70.2
V
mi/hr
8.5
8.7
9.2
8.7
7.6
6.9
6.5
6.3
6.7
6.9
7.6
8.1
7.6
I
Btu/ft2/day
761
1015
1395
1744
1902
1997
1934
1744
1458
1205
856
698
1395
Pa
lb/in2
14.53
Wilmington, NC
Tan
°F
34.3
36.3
43.2
50.5
59.4
67.5
71.8
71.1
65.3
53.8
44.8
37.6
52.9
Tax
°F
55.2
58.1
65.7
73.9
80.8
85.5
88.5
87.6
85.3
76.8
69.1
59.4
73.8
V
mi/hr
8.7
9.4
9.6
9.8
8.7
8.3
7.6
6.9
7.6
7.6
7.8
8.3
8.5
I
Btu/ft2/day
824
1078
1427
1807
1934
1997
1902
1712
1458
1236
919
761
1427
Pa
lb/in2
14.75
Bismarck, ND
Tan
°F
-1.7
5.2
17.8
30.9
42.3
51.6
56.5
54.0
43.2
32.5
17.8
3.4
29.5
Tax
°F
20.1
26.4
38.5
54.9
67.8
77.2
84.4
82.8
70.9
58.6
39.4
24.4
53.8
V
mi/hr
9.8
9.4
10.3
11.2
10.7
9.4
8.5
8.7
9.2
9.6
8.9
9.2
9.6
I
Btu/ft2/day
539
824
1205
1554
1902
2093
2156
1839
1332
888
539
444
1268
Pa
lb/in2
13.87
Fargo, ND
Tan
°F
-3.6
2.7
17.2
32.2
43.9
53.6
58.8
56.5
45.9
34.5
19.4
3.0
30.4
Tax
°F
15.4
21.0
34.5
53.8
68.5
77.4
83.5
81.3
69.4
56.7
36.9
20.1
51.4
V
mi/hr
12.3
12.1
12.5
13.0
12.1
11.0
10.1
10.3
11.0
11.9
11.6
11.4
11.6
I
Btu/ft2/day
507
793
1173
1490
1807
1966
2029
1744
1268
856
507
412
1205
Pa
lb/in2
14.26
Minot, ND
Tan
°F
0.3
6.3
18.0
31.5
42.8
52.9
57.7
55.2
45.0
34.5
19.6
5.4
30.7
Tax
°F
17.6
23.4
35.4
52.9
65.8
75.6
82.0
80.4
67.6
55.8
36.1
21.7
51.3
V
mi/hr
13.6
12.5
12.8
13.0
12.5
11.4
10.5
11.0
11.9
12.5
11.9
12.5
12.1
I
Btu/ft2/day
476
761
1141
1554
1839
2029
2093
1775
1268
856
507
380
1236
Pa
lb/in2
13.82
Akron, OH
Tan
°F
16.9
18.9
28.6
37.9
48.2
57.0
61.5
60.1
53.8
42.6
34.2
23.5
40.3
Tax
°F
32.5
36.0
47.3
59.2
69.6
78.4
82.2
80.4
73.8
62.1
49.6
37.8
59.2
-------
o
00
-Q
£
&
IT!
r-K
o
l-s
,p
CfQ
CD
ft
Location
Symbol
Units
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
V
mi/hr
11.6
11.0
11.4
10.7
9.2
8.3
7.6
7.4
8.1
9.2
10.7
11.4
9.6
I
Btu/ft2/day
539
761
1078
1458
1744
1934
1902
1649
1332
919
571
444
1205
Pa
lb/in2
14.11
Cleveland, OH
Tan
°F
17.6
19.2
28.2
37.2
47.3
56.8
61.3
60.3
54.1
43.5
35.1
24.4
40.5
Tax
°F
31.8
35.1
46.2
57.9
68.5
78.3
82.4
80.4
73.6
62.1
50.0
37.4
58.6
V
mi/hr
12.3
11.4
11.9
11.2
9.6
9.2
8.5
8.1
8.7
9.6
11.2
11.6
10.3
I
Btu/ft2/day
507
761
1046
1458
1775
1966
1934
1680
1300
888
539
412
1205
Pa
lb/in2
14.33
Columbus, OH
Tan
°F
18.5
21.2
31.3
39.9
50.2
57.9
62.8
60.8
54.9
43.0
34.3
24.6
41.5
Tax
°F
34.2
37.9
50.5
62.1
72.3
80.4
83.7
82.0
76.3
64.6
51.4
39.2
61.2
V
mi/hr
9.8
9.4
10.3
9.6
8.3
7.4
6.7
6.3
6.5
7.4
8.9
9.6
8.3
I
Btu/ft2/day
571
793
1110
1458
1744
1902
1871
1680
1363
983
602
476
1205
Pa
lb/in2
14.33
Dayton, OH
Tan
°F
18.0
20.8
30.9
40.5
51.1
59.2
63.3
61.3
55.0
43.5
34.3
24.1
41.9
Tax
°F
34.2
37.9
50.0
61.9
72.5
81.7
84.9
82.9
76.5
64.6
51.3
39.0
61.5
V
mi/hr
11.2
10.7
11.4
11.0
9.2
8.7
7.8
7.4
7.8
8.7
10.3
10.7
9.6
I
Btu/ft2/day
602
824
1141
1490
1807
1966
1902
1712
1395
1015
634
476
1236
Pa
lb/in2
14.23
Mansfield, OH
Tan
°F
16.9
18.9
28.6
38.1
48.4
57.4
62.1
60.4
54.0
43.2
34.0
22.6
40.5
Tax
°F
32.2
35.1
46.6
58.6
69.3
78.3
82.0
80.1
73.8
62.2
49.3
36.9
58.6
V
mi/hr
13.2
11.6
12.5
12.3
11.0
9.4
8.5
8.3
8.9
10.1
11.6
13.0
11.0
I
Btu/ft2/day
539
793
1078
1458
1744
1934
1902
1680
1332
951
571
444
1205
Pa
lb/in2
14.07
Toledo, OH
Tan
°F
14.9
17.1
26.8
36.3
46.8
55.9
60.6
58.5
51.4
39.9
31.5
20.5
38.5
Tax
°F
30.2
33.4
45.5
58.8
70.5
79.9
83.5
81.3
74.5
62.4
48.6
35.2
58.6
V
mi/hr
11.2
10.5
11.4
11.0
9.4
8.5
7.4
6.9
7.6
8.5
10.1
10.3
9.4
I
Btu/ft2/day
539
824
1110
1490
1839
1997
1966
1712
1363
951
571
444
1236
Pa
lb/in2
14.39
Youngstown, OH
Tan
°F
16.3
18.0
27.3
36.9
46.2
54.9
59.2
57.9
51.6
41.5
33.6
22.8
38.8
Tax
°F
30.7
34.0
45.3
57.7
68.7
77.4
81.3
79.5
72.7
61.0
48.4
36.0
57.7
V
mi/hr
11.6
11.0
11.4
10.7
9.4
8.3
7.6
7.4
8.1
9.2
10.5
11.2
9.6
I
Btu/ft2/day
507
761
1046
1395
1680
1871
1839
1585
1268
888
539
412
1141
Pa
lb/in2
14.13
-------
NJ
O
-Q
£
&
IT!
r-K
o
l-s
,p
CfQ
CD
ft
o
00
Location
Symbol
Units
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
Oklahoma City, OK
Tan
°F
25.2
29.7
38.5
48.7
57.7
66.0
70.5
69.6
62.2
50.4
38.7
28.6
48.7
Tax
°F
46.8
52.2
62.1
72.0
79.2
87.3
93.4
92.5
83.8
73.6
60.4
49.8
71.1
V
mi/hr
12.3
13.0
14.1
13.6
12.5
11.0
10.7
10.3
10.7
11.4
12.3
11.9
12.1
I
Btu/ft2/day
888
1110
1458
1807
1966
2156
2188
1966
1585
1268
919
761
1522
Pa
lb/in2
14.07
Tulsa, OK
Tan
°F
25.0
29.5
39.0
49.8
58.8
67.6
72.9
70.5
63.0
50.7
39.6
28.9
49.6
Tax
°F
45.3
51.1
62.1
73.0
79.7
87.6
93.7
92.5
83.7
73.8
60.3
48.7
71.1
V
mi/hr
10.3
10.7
11.9
12.1
11.0
9.8
9.4
9.2
9.2
9.6
10.5
10.1
10.3
I
Btu/ft2/day
793
1046
1363
1680
1871
2029
2124
1902
1490
1205
856
698
1427
Pa
lb/in2
14.39
Astoria, OR
Tan
°F
36.0
37.2
38.1
40.3
44.8
49.5
52.3
52.5
48.9
44.1
40.3
36.7
43.3
Tax
°F
47.8
51.1
53.2
55.9
60.1
64.0
67.5
68.7
67.8
61.2
53.4
48.2
58.3
V
mi/hr
9.6
9.4
9.2
9.2
8.7
9.2
8.9
8.5
7.8
7.8
9.2
9.2
8.9
I
Btu/ft2/day
349
571
888
1236
1554
1680
1712
1522
1205
761
412
317
1015
Pa
lb/in2
14.75
Burns, OR
Tan
°F
12.9
19.2
25.0
28.9
36.0
41.5
47.1
45.0
36.3
28.0
21.9
15.1
29.8
Tax
°F
33.6
39.6
47.7
56.5
65.7
74.5
85.1
83.3
73.6
61.9
45.1
35.2
58.5
V
mi/hr
4.7
4.9
6.7
7.8
7.6
6.7
6.7
5.1
5.6
5.1
4.9
5.4
6.0
I
Btu/ft2/day
571
824
1205
1649
2029
2251
2378
2061
1617
1078
602
476
1395
Pa
lb/in2
12.68
Eugene, OR
Tan
°F
35.2
37.0
38.8
40.6
44.4
49.6
52.9
53.2
49.3
43.5
39.7
36.0
43.3
Tax
°F
46.4
51.4
55.9
60.4
67.1
74.1
81.7
81.9
76.3
64.6
52.3
46.2
63.1
V
mi/hr
7.6
7.8
8.3
7.8
7.4
7.6
7.8
7.4
7.4
6.5
7.8
7.6
7.6
I
Btu/ft2/day
412
634
983
1395
1744
1966
2124
1839
1395
856
444
317
1173
Pa
lb/in2
14.56
Medford, OR
Tan
°F
30.4
32.2
35.4
37.9
43.3
50.7
55.2
55.0
48.2
40.5
35.4
31.3
41.4
Tax
°F
45.7
53.2
58.5
64.6
72.9
82.0
90.5
90.0
82.8
69.4
52.5
44.2
67.3
V
mi/hr
3.8
4.7
5.4
5.6
5.6
6.0
5.8
5.4
4.7
3.8
3.8
3.6
4.7
I
Btu/ft2/day
476
761
1173
1649
2061
2314
2441
2124
1649
1046
539
380
1395
Pa
lb/in2
14.07
North Bend, OR
Tan
°F
38.8
40.5
41.2
42.4
46.6
50.7
52.5
53.1
50.5
46.8
43.2
39.7
45.5
Tax
°F
51.8
54.0
54.9
56.5
60.3
63.9
66.4
67.1
66.9
63.0
56.8
52.3
59.5
V
mi/hr
8.5
8.7
9.4
9.6
10.1
10.7
11.4
9.8
8.7
7.6
8.7
8.5
9.4
I
Btu/ft2/day
476
698
1078
1490
1807
1966
2061
1775
1427
951
571
412
1236
-------
o
00
-Q
£
&
IT!
r-K
o
l-s
,p
CfQ
CD
ft
NJ
Location
Symbol
Units
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
Pa
lb/in2
14.76
Pendleton, OR
Tan
°F
27.1
31.6
35.4
39.4
45.9
52.9
57.9
57.7
49.8
41.0
34.2
27.9
41.7
Tax
°F
39.7
46.9
54.1
61.3
70.0
79.5
87.8
86.2
76.3
63.7
48.9
40.5
63.0
V
mi/hr
7.4
7.6
8.5
9.2
8.7
8.5
8.3
7.8
7.6
6.9
7.2
6.9
7.8
I
Btu/ft2/day
444
666
1078
1554
1966
2188
2346
1997
1522
951
507
349
1300
Pa
lb/in2
13.97
Portland, OR
Tan
°F
33.6
36.1
38.7
41.4
46.9
52.9
56.5
56.8
52.0
45.0
39.6
34.9
44.4
Tax
°F
45.3
51.1
55.9
60.6
67.1
73.9
79.9
80.2
74.7
64.0
52.5
45.7
62.6
V
mi/hr
9.8
9.4
8.5
7.6
7.6
7.6
7.8
7.4
6.9
6.7
8.9
9.4
8.1
I
Btu/ft2/day
380
602
951
1332
1680
1871
1997
1712
1300
793
444
317
1110
Pa
lb/in2
14.75
Redmond, OR
Tan
°F
21.4
25.0
26.2
28.9
34.7
42.1
46.4
46.2
38.7
32.2
27.3
21.7
32.5
Tax
°F
41.2
47.1
52.7
59.2
67.3
76.6
85.3
83.8
75.4
64.2
48.9
41.7
62.1
V
mi/hr
7.4
7.8
8.1
8.1
7.8
7.6
7.4
6.9
6.7
6.7
7.4
6.9
7.4
I
Btu/ft2/day
539
793
1205
1680
2061
2283
2410
2093
1617
1046
602
444
1395
Pa
lb/in2
13.18
Salem, OR
Tan
°F
32.7
34.2
35.6
37.8
42.3
48.4
50.9
51.4
47.1
41.2
37.6
33.6
41.0
Tax
°F
46.4
51.4
55.8
60.4
66.9
74.5
81.7
82.0
75.9
64.2
52.3
46.4
63.1
V
mi/hr
7.8
7.8
8.1
7.4
6.7
6.7
6.7
6.3
6.0
5.8
8.1
7.6
7.2
I
Btu/ft2/day
412
634
983
1395
1744
1934
2093
1807
1395
856
444
349
1173
Pa
lb/in2
14.66
Guam
Tan
°F
71.1
70.9
71.1
72.1
72.7
72.9
72.3
72.1
72.1
72.3
73.0
72.7
72.1
Tax
°F
83.7
83.5
84.6
85.8
86.7
86.9
86.4
85.8
86.2
85.8
85.3
84.2
85.5
V
mi/hr
9.8
11.0
10.5
10.3
9.4
7.4
6.7
5.6
6.0
6.7
8.9
9.8
8.5
I
Btu/ft2/day
1395
1522
1744
1839
1807
1744
1617
1554
1554
1458
1395
1332
1585
Pa
lb/in2
14.47
Allentown, PA
Tan
°F
18.9
20.8
29.8
38.8
49.3
58.8
63.7
62.1
54.1
42.4
34.2
24.4
41.5
Tax
°F
34.3
37.8
48.7
60.4
71.2
80.1
84.6
82.2
75.0
63.9
51.8
39.2
60.8
V
mi/hr
10.3
10.3
11.0
10.7
9.2
8.3
7.2
7.2
7.4
8.1
9.6
9.8
9.2
I
Btu/ft2/day
602
856
1173
1490
1712
1902
1871
1649
1332
983
634
507
1236
Pa
lb/in2
14.55
Bradford, PA
Tan
°F
11.8
12.4
22.1
32.0
41.0
49.5
54.0
52.5
46.2
36.9
28.8
18.0
33.6
Tax
°F
26.6
29.7
40.3
52.5
64.2
72.3
76.5
74.7
67.5
56.3
43.3
31.5
53.1
V
mi/hr
9.8
9.2
9.4
9.2
7.8
6.9
5.8
5.8
6.5
7.6
9.2
9.6
8.1
-------
0
1
NJ
NJ
-Q
£
&
IT!
r-K
o
l-s
,p
CfQ
CD
ft
o
00
Location
Symbol
Units
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
/
Btu/ft2/day
571
824
1141
1458
1712
1871
1839
1585
1236
888
539
444
1173
Pa
lb/in2
13.63
Erie, PA
Tan
°F
18.1
18.0
28.0
37.8
47.8
57.6
62.6
61.9
55.9
45.7
37.0
25.2
41.4
Tax
°F
32.5
33.6
43.5
54.5
65.8
75.4
79.9
78.4
72.1
61.0
49.5
37.8
57.0
V
mi/hr
13.6
12.3
12.5
11.9
10.7
10.1
9.4
9.4
10.3
11.6
13.6
13.9
11.6
I
Btu/ft2/day
507
761
1078
1458
1807
1997
1966
1680
1300
856
507
412
1205
Pa
lb/in2
14.36
Harrisburg, PA
Tan
°F
21.2
23.4
32.0
41.2
51.1
60.6
65.7
64.2
56.5
44.6
36.1
26.6
43.5
Tax
°F
36.0
39.2
50.4
62.1
72.5
81.1
85.8
83.8
76.3
64.8
52.5
40.6
62.1
V
mi/hr
8.5
8.5
9.2
9.2
7.4
6.7
6.3
5.8
6.0
6.7
7.8
8.1
7.6
I
Btu/ft2/day
634
888
1205
1522
1744
1934
1871
1680
1363
1015
634
507
1236
Pa
lb/in2
14.58
Philadelphia, PA
Tan
°F
22.8
24.8
33.3
42.1
52.7
61.9
67.3
66.4
58.6
46.4
37.6
28.0
45.1
Tax
°F
37.9
41.0
51.6
62.6
73.0
81.7
86.2
84.6
77.5
66.4
55.0
43.3
63.3
V
mi/hr
10.3
10.7
11.2
10.7
9.6
8.7
8.1
8.1
8.5
8.7
9.6
10.1
9.4
I
Btu/ft2/day
634
888
1205
1522
1744
1934
1902
1712
1395
1015
666
539
1268
Pa
lb/in2
14.74
Pittsburgh, PA
Tan
°F
18.5
20.3
29.8
38.8
48.4
56.8
61.5
60.3
53.4
42.3
34.2
24.4
40.6
Tax
°F
33.6
36.9
48.9
60.3
70.5
79.0
82.6
80.8
74.3
62.4
50.4
38.7
59.9
V
mi/hr
10.5
10.1
10.5
10.1
8.7
7.8
7.2
6.7
7.2
8.1
9.4
10.3
8.9
I
Btu/ft2/day
539
793
1110
1458
1744
1934
1871
1649
1332
951
571
444
1205
Pa
lb/in2
14.11
Wilkes-Barre, PA
Tan
°F
17.4
19.0
28.2
38.1
48.4
56.8
61.5
60.1
52.9
42.1
34.0
23.4
40.3
Tax
°F
31.8
34.5
45.5
57.7
69.3
77.5
81.9
79.7
72.3
61.0
48.7
36.7
58.1
V
mi/hr
8.7
8.7
9.4
9.4
8.5
7.8
7.2
6.9
7.4
7.8
8.5
8.7
8.3
I
Btu/ft2/day
571
793
1141
1458
1712
1902
1871
1649
1300
919
571
444
1205
Pa
lb/in2
14.26
Williamsport, PA
Tan
°F
17.1
19.2
28.6
38.1
47.8
56.7
61.5
60.4
53.1
41.5
33.6
23.9
40.1
Tax
°F
33.3
36.7
47.7
60.1
71.1
79.0
83.1
81.1
73.8
62.4
49.8
37.9
59.7
V
mi/hr
8.9
8.7
9.2
9.4
7.8
7.2
6.3
6.0
6.3
6.7
8.3
8.7
7.8
I
Btu/ft2/day
571
824
1141
1458
1712
1902
1871
1617
1268
919
571
444
1205
Pa
lb/in2
14.47
San Juan, PR
Tan
°F
70.9
70.5
71.6
72.9
74.5
76.1
76.8
76.6
76.3
75.6
73.9
72.3
73.9
Tax
°F
83.1
83.7
84.4
85.8
87.3
88.5
88.5
88.7
88.9
88.3
85.8
83.8
86.4
-------
o
00
-Q
£
&
IT!
