PB88-213194
PREVENTION REFERENCE MANUAL: OVERVIEWS ON
PREVENTING AND CONTROLLING ACCIDENTAL
RELEASES OF SELECTED TOXIC CHEMICALS
Radian Corporation
Austin, TX
May 88
U.S. DEPARTMENT OF COMMERCE
National Technical Information Service
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EPA/600/8-80/074
May 1988
PREVENTION REFERENCE MANUAL:
OVERVIEWS ON
PREVENTING AND CONTROLLING
ACCIDENTAL RELEASES
OF SELECTED TOXIC CHEMICALS
by:
D.S. Davis
G.B. Detfolf.
K.A. F«rland
J.D. Quass
C.O. Rueter
Radian Corporation
P.O. Box 201088
Austin, Texas 78720-1088
Contract No. 68-02-4286
Vork Assignment 104
EPA Project Officer:
Jane C. Bare
Air and Energy Engineering Research Laboratory
Research Triangle Park, North Carolina 27711
AIR AND ENERGY ENGINEERING RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, NC 27711
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TECHNICAL REPORT DATA .
(fitatt read Itmrucncns en rt* nverte before compltting/
1. REPORT NO
EPA/ 600/8-88/074
3.
4. TITLE AND SUBTITLE
Prevention Reference Manual: Overviews on Preven-
ting and Controlling Accidental Releases of Selected
Toxic Chemicals
7 AUTHQR(S)
D.S.Davis, G. B. DeWolf. K.A. Ferland. J. D.Quass,
and C.O.Rueter
B PERFORMING ORGANIZATION NAME AND ADDRESS
Radian Corporation
P. O. Box 201088
Austin, Texas 78720-1088
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Air and Energy Engineering Research Laboratory
Research Triangle Park, NC 27711
IB. SUPPLEMENTARY NOTES AEERL
1528.
3. RECIPIENT'S ACCESSION1 NO.
.PlXJff- J/3 i*¥r
B. REPORT DATE
May 1988
S. PERFORMING ORGANIZATION CODE
B. PERFORMING ORGANIZATION REPORT NO.
10. PROGRAM ELEM
ENT NO.
11. CONTRACT/GRANT NO.
68-02-4286. Task 104
13. TYPE OF REPORT AND PERIOD COVERED
Task final; 10/87 - 4/88
14. SPONSORING AGENCY CODE
EPA/600/13
project officer is Jane C. Bare, Mail Drop 62b. 919 /541-
is. ABSTRACT The manual can be used to orient personnel involved in inspecting and other-
wise evaluating potential toxic chemical release hazards to the fundamentals of rel-
ease hazard control for 13 of the specific chemicals chosen for evaluation under Sec-
tion 305(b) of the Superfund Amendments and Reauthorization- Act (SARA) of 1986. .It
also guides the user to other technical literature for additional information. Section
30 5 (b) requires that the EPA conduct a "review of emergency systems for monitor-
ing, detecting, and preventing releases of extremely hazardous substances at repre-
sentative domestic facilities that produce, use, or store extremely hazardous sub-
stances. " The EPA must also prepare and present to Congress a report with recom-
mendations for initiatives for the development of technologies and systems for mon-
itoring, detecting, and preventing the accidental release of chemical substances,
and for public alert systems that warn of imminent releases.
17.
L DESCRIPTORS
Pollution
Chemical Compounds
Emission
Accidents
Toxicity
18. DISTRIBUTION STATEMENT
Release to Public
KEY WORDS AND DOCUMENT ANALYSIS
b. IDENTIFIERS/OPEN ENDED TERMS
Pollution Control
Stationary Sources
Accidental Releases
19. SECURITY CLASS (ThuXtportl
Unclassified
20 SECURITY CLASS fnitpafl)
Unclassified
c. , COSATI Field/Group
13B
07B,07C
14G
13L
06T
21. NO OF PAGES
in
23. PRICE
ft/ A)
C»A Form »10-t (»-TJJ
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NOTICE
This document has been reviewed in accordance with
U.S. Environmental Protection Agency policy and
approved for publication. Mention of trade names
or commercial products does not constitute endorse-
ment or recommendation for use.
11
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ABSTRACT
Concerns about the potentially disastrous consequences of accidental
releases of toxic chemicals has led to increased interest in reducing the
probability of effects of such releases. This manual, one of a series,
presents an overview of the prevention of accidental releases of 13 specific
chemicals, selected randomly from a larger EPA list. Potential hazards
control in chemical processes is discussed, followed by a discussion of the
chemicals and their key characteristics. These discussions are intended to be
information capsules for quick reference. Formal methods of hazard identifi-
cation and evaluation are discussed and their major features compared, and an
overview of control principles for prevention, protection, and mitigation is
presented.
While most of the principles of effective prevention, protection, and
mitigation are generic, individual chemical properties, and the specific
processes in which individual chemicals are produced or used, influence some
of the details of how the principles are implemented. For example, while
overpressure is a generic issue, it is a more important hazard for accidental
releases for chemicals with high vapor pressures. Another example, is that,
while the primary release hazard for one chemical may be due to its flam-
mability, for another it may be due to its corrosiveness. Chemical specific
process related issues pertinent to accidental releases of the individual
chemicals are discussed.
