450R80105
vvEPA
United States
Environmental Protection
Agency
Office of Air Quality April
Planning and Standards 1980
Research Triangle Park, NC 27711
New Source Performance Standards
Petroleum Storage Tanks
Final Regulation
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-New Source Performance Standards-
Petrolrum Storage Tanks
Regulatory
Authority
The 1977 Clean Air Act Amendments call for a com-
prehensive national program to reduce air pollution
and improve air quality. Section 111 of the Act re-
quires the U.S. Environmental Protection Agency
(EPA) to establish uniform emission standards for
selected new, modified, and reconstructed stationary
sources. These new source performance standards
(NSPS) are intended to minimize new air pollution
problems. Once an NSPS becomes final, it must be
reviewed by EPA every four years to assess improve-
ments that have been made in emission control tech-
nology for the source under regulation. NSPS re-
cently promulgated for petroleum liquid storage
tanks are based on standards EPA originally published
in 1974. The new standards, which reflect the use of
improved emission control technology for petroleum
storage tanks, are discussed here.
Emission Limits
On March 8, 1974, EPA published regulations to re-
duce the amount of smog-forming pollutants escaping
into the atmosphere from storage tanks containing
petroleum liquids. These pollutants, volatile organic
compounds (VOC), are also found in engine exhausts,
gasoline vapors, or in vapors from cleaning solvents or
other similar products. VOC react photochemically
with other atmospheric substances to form smog, a
complex air pollutant that has been linked to respira-
tory impairments and eye irritations. Smog also
damages plant tissue, and causes the deterioration of
rubber and other substances.
VOC vapors escaping from
petroleum liquid storage
tanks are difficult to mea-
sure in terms of mass
emission rates. Because
conventional measurement
techniques cannot be used
to accurately gauge these
emissions, storage tank performance standards are
based on equipment specifications and maintenance
requirements rather than on emission limit criteria.
Affected Sources
About 4.5 percent of
stationary source VOC
emissions may be traced
to petroleum storage tanks,
which are used to store
petroleum, condensate
and other finished or inter-
»„ mediate products manu-
factured at petroleum refineries.
The new performance standards affect tanks that 1)
storage capacities greater than 40,000 gallons
and 2) contain liquid with a true vapor pressure
greater than 1.5 pounds per square inch. Only
tanks for which construction began after May 18,
1978, fall under these NSPS. The standards exempt
tanks with storage capacities less than 420,000
gallons if the tanks are used to store only crude oil or
natural gasoline before transfer to other facilities.
An estimated 2,600 tanks, located at refineries,
terminals, and other facilities throughout the United
States, will be affected by these regulations.
Control Options
In compliance with Clean Air Act mandates that re-
quire NSPS to be reviewed every four years, EPA re-
assessed the storage tank standards originally promul-
gated in 1974. New NSPS reflect the use of VOC
emission controls more effective than those outlined
in the 1974 standards.
To effectively reduce VOC emissions, the regulations
require owners and operators of external floating roof
tanks to install double seal systems. This type of
system incorporates a primary seal and secondary seal
to achieve emission reduction. Different types of pri-
mary seals may be installed, including metallic shoe
seals; liquid-mounted, foam-filled seals; liquid-
mounted, liquid-filled seals; or vapor-mounted foam-
filled seals. Any type of secondary seal may be used,
as long as it completely covers the space between the
roof edge and tank wall. The 1974 regulations had
required installation of only one seal to close the gaps
between the roof edge and tank wall.
Owners and operators of petroleum storage tanks
must minimize the size of gaps between the seats and
tanks walls by meeting the following requirements:
1) gaps between the tank wall and a liquid-mounted
or metallic shoe primary
seal should measure no
more than 212 cm2 per
meter of tank diameter, or
10.0 in2 per foot of tank
diameter, 2) gaps between
the tank wall and a vapor-
mounted primary seal
should measure no more than 21.2 cm2 per meter of
tank diameter, or 1.0 in2 per foot of tank diameter,
and 3) gaps between the tank wall and a secondary
seal can be no more than 21.2 cm2 per meter of tank
diameter, or 1.0 in2 per foot of tank diameter.
Control technology for tanks with fixed outer roofs is
the same as that outlined in the 1974 regulations,
which require these tanks to be equipped with internal
floating roofs and a single seal for reducing emissions
from gaps where the tank wall and floating roof do
not meet. Vapor recovery and return or disposal
systems may also be used if they are designed to re-
duce VOC emissions by 95 percent. Tanks which
store liquids with vapor pressures greater than 11.1
pounds per square inch must be equipped with vapor
recovery and return or disposal systems.
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