r-K
o
l-s
,p
CfQ
CD
ft
0
1
NJ
OJ
Location
Symbol
Units
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
V
mi/hr
7.8
8.5
8.9
8.5
7.8
8.5
9.2
8.3
7.2
6.5
7.2
7.8
8.1
I
Btu/ft2/day
1363
1554
1807
1934
1839
1934
1934
1902
1744
1554
1363
1268
1680
Pa
lb/in2
14.71
Providence, Rl
Tan
°F
19.0
20.8
28.8
37.8
47.3
56.8
63.1
61.9
53.8
43.0
34.9
24.4
41.0
Tax
°F
36.7
38.3
46.0
57.0
67.3
76.8
82.0
80.8
74.3
64.0
53.1
41.2
59.7
V
mi/hr
11.0
11.4
12.1
12.1
10.7
9.8
9.4
9.2
9.4
9.4
10.5
10.7
10.3
I
Btu/ft2/day
602
856
1173
1490
1775
1902
1871
1649
1332
983
602
507
1236
Pa
lb/in2
14.71
Charleston, SC
Tan
°F
37.8
39.9
47.5
54.0
63.0
69.1
72.7
72.1
67.8
56.3
47.1
40.6
55.8
Tax
°F
57.7
61.0
68.5
75.7
82.8
87.6
90.1
89.1
84.9
77.2
69.4
61.5
75.6
V
mi/hr
8.7
9.6
9.8
9.6
8.5
8.3
7.8
7.4
7.6
8.1
8.1
8.3
8.5
I
Btu/ft2/day
856
1110
1490
1871
1966
1966
1934
1744
1490
1300
983
793
1458
Pa
lb/in2
14.75
Columbia, SC
Tan
°F
32.2
34.2
42.3
49.5
58.3
66.0
70.0
69.3
63.1
50.2
41.5
34.9
50.9
Tax
°F
55.2
59.4
68.2
76.5
83.5
88.9
91.6
90.1
85.1
76.3
67.8
58.8
75.0
V
mi/hr
7.2
7.6
8.1
8.1
6.9
6.5
6.0
5.6
6.0
6.0
6.3
6.9
6.7
I
Btu/ft2/day
824
1078
1427
1807
1934
1997
1934
1744
1522
1268
919
761
1427
Pa
lb/in2
14.65
Greenville, SC
Tan
°F
30.0
32.4
39.9
47.7
56.5
64.4
68.4
67.5
61.2
48.9
40.5
33.4
49.3
Tax
°F
50.2
54.3
63.5
72.0
79.3
85.5
88.2
86.7
81.1
72.0
62.4
53.2
70.7
V
mi/hr
7.6
8.3
8.5
8.5
7.2
6.7
6.3
6.0
6.5
6.7
7.2
7.4
7.2
I
Btu/ft2/day
824
1046
1395
1775
1902
1997
1902
1744
1490
1236
888
729
1427
Pa
lb/in2
14.26
Huron, SD
Tan
°F
2.3
9.1
21.7
34.0
44.8
55.6
61.7
58.8
47.3
35.4
21.7
7.9
33.4
Tax
°F
24.1
29.7
42.1
58.6
70.3
80.2
87.1
84.7
74.1
61.5
43.0
28.2
57.0
V
mi/hr
11.4
11.0
12.3
12.5
11.6
10.5
9.6
9.8
10.5
10.7
11.0
10.7
11.0
I
Btu/ft2/day
571
824
1173
1554
1839
2061
2093
1839
1395
951
602
476
1300
Pa
lb/in2
14.05
Pierre, SD
Tan
°F
6.6
12.0
22.6
34.9
45.7
55.8
62.1
59.9
48.6
37.0
23.5
11.1
35.1
Tax
°F
27.1
32.7
44.1
59.4
70.9
81.5
90.0
88.0
76.3
63.0
44.6
30.7
59.0
V
mi/hr
12.3
11.6
13.0
13.2
12.5
11.0
10.7
11.0
11.4
11.2
11.2
11.6
11.6
I
Btu/ft2/day
571
856
1236
1585
1902
2124
2156
1902
1427
983
634
476
1332
Pa
lb/in2
13.82
-------
0
1
NJ
-P^
-Q
£
&
IT!
r-K
o
l-s
,p
CfQ
CD
ft
o
00
Location
Symbol
Units
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
Rapid City, SD
Tan
°F
10.8
15.3
22.3
32.2
42.3
51.6
58.3
56.1
45.5
34.9
22.8
12.7
33.6
Tax
°F
33.8
38.1
45.9
57.9
68.2
77.7
86.2
85.1
74.5
62.4
46.8
35.6
59.4
V
mi/hr
11.4
11.4
12.8
13.4
12.5
11.0
10.3
10.3
11.2
11.2
10.7
11.0
11.4
I
Btu/ft2/day
602
888
1268
1617
1902
2124
2156
1934
1490
1046
666
507
1363
Pa
lb/in2
13.11
Sioux Falls, SD
Tan
°F
3.4
9.7
22.6
34.9
45.9
56.1
62.2
59.4
48.7
36.0
22.6
8.6
34.2
Tax
°F
24.3
29.7
42.3
59.0
70.7
80.4
86.4
83.3
73.0
61.2
43.3
28.0
56.8
V
mi/hr
11.0
11.0
12.3
13.0
11.6
10.5
9.8
9.8
10.3
10.5
11.2
10.7
11.0
I
Btu/ft2/day
602
856
1205
1522
1839
2061
2093
1807
1363
983
602
476
1300
Pa
lb/in2
13.98
Bristol, TN
Tan
°F
24.3
26.8
35.4
43.0
51.6
59.9
64.0
63.1
56.7
44.2
36.0
28.2
44.4
Tax
°F
43.7
48.0
58.8
67.5
75.2
82.2
84.6
84.0
79.2
69.1
58.3
48.0
66.6
V
mi/hr
6.3
6.7
7.2
6.9
5.4
4.7
4.3
3.8
4.3
4.7
5.6
6.0
5.4
I
Btu/ft2/day
698
919
1268
1617
1807
1934
1839
1712
1427
1141
761
602
1300
Pa
lb/in2
13.98
Chattanooga, TN
Tan
°F
28.0
31.1
39.0
46.8
55.4
63.9
68.4
67.6
62.6
48.9
39.9
31.3
48.6
Tax
°F
46.8
52.3
61.9
71.4
78.4
86.4
89.1
88.2
82.0
72.0
61.2
50.7
70.0
V
mi/hr
6.7
7.2
7.6
7.2
5.8
5.1
4.9
4.7
4.9
4.9
5.8
6.5
6.0
I
Btu/ft2/day
761
983
1300
1680
1839
1934
1871
1744
1427
1205
824
666
1363
Pa
lb/in2
14.42
Knoxville, TN
Tan
°F
26.1
29.1
36.7
44.6
53.1
61.9
66.0
65.3
59.0
46.0
37.6
30.0
46.2
Tax
°F
45.9
50.9
61.3
70.3
77.5
84.6
87.1
86.7
81.1
70.5
59.9
50.2
68.9
V
mi/hr
7.6
7.8
8.3
8.3
6.7
6.3
6.0
5.6
5.6
5.6
6.7
7.2
6.7
I
Btu/ft2/day
729
951
1268
1649
1839
1966
1871
1744
1427
1173
793
634
1332
Pa
lb/in2
14.26
Memphis, TN
Tan
°F
30.9
34.9
43.0
52.3
61.2
68.9
72.9
71.1
64.6
52.0
42.6
34.9
52.3
Tax
°F
48.6
53.4
63.1
73.2
81.0
89.2
92.3
90.9
83.8
74.3
62.2
52.5
72.1
V
mi/hr
9.4
9.8
10.3
10.1
8.7
7.8
7.4
6.9
7.4
7.6
8.7
9.4
8.5
I
Btu/ft2/day
793
1015
1332
1712
1934
2093
2061
1902
1522
1268
856
698
1427
Pa
lb/in2
14.62
Nashville, TN
Tan
°F
26.4
29.8
39.0
47.5
56.7
64.8
68.9
67.6
61.2
48.4
39.6
30.9
48.4
Tax
°F
45.9
50.7
61.2
70.9
78.8
86.5
89.4
88.3
82.6
72.5
60.4
50.2
69.8
V
mi/hr
9.2
9.4
10.1
9.4
7.8
7.4
6.7
6.5
6.7
7.2
8.5
9.4
8.3
I
Btu/ft2/day
729
983
1300
1712
1902
2061
1997
1807
1490
1205
793
634
1395
-------
o
00
-Q
£
&
IT!
r-K
o
l-s
,p
CfQ
CD
ft
0
1
NJ
Lh
Location
Symbol
Units
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
Pa
lb/in2
14.45
Abilene, TX
Tan
°F
30.7
35.1
43.3
52.9
61.2
68.9
72.7
71.8
65.3
54.9
43.3
34.0
52.9
Tax
°F
54.9
59.7
68.9
77.7
84.4
91.4
95.2
94.5
86.7
77.9
66.4
57.0
76.3
V
mi/hr
11.2
11.6
13.2
13.0
12.8
11.4
10.3
9.4
9.8
10.5
11.2
10.7
11.2
I
Btu/ft2/day
983
1236
1617
1934
2061
2219
2219
1997
1649
1395
1046
919
1617
Pa
lb/in2
13.82
Amarillo, TX
Tan
°F
21.2
25.5
32.7
42.1
51.6
60.6
65.5
63.9
56.5
44.4
32.4
23.7
43.3
Tax
°F
48.9
52.9
61.5
71.4
79.2
87.6
91.8
89.1
81.9
72.5
59.7
50.2
70.5
V
mi/hr
13.2
13.9
15.2
15.2
14.8
13.9
13.0
11.9
12.8
13.0
13.2
12.8
13.4
I
Btu/ft2/day
951
1205
1554
1934
2093
2251
2219
1997
1649
1395
1015
856
1585
Pa
lb/in2
12.92
Austin, TX
Tan
°F
38.7
42.1
51.1
59.7
66.6
71.4
73.9
73.9
69.8
60.1
49.8
41.2
58.3
Tax
°F
58.8
63.3
72.0
79.3
84.7
91.0
95.0
95.5
90.5
82.0
71.8
62.1
79.0
V
mi/hr
9.6
10.3
10.5
10.1
9.4
8.5
7.8
7.6
7.8
7.8
8.9
9.2
8.9
I
Btu/ft2/day
951
1205
1490
1712
1871
2093
2156
1997
1649
1395
1046
888
1554
Pa
lb/in2
14.42
Brownsville, TX
Tan
°F
49.8
52.5
59.2
66.6
72.0
74.8
75.7
75.4
73.2
66.0
59.0
52.3
64.8
Tax
°F
68.9
72.1
78.4
84.0
87.8
91.0
93.4
93.6
90.3
85.3
78.3
71.8
82.9
V
mi/hr
10.5
11.9
13.2
13.4
12.8
11.4
11.2
10.3
9.4
9.2
10.5
10.7
11.2
I
Btu/ft2/day
919
1173
1458
1680
1839
2029
2061
1902
1649
1427
1078
856
1522
Pa
lb/in2
14.72
Corpus Christi, TX
Tan
°F
45.3
48.0
55.2
63.1
69.4
73.4
74.8
75.0
72.3
63.9
55.6
48.4
62.1
Tax
°F
64.9
69.1
75.7
81.7
86.2
90.3
93.4
93.4
89.8
83.8
75.7
68.4
81.0
V
mi/hr
12.1
13.4
14.3
14.3
12.8
11.2
11.4
11.2
11.0
10.7
12.3
12.3
12.3
I
Btu/ft2/day
888
1141
1395
1585
1744
1934
1997
1839
1585
1363
1046
856
1458
Pa
lb/in2
14.71
El Paso, TX
Tan
°F
29.5
34.0
40.3
48.0
56.5
64.2
68.4
66.6
61.5
49.6
38.5
30.7
48.9
Tax
°F
56.1
62.2
70.0
78.6
87.1
96.4
96.1
93.6
87.1
78.4
66.4
57.6
77.5
V
mi/hr
7.2
7.8
9.8
9.8
9.2
7.8
7.2
6.7
6.5
6.3
6.9
6.7
7.6
I
Btu/ft2/day
1110
1427
1871
2251
2473
2536
2346
2156
1871
1554
1205
1015
1807
Pa
lb/in2
12.79
Fort Worth, TX
Tan
°F
32.7
36.9
45.7
54.7
62.6
70.0
74.1
73.6
66.9
55.8
45.3
36.3
54.7
Tax
°F
54.1
58.8
67.8
76.3
82.9
91.9
96.4
96.3
87.8
78.4
66.7
57.6
76.3
V
mi/hr
11.4
12.1
13.0
12.8
11.6
10.3
9.6
8.9
9.4
9.8
11.0
11.0
11.0
-------
0
1
NJ
On
.Q
£
&
C/3
r-K
o
l-s
,p
CfQ
CD
ft
o
00
Location
Symbol
Units
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
/
Btu/ft2/day
919
1173
1490
1775
1966
2188
2219
2029
1649
1332
983
856
1554
Pa
lb/in2
14.45
Houston, TX
Tan
°F
39.7
42.6
50.0
58.1
64.4
70.5
72.3
72.0
67.8
57.6
49.6
42.3
57.4
Tax
°F
61.0
65.3
71.1
78.4
84.6
90.1
92.7
92.5
88.3
81.7
72.3
64.8
78.6
V
mi/hr
8.9
9.4
9.8
9.8
8.7
8.1
7.2
6.7
7.4
7.6
8.5
8.7
8.5
I
Btu/ft2/day
856
1078
1332
1585
1775
1902
1871
1775
1554
1332
983
793
1395
Pa
lb/in2
14.71
Lubbock, TX
Tan
°F
24.6
28.6
36.3
46.8
55.8
64.2
68.0
66.2
59.4
48.0
36.5
27.1
46.8
Tax
°F
52.9
57.6
66.0
75.4
83.1
90.0
91.9
89.6
82.9
74.7
63.1
54.1
73.6
V
mi/hr
12.5
13.2
14.5
15.0
14.5
13.2
11.4
10.1
10.5
11.4
11.9
11.9
12.5
I
Btu/ft2/day
983
1236
1617
1966
2124
2251
2219
1997
1649
1395
1046
888
1617
Pa
lb/in2
13.11
Lufkin, TX
Tan
°F
36.9
39.7
47.5
55.8
63.1
69.4
72.1
71.2
66.6
54.9
46.4
38.8
55.2
Tax
°F
58.3
63.1
71.4
79.0
84.6
90.1
93.2
93.6
88.2
80.4
70.2
61.7
77.7
V
mi/hr
7.2
7.6
8.1
7.8
6.9
5.8
5.4
5.4
5.8
5.8
6.7
7.4
6.7
I
Btu/ft2/day
856
1110
1427
1680
1871
2029
2029
1902
1617
1363
983
793
1458
Pa
lb/in2
14.59
Midland-Odessa, TX
Tan
°F
28.6
32.5
40.3
49.5
58.1
65.7
68.5
67.5
61.2
50.5
38.8
30.7
49.3
Tax
°F
56.5
61.5
71.2
79.9
87.4
93.4
95.4
94.1
85.5
77.4
66.2
58.5
77.2
V
mi/hr
10.7
11.4
13.0
13.2
13.0
12.5
11.2
10.5
10.3
10.3
10.7
10.5
11.4
I
Btu/ft2/day
1046
1332
1744
2061
2219
2314
2219
2061
1712
1458
1141
951
1680
Pa
lb/in2
13.28
Port Arthur, TX
Tan
°F
41.5
44.4
51.3
59.5
66.4
72.0
73.8
73.2
69.6
59.2
51.3
44.2
58.8
Tax
°F
60.3
64.2
71.4
78.3
84.0
89.4
91.9
91.8
87.3
80.2
71.2
64.2
77.9
V
mi/hr
10.3
11.0
11.2
11.4
9.8
8.5
7.2
6.9
8.1
8.5
9.8
10.1
9.4
I
Btu/ft2/day
856
1110
1363
1649
1839
1997
1934
1807
1585
1363
983
824
1458
Pa
lb/in2
14.75
San Angelo, TX
Tan
°F
30.6
34.7
43.5
52.7
61.2
66.4
69.1
68.4
64.0
53.6
42.6
33.1
51.6
Tax
°F
56.8
62.1
72.7
81.1
87.4
92.7
96.3
95.4
86.7
78.8
68.2
59.0
78.1
V
mi/hr
10.3
10.7
12.3
11.9
11.4
10.3
9.4
8.7
8.7
8.9
9.8
9.6
10.3
I
Btu/ft2/day
1015
1300
1649
1934
2061
2219
2188
2029
1680
1427
1110
951
1617
Pa
lb/in2
13.76
San Antonio, TX
Tan
°F
37.9
41.4
49.6
58.5
65.7
72.7
75.0
74.5
69.3
58.8
48.7
40.8
57.7
Tax
°F
60.8
65.7
73.6
80.2
85.3
91.8
95.0
95.4
89.2
81.7
72.0
63.5
79.5
-------
o
00
-Q
£
&
IT!