iii
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TABLE OF CONTENTS
Section Page
1 INTRODUCTION 1-1
1.1 BACKGROUND 1-1
1.2 Purpose of this Manual 1-2
2 HAZARD CONTROL 2-1
2.1 HAZARD IDENTIFICATION 2-1
2.1.1 "What If" Analysis 2-2
2.1.2 Hazard and Operability (HAZOP) Study 2-4
2.2 PRE-RELEASE PREVENTION, PROTECTION, AND POST-RELEASE
MITIGATION 2-4
2.' 1.1 General Considerations 2-4
2.2.2 Pre-Release Prevention 2-6
2.2.3 Protection 2-17
2.2.4 Operation and Maintenance Practices 2-33
2.2.5 Control Effectiveness 2-41
2.2.6 Estimating Costs of Release Prevention, Protection, and
Mitigation.' 2-42
3 INDIVIDUAL CHEMICAL SUMMARIES 3-1
3.1 ACRYLONITRILE 3-2
3.1.1 Chemical Characteristics 3-2
3.1.2 Facility Descriptions 3-6
3.1.3 Summary of Major Process Hazards and Control
Technologies 3-16
3.1.4 Storage and Handling 3-19
3.2 BENZENEARSONIC ACID 3-24
3.2.1 Chemical Characteristics 3-24
3.2.2 Facility Descriptions 3-26
3.2.3 Summary of Major Process Hazards and
Control Technologies 3-26
3.2.4 Storage and Handling 3-27
3.3 BENZOTRICHLORIDE 3-28
3.3.1 Chemical Characteristics 3-28
3.3.2 Facility Descriptions 3-30
3.3.3 Summary of Major Process Hazards and Control
Technologies 3-35
3.3.4 Storage and Handling 3-36
Preceding page blank
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TABLE OF CONTENTS (continued)
Section Page
3.4 CHLOROACETIC ACID 3-41
3.4.1 Chemical Characteristics 3-41
3.4.2 Facility Descriptions 3-44
3.4.3 Summary of Major Process Hazards and
Control Technologies 3-48
3.4.4 Storage and Handling 3-49
3.5 FURAN 3-53
3.5.1 Chemical Characteristics 3-53
3.5.2 Facility Descriptions 3-56
3.5.3 Summary of Major Process Hazards and Control
Technologies 3-61
3.5.4 Storage and Handling 3-65
3.6 HYDRAZINE 3-66
3.6.1 Chemical Characteristics 3-66
3.6.2 Facility Descriptions 3-70
3.6.3 Summary of Major Process Hazards and Control
Technologies 3-77
3.6.4 Storage:and Handling.: ' . 3-79
3.7 HYDROGEN SULFTDE 3-83
3.7.1 Chemical Characteristics 3-83
3.7.2 Facility Descriptions 3-86
3.7.3 Summary of Major Process Hazards and
Control Technologies 3-94
3.7.4 Storage and Handling 3-96
3.8 MECHLORETHAMINE 3-101
3.8.1 Chemical Characteristics 3-101
3.8.2 Facility Descriptions 3-103
3.8.3 Summary of Major Process Hazards and
Control Technologies 3-103
3.8.4 Storage and Handling '. 3-104
3.9 METHIOCARB 3-105
3.9.1 Chemical Characteristics 3-105
3.9.2 Facility Descriptions 3 -105
3.9.3 Summary of Major Process Hazards and Control
Technologies 3 -107
3.9.4 Storage and Handling 3-107
vi
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TABLE OF CONTENTS (continued)
Section
3.10 KETHYL BROMIDE ......................................... 3'108
3.10.1 Chemical Characteristics ............................... 3-108
3.10.2 Facility Descriptions .................................. 3-113
3.10.3 Summary of Major Process Hazards and Control
Technologies ........................................... 3'113
3.10.4 Storage and Handling ................................... 3-115
3.11 SODIUM AZIDE ........................................... 3'119
3.11.1 Chemical Characteristics ............................... 3-119
3.11.2 Facility Descriptions .................................. 3-121
3.11.3 Summary of Major Process Hazards and Control
Technologies ........................................... 3-123
3.11.4 Storage and Handling ................................... 3-124
3.12 TETRAETHYL TIN ......................................... 3'126
3.12.1 Chemical Characteristics ............................... 3-126
3 . 12 . 2 Facility Descriptions .................................. 3-128
3.12.3 Summary of Major Process Hazards and
Control Technologies ................................... 3-128
3.12.4 Storage and Handling ................................... 3-129
3.13 TRICHLOROACETYL CHLORIDE ............................... 5
3.13.1 Chemical Characteristics ............................... 3-130
3.13.2 Facility Descriptions .................................. 1-122
3.13.3 Summary of Major Process Hazards
and Control Technologies ............................... 3-132
3.13.4 Storage and Handling ................................... 3*133
4 REFERENCES [[[ 4 ' 1
APPENDIX A - Glossary ............................................. A- 1
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LIST OF TABLES
Number Page
2-1 Summary of Key Features of "What if* and Hazop Analyses 2-3
2-2 Example Guide Words and Corresponding Deviations for
Hazop Analysis 2-5
2-3 Some Air Toxic Release Protection Technologies Applicable to
Toxic Chemicals Discussed in this Manual 2-18
2-4 Important Considerations for Using Flares to Prevent
Accidental Chemical Releases 2-22
2-5 Typical Mitigation Technologies Applicable Co Toxic
Chemical Releases 2-26
2-6 Aspects of Training Programs for Routine Process Operations. 2-36
2-7 Examples of Major Prevention and Protection Measures for
Toxic Chemical Releases 2-43
2-8 Example of Levels of Control for Generic Toxic Chemical
Storage Tank 2-47
2-9 Summary Cost Estimates of Potential Levels of Controls for
Toxic Chemical Storage Tank 2-49
3-1 Physical Properties of Acrylonitrlle 3-3
3-2 Exposure Limits for Acrylonitrile 3-7
3-3 Estimated End Use Pattern of Acrylonitrile 3-9
3-4 Example Conditions, Process Hazards and Hazard Controls in
Acrylonitrile Manufacturing* and Use 3-2O
3-5 Chemical Resistance of Various Metals to Acrylonitrile 3-22
3-6 Physical Properties of Benzenearsonic Acid 3-25
3-7 Physical Properties of Benzotrichloride 3-29
3-8 Toxicity Data for Benzotrichloride 3-31
3-9 Typical Uses of Benzotrichloride 3-33
3-10 Example Conditions, Process Hazards and Hazard Controls in
Benzotrichloride Manufacturing, Use and Storage 3-37
3-11 Physical Properties of Chloroacetic Acid 3-42
3-12 Example Conditions, Process Hazards and Hazard Controls in
Chloroacetic Acid Manufacturing and Use 3-50
3-13 Acceptability of Various Metals and Alloys for Chloroacetic
Service 3-52
3-14 Physical Properties of Furan 3-54
3-15 Example Conditions, Process Hazards and Hazard Controls for
Accidental Furan Releases 3-63
3-16 Physical Properties of Hydrazine 3-67
3-17 LC.0 or LD . Data for Hydrazine 3-71
3-18 Typical End* Uses of Hydrazine 3-75
3-19 Common Hydrazine-Based Biocides and Growth Regulations 3-76
3-20 Example Conditions, Process Hazards and Hazard Controls in
Hydrazine Manufacturing and Use 3-80
3-21 Materials of Construction Reported to be Compatible with
Hydrazine 3-82
viii
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LIST OF TABLES (continued)
Number
3-22 Physical Properties of Hydrogen Sulfide 3-84
