United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S8-87/034k Feb. 1988
&EPA Project Summary
Prevention Reference Manual:
Chemical Specific, Volume 11:
Control of Accidental Releases of
Ammonia
D. S. Davis, G. B. DeWolf, J. D. Quass, and M. Stohs
The accidental release of a toxic
chemical at Bhopal, India, in 1984 was
a milestone in creating an increased
public awareness of toxic release prob-
lems. As a result of other, perhaps less
dramatic, incidents in the past, portions
of the chemical industry were aware of
this problem long before Bhopal. These
same portions of the industry have made
advances in this areas. Interest in
reducing the probability and conse-
quences of accidental toxic chemical
releases that might harm workers within
a process facility and people in the
surrounding community prompted the
preparation of a series of technical
manuals addressing accidental releases
of toxic chemicals. This manual is
chemically specific for ammonia. The
manual summarizes information to aid
regulators and industry personnel in
identifying and controlling release
hazards associated with ammonia.
Reducing the risk associated with an
accidental release of ammonia involves
identifying some of the potential causes
of accidental releases that apply to the
process facilities that handle and store
ammonia. In this manual, examples of
potential causes are identified as are
specific measures that may be taken to
reduce the accidental release risk. Such
measures include recommendations on:
plant design practices; prevention, pro-
tection, and mitigation technologies;
and operation and maintenance prac-
tices. Conceptual cost estimates of
example prevention, protection, and
mitigation measures are provided.
This Project Summary was developed
by EPA's Air and Energy Engineering
Research Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that Is fully docu-
mented In a separate report of the same
title (see Project Report ordering In-
formation at back).
Introduction
The accidental release of a toxic
chemical, methyl isocyanate, in Bhopal,
India, in 1984 was a milestone in creating
an increased public awareness of toxic
release problems. There have been other
less dramatic incidents of toxic chemical
releases in the past, and the chemical
industry was aware of this problem long
before this event. Safety and loss preven-
tion has long been a standard part of
industry activity, and over the years
industry has made many advances in this
area. There is renewed interest, however,
in reviewing technology and procedures
for preventing, protecting against, and
mitigating accidental releases.
As an aid to regulators and industry
personnel charged with reducing the
probability and consequences of acci-
dental toxic chemical releases, a series of
technical manuals was prepared that
addresses prevention, protection, and
mitigation measures for release. This
chemical specific manual on ammonia is
part of that series.
Ammonia is a major commodity chemi-
cal in industry. The dominant use of this
chemical is in the fertilizer industry which
accounts for nearly 80% of all ammonia
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<•*,'•
produced. The direct application of am-
monia to the soil is, in fact, the largest
single use of the chemical. The primary
industrial uses of ammonia are as a raw
material in the manufacture of nitric acid
and as the starting material in the pro-
duction of a number of commercially im-
portant synthetic materials. In addition to
the primary uses mentioned above,
ammonia has many other minor uses in a
wide variety of industries. Some of the
more common uses include neutralization
(especially the treatment of acidic wastes),
extraction, refrigeration, water purifica-
tion, the preparation of cleaners and
detergents, pulp and paper manufacture,
and food and beverage treatment.
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 coef-
ficient of expansion, an overpressurization
hazard exists if storage vessels have in-
sufficient expansion space or if pipelines
full of liquid ammonia are sealed at both
ends. In these situations, thermal ex-
pansion 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 ac-
cidental releases of ammonia that have
occurred in the past 15 years have re-
sulted from pressurized pipeline ruptures,
failed storage tanks, and road tanker
accidents.
Possible process causes of an ammonia
release include:
• Loss of feed composition control
resulting in the formation of am-
monia/air mixtures within the flam-
mability limits;
• Backflow of process reactants to an
ammonia feed tank;
• Excess feeds in any part of a process,
leading to overfilling or overpres-
suring of equipment;
• Loss of condenser cooling in distilla-
tion columns;
• Overheating of reaction vessels and
distillation columns; and
• Overpressure in ammonia storage
vessels from overheating caused by
exposure to fire, or from unrelieved
overfilling.
Equipment causes of accidental re-
leases result from hardware failures such
as failure of feed control systems from a
loss of power, clogged lines, jammed
valves, or instrument failure; from ex-
cessive stress caused by improper fabri-
cation, construction, or installation; from
failure of pressure relief systems; from
mechanical and thermal fatigue and
shock; from corrosion of equipment con-
structed of high alloys; and from 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 re-
leases result from incorrect procedures
and human error. These include: overfilled
storage vessels; improper process control
system operation; errors inloading and
unloading; poor quality control of replace-
ment parts; inadequate maintenance,
especially of pressure relief systems and
other preventive and protection devices;
and lack of inspection and nondestructive
testing of vessels and piping to detect
weakening from corrosion.
Hazard Prevention and Control
Prevention of accidental releases relies
on the proper design, construction, and
operation of facilities where ammonia is
stored and used and on the protective
systems that guard against an accidental
release.
Process design involves the basic
chemistry of a process and how this
chemistry is affected by the variables of
flow, pressure, temperature, composition,
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 pres-
sures and temperatures, the sequence of
operations, process control strategies, and
the instrumentation used.
The most important consideration for
systems containing ammonia is the pre-
vention of overheating and/or overpres-
suring. 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 equipment,
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 ammonia service, should be used due
to the cracking or embrittlement problem
mentioned previously. Certain aluminum
alloys can be used in parts of ammonia
systems. Metallic and non metal lie gasket I
materials (e.g., compressed asbestos,
graphited asbestos, carbon steel or stain-
less steel spiral-wound asbestos, and
aluminum) are considered suitable for
ammonia service based on current in-
dustry 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 exposures. Consider-
able 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 spillages flow away
from equipment into drains. Storage
facilities should be located in cool, dry,
well-ventilated areas.
Because heat causes significant thermal
expansion of ammonia, piping, storage
vessels, and other equipment should not
be located adjacent to piping containing
flammable materials, hot process piping
and equipment, or other sources of direct.
or radiant heat. Special consideration
should be given to the location of furnaces
and other permanent sources of ignition
in the plant. i
Two types of protection technologies '
for containment and neutralization include
enclosures and scrubbers. Enclosures
would capture ammonia spilled or vented
from storage or process equipment, con-
taining 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 scrub-
bers, and Venturis.
If an accidental release occurs, mitiga-
tion technologies can reduce the con-
sequences. Such measures include
physical barriers, water sprays and fogs,
and foams that will divert, limit, or dis-
perse the released chemical to the atmo-
sphere. 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
atmosphere. The primary means of dis-
persing and removing ammonia vapor
from the air is with water sprays or fogs.
A "capture zone" can be created down-
wind of the release into which the am- j
monia vapor will drift and be absorbed.
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, Since accidental releases of toxic
materials result not only from deficiencies
of design but also from deficiencies of
operation, safe operation of plants using
ammonia requires competent, experi-
enced managers and staff trained in the
proper way to handle and store ammonia.
D. Davis, G. DeWolf, J. Quass, and M. Stohs are with Radian Corporation,
Austin, TX 78766.
T. Kelly Janes is the EPA Project Officer (see below).
The complete report, entitled "Prevention Reference Manual: Chemical Specific,
Volume 11. Control of Accidental Releases of Ammonia," (Order No. PB87-
231262/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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Environmental Protection
Agency
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