r-K
o
l-s
,p
CfQ
CD
ft
NJ
Location
Symbol
Units
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
V
mi/hr
8.7
9.4
10.1
9.8
9.8
9.6
9.4
8.5
8.5
8.5
8.5
8.5
9.2
I
Btu/ft2/day
983
1236
1522
1744
1902
2124
2188
2029
1712
1427
1078
919
1554
Pa
lb/in2
14.33
Victoria, TX
Tan
°F
42.4
45.3
52.9
61.0
67.6
72.7
74.7
74.1
70.3
61.0
52.3
45.1
60.1
Tax
°F
62.8
66.7
73.8
80.2
85.3
90.7
93.6
93.9
88.9
82.4
73.4
66.0
79.9
V
mi/hr
10.5
11.4
11.9
11.6
11.0
9.6
9.2
8.5
8.9
9.2
10.1
10.3
10.3
I
Btu/ft2/day
888
1141
1395
1617
1807
1966
1966
1839
1585
1363
1046
856
1458
Pa
lb/in2
14.68
Waco, TX
Tan
°F
34.2
37.9
46.8
56.1
64.2
70.9
74.5
73.9
67.6
56.8
46.6
37.2
55.6
Tax
°F
56.1
60.8
69.6
78.1
84.4
91.9
96.8
97.2
89.6
80.2
68.7
59.4
77.7
V
mi/hr
11.4
12.3
13.2
13.0
12.1
11.0
10.7
10.1
10.1
10.3
11.0
11.0
11.4
I
Btu/ft2/day
919
1173
1490
1744
1902
2124
2188
2029
1649
1363
1015
856
1554
Pa
lb/in2
14.47
Wichita Falls, TX
Tan
°F
27.7
32.2
40.6
50.4
59.2
68.0
72.7
71.4
63.9
52.2
40.6
30.7
50.7
Tax
°F
52.0
57.2
66.4
75.7
83.3
91.6
97.2
95.9
86.7
76.8
64.2
54.9
75.2
V
mi/hr
11.4
12.1
13.2
13.2
12.8
11.6
11.2
10.3
10.5
11.0
11.4
11.0
11.6
I
Btu/ft2/day
919
1173
1522
1839
2029
2188
2219
1997
1649
1332
983
824
1554
Pa
lb/in2
14.20
Cedar City, UT
Tan
°F
17.2
22.1
27.1
33.4
41.2
49.6
57.9
56.5
47.1
36.1
26.8
18.1
36.1
Tax
°F
41.7
46.9
52.9
61.5
72.0
83.7
90.1
87.4
79.0
66.9
52.7
43.0
64.8
V
mi/hr
6.0
6.9
8.3
8.9
8.7
8.5
8.1
7.6
7.6
6.7
7.4
6.0
7.6
I
Btu/ft2/day
856
1110
1458
1902
2219
2473
2314
2061
1807
1363
919
761
1585
Pa
lb/in2
12.02
Salt Lake City, UT
Tan
°F
19.2
24.6
31.5
37.9
45.7
55.4
63.7
61.9
51.1
40.3
30.9
21.6
40.3
Tax
°F
36.3
43.5
52.2
61.3
72.0
82.8
92.1
89.4
79.2
66.0
50.7
37.8
63.7
V
mi/hr
7.8
8.5
9.6
9.8
9.4
9.4
9.6
9.6
9.4
8.5
8.5
7.6
8.9
I
Btu/ft2/day
602
919
1300
1712
2061
2346
2314
2061
1649
1173
698
539
1458
Pa
lb/in2
12.65
Burlington, VT
Tan
°F
7.5
9.0
21.9
34.2
45.3
54.7
59.7
57.9
48.7
38.7
29.7
15.4
35.2
Tax
°F
25.2
27.5
39.4
53.6
67.3
75.7
81.1
77.9
69.1
57.0
44.1
30.4
54.0
V
mi/hr
9.6
9.2
9.6
9.4
8.9
8.5
8.1
7.6
8.3
8.7
9.8
10.1
8.9
I
Btu/ft2/day
507
824
1141
1458
1744
1902
1934
1649
1268
824
507
380
1173
Pa
lb/in2
14.55
Lynchburg, VA
Tan
°F
24.6
27.3
35.4
43.9
52.5
60.8
65.1
64.4
57.7
45.7
37.2
29.1
45.3
-------
0
1
NJ
00
-Q
£
&
in
r-K
o
l-s
,p
CfQ
CD
ft
o
00
Location
Symbol
Units
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
Tax
°F
43.5
47.1
57.4
67.6
75.6
82.6
86.0
84.9
78.4
68.4
58.1
47.7
66.4
V
mi/hr
7.8
7.8
8.5
8.5
6.9
6.7
6.0
6.0
6.3
6.7
7.4
7.6
7.2
I
Btu/ft2/day
761
1015
1363
1712
1902
2061
1966
1775
1490
1173
824
666
1395
Pa
lb/in2
14.27
Norfolk, VA
Tan
°F
30.9
32.4
39.4
47.1
56.8
65.1
70.0
69.4
64.2
52.9
43.9
35.4
50.5
Tax
°F
47.3
49.6
57.9
66.9
75.4
82.9
86.4
85.1
79.5
69.4
61.2
52.2
67.8
V
mi/hr
11.4
12.1
12.5
11.9
10.7
10.1
9.2
8.9
9.8
10.3
10.7
11.4
10.7
I
Btu/ft2/day
729
951
1300
1617
1839
1966
1871
1712
1427
1110
793
634
1332
Pa
lb/in2
14.75
Richmond, VA
Tan
°F
25.7
28.0
36.3
44.6
54.1
62.8
67.5
66.4
59.0
46.6
37.9
29.8
46.6
Tax
°F
45.7
49.3
59.5
70.0
77.7
85.1
88.3
87.1
81.0
70.7
61.3
50.2
68.7
V
mi/hr
8.3
8.7
9.4
9.2
8.1
7.6
6.9
6.5
6.7
7.2
7.6
8.1
7.8
I
Btu/ft2/day
729
951
1300
1649
1839
1997
1902
1712
1427
1110
793
634
1332
Pa
lb/in2
14.68
Roanoke, VA
Tan
°F
25.0
27.1
35.8
43.9
52.5
60.3
64.8
63.9
56.8
44.8
37.0
28.9
45.0
Tax
°F
43.9
47.3
57.7
67.3
75.7
82.9
86.4
85.3
78.4
68.2
57.9
47.7
66.6
V
mi/hr
9.4
9.2
9.6
9.6
7.6
6.9
6.5
6.0
6.0
6.7
7.8
8.5
7.8
I
Btu/ft2/day
729
983
1300
1649
1839
1966
1871
1744
1427
1141
793
634
1332
Pa
lb/in2
14.16
Sterling, VA
Tan
°F
21.0
23.4
31.8
40.3
50.0
59.2
64.0
62.8
55.4
42.4
34.2
25.9
42.4
Tax
°F
40.1
43.9
54.7
65.1
74.3
82.8
87.1
85.5
79.0
67.6
56.7
45.0
65.1
V
mi/hr
8.3
8.5
9.2
8.7
7.6
6.7
6.3
5.8
6.0
6.7
7.6
7.8
7.6
I
Btu/ft2/day
666
919
1268
1585
1839
1997
1902
1712
1395
1078
729
571
1300
Pa
lb/in2
14.59
Olympia, WA
Tan
°F
31.6
32.7
33.6
36.1
41.0
46.4
49.3
49.5
44.8
38.8
35.1
32.2
39.2
Tax
°F
44.4
49.5
54.0
58.8
65.3
70.9
76.5
77.2
71.1
60.4
50.0
44.2
60.3
V
mi/hr
7.4
7.2
7.4
7.6
7.4
6.9
6.5
6.3
6.0
6.0
7.4
6.9
6.9
I
Btu/ft2/day
317
539
888
1268
1585
1775
1871
1617
1205
698
380
285
1046
Pa
lb/in2
14.65
Quillayute, WA
Tan
°F
33.6
34.9
35.2
37.2
41.7
46.6
49.5
49.6
46.2
41.4
37.2
34.3
40.6
Tax
°F
46.0
49.1
51.4
55.0
59.9
64.2
68.2
69.1
66.9
59.4
50.9
46.2
57.2
V
mi/hr
10.3
9.6
9.2
8.3
7.6
7.2
6.9
6.3
6.7
8.1
9.4
9.4
8.3
I
Btu/ft2/day
317
507
824
1173
1490
1617
1649
1427
1110
666
380
254
951
Pa
lb/in2
14.65
-------
o
00
-Q
£
&
IT!
r-K
o
l-s
,p
CfQ
CD
ft
0
1
NJ
vO
Location
Symbol
Units
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
Seattle, WA
Tan
°F
35.2
37.4
38.5
41.2
46.2
52.0
55.2
55.8
52.0
45.9
40.1
35.8
44.6
Tax
°F
45.0
49.5
52.7
57.2
63.9
70.0
75.2
75.2
69.3
59.7
50.5
45.1
59.4
V
mi/hr
9.2
8.9
8.9
8.9
8.3
8.3
7.8
7.6
7.6
7.8
8.9
8.9
8.5
I
Btu/ft2/day
317
539
888
1300
1680
1839
1934
1649
1205
698
380
254
1046
Pa
lb/in2
14.52
Spokane, WA
Tan
°F
20.8
25.9
29.7
34.7
41.9
49.3
54.3
54.3
45.9
36.0
28.8
21.7
36.9
Tax
°F
33.3
40.6
47.7
57.0
65.8
74.7
83.1
82.6
72.0
58.6
41.4
33.8
57.6
V
mi/hr
9.4
9.6
10.1
10.5
9.8
9.6
9.2
8.5
8.7
8.5
9.4
8.3
9.4
I
Btu/ft2/day
412
634
1015
1458
1839
2061
2219
1871
1395
856
444
349
1205
Pa
lb/in2
13.52
Yakima, WA
Tan
°F
21.7
26.4
30.7
35.4
42.3
49.3
53.1
52.3
44.6
35.2
28.9
22.1
36.9
Tax
°F
37.6
46.4
55.2
63.1
71.6
79.9
86.7
85.6
76.8
64.4
48.4
37.6
62.8
V
mi/hr
5.8
6.7
7.8
8.5
8.5
8.5
8.1
7.6
7.6
6.7
6.3
5.4
7.4
I
Btu/ft2/day
444
698
1141
1585
1966
2188
2283
1966
1490
951
507
349
1300
Pa
lb/in2
14.18
Charleston, WV
Tan
°F
23.0
25.7
35.1
42.8
51.4
59.7
64.4
63.3
56.5
44.2
36.3
28.0
44.2
Tax
°F
41.2
45.3
56.7
66.7
75.6
83.1
85.6
84.4
78.8
68.2
57.4
46.0
65.8
V
mi/hr
7.2
6.9
7.6
7.4
5.8
5.1
4.9
4.5
4.7
4.9
6.0
6.7
6.0
I
Btu/ft2/day
634
856
1173
1522
1775
1902
1839
1680
1363
1046
666
539
1236
Pa
lb/in2
14.26
Elkins, WV
Tan
°F
16.2
18.3
27.1
34.9
44.1
52.0
56.8
56.1
49.8
37.2
29.7
21.4
37.0
Tax
°F
37.9
41.4
52.2
61.5
70.9
77.5
80.4
79.3
73.6
63.7
52.9
42.6
61.2
V
mi/hr
7.4
7.2
7.8
7.8
6.3
4.9
4.5
4.0
4.3
5.1
6.7
7.2
6.0
I
Btu/ft2/day
602
824
1141
1427
1680
1807
1744
1585
1300
983
634
507
1205
Pa
lb/in2
13.73
Huntington, WV
Tan
°F
23.2
26.1
35.4
43.9
52.3
60.4
64.9
63.9
57.0
45.0
37.0
28.4
44.8
Tax
°F
40.6
44.2
56.5
66.7
75.2
81.3
84.4
83.1
78.1
67.3
55.9
45.3
64.9
V
mi/hr
7.6
7.6
8.1
7.8
6.3
5.8
5.4
5.1
5.4
5.8
7.2
7.4
6.7
I
Btu/ft2/day
634
856
1173
1522
1775
1902
1839
1649
1363
1046
666
539
1236
Pa
lb/in2
14.33
Eau Claire, Wl
Tan
°F
0.9
5.7
19.8
33.4
45.0
54.3
59.7
57.2
47.8
36.9
23.7
8.2
32.7
Tax
°F
20.5
26.8
39.4
56.5
69.4
78.3
83.1
80.1
70.0
58.3
40.8
25.3
54.1
V
mi/hr
8.9
8.7
9.8
10.3
9.4
8.9
8.1
7.6
8.3
8.7
9.2
8.9
8.9
I
Btu/ft2/day
539
856
1173
1458
1775
1934
1934
1649
1236
856
507
444
1205
-------
OJ
o
-Q
£
&
r-K
o
l-s
,p
CfQ
CD
ft
o
00
Location
Symbol
Units
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
Pa
lb/in2
14.26
Green Bay, Wl
Tan
°F
5.7
9.5
21.4
34.0
43.7
53.4
58.8
56.8
48.7
38.5
26.8
12.6
34.2
Tax
°F
22.8
27.1
38.5
54.0
67.3
75.6
80.4
77.5
69.1
57.4
42.1
27.7
53.2
V
mi/hr
10.7
10.3
10.7
11.0
9.8
8.9
7.8
7.6
8.5
9.4
10.3
10.3
9.6
I
Btu/ft2/day
539
824
1173
1490
1807
1997
1934
1649
1236
856
507
444
1205
Pa
lb/in2
14.36
La Crosse, Wl
Tan
°F
5.4
10.0
23.5
37.0
48.0
57.0
62.2
59.9
51.3
40.3
27.7
12.6
36.3
Tax
°F
23.5
29.7
42.1
58.5
70.9
79.9
84.6
81.7
72.3
60.3
43.3
28.0
56.1
V
mi/hr
8.7
8.3
9.2
9.8
8.9
8.3
7.6
7.4
8.1
8.7
9.2
8.5
8.5
I
Btu/ft2/day
571
856
1173
1490
1807
1997
1966
1712
1268
888
539
444
1236
Pa
lb/in2
14.39
Madison, Wl
Tan
°F
7.2
11.1
23.0
34.2
44.2
54.1
59.5
56.8
48.2
37.8
26.8
13.5
34.7
Tax
°F
24.8
30.0
41.5
56.7
68.9
78.3
82.4
79.5
71.4
59.9
44.1
29.8
55.6
V
mi/hr
10.3
10.1
11.0
11.2
9.6
8.9
8.1
7.6
8.5
9.4
10.3
10.1
9.6
I
Btu/ft2/day
602
888
1173
1490
1839
2029
1966
1712
1300
888
539
476
1236
Pa
lb/in2
14.29
Milwaukee, Wl
Tan
°F
11.7
16.0
26.2
35.8
44.8
55.0
62.1
60.8
52.9
41.7
30.7
17.4
37.9
Tax
°F
26.1
30.0
40.5
52.9
64.2
74.8
79.9
77.7
70.5
58.6
44.8
31.3
54.3
V
mi/hr
12.3
11.9
12.3
12.3
11.0
10.3
9.6
9.4
10.1
11.2
11.9
11.9
11.2
I
Btu/ft2/day
571
824
1110
1458
1839
2029
1997
1712
1300
919
571
444
1236
Pa
lb/in2
14.37
Casper, WY
Tan
°F
12.0
16.0
21.7
29.5
37.9
46.9
54.0
51.8
41.5
32.2
21.7
13.6
31.6
Tax
°F
32.7
37.0
45.1
56.1
66.6
78.6
87.6
85.6
73.8
60.4
44.2
34.0
58.5
V
mi/hr
17.0
15.2
13.9
12.5
11.6
10.7
10.3
10.3
11.0
12.1
14.3
15.4
12.8
I
Btu/ft2/day
634
919
1300
1649
1934
2219
2219
1997
1554
1078
698
539
1395
Pa
lb/in2
12.14
Cheyenne, WY
Tan
°F
15.3
18.1
22.1
30.0
39.4
48.4
54.7
52.9
43.7
34.0
23.7
16.7
33.3
Tax
°F
37.8
40.5
45.0
54.7
64.6
74.5
82.2
80.1
71.1
60.1
46.8
38.8
57.9
V
mi/hr
15.9
14.8
14.5
14.5
13.0
11.4
10.3
10.3
11.2
12.1
13.2
14.5
13.0
I
Btu/ft2/day
698
983
1332
1680
1902
2124
2124
1871
1554
1141
761
602
1395
Pa
lb/in2
11.76
Lander, WY
Tan
°F
7.9
13.6
22.1
30.7
39.9
48.7
55.9
53.8
44.2
33.6
19.9
9.3
31.6
Tax
°F
31.3
37.0
45.7
55.8
66.0
77.4
86.2
83.8
72.3
59.7
42.4
32.2
57.6
V
mi/hr
5.4
5.6
6.9
7.8
8.1
7.6
7.6
7.4
6.9
6.0
5.6
5.6
6.7
-------
Location
Symbol
Units
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
/
Btu/ft2/day
698
1015
1395
1775
2029
2251
2219
1997
1585
1141
729
602
1458
Pa
lb/in2
12.02
Rock Springs, WY
Tan
°F
11.1
14.4
20.7
28.4
36.9
45.7
52.9
50.7
41.0
31.3
19.9
11.8
30.4
Tax
°F
29.5
34.3
41.7
52.7
63.7
74.7
83.1
80.8
70.0
57.2
40.6
30.7
54.9
V
mi/hr
11.9
11.9
12.1
12.1
11.2
10.3
9.4
9.2
9.6
9.8
10.5
11.4
10.7
I
Btu/ft2/day
666
951
1332
1712
2029
2283
2283
2029
1649
1173
729
602
1458
Pa
lb/in2
11.52
Sheridan, WY
Tan
°F
8.4
14.5
21.6
30.4
39.0
47.3
53.1
51.6
41.4
31.6
19.8
10.2
30.7
Tax
°F
33.1
38.3
46.2
57.0
66.4
76.8
86.2
85.3
72.9
61.7
45.3
35.1
58.6
V
mi/hr
7.8
7.8
8.9
9.6
8.9
7.6
7.4
7.2
7.4
7.4
7.4
7.6
7.8
I
Btu/ft2/day
571
856
1236
1585
1839
2124
2188
1902
1458
983
634
507
1332
Pa
lb/in2
12.73
a References 22. Data for this table are 3 0-year averages for the years 1961 through 1990, prepared by the National Renewable Energy Laboratory
and distributed by the National Climatic Data Center. Similar historical averages of meteorological data from nearby National Weather Service
sites or site-specific data may also be used.