3-23 Exposure Limits for Hydrogen SulfLde 3-87
3-24 Effects of Hydrogen Sulfide Inhalation 3-88
3-25 Typical End Uses of Hydrogen Sulfide 3-91
3-26 Example Conditions, Process Hazards and Hazard Controls in
Hydrogen Sulfide Manufacturing and Use 3-97
3-27 Materials of Construction Reported to be Acceptable for
Hydrogen Sulfide Service 3-100
3-28 Physical Properties of Mechlorethamine 3-102
3-29 Physical Properties of Methiocarb 3-106
3-30 Physical Properties of Methyl Bromide 3-109
3-31 Exposure Limits for Methyl Bromide 3-112
3-32 Example Conditions, Process Hazards, and Hazard Controls in
Methyl Bromide Manufacturing and Use 3-116
3-33 Materials of Construction Reported to be Suitable for Methyl
Bromide Service...". 3-118
3-34 Physical Properties of Sodium Azide 3-120
3-35 Example Conditions, Process Hazards and Example Hazard
Controls in Sodium Azide Manufacturing and Use 3-125
3-36 Physical Properties of Tetraethyl Tin 3-127
3-37 Physical Properties of Trichloroacetyl Chloride*. ' 3-131
3-38 Example Conditions, Process Hazards and Hazard Controls in
Trichloroacetyl Chloride Manufacturing and Use. .- 3-134
ix
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LIST OF FIGURES
Figure Page
3-1 Conceptual flow diagram of Sohio acrylonitrile manufacturing
process 3-8
3-2 Conceptual flow diagram of typical acrylic fiber manufacturing
process 3-11
3-3 Conceptual flow diagram of typical emulsion acrylonitrile
butadiene-styrene (ABS) resin manufacturing process 3-12
3-4 Conceptual flow diagram of typical suspension acrylonitrile
butadiene-styrene (ABS) manufacturing process 3-14
3-5 Conceptual flow diagram of benzotrichloride and benzoyl chloride
batch production processes 3-34
3-6 Conceptual flow diagram of typical chloracetic acid
manufacturing process 3-45
3-7 Conceptual flow diagram of carboxymethyl cellulose
manufacturing process 3-47
3-8 Conceptual flow diagram of typical furan manufacturing process.. 3-57
3-9 Conceptual flow diagram of typical tetrahydrofuran manufacturing
process 3-59
3-10 Conceptual flow diagram of typical thiophene manufacturing
process . • 3-60
3-11 Conceptual flow diagram of typical ketazine-based hydrazine
'hydrate manufacturing process 3-72
3-12 Conceptual flow diagram of typical anhydrous hydrazine
separation process 3-74
3-13 Conceptual flow diagram of a process for absorbing hydrogen
sulfide 3-90
3-14 Conceptual flow diagrams of two configurations of the Clans
process 3-93
3-15 Conceptual flow diagram of typical methyl bromide manufacturing
process 3-114
3-16 Conceptual flow diagram of typical sodium azide manufacturing
process 3-122
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SECTION 1
INTRODUCTION
1.1 BACKGROUND
Increasing concern about the potentially disastrous consequences of
accidental releases of toxic chemicals resulted from the Bhopal, India acci-
dent of December 3, 1984, which killed approximately 2.000 people and injured
thousands more when a toxic cloud of methyl isocyanate was released. This
tragedy led to worldwide concern about the potential for accidents of similar
magnitude elsewhere. In the United States, the concern intensified when a
major release of aldicarb oxime occurred soon thereafter from a chemical
facility in Institute, West Virginia, fortunately without loss of life. These
incidents clearly demonstrated the potential for disaster as the result of an
accidental release-of chemicals that haVe become a part of modern life; they
also focussed attention on the fact that releases of chemicals from the
facilities where they are manufactured, processed, used, or stored not only
can occur, but do occur commonly.
The result was a new urgency in efforts to establish national programs to
address chemical emergencies. The Chemical Emergency Preparedness Program
(CEPP) of the U.S. Environmental Protection Agency (EPA), designed to foster
planning and preparation within communities for serious releases of extremely
hazardous substances from local chemical facilities, was launched nationally
in November 1985. Concurrently, the Chemical Manufacturers Association (CMA)
initiated the Community Awareness and Emergency Response Program (CAER) to
encourage communication between industry and local communities about chemical
hazards. By October 1986, the local planning encouraged on a voluntary basis
by CEPP was made mandatory by Congressional enactment of Title III of the
Superfund Amendments and Reauthorization Act of 1986 (SARA). Title III of
1-1
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SARA is entitled the "Emergency Planning and Community Right-to-Know Act of
1986."
The emergency planning provisions of Title III require communities to
prepare for the possibility of accidents at facilities handling extremely
hazardous substances. The "community right-to-know" provisions require
industry to share information with communities about toxic chemicals present
at a local facility. To enable communities to recognize the potential hazards
associated with local chemical production or use, Congress included in Title
III requirements for facilities to report regularly the presence of hazardous
chemicals on site, as well as emissions of such chemicals to any environmental
medium; air, water, or land (soil).
The overall thrust of all of these activities is to reduce the risk of
harm to people, while at the same time ensuring that the people are aware of
risks so that they may take actions of their own, if necessary, to reduce the
risks.
1.2 PURPOSE OF THIS MANUAL
The purpose of this manual is to orient regulatory personnel and others
involved in inspecting and otherwise evaluating potential toxic chemical
release hazards to the fundamentals of release hazard control for some
specific chemicals. It also guides the user to other technical literature for
additional information. One specific purpose is to assist the EPA evaluation
teams in a review of emergency systems mandated under SARA.
Section 305(b) of SARA requires that the EPA conduct a "review of
emergency systems for monitoring, detecting, and preventing releases of
extremely hazardous substances at representative domestic facilities that
produce, use, or store extremely hazardous substances." The EPA must also
prepare and present to Congress a report with recommendations for initiatives
for the development of technologies and systems for monitoring, detecting, and
1-2
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preventing the accidental release of chemical substances, and for public alert
systems that warn of an imminent release.
