United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S8-87/034d Dec. 1987
6ER& Project Summary
Prevention Reference Manual:
Chemical Specific, Volume 4:
Control of Accidental
Releases of Ammonia
(SCAQMD)
D. S. Davis, G. B. DeWolf, J. D. Quass, and M. Stohs
The South Coast Air Quality Manage-
ment District (SCAQMD) of southern
California has considered strategies for
reducing the risk of a major accidental
air release of toxic chemicals. One
strategy, which would serve as a guide
to industry and communities, includes
monitoring activities associated with
the storage, handling, and use of
certain chemicals. This manual sum-
marizes information that can aid in
identifying and controlling release
hazards associated with ammonia
specific to the SCAQMD.
Ammonia has an IDLH (Immediately
Dangerous to Life and Health) concen-
tration of 500 ppm indicating a sub-
stantial acute toxic hazard.
To reduce the risk associated with an
accidental release of ammonia, the
potential causes of releases from
processes using ammonia in the
SCAQMD must be identified. Some of
these potential causes and specific
measures for reducing the risk of an
accidental release are identified. Such
measures include recommendations
on: plant design practices; prevention,
protection, and mitigation technolo-
gies; and operation and maintenance
practices. Conceptual costs for some
of these measures are estimated.
This Project Summary was devel-
oped by EPA's Air and Energy Engi-
neering Research Laboratory. Research
Triangle Park, NC. to announce key
findings of the research project that is
fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Introduction
The South Coast Air Quality Manage-
ment District (SCAQMD) conducted a
study in 1985 to determine the presence,
quantities, and uses of hazardous chem-
icals in the SCAQMD, which comprises
Los Angeles, Orange, San Bernadino,
and Riverside Counties. This study
culminated in a 1985 report, "South
Coast Air Basin Accidental Toxic Air
Emissions Study," which outlined an
overall strategy for reducing the potential
for a major toxic chemical release. The
strategy involves monitoring industry
activities associated with the storage,
handling, and use of certain chemicals
to minimize the potential for accidental
releases as well as the consequences of
any releases that might occur. This
volume of the manual discusses process
operations and practices relating to the
prevention of accidental releases of
anhydrous ammonia as it is used in the
SCAQMD.
Anhydrous ammonia (NH3) is a signif-
icant commodity chemical, produced by
the reaction of hydrogen and nitrogen
over a catalyst. The primary use of
anhydrous ammonia is in the fertilizer
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industry, which accounts for nearly 80%
of all ammonia produced. It is also used
as a raw material in the manufacture of
nitric acid, as a reactant with nitric acid
in the production of explosives, and in
the fibers and plastics industry in the
production of synthetic materials. In the
SCAQMD, anhydrous ammonia is used
or produced in seven processes: (1) a
patented waste water treatment process,
(2) the manufacture of resins, (3) refrig-
eration, (4) neutralization of acidic waste
streams, (5) preparation of ammonia
thiosulfate, (6) reduction of nitrogenoxide
(NO,) emissions, and (7) repackaging.
Potential Causes of Releases
At atmospheric temperatures and
pressures, anhydrous ammonia is a
pungent, colorless gas that may easily
be cooled to a colorless liquid. Because
liquid anhydrous ammonia has a large
coefficient of expansion, an over-
pressurization hazard exists if storage
vessels have insufficient expansion
space or if pipelines full of liquid ammo-
nia are sealed at both ends. In these
situations, thermal expansion of the
liquid and an increase in temperature can
result in containment failure from the
hydrostatic pressure exerted by the
liquid.
Failure leading to accidental releases
may be caused by process, equipment,
or operational problems. Most of the
accidental releases of ammonia that
have occurred in the past 15 years have
resulted from pressurized pipeline rup-
tures, failed storage tanks, and road
tanker accidents.
Possible process causes of an ammo-
nia release include: (1) backflow of
process reactants to an ammonia feed
tank; (2) excess feeds in any part of a
process, leading to overfilling or over-
pressurizing of equipment; (3) loss of
condenser cooling in distillation
columns; (4) overheating of reaction
vessels and distillation columns; and (5)
overpressure in ammonia storage ves-
sels from overheating caused by expo-
sure to fire, or from unrelieved overfilling.
Equipment causes of accidental
releases result from: hardware failures
such as failure of feed control systems
from a loss of power, clogged lines,
jammed valves, or instrument failure;
excessive stress caused by improper
fabrication, construction, or installation;
failure of pressure relief systems;
mechanical and thermal fatigue and
shock; corrosion of equipment con-
structed of high alloys; and brittle
fracture or creep failure. A significant
concern for anhydrous ammonia is use
of the proper alloy grade of steel. Certain
grades of steel are prone to catastrophic
failure due to cracking or embrittlement
from anhydrous ammonia.