Tax = average daily maximum ambient temperature
Tan = average daily minimum ambient temperature
V = average wind speed
I = average daily total insolation factor
Pa = average atmospheric pressure
-------
Table 7.1-8. RIM-SEAL LOSS FACTORS, KRa, KRb, and n,
FOR FLOATING ROOF TANKS3
Tank Construction And
Average-Fitting Seals
KRa
KRb
Rim-Seal System
n
(lb-mole/ft-yr)
rib-mole/(mph)n-Pt-yr|
(dimensionless)
Welded Tanks
Mechanical-shoe seal
Primary onlyb
5.8
0.3
2.1
Shoe-mounted secondary
1.6
0.3
1.6
Rim-mounted secondary
0.6
0.4
1.0
Liquid-mounted seal
Primary only
1.6
0.3
1.5
Weather shield
0.7
0.3
1.2
Rim-mounted secondary
0.3
0.6
0.3
Vapor-mounted seal
Primary only
6.7°
0.2
3.0
Weather shield
3.3
0.1
3.0
Rim-mounted secondary
2.2
0.003
4.3
Kin clod 1;
llks
Mechanical-shoe seal
Primary only
10.8
0.4
2.0
Shoe-mounted secondary
9.2
0.2
1.9
Rim-mounted secondary
1.1
0.3
1.5
Tank Construction And
Rim-Seal System
Tight-Fitting"1 Seals
KRa
(lb-mole/ft-yr)
KRb
rib-mole/(mph)n-ft-yr|
n
(dimensionless)
W elded Tanks
Mechanical-shoe seal
Primary only
1.5
0.4
1.9
Shoe-mounted secondary
1.0
0.4
1.5
Rim-mounted secondary
0.4
0.4
1.0
Liquid-mounted seal
Primary only
1.0
0.08
1.8
Weather shield
0.4
0.2
1.3
Rim-mounted secondary
0.2
0.4
0.4
Vapor-mounted seal
Primary only
5.6
0.2
2.4
Weather shield
2.8
0.1
2.3
Rim-mounted secondary
2.2
0.02
2.6
Note: The rim-seal loss factors Ki<;,. Kkh. and n may only be used for wind speeds below 15 miles per
hour.
a References 5 and 15.
b If no specific information is available, a welded tank with an average-fitting mechanical-shoe primary
seal can be used to represent the most common or typical construction and rim-seal system in use for
external and domed external floating roof tanks.
c If no specific information is available, this value can be assumed to represent the most common or
typical rim-seal system currently in use for internal floating roof tanks.
7.1-132
Liquid Storage Tanks
06/18
-------
d "Tight-fitting" means that the rim seal is maintained with no gaps greater than 1/8 in. wide between the
rim seal and the tank shell. It is not appropriate to use the values for tight-fitting seals unless the seal is
known to be maintained with gaps no greater than 1/8 in. through the full range of liquid level in the
tank.
06/18
Liquid Storage Tanks
7.1-133
-------
Table 7.1-9. RESERVED
7.1-134 Liquid Storage Tanks 06/18
-------
Table 7.1-10. AVERAGE CLINGAGE FACTORS, CV
(bbl/103 ft2)
Product Stored
Shell Condition
Light Rust
Dense Rust
Gunite Lining
Gasoline
0.0015
0.0075
0.15
Single-component stocks
0.0015
0.0075
0.15
Crude oil
0.0060
0.030
0.60
a Reference 5. If no specific information is available, the values in this table can be assumed to represent
the most common or typical condition of tanks currently in use.
Table 7.1-11. TYPICAL NUMBER OF COLUMNS AS A FUNCTION OF TANK
DIAMETER FOR INTERNAL FLOATING ROOF TANKS WITH COLUMN-
SUPPORTED FIXED ROOFS3
Tank Diameter Range D, (ft)
Typical Number
Of Columns, Nc
0 < D < 85
1
85
-------
Table 7.1-12. DECK-FITTING LOSS FACTORS, KFa, KFb,
AND m, AND TYPICAL NUMBER OF DECK FITTINGS, NFa
Fitting Type And Construction Details
KFa Loss
Factor
(lb-mole/yr)
KFb Loss Factor
(lb-mole^mph^-yr)
mLoss Factor
(dimensionless)
Typical Number Of
Fittings, Nf
Access hatch
Bolted cover, gasketedb
Unbolted cover, ungasketed
Unbolted cover, gasketed
Fixed roof support column welld
Round pipe, ungasketed sliding cover
Round pipe, gasketed sliding cover
Round pipe, flexible fabric sleeve seal
Built-up column, ungasketed sliding
coverc
Built-up column, gasketed sliding cover
1.6
36c
31
31
25
10
51
33
0
5.9
5.2
0
1.2
1.3
1
Nc
(Table 7.1-11)
Unslotted guidepole and well
Ungasketed sliding cover
Ungasketed sliding cover w/pole sleeve
Gasketed sliding cover
Gasketed sliding cover w/pole wiper
Gasketed sliding cover w/pole sleeve
31
25
25
14
8.6
150
2.2
13
3.7
12
1.4
2.1
2.2
0.78
0.81
f
Slotted guidepole/sample well6
Ungasketed or gasketed sliding cover
Ungasketed or gasketed sliding cover,
with float8
Gasketed sliding cover, with pole wiper
Gasketed sliding cover, with pole sleeve
Gasketed sliding cover, with pole sleeve
and pole wiper
Gasketed sliding cover, with float and
pole wiper®
Gasketed sliding cover, with float, pole
sleeve, and pole wiper11
Flexible enclosure1
43
31
41
11
8.3
21
11
21
270
36
48
46
4.4
7.9
9.9
7.9
1.4
2.0
1.4
1.4
1.6
1.8
0.89
1.8
f
Gauge-float well (automatic gauge)
Unbolted cover, ungasketedb
Unbolted cover, gasketed
Bolted cover, gasketed
14c
4.3
2.8
5.4
17
0
1.1
0.38
0
1
Gauge-hatch/sample port
Weighted mechanical actuation,
gasketedb
Weighted mechanical actuation,
ungasketed
Slit fabric seal, 10% open areac
0.47
2.3
12
0.02
0
0.97
0
1
Vacuum breaker
Weighted mechanical actuation,
ungasketed
Weighted mechanical actuation,
gasketedb
7.8
6.2°
0.01
1.2
4.0
0.94
Nvb (Table 7.1-13))
Deck drain (3-inch diameter)
Openb
90% closed
Stub drain (1-inch diameter)15
1.5
1.8
1.2
0.21
0.14
1.7
1.1
Nd (Table 7.1-13),
Nd (Table 7.1-15)
7.1-136
Liquid Storage Tanks
06/18
-------
KfsLoSS
Factor
KFb Loss Factor
mLoss Factor
Typical Number Of
Fitting Type And Construction Details
(lb-mole/yr)
(lb-mole^mph^-yr)
(dimensionless)
Fittings, Nf
Deck leg, IFR-type (total sleeve length
approx. 12 inches)111
Ni (Table 7.1-15)
Adjustable0
7.9
Deck leg, EFR-type (pontoon area of
pontoon roofs; total sleeve length
approx. 30 inches)
Ni (Table 7.1-14)
Adjustable - ungasketedb
2.0
0.37
0.91
Adjustable - gasketed
1.3
0.08
0.65
Adjustable - sock
1.2
0.14
0.65
Deck leg, EFR-type (double-deck roofs
and center area of pontoon roofs, total
sleeve length approx. 48 inches)
Ni (Table 7.1-14)
Adjustable - ungasketedb
0.82
0.53
0.14
Adjustable - gasketed
0.53
0.11
0.13
Adjustable - sock
0.49
0.16
0.14
Deck leg or hanger (no opening through
Ni may be set as 0
deck)
(no openings)
Fixed
0
0
0
Rim vent11
1
Weighted mechanical actuation,
0.68
1.8
1.0
ungasketed
Weighted mechanical actuation,
0.71
0.10
1.0
gasketedb
Ladder well
ld
Sliding cover, ungasketedc
98
Sliding cover, gasketed
56
Ladder-guidepole combination well
ld
Sliding cover, ungasketed
98
Ladder sleeve, ungasketed sliding cover
65
Ladder sleeve, gasketed sliding cover
60
Note: The deck-fitting loss factors, K|.;i. KFb, and m, may only be used for wind speeds below 15 miles
per hour.
a Reference 5, unless otherwise indicated.
b If no specific information is available, this value can be assumed to represent the most common or
typical deck fitting currently in use for external and domed external floating roof tanks.
c If no specific information is available, this value can be assumed to represent the most common or
typical deck fitting currently in use for internal floating roof tanks.
d Column wells and ladder wells are not typically used with self-supported fixed roofs.
e References 16,19.
f There is no typical quantity or configuration of unslotted or slotted guidepoles, and thus tank specific
data should be obtained.
8 Tests were conducted with floats positioned with the float wiper at and 1 inch above the sliding cover.
The user is cautioned against applying these factors to floats that are positioned with the wiper or top of
the float below the sliding cover ("short floats"). The emission factor for such a float is expected to be
between the factors for a guidepole without a float and with a float, depending upon the position of the
float top and/or wiper within the guidepole.
h Tests were conducted with floats positioned with the float wiper at varying heights with respect to the
sliding cover. This fitting configuration also includes a pole sleeve which restricts the airflow from the
06/18
Liquid Storage Tanks
7.1-137
-------
well vapor space into the slotted guidepole. Consequently, the float position within the guidepole (at,
above, or below the sliding cover) is not expected to significantly affect emission levels for this fitting
configuration, since the function of the pole sleeve is to restrict the flow of vapor from the vapor space
below the deck into the guidepole.
1 EPA's Storage Tank Emission Reduction Partnership Program granted the flexible enclosure system
equivalency to the pole float system. [65 FR 19891(04/13/00)]
J Nvb = 1 for internal floating roof tanks.
k Stub drains are not used on welded contact internal floating decks.
m Loss factors for EFR-type deck legs may be used for an IFR if the total height of the leg sleeves,
including the portion extending down into the liquid, is similar to that of the EFR-type deck leg.
n Rim vents are used only with mechanical-shoe primary seals.
7.1-138
Liquid Storage Tanks
06/18
-------
Table 7.1-13. EXTERNAL FLOATING ROOF TANKS: TYPICAL NUMBER OF
VACUUM BREAKERS, Nvb, AND DECK DRAINS, Nda
Tank Diameter
Number Of Vacuum Breakers, NVb
Number Of Deck drains, Nd
D (feet)b
Pontoon Roof
Double-Deck Roof
50
1
1
1
100
1
1
1
150
2
2
2
200
3
2
3
250
4
3
5
300
5
3
7
350
6
4
ND
400
7
4
ND
a Reference 5. This table was derived from a survey of users and manufacturers. The actual number of
vacuum breakers may vary greatly depending on throughput and manufacturing prerogatives. The
actual number of deck drains may also vary greatly depending on the design rainfall and manufacturing
prerogatives. For tanks more than 350 feet in diameter, actual tank data or the manufacturer's
recommendations may be needed for the number of deck drains. This table should not be used when
actual tank data are available. ND = no data.
b If the actual diameter is between the diameters listed, the closest diameter listed should be used. If the
actual diameter is midway between the diameters listed, the next larger diameter should be used.
06/18
Liquid Storage Tanks
7.1-139
-------
Table 7.1-14. EXTERNAL FLOATING ROOF TANKS: TYPICAL NUMBER OF
ROOF LEGS, Nia
Tank Diameter, D (feet)b
Pontoon Roof
Number Of Legs On
Double-Deck Roof
Number Of Pontoon
Legs
Number Of Center Legs
30
4
2
6
40
4
4
7
50
6
6
8
60
9
7
10
70
13
9
13
80
15
10
16
90
16
12
20
100
17
16
25
110
18
20
29
120
19
24
34
130
20
28
40
140
21
33
46
150
23
38
52
160
26
42
58
170
27
49
66
180
28
56
74
190
29
62
82
200
30
69
90
210
31
77
98
220
32
83
107
230
33
92
115
240
34
101
127
250
35
109
138
260
36
118
149
270
36
128
162
280
37
138
173
290
38
148
186
300
38
156
200
310
39
168
213
320
39
179
226
330
40
190
240
340
41
202
255
350
42
213
270
360
44
226
285
370
45
238
300
380
46
252
315
390
47
266
330
400
48
281
345
a Reference 5. This table was derived from a survey of users and manufacturers. The actual number of roof legs
may vary greatly depending on age, style of floating roof, loading specifications, and manufacturing prerogatives.
This table should not be used when actual tank data are available.
b If the actual diameter is between the diameters listed, the closest diameter listed should be used. If the actual
diameter is midway between the diameters listed, the next larger diameter should be used.
7.1-140
Liquid Storage Tanks
06/18
-------
Table 7.1-15. INTERNAL FLOATING ROOF TANKS: TYPICAL NUMBER
OF DECK LEGS, Ni, AND STUB DRAINS, Nda
Deck fitting type
Typical Number Of Fittings, Nf
Deck leg or hanger wellb
Stub drain (1-inch diameter)bc
(5 + ° + °2)
10 600
D2
(—)
125
a Reference 5.
b D = tank diameter, ft
c Not used on welded contact internal floating decks.
Table 7.1-16. DECK SEAM LENGTH FACTORS (SD) FOR TYPICAL DECK
CONSTRUCTIONS FOR INTERNAL FLOATING ROOF TANKS3
Deck Construction
Typical Deck Seam Length Factor,
SD (ft/ft2)
Continuous sheet construction13
5 ft wide
0.20c
6 ft wide
0.17
7 ft wide
0.14
Panel constructiond
5 x 7.5 ft rectangular
0.33
5 x 12 ft rectangular
0.28
a Reference 5. Deck seam loss applies to bolted decks only.
b Sd = 1/W, where W = sheet width (ft).
c If no specific information is available, this value can be assumed to represent the most common bolted
decks currently in use.
d Sd = (L+W)/LW, where W = panel width (ft) and L = panel length (ft).
06/18
Liquid Storage Tanks
7.1-141
-------
Table 7.1-17. ROOF LANDING LOSSES FOR INTERNAL FLOATING ROOF TANK WITH A
LIQUID HEELa
Standing Idle Loss
LsL=ndKE Mv Ks Equation3-7
K lv
Lsl < 5.9 D2 hk Wt Equation 3-4
Standing Idle Saturation Factor
1
1 + 0.053 PVA Hvo Equation 1-21
Where Hvo is set equal to hv.
K :i~ s S
Filling Loss Equation
Lfl= dt Mv{c,fS) Equation 3-18
\K-ly )
Where CSf is set equal to 1.
Lfl —{^¦9D2hleWl) — LSL +0.\5^-Mv Equation3-16
K lv
Filling Saturation Factor (S)
S = 0.60 for a Ml liquid heel
S = 0.50 for a partial liquid heel
a Reference 21.
7.1-142
Liquid Storage Tanks
06/18
-------
Table 7.1-18. ROOF LANDING LOSSES FOREXTERNAL FLOATING ROOF TANK WITH A
LIQUID HEEL3
Standing Idle Loss
Lsl = 0.57 nd DP Mv
Lsl < 5.9 D2 hle W,
Equation 3-10
Equation 3-4
Standing Idle
Saturation Factor
Not applicable
Filling Loss
Equation
Lfl
'PviZv}
\RTV
M,, (Q 5)
Equation 3-18
-s/
/ (0.57-1-D-P*-Mv)-(i-Ke{^^}mv-Ks) \
= 1-1 V ,) RTv ^ Equation3-21
LfL -{^¦9D2hleWl)-LSL +0.\5^^^MV
K Irr
Equation 3-16
Filling Saturation
Factor (S)
S = 0.6 for a full liquid heel
S = 0.5 for a partial liquid heel
Reference 21.
06/18
Liquid Storage Tanks
7.1-143
-------
Table 7.1-19. ROOF LANDING LOSSES FOR ALL DRAIN-DRY TANKS
Standing Idle Loss
s Equation 3-12
7T D
Lsl = 0.0063 W,
v 4 J
P V
Lsl < 0.60—^——Mv Equation3-15
R Tv
Standing Idle Saturation
Factor
Not applicable
Filling Loss Equation
Lfl= Mv (cs/ s) Equation 3-18
V J
Where Csf is set equal to 1.
Filling Saturation Factor (S)
S = 0.15
a Reference 21.
7.1-144
Liquid Storage Tanks
06/18
-------
Table 7.1-20. TANK CLEANING EQUATIONS - VAPOR SPACE PURGE EMISSIONS3
Vapor Space Purge
LP = ^VA ^'v Mv S Equation 4-2
R Ty
Vapor Space Volume, Vv
Fixed Roof Tank
Vv = Hvo (n D ^/4) Equation 4-3
where:
Hvo = the fixed-roof tank vapor space outage (ft)
Floatins Roof Tank
Vv = hv(%D ^ IX) Equation 4-9
where:
/?,¦ = the height of the vapor space under the landed floating roof (ft)
Saturation Factor, S
Fixed Roof Tank
S= (0.5 nj+1) / 6 Equation 4-6
where:
nj = period of time standing idle after emptying and before commencement of
forced ventilation (days)
S > 0.25 Equation 4-7
S <0.5 Equation 4-8
Floatins Roof Tank (function of heel condition and tank tvpe)
S = 0.6 Csf full liquid heel
S = 0.5 Csf partial liquid heel
S = 0 drain dry tanks
where:
C^f = 1.0 for IFRTs (and Domed EFRTs);
evaluated per Equation 3-21 for EFRTs for the initial vapor space purge; set
to 1.0 for subsequent vapor space purges that follow ventilation
having been shut off overnight.
a Reference 23.
06/18
Liquid Storage Tanks
7.1-145
-------
Table 7.1-21. TANK CLEANING EQUATIONS - CONTINUED FORCED VENTILATION
EMISSIONS3
Continued Forced
Ventilation
Lcv - 60 Qv ncv tv Cv
(PaMca^
I RTV J
Equation 4-10
Prior Stock Remains
Lev <_5.9D2h,e W,
Equation 4-12
Distillate Flushing
If liquid is being circulated through the tank, there would be no mass-based limit
on emissions in that the liquid is being continually replenished. If a fixed amount
of liquid is added to the tank, emissions could not then exceed the mass of the
remaining heel plus the added distillate.
Only Sludge Remains
Lev < 0.49 FeD2 ds
W,
Equation 4-13
a Reference 23.
7.1-146
Liquid Storage Tanks
06/18
-------
7.1.5 Sample Calculations
The examples given in this section present estimated emissions to two significant figures. This
level of precision is chosen arbitrarily, and may overstate the accuracy of the loss estimates given the
uncertainty associated with the multiple parameters affecting emissions from storage tanks.
Example 1 - Chemical Mixture in a Fixed Roof Tank
Determine the yearly emission rate of the total product mixture and each component for a
chemical mixture stored in a vertical cone roof tank in Denver, Colorado. The chemical mixture contains
(for every 3,171 lb of mixture) 2,812 lb of benzene, 258 lb of toluene, and 101 lb of cyclohexane. The
tank is 6 ft in diameter, 12 ft high, usually holds about 8 ft of product, and is painted white. The liquid
level typically ranges between 4.5 feet and 11.5 feet, and thus the tank working volume is 1,480 gallons.
The throughput of the tank is 8,450 gal/yr. The liquid bulk temperature is not known, but the tank is not
insulated and storage conditions are in approximate equilibrium with ambient conditions.
Solution
1. Determine tank type. The tank is a fixed-cone roof, vertical tank.
2. Determine estimating methodology. The product is made up of three organic liquids, all of which are
miscible in each other, which makes a homogenous mixture if the material is well mixed. The tank
emission rate will be based upon the properties of the mixture. Raoult's Law (as discussed in the
Speciation Section) is assumed to apply to the mixture and will be used to determine the properties of the
mixture.