To prepare the report to Congress, the EPA is surveying a sample of
domestic facilities which handle one or more of 20 chemicals selected from the
SARA Section 302(a) list of "extremely hazardous substances." The 20
chemicals were selected from the list of extremely hazardous substances by the
following procedure. First, EPA identified seven chemicals distinguished by
their large production volumes, widely recognized hazards, involvement in past
plant and transportation accidents, and generally recognized special handling
procedures and controls. These chemicals •• ammonia, chlorine, hydrocyanic
acid (hydrogen cyanide), hydrogen fluoride, methyl isocyanate, sulfur dioxide,
and sulfur trioxide -- represent a wide range of toxicity, reactivity,
flammability, and corrosivity hazards.
The remaining chemicals from the list of 20, discussed in this manual,
were randomly selected by the U.S. EPA Office of Solid Waste and Emergency
Response from subgroups of certain specified criteria (e.g., vapor pressure,
ambient physical state, etc.) with the same proportion of chemicals in each
physical state as the full list of extremely hazardous substances.
Accordingly, two gases, seven liquids, and four solids were chosen. The seven
liquids were selected to represent a range of vapor pressures (less than 1 nun
Hg to greater than 100 mm Hg) at 25°C. These chemicals are: acrylonitrile,
benzenearsonic acid, benzotrichloride, chloroacetic acid, furan, hydrazine,
hydrogen sulfide, methiocarb, mechlorethamine, methyl bromide, sodium azide,
tetraethyl tin, and trichoroacetyl chloride.
The EPA evaluated each chemical selected in this manner with respect to
factors influencing the type of monitoring, detection, prevention, and
mitigation measures likely to be employed in handling the chemical:
corrosivity, flammability, and reactivity ratings; manufacturing, processing,
and use volumes; number of sites where the substance may be manufactured,
processed, or used; physical state and volatility; and information on past
1-3
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accidental releases. In considering these factors, the EPA tried to ensure
that a wide range of industrial activities would be covered in the review and
that the review addressed only chemicals produced or handled in sufficient
volume to warrant inclusion. Based on this final screening, one of the
chemicals initially selected, 3-chloropropionitrile, was dropped and
hydrazine, which meets the same physical property criteria (liquid, medium
vapor pressure), was selected as a replacement.
A written questionnaire has been sent to a sample of domestic facilities
which produce, use or store one or more of the 20 extremely hazardous sub-
stances. The questionnaire has two purposes: 1) to gather additional data on
available technologies and procedures and practices for monitoring, detection,
prevention, and mitigation of accidental releases; and 2) to determine which
technologies, operating procedures, and management practices are being used,
and why. Trained inspectors will visit a limited number of the surveyed
facilities to obtain in-depth information, as well as to corroborate the
survey responses.
It is intended that this manual provide information useful to EPA
inspection or evaluation teams for release hazards of some of the specific
chemicals at facilities they will be visiting and for reviewing survey
questionnaires from an even greater number of facilities. In addition to
descriptive text, tables on chemical and process specific hazards are provided
to provide easy reference for the user. It is intended that this manual be
used in conjunction with other manuals in a set of prevention reference
manuals whose overall purpose is to summarize the major concepts of release
hazard identification and control so that the probability and consequences
(risk is the product of probability and consequences; risk - probability x
consequences) of accidental toxic chemical releases can be reduced. The
volumes in the series include: a User's Guide, or overview for controlling
accidental releases of air toxics; a Control Technologies manual describing
the methods available for preventing and protecting against accidental toxic
chemical releases; and a series of chemical-specific manuals describing the
1-4
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release hazards associated wich certain toxic chemicals (chlorine, hydrogen
fluoride, hydrogen cyanide, sulfur dioxide, ammonia, sulfur trichloride,
methyl isocyanate). A series of chemical-specific manuals for the South Coast
Air Quality Management District of California has also been prepared
(chlorine, hydrogen fluoride, hydrogen cyanide, sulfur dioxide, ammonia,
carbon tetrachloride, and chloropicrin). A manual on mitigation technologies
for controlling accidental releases of air toxics is being prepared.
The PRM-Chemical Specific manual actually consists of a number of
individual volumes for specific chemicals, while this manual provides an
overview of hazard control for thirteen toxic chemicals: acrylonitrile,
benzenearsonic acid, benzotrichloride, chloroacetic acid, furan, hydrazine,
hydrogen sulfide, mechlorethamine, methiocarb, methyl bromide, sodium azide,
tetraethyl tin, and trichloroacetyl chloride.
The PRM-User's Quide is a general introduction to the subject of toxic
chemical releases, overview of the accidental-release problem, and summary of
methods commonly used in hazard identification, and evaluation and principles
of hazard control. The PRM-Control Technologies volumes address prevention,
protection and mitigation measures which can generally be applied to reduce
the probability and consequences of an accidental toxic chemical release.
Taken together, the PRM series stresses the importance of technology,
management and operations in achieving this goal. Used by qualified technical
personnel, these manuals, in conjunction with other knowledge and experience,
should provide the hazard orientation required to effectively evaluate equip-
ment, systems, and procedures in facilities manufacturing, using, or storing
toxic chemicals.
Since the purpose of the FRM series is to summarize the major concepts of
release hazard control, the reader is referred to other information sources
for more detailed discussions. Other sources include manufacturers and
distributors of the various chemicals and technical literature on loss preven-
tion in facilities handling toxic chemicals. Examples of technical literature
1-5
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include the American Institute of Chemical Engineering (AIChE) Loss Prevention
Series and AIChE's Center for Chemical Process Safety publications.
The remainder of this manual contains two sections. Section 2 discusses
release hazard control which begins with hazard identification and is the
application of specific measures for pre-release prevention and protection,
and post-release mitigation. In general, many of the technological,
operational, and managerial aspects of hazard control are applicable to toxic
chemicals in general. Section 3 presents an overview of chemical specific
hazards that can contribute to a release. Topics discussed are: physical,
chemical, and toxicological properties; information on the manufacture and
use, including facility descriptions where appropriate; hazards associated
with the various processes; and hazard prevention and control information
specific to' the chemical. Appendix A is a glossary of key technical terms
that might not be familiar to all users of the manual. Appendix B presents
selected conversion factors between metric (SI) and English measurement units.