Operational causes of accidental
releases result from incorrect procedures
and human error, including: (1) overfilled
storage vessels; (2) improper process
control system operation; (3) errors in
loading and unloading; (4) poor quality
control of replacement parts; (5) inade-
quate maintenance, especially of pres-
sure relief systems and other preventive
and protection devices; and (6) lack of
inspection and nondestructive testing of
vessels and piping to detect corrosion
weakening.
Hazard Prevention and Control
Prevention of accidental releases
relies on the proper design, construction,
and operation of facilities where ammo-
nia is stored and used and on the
protective systems that guard against
accidental release.
Process design involves the basic
chemistry of a process and how this
chemistry is affected by the variables of
flow, pressure, temperature, composi-
tion, and quantity. Any aspect of a
process may be modified to enhance the
integrity of the system. Such changes
could involve the quantities of materials,
process pressure and temperature con-
ditions, the sequence of operations,
process control strategies, and the
instrumentation used.
The most important consideration for
systems containing ammonia is the
prevention of overheating and/or over-
pressuring. In addition to overpressure,
overheating can also weaken process
equipment and increase the probability
of leaks developing at joints and valves.
Physical plant design covers equip-
ment, siting and layout, and transfer/
transport facilities. Dry ammonia is
noncorrosive to most common metals;
however, moist ammonia corrodes
copper, tin, zinc, and many alloys,
especially copper alloys. Only specific
grades of steel, recommended for ammo-
nia service, should be used due to the
possibility of cracking or embrittlement.
Certain aluminum alloys can be used in
parts of ammonia systems. Metallic and
nonmetallic gasket materials (e.g., com-
pressed asbestos, graphited asbestos,
carbon steel or stainless steel spiral-
wound asbestos, and aluminum) are
considered suitable for ammonia service
based on current industrial practice.
The siting and layout of any facility
handling ammonia and of individual
equipment should be designed to reduce
personnel exposure in the event of a
release. Siting should allow ready
ingress and egress and take advantage
of barriers that reduce release expo-
sures. Considerable distance between
large inventories and sensitive receptors
is desirable. The ground under process
equipment and storage vessels should be
sloped so that fire water and liquid spills
flow away from equipment into drains.
Storage facilities should be located in
cool, dry, well-ventilated areas.
Because heat causes significant ther-
mal expansion of ammonia, piping,
storage vessels, and other equipment
should not be located adjacent to piping
containing flammable materials, hot
process piping, equipment, or other
sources of direct or radiant heat. Special
consideration should be given to the
locations of furnaces and other perman-
ent sources of ignition in the plant.
Enclosures and scrubbers are protec-
tion technologies for containment and
neutralization. Enclosures would capture
any ammonia spilled or vented from
storage or process equipment, contain-
ing the spilled liquid or gas until it could
be transferred to other containment and
discharged at a controlled rate or to water
scrubbers for absorption.
Scrubbers can also be used for con-
trolling ammonia releases. Because of its
high solubility, ammonia discharges can
be absorbed in water in scrubbing
devices such as spray towers, packed bed
scrubbers, and Venturis.
If an accidental release occurs, mitiga-
tion technologies can reduce the conse-
quences. Such measures include phys-
ical barriers, water sprays and fogs, and
foams that will divert, limit, or disperse
the released chemical to the atmosphere.
In spite of the lower specific gravity of
pure ammonia vapor relative to air, large
accidental releases of ammonia have
often formed ammonia/air mixtures that
are denser than the surrounding atmos-
phere. The primary means of dispersing
and removing ammonia vapor from the
air is with water sprays or fogs. A capture
zone can be created downwind of the
release into which the ammonia vapor
will drift and be absorbed.
Since accidental releases of toxic
materials result not only from deficien-
cies of design but also from deficiencies
of operation, safe operation of plants
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using ammonia requires competent,
experienced managers and staff trained
in handling and storing ammonia.
D. S. Davis, G. B. DeWolf. J. D. Quass. andM. Stohsare with Radian Corporation,
Austin, Texas 78766.
T. Kelly Janes is the EPA Project Officer (see below).
The complete report, entitled "Prevention Reference Manual: Chemical Specific,
Volume 4. Control of Accidental Releases of Ammonia (SCAQMD)," (Order
No. PB 87-231 254/AS; Cost: $18.95. subject to change) will be available
only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Officer can be contacted at:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
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United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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