3. Select equations to be used. For a vertical, fixed roof storage tank, the following equations apply:
Lt = Ls + Lw (1-1)
Ls = 365 VvWvKeKs (1-2)
Lw = VqKnKpWvKb (1-35)
where:
Lt = total loss, lb/yr
Ls = standing loss, lb/yr
Lw = working loss, lb/yr
Vv = tank vapor space volume, ft3
Vv = ti/4D2Hvo (1-3)
Wv = vapor density, lb/ft3
= ^ (1-22)
Ke = vapor space expansion factor, per day
^ATv + AF.-APe (1_5)
Tla Pa-Pva
Ks = vented vapor space saturation factor, dimensionless
Ks = (1-21)
1 + 0.053 PvaHvo
06/18
Liquid Storage Tanks
7.1-147
-------
D =
diameter, ft
Hvo=
vapor space outage, ft
Mv =
molecular weight of vapor, lb/lb-mole
PvA =
vapor pressure at the average daily liquid surface temperature, psia
R =
• j , + + 10.731 psia-ft3
ideal gas constant =
lb-mole - °R
Tv =
average vapor temperature, °R
Tla =
average daily liquid surface temperature, °R
ATV =
average daily vapor temperature range, °R
APV =
average daily vapor pressure range, psia
A Pb =
breather vent pressure setting range, psi
Pa =
atmospheric pressure, psia
Vq =
net working loss throughput, ft3/yr
Kn =
working loss turnover factor, dimensionless
Kp =
working loss product factor, dimensionless
Kb =
vent setting correction factor, dimensionless
4. Calculate each component of the standing loss and working loss functions,
a. Tank vapor space volume, Vv:
Vv = ti/4D2Hvo (1-3)
where:
D = 6 ft (given)
For a cone roof, the vapor space outage, Hvo is calculated by:
Hvo = Hs-Hl + Hro (1-16)
where:
Hs = tank shell height, 12 ft (given)
Hl = stock liquid height, 8 ft (given)
Hro = roof outage, 1/3 Hr = 1/3(Sr)(Rs) (1-17)
Sr = tank cone roof slope, 0.0625 ft/ft (given) (see Note 1 to Equation 1-16)
Rs = tank shell radius = 1/2 D = 1/2 (6) = 3
Substituting values in Equation 1-17 yields,
Hro = 1/3 (0.0625)(3) = 0.0625 ft
Then use Equation 1-16 to calculate Hvo,
Hvo = 12 - 8 + 0.0625 = 4.0625 ft
Therefore,
Vv = — (6)2 (4.0625) = 114.86 ft3
4
7.1-148
Liquid Storage Tanks
06/18
-------
b. Vapor density, Wv:
where:
Wv = (1-22)
nsia ¦ ft3
R = ideal gas constant = 10.731 -
lb - mole ¦ °R
Mv = stock vapor molecular weight, lb/lb-mole
Pva = stock vapor pressure at the average daily liquid surface temperature Tla, psia
Tv = average vapor temperature, °R
First, calculate Tla using Equation 1-28.
Tla = 0.4 Taa + 0.6 TB + 0.005 a I (1-28)
where:
Taa = average daily ambient temperature, °R
Tb = liquid bulk temperature, °R
I = average daily total insolation, Btu/ft2,d = 1,458 (see Table 7.1-7)
a = tank surface solar absorptance = 0.25 (see Table 7.1-6, for white paint in average
condition)
Taa and Tb must be calculated from Equations 1-30 and 1-31.
T T«1Tan 3
2
from Table 7.1-7, for Denver, Colorado (use Boulder as the nearest location listed):
Tax = average daily maximum ambient temperature = 64.2°F
Tan = average daily minimum ambient temperature = 36.1°F
Converting to °R:
Tax = 64.2 +459.7 = 523.9°R
Tan = 36.1 +459.7 = 495.8°R
Therefore,
Taa = (523.9 + 495.8)/2 = 509.85 °R
Tb = liquid bulk temperature = Taa + 0.003 « I (1-31)
Taa = 509.85 °R from previous calculation
a = surface solar absorptance = 0.25 (see Table 7.1-6)
I = average daily total insolation on a horizontal surface = 1,458 Btu/ft2,d (see
Table 7.1-7)
Substituting values in Equation 1-31
06/18
Liquid Storage Tanks
7.1-149
-------
Tb = 509.85 + 0.003 (0.25) 1,458 = 510.9 °R
Using Equation 1-28,
Tla = (0.4) (509.85°R) + 0.6 (510.9°R) + 0.005 (0.25) (1,458) = 512.3°R
Second, calculate Pva using Raoult's Law.
According to Raoult's Law, the partial pressure of a component is the product of its pure vapor
pressure and its liquid mole fraction. The total vapor pressure of the component mixture stock is equal to
the sum of the partial pressures of its components.
The pure vapor pressures for benzene, toluene, and cyclohexane can be calculated from Antoine's
equation. Table 7.1-3 provides the Antoine's coefficients for benzene, which are A = 6.906, B = 1,211.0,
and C = 220.79. For toluene, A = 7.017, B = 1,377.6, and C = 222.64. For cyclohexane, A = 6.845,
B = 1,203.5, and C = 222.86. Therefore:
Tla, average liquid surface temperature (°C) = (512.3 — 491,7)/l .8 = 11.4
For benzene,
log P= 6.906 — 1,2110
b (11.4+220.79)
P = 49.03 mmHg = 0.948 psia
Similarly for toluene and cyclohexane,
P = 0.261 psia for toluene
P = 0.986 psia for cyclohexane
In order to calculate the mixture vapor pressure, the partial pressures need to be calculated for
each component. The partial pressure is the product of the pure vapor pressures of each component
(calculated above) and the mole fractions of each component in the liquid.
The mole fractions of each component are calculated as follows:
Component
Amount, lb
Mi
Moles
Xi
Benzene
2,812
78.11
36.0
0.90
Toluene
258
92.14
2.80
0.07
Cyclohexane
101
84.16
1.20
0.03
Total
40.0
1.00
7.1-150
Liquid Storage Tanks
06/18
-------
where:
Mi = molecular weight of component
x, = liquid mole fraction
The partial pressures of the components can then be calculated by multiplying the pure vapor
pressure by the liquid mole fraction as follows:
Component
P at 52.6°F
Xi
P partial
Benzene
0.948
0.90
0.853
Toluene
0.261
0.07
0.018
Cyclohexane
0.986
0.03
0.030
Total
1.0
0.901
The vapor pressure of the mixture is then 0.901 psia.
Third, calculate the molecular weight of the vapor, Mv. Molecular weight of the vapor depends
upon the mole fractions of the components in the vapor.
Mv = EMiyi
where:
Mi = molecular weight of the component
yi = vapor mole fraction
The vapor mole fractions, yi, are equal to the partial pressure of the component divided by the
total vapor pressure of the mixture.
Therefore,
ybenzene = Ppartial/Ptotal = 0.853/0.901 = 0.947
Similarly, for toluene and cyclohexane,
ytoluene Ppartial/Ptotal 0.020
ycyclohexane Ppartial/Ptotal 0.033
The mole fractions of the vapor components sum to 1.0.
06/18 Liquid Storage Tanks 7.1-151
-------
The molecular weight of the vapor can be calculated as follows:
Component
Mi
y>
Mv
Benzene
78.11
0.947
74.0
Toluene
92.14
0.020
1.84
Cyclohexane
84.16
0.033
2.78
Total
1.0
78.6
Now calculate Tv using Equation 1-33.
Tv = 0.7Taa + 0.3Tb + 0.009 a I (1-33)
Tv = 0.7 (509.85) + 0.3 (510.9) + 0.009 (0.25) (1,458)
Tv= 513.4 °R
Since all variables have now been solved, the stock density, Wv, can be calculated:
W MvPva
v RTV
(78.6)(0.901) _ on ^ 1n-2 lb
;= 1.29xl0_z^
(10.731)(513.4) ft3
c. Vapor space expansion factor, Ke:
Ke , atv + APV-APB (l.5)
TlA Pa - PVA
where:
A Tv = average daily vapor temperature range, °R
A Pv = average daily vapor pressure range, °R
A Pb = breather vent pressure setting range, psia
Pa = atmospheric pressure, 12.12 psia for Denver, Colorado (use Boulder as the nearest
location listed)
Pva = vapor pressure at average daily liquid surface temperature, psia = 0.901 psia (from
Step 4b)
Tla = average daily liquid surface temperature, °R = 512.3°R (from Step 4b)
First, calculate the average daily vapor temperature range from Equation 1-7:
A Tv = 0.7 A Ta + 0.02a I (1-7)
where:
7.1-152 Liquid Storage Tanks 06/18
-------
A Tv = average daily vapor temperature range, °R
A Ta = average daily ambient temperature range = Tax - Tan
a = tank surface solar absorptance, 0.25 (given)
I = average daily total insolation, 1,458 Btu/ft2,d (given)
from Table 7.1-7, for Denver (Boulder), Colorado:
Tax = 64.2°F
Tan = 36.1°F
Converting to °R,
Tax = 64.2 +459.7 = 523.9°R
Tan = 36.1 +459.7 = 495.8°R
From Equation 1-11: A Ta = Tax - Tan
ATa = 523.9 -495.8 = 28.1°R
Therefore,
ATV = 0.7 (28.1) + (0.02)(0.25) (1458) = 27.0°R
Second, calculate the average daily vapor pressure range using Equation 1-9:
APv = Pvx-Pvn (1-9)
Pvx, Pvn = vapor pressures at the average daily maximum, minimum liquid temperatures can be
calculated in a manner similar to the Pva calculation shown earlier.
Tlx = maximum liquid temperature, Tla + 0.25 A Tv (from Figure 7.1-17)
Tln = minimum liquid temperature, Tla - 0.25 A Tv (from Figure 7.1-17)
Tla = 512.3 (from Step 4b)
ATV = 27.0°R
Tlx = 512.3 + (0.25) (27.0) = 519.05°R or 59.35°F
Tln = 512.3 -(0.25) (27.0) = 505.55°Ror 45.85°F
Using Antoine's equation, the pure vapor pressures of each component at the minimum liquid
surface temperature are:
Pbenzene 0.780 pSia
Ptoluene = 0.210 psia
P cyclohexane 0.815 psia
06/18
Liquid Storage Tanks
7.1-153
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The partial pressures for each component at Tln can then be calculated as follows:
Component
P at 45.85°F
Xi
P partial
Benzene
0.780
0.90
0.702
Toluene
0.210
0.07
0.015
Cyclohexane
0.815
0.03
0.024
Total
1.0
0.741
Using Antoine's equation, the pure vapor pressures of each component at the maximum liquid
surface temperature are:
Pbenzene 1.150 pSia
Ptoluene = 0.324 psia
P cyclohexane 1.191 psia
The partial pressures for each component at Tlx can then be calculated as follows:
Component
P at 59.35°F
Xi
P partial
Benzene
1.150
0.90
1.035
Toluene
0.324
0.07
0.023
Cyclohexane
1.191
0.03
0.036
Total
1.0
1.094
Therefore, the vapor pressure range, APv = Plx - Pln = 1.094 - 0.741 = 0.353 psia.
Next, calculate the breather vent pressure, A Pb, from Equation 1-10:
APb = Pbp-Pbv (1-10)
where:
Pbp = breather vent pressure setting = 0.03 psia (given) (see Note 3 to Equation 1-5)
Pbv = breather vent vacuum setting = -0.03 psig (given) (see Note 3 to Equation 1-5)
A Pb = 0.03 - (-0.03) = 0.06 psig
Pa = 12.12 psia from Table 7.1-7, for Denver, Colorado (use Boulder as the nearest location
listed)
Finally, Ke, can be calculated by substituting values into Equation 1-5.
7.1-154
Liquid Storage Tanks
06/18
-------
KE=2L0.079
b 512.3 (12.12-0.901)
d. Vented vapor space saturation factor, Ks:
KS = (1-21)
1 + 0.053 PvA Hvo
where:
Pva = 0.880 psia (from Step 4b)
Hvo = 4.0625 ft (from Step 4a)
Ks = —-—— = 0.838
^ 1+0.053 (0.901) (4.0625)
5. Calculate standing losses.
Ls = 365 VvWvKeKs
Using the values calculated above:
lb_
J'
Vv = 114.86 ft3 (from Step 4a)
Ke = 0.079 (from Step 4c)
Ks = 0.838 (from Step 4d)
Ls = 365 (1.29 x 10"2)(114.86)(0.079)(0.838) = 36 lb/yr
6. Calculate working losses.
The amount of VOCs emitted as a result of filling operations can be calculated from the following
equation:
Lw = VqKnKpWvKb (1-35)
Wv= 1.29 xlO 2 —— (from step 4b)
where:
Vq = 5.614 Q (when ZHqi is unknown; equation 1-39)
Q = 8,450 gal/yr / 42 bbl/gal = 201.2 bbl/yr (given)
VQ = 5.614 (201.2) = 1,130 ft3/yr
Kp = product factor, dimensionless = 0.75 for crude oils, 1.0 for all other stocks
Kn = 1 for turnovers N <36 (given)
N = turnovers per year
N = IHQi/(Hlx-Hln) (1-36)
IHQi = (5.614 Q) / ((ti/4) D2) (1-37)
IHqi =(5.614) (201.2) / ((ti/4) 62) = 39.9 ft
Hlx =11.5 ft (given)
Hln =4.5 ft (given)
N =39.9/(11.5-4.5) = 5.7
Wv= 1.29 x 10"2 lb/ft3 (from Step 4b)
06/18
Liquid Storage Tanks
7.1-155
-------
Kb = 1 for vent settings of +/- 0.03 psig (from Equation 1-35)
Lw = (1,130)(1)( 1)(0.0129) (1) = 15 lb/yr
7. Calculate total losses. Lt.
Lt = Ls + Lw
where:
Ls = 36 lb/yr
Lw= 15 lb/yr
Lx= 36+15 = 51 lb/yr
8. Calculate the amount of each component emitted from the tank.
The amount of each component emitted is equal to the weight fraction of the component in the
vapor times the amount of total VOC emitted. Assuming 100 moles of vapor are present, the number of
moles of each component will be equal to the mole fraction multiplied by 100. This assumption is valid
regardless of the actual number of moles present. The vapor mole fractions were determined in Step 4b.
The weight of a component present in a mixture is equal to the product of the number of moles and
molecular weight, Mi, of the component. The weight fraction of each component is calculated as follows:
... , , . poundsi
Weight fraction=
total pounds
Therefore,
Component
No. of moles x
M;
Poundsi
Weight fraction
Benzene
(0.947 x 100) = 94.7
78.11
7,397
0.94
Toluene
(0.02x 100) = 2.0
92.14
184
0.02
Cyclohexane
(0.033 x 100) = 3.3
84.16
278
0.04
Total
100
7,859
1.0
The amount of each component emitted is then calculated as:
Emissions of component = (weight fractioni)(L[)
7.1-156
Liquid Storage Tanks
06/18
-------
Component
Weight fraction x
Total VOC emitted, lb/yr =
Emissions, lb/yr
Benzene
0.94
51
48
Toluene
0.02
51
1.0
Cyclohexane
0.04
51
2.0
Total
51
06/18
Liquid Storage Tanks
7.1-157
-------
Example 2 - Chemical Mixture in a Horizontal Tank - Assuming that the tank mentioned in Example 1 is
now horizontal, calculate emissions. (Tank diameter is 6 ft and length is 12 ft.)
Solution:
Emissions from horizontal tanks can be calculated by adjusting parameters in the fixed roof
equations. Specifically, an effective diameter, De, is used in place of the tank diameter, D. The vapor
space height, Hvo, is assumed to be half the actual tank diameter.
1. Horizontal tank adjustments. Make adjustments to horizontal tank values so that fixed roof tank
equations can be used. The effective diameter, De, is calculated as follows:
The vapor space height, Hvo is calculated as follows:
Hvo = vapor space outage, ft; use He/2 from Equation 1-15 for horizontal tanks
(1-15)
Hvo = (ti/4) D / 2 = 2.36 ft
2. Given the above adjustments the standing loss. Ls. can be calculated.
Calculate values for each effected variable in the standing loss equation.
Ls =365 VvWvKeKs
Vv and Ks depend on the effective tank diameter, De, and vapor space height, Hvo.
These variables can be calculated using the values derived in Step 1:
_ 71 r n2
Vv (De ) Hvo
Vv = | (9.57)2 (2.36) = 170 ft3
1
Ks 1 + (0.053) (pVA) (Hvo)
7.1-158
Liquid Storage Tanks
06/18
-------
3. Calculate standing loss using the values calculated in Step 2.
Ls = 365 VvWvKeKs
Vv = 170 ft3 (from Step 2)
Wv = 1.29 x 10"2 lb/ft3 (from Step 4b, example 1)
Ke = 0.079 (from Step 4c, example 1)
Ks = 0.899 (from Step 2)
Ls = (365)( 1.29 x 10-2)(170)(0.079)(0.899)
Ls = 57 lb/yr
4. Calculate working loss. Since the parameters for working loss do not depend on diameter or vapor
space height, the working loss for a horizontal tank of the same capacity as the tank in Example 1 will be
the same.
Lw = 15 lb/yr
5. Calculate total emissions.
Lt = Ls + Lw
Lx = 57 + 15 = 72 lb/yr
06/18
Liquid Storage Tanks
7.1-159
-------
Example 3 - Chemical Mixture in an External Floating Roof Tank - Determine the yearly emission rate of
a mixture that is 75 percent benzene, 15 percent toluene, and 10 percent cyclohexane, by weight, from a
100,000-gallon external floating roof tank with a pontoon roof. The tank is 20 feet in diameter. The tank
has 10 turnovers per year. The tank has a mechanical shoe seal (primary seal) and a shoe-mounted
secondary seal. The tank is made of welded steel and has a light rust covering the inside surface of the
shell. The tank shell is painted white, and the tank is located in Newark, New Jersey. The floating deck is
equipped with the following fittings: (1) an ungasketed access hatch with an unbolted cover, (2) an
unspecified number of ungasketed vacuum breakers with weighted mechanical actuation, and (3)
ungasketed gauge hatch/sample ports with weighted mechanical actuation.
Solution:
1. Determine tank type. The tank is an external floating roof storage tank.
2. Determine estimating methodology. The product consists of three organic liquids, all of which are
miscible in each other, which make a homogenous mixture if the material is well mixed. The tank
emission rate will be based upon the properties of the mixture. Because the components have similar
structures and molecular weights, Raoult's Law is assumed to apply to the mixture.