1-6
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SECTION 2
HAZARD CONTROL
Hazard identification is the first step in hazard control. Section 2.1
provides an overview of hazard identification and discusses two of the most
commonly applied hazard identification methodologies. Once hazards are
identified, specific measures may then be taken to control them.
General pre-release prevention, protection and mitigation measures are
addressed in Section 2.2. Administrative and operational, as well as
technological measures are covered in Section 2.2, since the prevention of
toxic chemical accidental releases and a reduction in the severity of adverse
effects on people after a release involves facility management and operational
practices in addition to technology. Section 2.3 concludes the discussion of
the mitigation aspect of hazard control by examining the use of models in
simulating the movement of hazardous vapor or gas clouds. Models can be used
as planning tools for predicting the effects of various accidental release
scenarios and as emergency response tools aiding decision-making during an
actual release event.
2.1 HAZARD IDENTIFICATION
The first step in hazard control on a specific process or facility is
hazard identification. A publication of the American Institute of Chemical
Engineers (AIChE) on guidelines for hazard evaluation lists the following
methods of formal hazard identification (1):
• Checklists,
• Safety Review,
• Relative Ranking,
• Preliminary Hazard Analysis,
2-1
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• What-If Analysis.
• Hazard and Operability Studies,
• Failure Modes, Effects, and Criticality Analysis,
• Fault Tree Analysis,
• Event Tree Analysis,
• Cause Consequence Analysis, and
• Human Error Analysis.
For an overview summary of Che key features and use of these methods, see
other manuals in this series. The reader may also refer to an AlChE
publication for more detailed descriptions of the methodologies (1). In
addition, these methods are discussed in other technical literature (e.g.
Reference 2) and the AIChE and other organizations present short courses on
hazard identification at national meetings and special symposia and con-
ferences .
In a survey by the Chemical Manufacturer's Association. "What-If"
analyses and Hazard and Operability (HAZOP) studies were named as the methods
most often used for hazard identification (3). Key features of these two
methods are summarized below.
2.1.1 "What If" Analysis
A "What If" analysis systematically considers the consequences of
unexpected abnormal events that may occur in a process facility. It can
include design, construction, operating, or other deviations from the norm. A
"What If" examination can include all parts of a process facility. Its
comprehensiveness and success depends on the experience of the staff
conducting the analysis. Table 2-1 lists the purpose, time of use, type of
results, staff requirements and relative cost of the "What If" analysis as
well as the HAZOP method discussed next.
2-2
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TABLE 2-1. SUMMARY OF KEY FEATURES OF "WHAT IF" AND HAZOP ANALYSES
METHOD
What If
Analysis
HAZOP
PURPOSE
WHEN TO
USE
Identify hazards
Identify event
sequences
Identify possible
methods of risk
reduction
NATURE OF
RESULTS
Process
development
Pre-startup
Operation
Qualitative
Identify hazards
Identify
operability
problems
Identify event
sequences
Identify possible
methods of risk
reduction
Late design
Operation
Qualitative
STAFF SIZE
RELATIVE
COST
Small - Moderate
Moderate
Moderate - Large
Moderate - High
2-3
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2.1.2 Hazard and Qperabilitv fHAZOP^ Study
A HAZOP study can identify process hazards and operability problems. A
multidisciplinary team conducts a HAZOP study by searching for deviations from
intended design and operating conditions. The team carefully examines each
individual stream and component of a process facility using standard design
"guide words" applied to each process variable such as flow, for example.
Consequences of deviations expressed by the guide words are identified. In
this way, hazards, some of which may result in accidental releases, are
identified. Key features of the methodology are shown in Table 2-1. Example
guide words are presented in Table 2-2.
2.2 PRE-RELEASE PREVENTION, PROTECTION, AND POST-RELEASE MITIGATION
2.2.1 General Considerations
Prevention of accidental releases and their adverse consequences relies
on a combination of administrative, operational, and technological measures
that apply to the design, construction, operation and maintenance of facili-
ties that manufacture, use and store toxic chemicals. These measures are
based on various principles and considerations that can be grouped as follows:
• Pre-release Prevention
- Process design
- Physical facility design
- Operating and maintenance practices (including management);
• Pre-release Protection systems; and
• Post-release Mitigation systems.
In each of these areas, defined subsequently, specific factors are
considered that could lead to a process upset (e.g., overpressure) or
2-4
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TABLE 2-2. EXAMPLE GUIDE WORDS AND CORRESPONDING DEVIATIONS FOR HAZOP
ANALYSIS
Guide Word
Deviations
None No forward flow, material present, or action when there should
be.
More of More of any relevant physical property than there should be.
e.g.. higher flow (rate or total quantity), higher temperature.
higher pressure, higher viscosity, etc.
Less of Less of any relevant physical property than there should be.
e.g.. lower flow (rate or total quantity), lower temperature,
lower pressure, etc.
Part of Composition of system different from what it should be, e.g.,
change in ratio of components, component missing, etc.
More than More components present in the system than there should be,
e.g.. extra phase present (vapor, solid), impurities (air.
water, acids, corrosion products), etc.
Other than. What else can happen apart from normal' operation, e.g..
startup, shutdown, uprating. low running, alternative operation
mode, failure of plant services, maintenance, catalyst change,
etc.
Reverse Variable or activity is reverse of what it should be. e.g..
reverse flow.
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operational failure (e.g., opening a drain valve) that could directly cause a
release of the chemical co the environment, or result in an equipment failure
(e.g., pipe rupture) chat would then cause the release. At a minimum, equip-
ment and procedures should be designed, constructed, operated, and maintained
in accordance with applicable codes, standards, and regulations. In addition,
stricter equipment and procedural specifications may be necessary to reduce
the probability or consequences of accidental releases below levels that still
might exist in spite of such codes, standards, or specifications.
The following subsections define and discuss prevention, protection, and
mitigation in a little more detail. Further discussion can be found in other
volumes of this series and in the technical literature.
2.2.2 Pre-Release Prevention
Pre-release prevention refers to measures taken to reduce the probability
than an accidental release of a toxic chemical will occur. Prevention begins
with process design and is an inherent part of each phase of activity in the
life cycle of a process facility, from the Initial design through facility
startup, routine operation, and shut down. The most fundamental principles of
release prevention include process design, physical facility design, and
operations (which here is defined to include management and maintenance
practices).