3. Select equations to be used. For an external floating roof tank,
Lt = Ls + Lw (2-1)
Ls = Lr + Lf + Ld (2-2)
Lw = (0.943) QCsWl/D (2-19)
LR = (KRa + KRbVn)P*DMvKc (2-3)
Lf = FfP*MvKc (2-13)
Ld = KdSdD2P*MvKc (2-18)
where:
Lt =
total loss, lb/yr
Lw =
working (withdrawal) loss, lb/yr
Lr =
rim seal loss from external floating roof tanks, lb/yr
Lf =
deck fitting loss, lb/yr
Ld =
deck seam loss, lb/yr = 0 for external floating roof tanks
Q =
product average throughput, bbl/yr
Cs =
product withdrawal shell clingage factor, bbl/1,000 ft2; see Table 7.1-10
Wl =
density of liquid, lb/gal
D =
tank diameter, ft
KRa =
zero wind speed rim seal loss factor, lb-mole/ft»yr; see Table 7.1.8
KRb =
wind speed dependent rim seal loss factor, lb-mole/(mph)nft»yr; see Table 7.1-:
v =
average ambient wind speed for the tank site, mph
7.1-160
Liquid Storage Tanks
06/18
-------
n = seal wind speed exponent, dimensionless
P* = the vapor pressure function, dimensionless
PVA
where:
Pva= the true vapor pressure of the materials stored, psia
Pa = atmospheric pressure, psia = 14.74 psia from Table 7.1-7 for Newark, New Jersey
Mv = molecular weight of product vapor, lb/lb-mole
Kc = product factor, dimensionless
Ff = the total deck fitting loss factor, lb-mole/yr
= [(JVFl^l)+(JVF2Xr2) + ... + (JVF„/Xr„/)j
z=l
where:
Nf; = number of fittings of a particular type, dimensionless. N|.-. is determined for the specific
tank or estimated from Tables 7.1-12, 7.1-13, or 7.1-14
Kfj = deck fitting loss factor for a particular type of fitting, lb-mole/yr. Kf; is determined for
each fitting type from Equation 2-15 and the loss factors in Table 7.1-12
nf = number of different types of fittings, dimensionless; nf = 3 (given)
Kd = deck seam loss per unit seam length factor, lb-mole/ft/yr
Sd = deck seam length factor, ft/ft2
4. Identify parameters to be calculated/determined from tables. In this example, the following parameters
are not specified: Wl, Ff, C, Kr3, KRb, v, n, Pva, P*, Mv, and Kc. The following values are obtained from
tables or assumptions:
Kc = 1.0 for all stocks other than crude oil (given in Section 7.1.3.2)
C = 0.0015 bbl/1,000 ft2 fortanks with light rust (from Table 7.1-10)
KRa= 1.6 (from Table 7.1-8)
K^ = 0.3 (from Table 7.1-8)
n = 1.6 (from Table 7.1-8)
Since the wind speed for the actual tank site is not specified, the wind speed for Newark, New Jersey is
used:
v= 10.3 mph (see Table 7.1-7)
Ff, Wl, Pva, P*, and Mv still need to be calculated.
Ff is estimated by calculating the individual K|.-. and N|.-. for each of the three types of deck fittings used in
this example. For the ungasketed access hatches with unbolted covers, the Kf value can be calculated
using information from Table 7.1-12. For this fitting, Kh, = 36, Km, = 5.9, and m = 1.2. The value for Kv
06/18
Liquid Storage Tanks
7.1-161
-------
for external floating roof tanks is 0.7 (see Section 7.1.3, Equation 2-15). There is normally one access
hatch. So,
Kpaccess hatch KFa + KFb(Kvv)m
= 36 + 5.9 [(0.7)( 10.3)]12
Kpaccess hatch 99.2 lb-mole/yr
N I'acccss hatch 1
The number of vacuum breakers can be taken from Table 7.1-13. For atank with a diameter of 20 feet
and a pontoon roof, the typical number of vacuum breakers is one. Table 7.1-12 provides fitting factors
for weighted mechanical actuation, ungasketed vacuum breakers when the average wind speed is 10.3
mph.
Based on this table, Kf3 = 7.8, Ka = 0.01, and m = 4. So,
KFvacuum breaker KFa + Kpb (Kvv)m
KFvacuum breaker 7.8 "I" 0. 01 [(0.7)(10.3)]4
KFvacuum breaker 34.8 lb-mole/yr
NFvacuum breaker 1
For the ungasketed gauge hatch/sample ports with weighted mechanical actuation, Table 7.1-12 indicates
that floating roof tanks normally have only one. This table also indicates that KFa = 2.3, KFb = 0, and
m = 0. Therefore,
KFgauge hatch/sample port
KFgauge hatch/sample port
KFgauge hatch/sample port
NFgauge hatch/sample port
Ff can be calculated from Equation 2-14:
Ff = t,(KFl)(NFl)
Z=1
=(99.2)(1)+(34.8)(1)+(2.3)(1)
= 136.3 lb-mole/yr
5. Calculate mole fractions in the liquid. The mole fractions of components in the liquid must be
calculated in order to estimate the vapor pressure of the liquid using Raoult's Law. For this example, the
weight fractions (given as 75 percent benzene, 15 percent toluene, and 10 percent cyclohexane) of the
mixture must be converted to mole fractions. First, assume that there are 1,000 lb of liquid mixture. Using
this assumption, the mole fractions calculated will be valid no matter how many pounds of liquid actually
are present. The corresponding amount (pounds) of each component is equal to the product of the weight
fraction and the assumed total pounds of mixture of 1,000. The number of moles of each component is
calculated by dividing the weight of each component by the molecular weight of the component. The
mole fraction of each component is equal to the number of moles of each component divided by the total
number of moles. For this example the following values are calculated:
— KFa + KFb (Kvv)m
= 2.3 + 0
= 2.3 lb-mole/yr
= 1
7.1-162
Liquid Storage Tanks
06/18
-------
Component
Weight
fraction
Weight, lb
Molecular
weight, Mi,
lb/lb-mole
Moles
Mole
fraction
Benzene
0.75
750
78.1
9.603
0.773
Toluene
0.15
150
92.1
1.629
0.131
Cyclohexane
0.10
100
84.2
1.188
0.096
Total
1.00
1,000
12.420
1.000
For example, the mole fraction of benzene in the liquid is 9.603/12.420 = 0.773.
6. Determine the average daily liquid surface temperature. The average daily liquid surface temperature is
equal to:
Tla = 0.7 Taa + 0.3 Tb + 0.008 OC I
Taa = (Tax + Tan)/2
Tb = Taa + 0.007 oc I
For Newark, New Jersey (see Table 7.1-7):
Tax = 63.3°F = 523.0°R
Tan = 46.0°F = 505.7°R
1= 1.236 Btu/ft2«d
From Table 7.1-6, OC = 0.25
Therefore;
Taa = (523.0 + 505.7)/2 = 514.35°R
Tb = 514.35 + 0.007 (0.25)(1236) = 516.51°R
Tla = 0.7 (514.35) + 0.3 (516.51) + 0.008 (0.25)(1236)
= 517.5°R= 57.8°F
7. Calculate partial pressures and total vapor pressure of the liquid. The vapor pressure of each component
at 57.8°F can be determined using Antoine's equation. Since Raoult's Law is assumed to apply in this
example, the partial pressure of each component is the liquid mole fraction (x,) times the vapor pressure
of the component (P).
06/18
Liquid Storage Tanks
7.1-163
-------
Component
P at 57.8°F
Xi
P partial
Benzene
1.10
0.773
0.850
Toluene
0.31
0.131
0.041
Cyclohexane
1.14
0.096
0.109
Totals
1.00
1.000
The total vapor pressure of the mixture is estimated to be 1.000 psia.
8. Calculate mole fractions in the vapor. The mole fractions of the components in the vapor phase are
based upon the partial pressure that each component exerts (calculated in Step 7).
So for benzene:
Ybenzene = Pparttal/Ptotal = 0.850/1.000 = 0.850
where:
ybenzene = mole fraction of benzene in the vapor
P partial partial pressure of benzene in the vapor, psia
Ptotal = total vapor pressure of the mixture, psia
Similarly,
ytoluene= 0.041/1.000 = 0.041
ycyclohexane = 0.109/1.000 = 0.109
The vapor phase mole fractions sum to 1.0.
9. Calculate molecular weight of the vapor. The molecular weight of the vapor depends upon the mole
fractions of the components in the vapor.
where:
Mv = EMiyi
Mv = molecular weight of the vapor, lb/lb-mole
Mi = molecular weight of component i, lb/lb-mole
yi = mole fraction of component i in the vapor, lb-mole/lb-mole
7.1-164
Liquid Storage Tanks
06/18
-------
Component
Mi
y>
Mv = E(Mi)(yi)
Benzene
78.1
0.850
66.39
Toluene
92.1
0.041
3.78
Cyclohexane
84.2
0.109
9.18
Total
1.00
79.4
The molecular weight of the vapor is 79.4 lb/lb-mole.
10. Calculate weight fractions of the vapor. The weight fractions of the vapor are needed to calculate the
amount (in pounds) of each component emitted from the tank. The weight fractions are related to the mole
fractions calculated in Step 7 and total molecular weight calculated in Step 9:
7 = IiM
ZiVj
Mv
= (0-85)(78.1) = Q 836 for benzene
v' 79.3
(0040X9Z1) ^0048fortoluene
v' 79.3
(0.110)(84.2)
Zv = = 0.116 for cyclohexane
v' 79.3
11. Calculate total VOC emitted from the tank. The total VOC emitted from the tank is calculated using
the equations identified in Step 3 and the parameters calculated in Steps 4 through 9.
Lt = Lw + Ls
Ls = Lr + Lf
a. Calculate working (withdrawal) losses:
Lw= 0.943 QCWl/D
where:
Q = 100,000 gal x 10 turnovers/yr (given)
= 1,000,000 gal x 2.381 bbl/100 gal = 23,810 bbl/yr
C = 0.0015 bbl/103 ft2 (from Table 7.1-10)
Wl = 1/|I (wt fraction in liquid)/(liquid component density from Table 7.1-3)]
Weight fractions
Benzene = 0.75 (given)
Toluene = 0.15 (given)
Cyclohexane = 0.10 (given)
06/18
Liquid Storage Tanks
7.1-165
-------
Liquid densities
Benzene = 7.32 (see Table 7.1-3)
Toluene = 7.24 (see Table 7.1-3)
Cyclohexane = 6.46 (see Table 7.1-3)
WL = l/[(0.75/7.32) + (0.15/7.24) + (0.10/6.46)]
= 1/(0.1025 + 0.0207 + 0.0155)
= 1/0.1387
= 7.2 lb/gal
D = 20 ft (given)
Lw= 0.943 QCWl/D
= [0.943(23,810)(0.0015)(7.2)/20]
= 12 lb of VOC/yr from withdrawal losses
b. Calculate rim seal losses:
Lr= (KRa + KRbVn)DP*MvKc
where:
Kr3 = 1.6 (from Step 4)
KRb = 0.3 (from Step 4)
v = 10.3 mph (from Step 4)
n= 1.6 (from Step 4)
Kc = 1 (from Step 4)
Pva = 1.000 psia (from Step 7) (formula from Step 3)
D = 20 ft
p* =
PVA
Pa
= (1.000/14.74)/(1+[1-(1.000/14.74)]°5)2 = 0.018
Mv = 79.4 lb/lb-mole (from Step 9)
Lr = [(1.6 + (0.3)(10.3)16)](0.018)(20)(79.4)(1.0)
= (14.1)(0.018)(20)(79.4)(1.0)
= 403 lb of VOC/yr from rim seal losses
c. Calculate deck fitting losses:
Lf= FfP*MvKc
where:
Ff = 136.3 lb-mole/yr (from Step 4)
P*= 0.018
Mv= 79.4 lb/lb-mole
Kc = 1.0 (from Step 4)
Lf= (136.3)(0.018)(79.4)(1.0)
= 195 lb/yr of VOC emitted from deck fitting losses
d. Calculate total losses:
Lt = Lw + Lr + Lf
7.1-166
Liquid Storage Tanks
06/18
-------
= 12 + 403 + 195
= 610 lb/yr of VOC emitted from tank
12. Calculate amount of each component emitted from the tank. For an external floating roof tank, the
individual component losses are determined by Equation 40-2:
Lt- = (Zv;)(Lr + Lf) + (Zl;)(Lw)
Therefore,
LTbenzene (0.836)(598) + (0.75)(12) = 510 lb/yr benzene
LTtoluene (0.048)(598) + (0.15)( 12) = 31 lb/yr toluene
LTcyclohexane (0.116)(598) + (0.10)( 12) = 71 lb/yr cyclohexane
06/18
Liquid Storage Tanks
7.1-167
-------
Example 4 - Gasoline in an Internal Floating Roof Tank - Determine emissions of product from a
1 million gallon, internal floating roof tank containing gasoline (RVP 13). The tank is painted white and
is located in Tulsa, Oklahoma. Product is pumped into and out of the tank simultaneously. The sum of
decreases in the liquid level is 1,735 feet. The tank is 70 ft in diameter and 35 ft high and is equipped with
a liquid-mounted primary seal plus a secondary seal. The tank has a column-supported fixed roof. The
tank's deck is welded and equipped with the following: (1) two access hatches with unbolted, ungasketed
covers; (2) an automatic gauge float well with an unbolted, ungasketed cover; (3) a pipe column well with
a flexible fabric sleeve seal; (4) a sliding cover, gasketed ladder well; (5) adjustable deck legs; (6) a
slotted guidepole/sample pipe well with a gasketed sliding cover; and (7) a weighted, gasketed vacuum
breaker. The following data are available on the concentrations of air toxics in the liquid phase, by
weight:
Component
Weight Percent In Liquid
Benzene
0.55
Toluene
7.6
Ethylbenzene
1.4
Xylenes
6.9
Solution:
1. Determine tank type. The following information must be known about the tank in order to use the
floating roof equations:
-- the number of columns
-- the effective column diameter
-- the rim seal description (vapor- or liquid-mounted, primary or secondary seal)
-- the deck fitting types and the deck seam length
Some of this information depends on specific construction details, which may not be known. In
these instances, approximate values are provided for use.
2. Determine estimating methodology. Gasoline consists of many organic compounds, all of which are
miscible in each other, which form a homogenous mixture. The tank emission rate will be based on the
properties of RVP 13 gasoline. Since Reid vapor pressure is available, Raoult's Law will not be used to
determine the true vapor pressure of the liquid (as it was in the prior example), but it will be used to
estimate vapor phase fractions of the air toxic components. The molecular weight of gasoline will be
taken from a table and will not be calculated.
3. Select equations to be used.
Lt = Ls + Lw (2-1)
Ls = Lr + Lf + Ld (2-2)
7.1-168
Liquid Storage Tanks
06/18
-------
Lw —
(0.943)QCsWl
D
1 +
NCFC
D
Lk = (Kkil + Kkhvn)DP'!MvK.
Lf =FfP*MvKc
Ld =KdSdD2P*MvKc
(2-19)
(2-3)
(2-13)
(2-18)
total loss, lb/yr
standing loss, lb/yr
working (withdrawal) loss, lb/yr
rim seal loss, lb/yr
deck fitting loss, lb/yr
deck seam loss, lb/yr
annual net throughput, bbl/yr
product withdrawal shell clingage factor, bbl/1,000 ft2
density of liquid, lb/gal
tank diameter, ft
number of fixed roof support columns, dimensionless
effective column diameter, ft
zero wind speed rim seal loss factor, lb-mole/ft»yr
wind speed dependent rim seal loss factor, lb-mole/(mph)nft»yr
average ambient site wind speed (zero for internal floating roof tanks), mph
the average molecular weight of the product vapor, lb/lb-mole
the product factor, dimensionless
the vapor pressure function, dimensionless
PVA
KkStT
the vapor pressure of the material stored, psia
average atmospheric pressure at tank location, psia
the total deck fitting loss factor, lb-mole/yr
^(KFj) (NFj) - [(NfjKfj) + (Nf2Kf2) + ... + (NFnKFnf)]
and:
Nf; = number of deck fittings of a particular type, dimensionless. N|.-. is
determined for the specific tank or estimated from Table 7.1-12
Liquid Storage Tanks
7.1-169
-------
Kfj = deck fitting loss factor for a particular type of deck fitting, lb-
mole/yr. Kfis determined for each fitting type using Table 7.1-12 and,
for an internal floating roof tank, Equation 2-16
nf = number of different types of fittings, dimensionless
Kd = the deck seam loss factor, lb-mole/ft»yr
= 0.14 for nonwelded decks
= 0 for welded decks
Sd = deck seam length factor, ft/ft2
Lseam/A deck
where:
Lseam total length of deck seams, ft
Adeck = area of deck, ft2 = 7iD2/4
4. Identify parameters to be calculated or determined from tables. In this example, the following
parameters are not specified: Wl, Nc, Fc, C, Pva, Mv, Kr3, v, P*, Kc, Ff, Kd, Sd, and weight fractions of
air toxic components in the vapor.
The wind speed, v, is assumed to be zero for an internal floating roof tank, and thus values are not needed
for KRb and n for the rim seal. Similarly, the deck fitting loss factor Kfi is equal to K|;M- from Equation 2-
16.
The following parameters can be obtained from tables or assumptions:
Kc = 1.0 for all stocks other than crude oil
Nc = 1 (from Table 7.1-11)
Fc = 1.0 (assumed)
KRa= 0.3 (from Table 7.1-8)
v = 0 for internal floating roof tanks
Mv = 62 lb/lb-mole (from Table 7.1-2)
Wl = 5.6 lb/gal (from Table 7.1-2)
7.1-170
Liquid Storage Tanks
06/18
-------
C = 0.0015 bbl/1,000 fit2 (from Table 7.1-10)
Kd = 0 for welded decks so Sd is not needed
Ff = I (Kf3iNfi), where values for K|.;M. are from Table 7.1-12
5. Calculate mole fractions in the liquid. Mole fractions of the air toxic components in the liquid can be
calculated using Raoult's Law. Assume that the properties of m-xylene will suitably represent the
component identified as Xylenes. The molecular weight of the liquid stock is given as 92 lb/lb-mole, and
thus liquid mole fractions of individual components can be calculated using Equation 40-4.
_ ZliMl
Xi
Mi
= (0.0055)(92) = Q 0Q65 for benzene
78.1
(0.076)(92)
Xi
Xi
92.1
(0.014)(92)
= 0.0759 for toluene
106.2
= 0.0121 for ethylbenzene
= (0.069)(92) = Q Q598 for leneg
106.2
6. Calculate the average daily liquid surface temperature. The average daily liquid surface temperature is
equal to:
[2.86 (Hs/D) + 1.43] TAA + [3.52 (Hs/D) + 3.79] TB + 0.027 ocR / + 0.017(H5/D) oc5 /
Tla ~ 6.38 (Hs/D) + 5.22
Taa = (Tax + Tan)/2
Tb = Taa + 0.003 a I
For Tulsa, Oklahoma (see Table 7.1-7):
Tax = 71.1°F = 530.8°R
Tan = 49.6°F = 509.3°R
1= 1,427 Btu/ft2'd
06/18
Liquid Storage Tanks
7.1-171
-------
From Table 7.1-6, a = 0.25
Therefore,
Taa= (530.8 + 509.3)/2 = 520.05°R
Tb = 520.05 + 0.003 (0.25) 1,427 = 521.12°R
Tla = 0.34 (520.05) + 0.66 (521.12) + 0.0032 (0.25)(1,427) + 0.0010 (0.25)(1,427)
Tla = 176.82 + 343.94+ 1.14 + 0.36
Tla = 522.26°R or 62.6°F
7. Calculate partial pressures and total vapor pressure of the liquid. The total vapor pressure of gasoline
RVP 13 can be calculated from Equation 1-25, using values for the vapor pressure constants A and B
from Table 7.1-2..