Process Design--
Process design considerations involve several fundamental principles
applied to the process materials, process variables, and equipment. These
principles are addition, substitution, deletion, and redundancy (or duplica-
tion). Each process, chemical, operation, or piece of equipment in a process
facility should be viewed in terms of hov changes based on these qualities may
lead to a reduction in the probability of an accidental release. For example,
substitution might involve the replacement of a toxic chemical with one less
toxic. Duplication or redundancy night involve the use of a second
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thermocouple to measure a critical temperature. In each case, a hazard
reduction is achieved. The substitution reduces the probability of the toxic
release to zero by removing the chemical from the process. In the
thermocouple example, the second thermocouple serves as a backup to the first,
which improves the chances for controlling a process upset. This reduces the
chance that an upset can lead to an accidental release.
There are a number of fundamental aspects of process design and operation
which are an inherent part of process control and essential to reducing the
probability of process upsets and accidental releases. Each of these are
discussed below.
Control Characteristics of the Process--Good process control, including
the interaction of human operators with the process system, is basic to
successful process operations. Process control is achieved by manipulating
the process variables of flow, temperature, pressure, composition, and
quantity. Loss of containment through loss of control occurs when a process
variable exceeds the physical limits of the containment system. Process
control systems, both strategies and hardware, may differ in their control
characteristics and ability to reduce the probability of an accidental
release. A process control system performs the following functions:
measurement, normal control, and emergency or protective control. How each of
these is achieved determines the control effectiveness of the control system
in release prevention.
Process Characteristics and Chemistry--Fundamental process changes can
often reduce the inherent process hazards by reducing in-process inventories
of toxic materials and by reducing the severity of operating conditions, such
as temperature and pressure.
Pressure Control--Pressure above or below the design intent of a process
can increase the probability of an accidental chemical release. Overpressure
can cause the opening of a relief device and the discharge of a toxic chemical
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co Che environment. Eicher can cause physical failure of process or storage
equipment and loss of containment. Generally, overpressure is considered more
hazardous Chan underpressure, but both should be considered as potential
causes of a hazardous release.
Three related process events-- thermal expansion, excess material genera-
tion and flow blockage-can lead to loss of pressure control. One example of
chis first hazard is posed by liquid-full equipment; equipment with little or
no vapor space above the liquid. Liquid expansion with heating can cause
equipment rupture. An example of excess material generation is the continued
heating of a vaporizing liquid in a closed vessel, increasing the pressure in
the vessel. An example of excess pressure can be created by flow blockage
when a positive displacement pump is used to pump a liquid.
Flow Measurement and Control--Process hazards associated with flow
involve deviations that cause the flow to be too low. too high, reversed or
fluctuating. Flow deviations can result in process hazards and accidental
releases due to: overheating, inadequate heating, incorrect feed rates to
reacting systems, overfilling of vessels, unwanted siphoning of liquids,
unintended chemical or physical reactions, obstruction of vent lines,
contamination by leakage, excessive back pressure on relief valves, severe
pulsations leading to construction materials' fatigue, and a reduction in
process controllability.
Temperature Control--Loss of temperature control may result in an
exothermic runaway reaction which can lead to an accidental release through
direct equipment failure from overheating or overpressure. Since the volume
of gases, and to some extent liquids, depends on temperature, a loss of
temperature control will often result in a loss of pressure control.
Quantity Control--The two primary objectives of quantity control are to
achieve proper process material ratios and the proper level and/or weight of
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materials in process or storage vessels. Failure to achieve these objectives
could result in overfilling or overpressuring of equipment.
Mixing--A loss of agitation is usually the primary hazard in mixing
systems. Loss of agitation and mixing can cause: incomplete reactions or
formation of unwanted by-products; reactant accumulation in poorly mixed
zones; and poor heat transfer. These conditions can initiate or be a pare of
a chain of events leading to an accidental release.
Composition Control--When a stream's composition varies from design
specifications, its chemical and physical properties also vary. The
consequences are process specific but may be contributory to a loss of process
control by affecting the other process variables already discussed. A common
and significant manifestation of poor composition control is unexpected
corrosion.
Physical Facility Design--
Physical facility design covers process and storage equipment, siting and
layout, and transfer/transport facilities. Vessels, piping and valves,
process machinery, instrumentation, and factors such as the location of
process systems and individual equipment items are all considered. The
following subsections review various aspects of physical facility design,
beginning with a discussion of materials of construction. This section on
physical plant design is not intended to provide detailed specifications for
the design of facilities handling the toxic chemicals discussed in this
manual; it is intended to illustrate major considerations of release preven-
tion. Additional discussion can be found in other volumes in this series.
Equipment--The primary function of storage and process equipment is
containment. Direct equipment failure and loss of containment can occur due
to rupture, leaks at joints and connections such as separated flanges,
actuated relief valves or rupture disks. Equipment failure such as failed
pumps or control valves, while not a direct loss of containment, can cause
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process upsets and initiate a chain of events leading to an accidental
release. Special hazards associated with equipment are noted below.
Materials of Construction--The materials of construction required for
process equipment depend on the compatibility of the chemicals with various
materials under the operating conditions of each specific process. This
compatibility can vary with temperature, pressure, and composition. As is
discussed for the individual chemicals in Section 3, materials compatible with
the chemical at ambient conditions were noted. These conditions would repre-
sent a starting point, or minimum basis, for materials selection. Selecting
the wrong material of construction can lead to equipment failure from corro-
sion, erosion, or mechanical wear. Process fluid characteristics such as
alkalinity, acidity, solvency, abrasiveness, and reactivity must be considered
with both normal pressure and temperature as well as extremes, and with the
frequency and magnitude of temperature and pressure fluctuations in selecting
materials of construction.
Even if an appropriate material is specified in the original design, a
contractor or vendor may substitute one material for another, or maintenance
personnel may replace a part with one made of an inappropriate material.
Incorrect substitutions are potentially dangerous and can cause a system
failure leading to a release. Ensuring that the correct materials are
selected and used begins with the initial design specifications but requires
proper supervision from design through maintenance during the life of an
operating facility.
The most common materials of construction are carbon steel and various
stainless steels. Other metals and alloys are sometimes required for certain
corrosion and opetating conditions. Plastics and glass as liners of process
equipment also are used where corrosion is a problem. Some process equipment
is also fabricated from plastics and glass. Such equipment may be more easily
broken than metal equipment, and this must be taken into consideration when
toxic chemicals are involved. Liner materials have been noted in the
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individual chemical summaries of Section 3 where applicable. No general
principles were found in the technical literature concerning the use of
plastics with toxic chemicals.
Vessels--Vessels. which include both process and storage equipment,
include all major items of equipment containing significant inventories of a
toxic chemical. As used here, vessels include tanks, reactors, heat exchanger
shells, columns, and similar equipment. Vessels may be atmospheric,
pressurized, or operate under vacuum.
Vessels must be protected from overpressure, overfilling, overheating,
and corrosion. Prevention of accidental releases depends on proper initial
design of the vessel and process system of which it is a part, as well as on
proper operation and maintenance while it is in service.
Overpressure protection of vessels is commonly provided by relief
devices. These include rupture disks and relief valves. Such devices protect
against catastrophic rupture or explosion by allowing a controlled release of
overpressurized vessel contents. The type of device used depends on the
vessel service and potential causes of the overpressure. Relief devices for
overpressure caused by fire or other overheating may be fusible plugs that
melt at a predetermined temperature. While these devices are designed to
prevent a catastrophic sudden release of vessel contents, a significant
release can still occur unless the relief device discharge is routed to a
protection system such as an emergency vent scrubber or flare for gases,
vapors, or particulate fumes, or overflow catch tanks for liquids
Overfilling can be prevented by using level-sensing devices and alarms,
including these devices with automatic feed shut-off interlocks, pressure
relief devices, and well-trained operating personnel. The overfill relief
would discharge to an overflow catch tank or to another suitable receiver.
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Careful attention should be given to vessel corrosion; suitable materials
of construction, adequate corrosion allowances should be provided. Special
attention should be given to welds and the possibility of external corrosion
under insulation.
Piping--As used here, the tern "piping" describes three closely
associated equipment components: piping, fittings, and valves. Straight
piping can be drawn, rolled and welded, or cast. Fittings, used to connect
various pipe sections or to connect pipe to another piece of equipment, to
change the direction of flow, or to provide a branch, are forged or cast. The
method of fabrication and the material of which the pipes and fittings are
made determine the ultimate strength or pressure rating in different types of
service. Each type of pipe has definite limitations on temperature, pressure.
and chemical environment. Specific information can be obtained from vendors
and in standard technical references (e.g. Reference 4).
Valves, used to regulate the flowrate or direction of flow through lines,
can be ball valves, gate valves, globe valves, plug valves diaphragm valves,
butterfly valves, and check valves. Fabrication and materials of construction
considerations are similar to those Just discussed for pipe and fittings.
In addition to the considerations of pressure, temperature, and chemical
environment for piping selection and design for toxic chemical service,
simplicity of design is desirable. The number of joints and connections
should be minimized. Piping should be securely supported to avoid excess
vibration and overstress due to mechanical loading and thermal gradients.
Piping should be constructed to allow room for thermal expansion and should be
protected from exposure to fire and temperatures that exceed design limits.
Long pipe runs should be sloped, with drainage provided at the low points.
Special attention must be paid to piping joints, whether threaded.
flanged or welded. For toxic chemicals, special precautions must be taken to
ensure that threaded joints are fully threaded and properly installed, that
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Che correct gaskets and flanges are used for flanged joints, the joints are
properly torqued, and that welded joints are inspected for weld integrity.
Valves in piping systems should be placed so that leaking or ruptured
pipes and equipment up or downstream of the values may be isolated, but no
section of pi-ping should be isolated from some form of overpressure relief or
expansion chamber while in service. Valves should be easy to remove and
maintain, and should have high-quality leak-tight packings or be leakproof,
like a diaphragm, or bellow-sealed.
Process Machinery--Process machinery refers to rotating or reciprocating
equipment used in the transfer or processing of a chemical. This includes
pumps, blowers, and compressors that may be used to move a liquid or gas, and
items such as screw and belt conveyors for solids.
Pumps--Many of the general considerations for piping and valves also
apply to pumps. Pump failures can be initiating or propagating events in a
chain of events leading to accidental releases. To ensure that a given pump
is suitable for a given service application, the system designer should obtain
information from the pump manufacturer certifying that the pump will perform
properly in the intended application. Materials of construction is always an
important consideration for pumps since they contain moving parts.
Pumps should be installed dry and oil-free to prevent process contamina-
tion with oil. Net positive suction head (NPSH) considerations are especially
important for pumping a liquid near its boiling point. In critical applica-
tions where a pump failure could lead to an accidental release, the pump
supply vessel should have high and low level alarms; the pump might even be
interlocked to shut off at low supply level or low discharge pressure.
The type of pump selected depends on pumping requirements and process
operating conditions. Centrifugal, rotary, and positive displacement pumps
are typically used. In some situations, the potential for seal leakage of a
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toxic or flammable material precludes standard rotating shaft seals. Some
seals use a flushing fluid to prevent entry of the process fluid into the seal
area. Pumps using stuffing boxes and packing are often provided with double-
packed seal chambers designed to prevent the toxic material from contacting
any reactive material. These chambers can be purged with an appropriate inert
fluid such as dry and oil-free nitrogen, or a suitable seal liquid. The seal
gas pressure should exceed the tank pressure by an appropriate margin.
Canned-motor pumps, vertical submersible pumps, magnetically coupled pumps and
diaphragm pumps eliminate shaft seals altogether.
Canned motor pumps have the motor housing integral with the pump casing.
Here, the process liquid actually serves as the bearing lubricant. An
alternative is the vertical pump often used on storage tanks. The advantage
of these pumps, which consist of a submerged impeller housing connected by a
drive shaft to the motor, is that the shaft seal is above the maximum liquid
level (and is therefore not vetted by the pumped liquid) and the pump is self
priming because the liquid level is above the impeller.
Magnetically-coupled pumps replace the drive shaft with a rotating
magnetic field as the pump-motor coupling device. Diaphragm pumps are posi-
tive displacement units in which a reciprocating flexible diaphragm drives the
fluid. This arrangement eliminates exposure of packing and seals to the
pumped liquid. However, a major consideration in the application of such
pumps is that at some point, diaphragm failure will probably occur.