PVA = exp
A -
B
PVA = exp
11.644
5043.6
62.6 + 459.7j
Pva = 7.30 psia at 62.6°F
From Table 7.1-7, Pa = 14.39 psi
Therefore,
P
VA
P =
P„
1 +
1-
Pv,
P
A J
P* = (7.30/14.3 9)/[ 1 + (1 -(7.30/14.39))°5]2
P* = 0.175
The vapor pressure of each component at 62.6°F can be determined using Antoine's equation. Since
Raoult's Law is assumed to apply in this example, the partial pressure of each component is the liquid
mole fraction (x,) times the vapor pressure of the component (P), from Equation 40-3.
7.1-172
Liquid Storage Tanks
06/18
-------
Component
P at 62.6°F
Xi
P partial
Benzene
1.2579
0.0065
0.0082
Toluene
0.3587
0.0759
0.0272
Ethylbenzene
0.1135
0.0121
0.0014
Xylenes
0.0989
0.0598
0.0059
8. Calculate mole fractions of components in the vapor. The mole fraction of each component in the vapor
phase is the partial pressure of the component (Ppartiai) divided by the total vapor pressure of the mixture
(Pva), from Equation 40-3.
yi Ppartial/PvA
yi = 0.0082 / 7.30 = 0.0011 for benzene
yi = 0.0272 / 7.30 = 0.0037 for toluene
yi = 0.0014 / 7.30 = 0.0002 for ethylbenzene
yi = 0.0059 / 7.30 = 0.0008 for xylenes
9. Calculate molecular weight of the vapor. This step is not required because the molecular weight of
gasoline vapor is already specified.
10. Calculate weight fractions of components of the vapor. The weight fraction of each component in the
vapor phase can be calculated using Equation 40-6.
-7
Z V i
Mf
(0.0011X78.1) ,
Zvi= = 0.0014 for benzene
62
^i= (0.0037X92.1) = 0 0055fortoluene
62
= (00002X1062) = 0.0003 for ethylbenzene
62
06/18
Liquid Storage Tanks
7.1-173
-------
(0.0008)(106.2) ,
Zvi= = 0.0014 for xylenes
62
11. Calculate total VOC emitted from the tank. The total VOC emitted from the tank is calculated using
the equations identified in Step 3 and the parameters specified in Step 4.
Lt = Lw + Ls
Ls = Lr + Lf + Ld
a. Calculate working (withdrawal) losses:
Lw = [(0.943)QCWl]/D [1 + (NCFC)/D]
where:
Q = (tt/4) D2 (IHqu/5.6 14)
= (tt/4) (70)2 (1,735/5.614) = 1,189,359 bbl/yr
C = 0.0015 bbl/1,000 ft2
Wl= 5.6 lb/gal
D = 70 ft
Nc= 1
Fc= 1
Lw = [(0.943)(1,189,359) (0.0015)(5 6)]/70[ 1 + (l)(l)/70]
= 140 lb/yr VOC for withdrawal losses
b. Calculate rim seal losses:
Lr = (KRa + KRbvn)DP*MvKc
Since v = 0 for IFRT's:
Lr= KRaDP*MvKc
where:
Kr3 = 0.3 lb-mole/ft'yr
7.1-174
Liquid Storage Tanks
06/18
-------
D = 70 ft
P*= 0.175
Mv = 62 lb/lb-mole
Kc= 1.0
Lr = (0.3)(0.175) (70)(62)(1.0) = 230 lb/yr VOC from rim seals
c. Calculate deck fitting losses:
Lf= FfP*MvKc
where:
Ff= S(KFiNFi)
Kfj = K| ;, for internal floating roof tanks since the wind speed is zero (see Equation 2-16).
The number of deck legs is determined from Table 7.1-15 as follows:
Nfdi = (5 + D/10 + D2/600)
Nfdi = (5 + 70/10 + (70)2/600)
Nfdi = 20
Substituting values for Kh, taken from Table 7.1-12 for access hatches, gauge float well, pipe column
well, ladder well, deck legs, sample pipe well, and vacuum breaker, respectively, yields:
Ff = (36)(2) + (14)(1) + (10)(1) + (56)(1) + (7.9)(20) + (43)(1) + (6.2)(1)
= 359 lb-mole/yr
P* = 0.175
Mv = 62 lb/lb-mole
Kc= 1
Lf = (359)(0.175)(62)( 1.0) = 3,900 lb/yr VOC from deck fittings
d. Calculate deck seam losses:
Ld= KdSdD2P*MvKc
06/18 Liquid Storage Tanks 7.1-175
-------
Since Kd = 0 for IFRT's with welded decks,
Ld = 0 lb/yr VOC from deck seams
e. Calculate total losses:
Lt Lw Lr Lf Ld
= 140 + 230 + 3,900 + 0 = 4,300 lb/yr of VOC emitted from the tank
12. Calculate amount of each component emitted from the tank. The individual component losses are
equal to:
Lt; = (Zv^Lr + Lf + Ld) + (Zi^XLw)
Therefore,
Llbenzene (0.0014)(4,130) + (0.0055)(140) = 6.6 lb/yr benzene
LTtoluene (0.0055)(4,130) + (0.076)(140) = 33 lb/yr toluene
LTethylbenzene (0.0003)(4,130) + (0.014)(140) = 3.2 lb/yr ethylbenzene
LTxylenes (0.0014)(4,130) + (0.069)(140) = 15 lb/yr xylenes
7.1-176
Liquid Storage Tanks
06/18
-------
Example 5 - Floating Roof Landing Loss for an External Floating Roof Tank - Determine emissions of
product from the landing of a floating roof in an external floating roof tank containing gasoline during the
month of April. The tank is painted white and is located in Port Arthur, Texas. The tank is 120 ft in
diameter and 40 ft high, and has a nominally flat bottom. The floating roof is landed while the tank
contains gasoline having an RVP of 12, and is refloated with gasoline having an RVP of 7.0. For both
gasolines, the benzene concentration is known to be 0.5 percent by weight in the liquid. The deck support
legs are set at a height of 3 feet, and the liquid is lowered to a level of one foot. The tank is refilled three
days after the landing of the floating roof.
Solution:
1. Determine tank type. The tank is an external floating roof storage tank.
2. Determine estimating methodology. Gasoline consists of many organic compounds, all of which are
miscible in each other, which form a homogenous mixture. The molecular weight of gasoline will be
taken from a table and the true vapor pressure will be calculated from the Reid vapor pressure of the
mixture. Weight fractions of components of interest in the vapor phase will be calculated from
concentrations in the liquid phase, using Raoult's Law.
3. Select equations to be used.
Ltl = Lsl + Lfl (3-1)
LsLwind 0. 57ndDP* Mv<5.9D2hieWi (3-4,3-10)
Lfl ~
fPvAVy}
RTV J
Mv(psfs) <(5.9D2hieWi-LSL) + (0.15 PvaVvMv/RTv) (3-16,3-18)
where:
Ltl = total losses during roof landing, lb
Lsl = standing idle loss during roof landing, lb (= LsLwmd for external floating-roof tanks)
¦^SLwind standing idle loss due to wind, lb
0.57 = daily rim seal factor; (Ki<;, + KRb vn)/365, where Ki<;, = 6.7, KRb = 0.2, v = 10, and n = 3.0
na = number of days that the tank is standing idle, days
D = tank diameter, ft
P* = a vapor pressure function, dimensionless
Mv = stock vapor molecular weight, lb/lb-mole
5.9 = combination of constants (id A) and 7.48 gal/ft3
hie = effective height of the stock liquid, feet
Wi = density of the liquid inside the tank, lb/gal
Lfl = filling loss during roof landing, lb
06/18
Liquid Storage Tanks
7.1-177
-------
Pva = true vapor pressure of the liquid inside the tank, psia
Vv = volume of the vapor space, ft3
R = ideal gas constant, 10.731 psia ft3 /lb-mole °R
Tv = average temperature of the vapor and liquid below the floating roof, °R (= Taa)
Csf = filling saturation correction factor for wind, dimensionless
S = filling saturation factor, dimensionless (0.60 for a full liquid heel; 0.50 for a partial liquid
heel).
4. Identify parameters to be calculated/determined from tables. In this example, the following parameters
are not specified: P*, Mv, Wi, Pva, Vv, Tv, Csf and S.
The following values are obtained from tables or assumptions:
Mv = 66 lb/lb-mole, from Table 7.1-2 as a default value for the vapor phase molecular weight
of all gasolines.
Wi = 5.6 lb/gal, from Table 7.1-2 for gasoline.
Tv = 68.9 °F (528.6 °R) from Table 7.1-7, the average ambient temperature (Taa) for April in
Port Arthur, TX.
S = 0.60 for a full liquid heel.
Values for the following parameters still need to be calculated:
P* = a vapor pressure function, dimensionless. P* is needed to calculate the standing idle loss,
which occurs with a heel of gasoline (RVP 12) in the tank.
PVA
The true vapor pressure, Pva, in the equation for P* is the same as the true vapor
pressure, Pva, in the calculation of the landing loss. Typical atmospheric pressure, Pa, for
Port Arthur, TX is obtained from Table 7.1-7, as 14.75 psi.
Pva = true vapor pressure of the liquid inside the tank, psia
Determine Pva using Equation 1-25, with values for the constants A and B determined
from the equations in Figure 7.1-15 using the given Reid vapor pressure and the default
value of 3.0 given for the distillation slope S in Table 7.1-2.
A = 15.64 - 1.854 S05 - (0.8742-0.3280 S05)ln(RVP)
7.1-178
Liquid Storage Tanks
06/18
-------
B = 8,742 - 1,042 S0 5 - (1,049-179.4 S05)ln(RVP)
For gasoline RVP 12, the calculated values of A, B, P and P* are:
A = 11.668
B =5102.7
Pva = 7.50 psia at 68.9 °F
P* = 0.176
For gasoline RVP 7.0, the calculated values of A, B and Pva are:
A= 11.833
B = 5500.6
Pva = 4.16 psia at 68.9 °F
Vv = volume of the vapor space, ft3
Determine the vapor space volume Vv using Equation 3-22, where the height of the vapor
space under the floating roof is the difference between the floating roof leg height and the
depth of the liquid heel, which are given as 3 feet and 1 foot respectively. Thus the height
of the vapor space under the floating roof is 2 feet, and the vapor space volume is:
Vv = (2) (ti 1202/4)
Vv = 22620 ft3
CSf = filling saturation correction factor for wind, dimensionless
/ (o.57.1.n.P-.Mv)-(1.^.(M-).Mv.^)
" i-»
Solve for Ke:
kb =^+APk ~m>b >0
Tla Pa ~^va
(1-5)
where:
ATV = 0.7 ATa + 0.02 a I (1-7)
For Port Arthur, TX in April, Tax equals 78.3°F, Tan equals 59.5°F, and I equals 1,649
Btu/ft2 d per Table 7.1-7.
ATv = 0.7 (78.3 - 59.5) + 0.02 (0.25 for a white tank in average condition) (1,649) = 21.4°R
A Pv = Pvx - Pvn
Pvx and Pvn are the true vapor pressures at Tlx and Tln, respectively.
06/18
Liquid Storage Tanks
7.1-179
-------
From Figure 7.1-17:
Tlx = Tla + 0.25 ATv = 68.9 + 0.25 (21.4) = 74.3°F
Tln= Tla-0.25 ATv = 68.9-0.25 (21.4) = 63.5°F
Pvx= 8.27 psia
Pvn = 6.79 psia
APV= (8.27-6.79)= 1.48 psi
b 528.6 (14.75-7.50)
Solve for Ks:
where:
Pva = 7.50 psia
Hvo = 2 feet
then:
Ks 1 + 0.053 PvaHvo (1"21)
Ks = i — = 0.557
^ 1+0.053 (7.50)(2)
( (0.57-1-120-0.176-66)—f1-0.245 f 7'50'22'620 )-66-0.557) \
r — 1 _ | __v V10.731-528.6/ !_ | __ Q rA
Sf \ (l-0.245< 7 50 22'620 >66-0.557)+(Y 7 50 22'62° )-66-0.6o) j '
\\ VlO.731-528.6/ J \\10.731-528.6/ //
5. Calculate mole fractions in the liquid. The mole fraction of benzene in the liquid can be calculated
using Raoult's Law. The molecular weight of the liquid stock is given as 92 lb/lb-mole, and thus liquid
mole fractions of individual components can be calculated using Equation 40-4.
_ ZliMl
Xi
= (0.005)(92) = o 0059 for benzene
78.1
6. Calculate partial pressures and total vapor pressure of the liquid. The total vapor pressure of gasoline
RVP 12 and of gasoline RVP 7 is given in Step 4.
For gasoline RVP 12, the calculated value of Pva is:
Pva = 7.50 psia at 68.9 °F
For gasoline RVP 7.0, the calculated value of Pva is:
Pva = 4.16 psia at 68.9 °F
From Table 7.1-7, Pa = 14.75 psi
7.1-180
Liquid Storage Tanks
06/18
-------
The vapor pressure of benzene at 68.9°F can be determined using Antoine's equation. Since Raoult's Law
is assumed to apply in this example, the partial pressure of benzene is the liquid mole fraction (x,) times
the vapor pressure of benzene (P), from Equation 40-3.
Component
P at 68.9°F
Xi
P partial
Benzene
1.4912
0.0059
0.0088
7. Calculate mole fractions of components in the vapor. The mole fraction of benzene in the vapor phase
is the partial pressure of the component (Ppartiai) divided by the total vapor pressure of the mixture (Pva),
from Equation 40-5. The total pressure depends upon the RVP, and thus the mole fraction of benzene
must be calculated separately for gasoline RVP 12 and for gasoline RVP 7.0.
yi Ppartial/PvA
RVP 12
yi = 0.0088 / 7.50 = 0.0012 for benzene
RVP 7
yi = 0.0088 / 4.16 = 0.0021 for benzene
8. Calculate molecular weight of the vapor. This step is not required because the molecular weight of
gasoline vapor is already specified.
9. Calculate weight fractions of components of the vapor. The weight fraction of each component in the
vapor phase can be calculated using Equation 40-6.
-7 =ZiMi
Z V i
RVP 12
(0.0012)(78.1) =0.0014 for benzene
66
RVP 7
Zfi = (0-0021)(78'1) =0.0025 for benzene
66
10. Calculate standing idle loss,
a. Check the limit on standing idle loss:
06/18
Liquid Storage Tanks
7.1-181
-------
LsLmax ^ 5.9 D2 hieWi
LsLmax ^ 5.9(120)2(1) (5.6) = 480,000 lb
b. Check the calculated standing idle loss:
LsLwind = 0.57 nd D P* Mv
LsLwmd = 0.57 (3) (120) (0.176) (66) = 2,400 lb < 480,000 lb
LsLwind 2,400 lb
c. Calculate the benzene standing idle loss:
LsLbenzene = 2,400(0.0014) lb benzene
LsLbenzene = 3.4 lb benzene
11. Calculate the filling loss.
a. Check the limit on filling loss:
LFLmax (5.9 D2 hk Wi)- Lsl + 0.15 (Pva Vv / RTV) Mv
LFLmax< 5.9 (120)2 (1) (5.6) -2,400 + 0.15 [(4.16)(22,620)]/[(10.731)(528.6)] (66) = 470,000 lb
b. Check the calculated filling loss:
The prior stock was gasoline having an RVP of 12, and the roof was refloated with gasoline having an
RVP of 7.0. It may be reasonably assumed that the arrival vapors were remaining from the prior stock,
and the generated vapors were from the incoming stock. The vapor saturation factor for incoming vapors
is 0.15 per the discussion on drain-dry tanks in section 7.1.3.3.2.
Check the total wind-corrected saturation factor for refilling of a landed external floating roof, using the
value for CSf calculated in Step 4:
CsfS= (0.64) (0.60) = 0.38
Given the saturation factor of 0.15 for the generated vapors, the saturation factor for the arrival vapors is
therefore (0.38 - 0.15) = 0.23.
Calculate the arrival loss:
Lfl (arrival) = (¦
10.731-528.6.
7.5-22,620
¦) ¦ 66 ¦ 0.23 = 4501b
7.1-182
Liquid Storage Tanks
06/18
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Calculate the generated loss:
/ 4.16- 22,620 \
Lfl (generated) = I — ¦ 66 ¦ 0.15 = 160 lb
tLK& J VlO.731 ¦ 528.6J
Calculate the total filling loss:
Lfl = 450+ 160 = 610 lb <480,000 lb
Lfl = 6101b
c. Calculate the benzene filling loss: Apply the vapor weight fraction of RVP 12 gasoline to the arrival
loss and the vapor weight fraction of RVP 7 gasoline to the generated loss.
LFLbenzene 450(0.0014) + 160(0.0025) lb benzene
LFLbenzene = 1.0 lb benzene
12. Calculate total losses for the floating roof landing event. The total loss is the sum of the standing loss
and the filling loss.
Ltl = Lsl + Lfl
Ltl = 2,400+ 610 = 3,000 lb
LlLbenzene 3.4 + 1.0 = 4.4 lb benzene
06/18
Liquid Storage Tanks
7.1-183
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Example 6 - Cleaning Loss for an External Floating Roof Tank - Calculate emissions for cleaning the
tank mentioned in Example 5, assuming that tank cleaning operations began on the third day after the
floating roof was landed, rather than the tank having been refilled as described in Example 5.
Assume that on the third day of the floating roof landing, forced ventilation was started up to vent
the vapor space to a control device which had a vapor reduction efficiency of 95%. Commencement of
forced ventilation marked the end of the floating roof landing and the beginning of the tank cleaning
event. The one-foot heel of remaining gasoline described in Example 5 was removed by means of vacuum
trucks. The amount of gasoline then remaining in puddles in the bottom of the tank was judged to be the
equivalent of about one-eighth of an inch deep if it were spread evenly over the bottom of the tank, and
about three inches of gasoline remained in the bottom of a 24-inch diameter sump. The equivalent of six
inches of diesel was then added to the tank. The forced ventilation continued to be operated at 3,000 cubic
feet per minute (cfm) throughout the day and night of the first day of tank cleaning.
The next morning, the beginning of the second day of tank cleaning, the vapor concentration was
found to be less than 10,000 ppmv. At this time the mixture of diesel and gasoline in the bottom of the
tank was vacuumed out, leaving an average of about one-half inch of wet sludge remaining on the tank
bottom. The control device was disconnected and forced ventilation continued through the second day of
tank cleaning, venting directly to atmosphere, as workers cleaned out the sludge. At the end of the second
day of tank cleaning, the vapor concentration was measured at 3,800 ppmv and the forced ventilation was
turned off over night. The equivalent of about one-eighth inch of wet sludge remained in the bottom of
The forced ventilation was restarted on the morning of the third day of tank cleaning, venting to
atmosphere. Workers rinsed the tank bottom and removed all remaining volatile material, leaving the tank
clean and gas free by the end of the day. At this point, the tank cleaning operation was deemed to be
complete from an emissions estimating viewpoint, and the tank was deemed to be out of service. While
forced ventilation was continued on subsequent days for the safety of workers inspecting the tank,
emissions had ceased due to the removal of all volatile material.
The tank cleaning events and hourly readings of vapor concentration are listed below:
Day Time Concentration Activity
the tank.
(PPmv)
1 10:00
380,000
Start up forced ventilation to control device.
Vacuum out gasoline heel.
Begin pumping in diesel.
First hour is considered vapor space purge.
11:00
12:00
13:00
14:00
15:00
16:00
17:00
18:00
190,000
130,000
101,000
85,000
73,000
63,000
53,500
46,000
Continued forced ventilation, routed to control device.
7.1-184
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Day Time Concentration Activity
(ppmv)
19:00 40,000
20:00 35,000
21:00 31,000
22:00 27,700
23:00 24,700
0:00 22,000
1:00 19,700
2:00 17,700
3:00 16,000
4:00 14,400
5:00 12,900
6:00 11,500
7:00 10,200
8:00 9,100
9:00 8,200 45,300 ppmv, average for first day of continued forced ventilation.
Disconnect control device.
Vacuum out all free flowing liquid.
10:00
7,400
Continued forced ventilation, vented to atmosphere.
11:00
6,700
12:00
6,100
13:00
5,550
14:00
5,100
15:00
4,700
16:00
4,350
17:00
4,050
18:00
3,800
5,300 ppmv, average for second day of continued forced ventilation.
Forced ventilation turned off.
6:00 19,000 Re-start of forced ventilation (to atmosphere).
First hour is considered vapor space purge.
Continued forced ventilation, vented to atmosphere,
7:00
10,100
8:00
5,500
9:00
3,800
10:00
2,200
11:00
1,500
12:00
1,050
13:00
700
14:00
400
15:00
150
16:00
0
06/18
Liquid Storage Tanks
7.1-185
-------
Day Time Concentration
(ppmv)
Activity
17:00
18:00
0
0
Solution:
1. Select equations to be used.
2,100 ppmv, average for third day of continued forced ventilation.
Tank cleaning is complete; forced ventilation may continue for
worker safety during inspections, but all volatile material has
been removed and the tank is deemed out of service.
LFV = Lp + LCV
(4-1)
l' = (CT¥t)m's
(4-2)
LCv — 60 Qv ncv tv Cv ( ^T^G) — 5-9 D2 h
leWt
(4-10, 4-12)
Lsr = 60 Qv ncv tv Cv (^f) < 0.49 Fe D2 ds Wt
(4-10, 4-13)
where:
LFV = total emissions due to forced ventilation during a tank cleaning event, lb
Lp = vapor space purge emissions associated with the first air change following
commencement of forced ventilation, lb
emissions from continued forced ventilation following the first air change, lb
the true vapor pressure of the exposed volatile material in the tank (psia)
LCV
PvA
Vv = volume (fr') of the vapor space
R
the ideal gas constant (psia ft^ per lb-mole °R)
= 10.731 psia ft^ per lb-mole °R
Tv = the average temperature of the vapor space (°R)
= the average ambient temperature (°R),
My = the stock vapor molecular weight (lb/lb-mole)
S = the vapor space saturation factor during the initial vapor space purge (dimensionless)
7.1-186
Liquid Storage Tanks
06/18
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60 is the conversion of hours to minutes, min/hr
3
Qv = average ventilation rate during continued forced ventilation, ft /min
ncv = the duration of continued forced ventilation, days
tv = the daily period of forced ventilation, hr/day
Cv = average vapor concentration by volume during continued forced ventilation,
dimensionless
Pa = atmospheric pressure at the tank location, psia
MCG = calibration gas molecular weight, lb/lb-mole
D = the tank diameter, feet
hie = the effective height of the stock liquid and sludge for the given stage of continued forced
ventilation, ft
Wj = the density of the stock liquid, pounds per gallon
5.9 = combination of constants (id A) and 7.48 gal/ft3
l'e = the fraction of the sludge that evaporates (= 0.20 if unknown)
ds = the average depth of sludge, inches
2. Identify parameters to be calculated/determined from tables. In this example, the following parameters
are not specified: Pva, Vv, Tv, Mv, S, Mcg, and Wi.
The following values are obtained from tables or assumptions:
Pva = 7.50 psia for the RVP 12 gasoline, from Example 5.
Vv = 22,620 ft3 for the initial condition of one foot of stock remaining, from Example 5.
Tv = 68.9 °F (528.6 °R), from Example 5.
Mv = 66 lb/lb-mole for gasoline, from Table 7.1-2.
S= 0.38 from Example 5.
Mcg = 16 lb/lb-mole for methane, from Table 7.1-3.
Wi = 5.6 lb/gal for gasoline and 7.1 lb/gal for diesel, from Table 7.1-2.
06/18
Liquid Storage Tanks
7.1-187
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3. Calculate the initial vapor space purge emissions.
l' = ^T¥?)mvs
= ( 7-5-22,620 \ 66 = y50
^ V10.731-528.6/
The vapor space purge emissions were routed to a control device having an efficiency of 95%, and thus
the net vapor space purge emissions are calculated as follows:
Lpi = 750 (1 -0.95) = 38 lb
4. Calculate first day of continued ventilation emissions (routed to control device).
a. Check the limit on continued ventilation emissions for the first day:
Calculate the mass of liquid remaining in the tank after vacuuming out the one foot of remaining gasoline
and flooding the tank bottom with diesel.
The remaining gasoline is the equivalent of one-eighth of an inch across the entire bottom of the tank,
plus 3 inches in a 24-inch diameter sump.
Equivalent depth of the liquid in the sump, if spread across the entire tank bottom:
(3 inches)*(7i (2/12)2/4) / (n 1202/4) = 0.0008 inches
Total effective depth of gasoline remaining in the bottom of the tank:
(0.125 inches) + (0.0008 inches) = 0.1258 inches = 0.010 feet
The depth of diesel in the bottom of the tank is:
6 inches = 0.5 feet
LcVmax < 5.9 D2 hieWi
LcVmax < 5.9 (120)2 (0.010-5.6 + 0.5-7.1) = 310,000 lb
b. Check the calculated continued ventilation emissions for the first day:
-------
Levi —
8,100 (1 -0.95) = 410 lb
5. Calculate the second day vapor space purge emissions.
The forced ventilation ran throughout the night on the first day of tank cleaning, and thus there was no
standing idle period during which vapors could build up in the vapor space, and there were no vapor
space purge emissions on the morning of the second day of tank cleaning.
Lp2= 01b
6. Calculate second day of continued ventilation emissions (routed directly to atmosphere).
a. Check the limit on continued ventilation emissions for the second day:
Calculate the mass of liquid remaining in the tank after vacuuming out all free flowing liquid and leaving
one-half inch of wet sludge in the bottom of the tank.
LCV < 0.49 Fe D2 ds W[
where:
l'e = the fraction of the sludge that evaporates (= 0.20 if unknown)
D = the tank diameter, feet
ds = the average depth of sludge, inches
W[ = the density of the stock liquid, pounds per gallon
9
the constant, 0.49, has units of gal/(in. ft ), and the other terms are defined as shown above.
In the liquid phase, the density of diesel is greater than the density of gasoline and, as shown in the
calculations above for the first day, most of the remaining liquid is diesel. It would, then, be both
reasonable and conservative to use the density of diesel in calculating the mass of remaining liquid.
LCV < 0.49 (0.20) (120)2 (0.5) (7.1) = 5,000 pounds
b. Check the calculated continued ventilation emissions for the second day:
(Pa Mcg'
LCv — 60 Qv ncv tv Cvy
( 5,300 \ / 14.75-16 \
Lrv = 60 ¦ 3,000 ¦ 1 - 9 ¦ ¦ = 3601b < 5,0001b
VI,000,000/ V10.731 ¦ 528.6/
Lcv2 = 360 lb
The second day of continued ventilation emissions were routed directly to atmosphere, and thus the net
06/18 Liquid Storage Tanks 7.1-189
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vapor space purge emissions are calculated as follows:
LCv2 = 360 (1 -0.0) = 360 lb
7. Calculate the third (last) day vapor space purge emissions.
The forced ventilation was discontinued overnight between the second and third days of tank
cleaning, and thus there was an overnight standing idle period. There would, then, be a vapor space purge
on the morning of the third day of tank cleaning. The vapors originated from a mixture of diesel and
gasoline. While most of the liquid was pumped out during the second day, the relative volumes of diesel
and gasoline would have been as described above for the limit on continued ventilation emissions for the
first day. The effective depths were 0.01 feet for gasoline and 0.5 feet for diesel, for a total initial depth of
0.51 feet. The volumes are then calculated from the liquid depths and the diameter of the tank:
Gasoline: 0.01 (7i)(120)2 / 4 = 113 ft3
Diesel: 0.50 (ti)(120)2 / 4 = 5,655 ft3
Multiply the volumes of each liquid by its liquid density to calculate the mass of each. Values of 5.6
lb/gal for gasoline and 7.1 lb/gal for diesel are obtained from Table 7.1-2.
Gasoline: 113 (5.6) (7.48) = 4,733 1b
Diesel: 5,655 (7.1) (7.48) = 300,3261b
The conversion factor of 7.48 has units of gallons per cubic foot.
The total weight is 4,733 + 300,326 = 305,059 lb. The weight of each liquid may then be divided by the
liquid phase molecular weight to calculate the number of moles of that liquid. Molecular weights are
obtained from Table 7.1-2.
Gasoline: 4,733 /92 = 51
Diesel: 300,326/188 = 1,597
The total number of moles is (51 + 1,597) = 1,648, and the mole (volume) fractions in the liquid phase
may be calculated:
Gasoline: 51 / 1,648 = 0.031
Diesel: 1,597/1,648 =0.969
From Example 5, the temperature at the bottom of the tank is 68.9 F, and the true vapor pressure of the
gasoline at that temperature is 7.50 psia. Calculate the true vapor pressure of the diesel at 68.9 F, using
Equation 1-25 with values for the A and B constants from Table 7.1-2.
P = exp
B
A--
A = 12.101
B = 8907°R
7.1-190
Liquid Storage Tanks
06/18
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P= 0.0087 psia
The partial pressure of each component is the liquid mole (volume) fraction times the true vapor pressure:
Gasoline: 0.031*7.50 = 0.233 psia
Diesel: 0.969*0.0087 = 0.0084 psia
The vapor space purge emissions for the third day can then be computed separately for each component:
L' = {^)u"s
where:
Pva = the partial pressure of the given component, psia
Vy = the volume under the landed floating roof, cubic feet
Determine the vapor space volume IV using Equation 3-22, where the height of the vapor
space under the floating roof is the floating roof leg height (neglecting the one-eighth
inch height of sludge remaining in the tank). In that this example is a continuation of the
floating roof landing in Example 5, the leg height is given as 3 feet. However, it is more
common for the legs to be set in the high leg position when cleaning the tank.
Vv = (3) (ti 1202/4) = 3 3 9 3 0 ft3
R = 10.731 psia ft^ per lb-mole °R
Tv = temperature °R = 68.9 + 459.7 = 528.6
Mv= vapor phase molecular weight of the given component, from Table 7.1-2
Gasoline: 66
Diesel; 130
S = saturation factor = 0.50 from 7.1.3.4.1
0.233 ¦ 33,930
10.731 ¦ 528.£
0.0084-33,930
Lpnninlinp = I ¦ 66 ¦ 0.50 = 46 lb
Pgasoline ^10.731 ¦ 528.6/
Lpdiesei = ¦ 130 ¦ 0.50 = 3 lb
Pdiesel \ 10.731-528.6
Lp3 = 46+ 3 = 49 lb
8. Calculate third (last) day of continued ventilation emissions (routed directly to atmosphere),
a. Check the limit on continued ventilation emissions for the last stage:
After a day of removing sludge, about one-eighth inch of sludge remained in the bottom of the tank.
Lcvmax< 0.49FeD2dsWi
06/18
Liquid Storage Tanks
7.1-191
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LcVmax < 0.49 (0.20) (120)2 (0.125) (7.1) = 1,300 lb
b. Check the calculated continued ventilation emissions for the last day:
(Pa Mcg'
LCv — 60 Qv ncv tv Cvy
( 2,100 \ / 14.75-16 \
Lcv = 60 ¦ 3,000 ¦ 1 ¦ 12 ¦ --rT^r-rT^r ¦ mo J = 190 lb < i'300 lb
cv Vl,000,000/ V10.731 ¦ 528.6/
Lcv3 = 190 lb
The last day of continued ventilation emissions were routed directly to atmosphere, and thus the net vapor
space purge emissions are calculated as follows:
LCv3 = 190 (1 -0.0)= 1901b
6. Calculate total losses for the tank cleaning event. The total loss is the sum of the vapor space purge
emissions and the continued ventilation emissions for each day of forced ventilation while volatile
material remained in the tank. These emissions are summarized as follows:
Lp Lev
Day 1
38
410
Day 2
0
360
Day 3
49
190
Total
87
960
The total emissions during tank cleaning (forced ventilation) are then:
Lfv = Lp + Lev
Lfv = 87 + 960 = 1,000 lb
Note that emissions from this example were significantly mitigated by the flushing of the tank bottom
with diesel to reduce the vapor concentration relatively quickly, and by the routing of vapors to a control
device until the vapor concentration was reduced substantially (comparing the start of day 2 to the start of
day 1 shows that the vapor concentration when the control device was disconnected was about two
percent of the initial reading). It's evident from step 4.b above that emissions would have been several
tons per day if these mitigation steps had not been taken.
7.1-192
Liquid Storage Tanks
06/18
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7.1.6 Historical Equations
Equations in this section were historically used to obtain approximate values, but have been
replaced with more accurate equations.
7.1.6.1 Average Daily Vapor Pressure Range
The following method was historically available for approximating APv, with some loss of
accuracy, however it is no longer recommended.
An 0.50BPvaATv
= T i (60-1)
LA
where:
APv = average daily vapor pressure range, psia
B = constant in the vapor pressure equation, °R; the value used here must be the B constant
for the two-constant expression in Equation 1-25
Pva = vapor pressure at the average daily liquid surface temperature, psia; see Notes 1 and 2 to
Equation 1-22
Tla = average daily liquid surface temperature, °R; see Note 3 to Equation 1-22
ATv = average daily vapor temperature range, °R; see Note 1 to Equation 1-5
7.1.6.2 Fixed Roof Tank Working Loss
Working loss for fixed roof tanks had historically been estimated using Equation 60-2. The
temperature for purposes of determining the vapor density was assumed to be 63°F (523°R) in Equation
60-2, and thus the vapor density was represented as (Mv Pva)/(10.731*523). The coefficient of 0.0010
was based on this simplification of the vapor density, combined with the 5.614 term for converting barrels
to cubic feet, resulting in (5.614)7(10.731»523) = 0.0010.
where:
Lw ~0-0010 Mv PVA Q KN KP (60-2)
Lw = working loss, lb/yr
Mv = vapor molecular weight, lb/lb-mole; see Note 1 to Equation 1-22
Pva = vapor pressure at average daily liquid surface temperature, psia; see Notes 1 and 2 to
Equation 1-22
Q = annual net throughput (tank capacity [bbl] times annual turnover rate), bbl/yr
Kn = working loss turnover (saturation) factor, dimensionless
for turnovers >36, Kn = (180 + N)/6N
for turnovers <36, Kn = 1
N = number of turnovers per year, dimensionless
5.614 Q
N =— (60-3)
V LX
where:
06/18
Liquid Storage Tanks
7.1-193
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Vlx = tank maximum liquid volume, fit3
where:
D
Hlx
KP
Vu =fD2H
LX
(60-4)
diameter, ft
maximum liquid height, ft
working loss product factor, dimensionless
for crude oils Kp = 0.75
for all other organic liquids, Kp = 1
7.1-194
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December 1980.
8. Evaporative Loss from Fixed-Roof Tanks. Manual of Petroleum Measurement Standards. Chapter
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Laboratory, Golden, CO, distributed by National Climatic Data Center, Asheville, NC, September
1992.
06/18
Liquid Storage Tanks
7.1-195
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15. Ferry. R.L.. Documentation Of Rim Seal Loss Factors For The Manual Of Petroleum Measurement
Standards: Chapter 19—Evaporative Loss Measurement: Section 2—Evaporative Loss From Floating
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17. Written communication from A. Parker and R. Neulicht. Midwest Research Institute, to
D. Beauregard. U. S. Environmental Protection Agency. Fitting Wind Speed Correction Factor For
External Floating Roof Tanks. September 22. 1995.
18. Use Of Variable Vapor Space Systems To Reduce Evaporation Loss. Bulletin No. 2520. American
Petroleum Institute, New York, NY, 1964.
19. Written communication from A. Parker, Midwest Research Institute, to D. Beauregard, U. S.
Environmental Protection Agency, Final Deck Fitting Loss Factors for AP-42 Section 7.1, February
23, 1996.
20. Courtesy of R. Ferry, TGB Partnership, Hurdle Mills, NC.
21. Evaporative Loss from Storage Tank Floating Roof Landings, Manual of Petroleum Measurement
Standards, Chapter 19.6, Part 1, First Edition, American Petroleum Institute, Washington, D.C.,
February 2017.
22. Evaporative Loss Reference Information and Speciation Methodology, Manual of Petroleum
Measurement Standards, Chapter 19.4, Third Edition, Addendum 2, American Petroleum Institute,
Washington, D.C., June 2017.
23. Evaporative Loss from the Cleaning of Storage Tanks, Technical Report 2568, American Petroleum
Institute, Washington, D.C., November 2007.
24. Ferry, R.L., Distillate Flushing Study - Bench and Field Testing - Final Report, prepared for the
American Petroleum Institute, December 2013.
25. 2016 Emissions Inventory Guidelines, RG-360/16, Appendix A, Technical Supplement 6, Texas
Commission on Environmental Quality, Austin, TX, January 2017.
26. Short-term Evaporative Loss Estimation from Atmospheric Storage Tanks, Technical Report 2576,
First Edition, American Petroleum Institute, Washington, D.C., July 2016.
27. Evaporative Loss from Closed-vent Internal Floating-roof Storage Tanks, Technical Report 2569,
American Petroleum Institute, Washington, D.C., August 2008.
28. Guide to Fire Hazard Properties of Flammable Liquids, Gases, and Volatile Solids, NFPA 325, 1994
edition, National Fire Protection Institute, Quincy, MA, 1994.
7.1-196
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