Improper operation of pumps, i.e. cavitation, running dry, and deadhead-
ing, can cause pump damage and failure. Cavitation can be a problem in
pumping materials with low boiling point because of their tendency to vaporize
easily. If cavitation is allowed to occur, pitting and eventual serious
damage to the impeller can result. Running a pump dry because of loss of head
in a feed tank, for example, can seriously damage a pump. Finally, pumping
against a closed valve, deadheading, can have serious ramifications. A pump
bypass and recycle loop back to the feed container avoid such an occurrence.
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Deadheading is a special concern with positive displacement pumps. To prevent
rupture, positive displacement pumps commonly have a pressure relief valve
that bypasses to the pump suction. Centrifugal pumps often have a recycle
loop back to the feed container.
Compressors--Reciprocating, centrifugal, liquid-ring rotary, and non-
lubricated screw compressors are used to transfer gases. Like pumps, com-
pressors have the potential for shaft seal leakage. Overheating can cause
real damage and leakage. Heat sources in a compressor include the heat of
compression as well as the heat generated through mechanical friction. Host
multistaged compressors can be equipped with intercoolers that limit heat
buildup and increase compressor efficiency by reducing the volume of gas going
to the next compression stage.
While it is sometimes possible to avoid using rotary shaft seals with
pumps, rotary compressors usually require seals. Special seals such as double
labyrinth seals are often used. These seals have a series of interlocking
touch points which, by creating many incremental pressure drops, reduce total
leakage. Also, to further reduce leakage, dry air is injected into the seal.
In the event of deadheading, a compressor discharge can have a pressure relief
mechanism that vents to the compressor inlet or to a scrubber system. The
former appears to be satisfactory for a short term downstream flow interrup-
tion. Where a sustained interruption might occur, relief to a scrubber system
may be safer. Positive displacement compressors and pumps must always be
equipped with non-isolatable overpressure relief as close to the discharge as
possible.
Solids' Conveyors--Conveyors for solids may not be as critical to
accidental releases as are pumps and compressors because conveyors do not
pressurize a fluid. They are included in this discussion only because where a
toxic solid chemical is processed, used, or stored, conveyors may be a type of
process machinery required for the transfer of the solids. The primary
prevention consideration for conveyors is that they be limited in their size
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as much as possible to avoid large in-process inventories of dry toxic
materials. They should also be enclosed and have high-quality dust control
equipment associated vith their vents.
Plant Siting and Layout--The siting and layout of a facility using a.
toxic chemical requires careful consideration of numerous factors, including
other processes in the area, the proximity of population centers, prevailing
winds, local terrain, and natural external events such as flooding.
The siting of facilities and individual equipment items within facilities
should minimize personnel exposure, both plant and public, in the event of a
release. Since other siting considerations are also important, there may be
trade-offs between this requirement and others in a process, some directly
related to safety. Siting should provide ready ingress or egress in the event
of an emergency and also take advantage of barriers, either man-made or
natural,'that could reduce the consequences of releases.
Layout refers to the placement and arrangement of equipment in the
process facility. Some general layout considerations pertinent to accidental
release prevention include:
• Inventories of a toxic chemical should be kept away from sources of
fire or explosion hazard;
• Vehicular traffic near toxic chemical process or storage areas
should be minimized;
• Where such traffic is necessary, precautions should be taken to
reduce the chances for vehicular collisions with equipment, espe-
cially pipe racks carrying the toxic chemical across or next to
roadways;
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• Piping containing a Coxic chemical preferably should not be located
adjacent to other piping that is under high pressure or temperature;
• Toxic chemical storage facilities should be segregated from the main
process unless the hazards of pipe transport are determined to
outweigh the hazard of the storage for site-specific cases;
• Toxic chemical storage facilities should be situated away from
control rooms, offices, utilities, storage, and laboratory areas;
• In the event of an emergency, there should be at least two means of
access to the facility for emergency vehicles and crew.
Various techniques available for formally assessing plant layout should be
considered when planning high-hazard facilities handling a. toxic chemical (2).
These techniques allow a systematic evaluation of key siting and layout
factors.
2.2.3 Protection
Pre-release protective systems include measures taken to capture or
destroy a toxic chemical before there is an uncontrolled release to the
environment after a release from primary containment has occurred. This
subsection describes three types of protection technologies for secondary
containment, capture, neutralization, or destruction:
• Enclosures;
• Flares; and
• Scrubbers.
Table 2-3 lists air toxic protection technologies applicable to the various
toxic chemicals discussed in this manual. A brief discussion of these
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TABLE 2-3. SOME AIR TOXIC RELEASE PROTECTION TECHNOLOGIES APPLICABLE TO
TOXIC CHEMICALS DISCUSSED IN THIS MANUAL
Chemical
(physical state) a
Acrylonitrile (L)
Benzenes rsonic Acid (S)
Benzotrichloride (L)
Chloroacetic Acid (S)
Furan (L)
Hydrazine (L)
Hydrogen Sulfide (G)
Mechlorethamiae (L)
Methiocarb (S)
Methyl Bromide (G)
Sodium Azide (S)
Tetraethyl Tin (L)
Trichloroacetyl Chloride
Enclosure
X
X
X
X
X
X
X
X
X
X
X
X
(L) X
Protection
Venturi
Flare Scrubber
X X
X
X
X
X X
X X
X X
X
X X
X
X
X
Technology
Packed Bed Spray Tower
Scrubber Scrubber
X X
X
X X
X
X X
X X
X X
X
X X
X
X
X X
Notes:
aPhysical state of 70°F. S = Solid. L = Liquid. G = gas.
The applicability of a protection technology depends on the physical state.
It should be borne in mind that solids and liquids at ambient conditions can
still cause a vapor air toxic hazard at elevated temperatures as may be found
in some processes. Some air toxic vapors will also be caused by liquids at
ambient conditions. Also, some solids may form fine dusts or fumes which
could be captured by scrubbers prior to an accidental release
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protection technologies follows. More detailed information on these systems
can be found in other volumes in this series.
Enclosures•-
Enclosures refer to containment structures that capture any toxic
material spilled or vented from storage or process equipment, thereby prevent-
ing immediate discharge of the chemical to the environment. The enclosures
contain a spilled liquid or solid until it can be transferred to other
containment, discharged at a controlled rate that would not be injurious to
people or to the environment, or transferred at a controlled rate to a
scrubber for neutralization or a flare for destruction.
Specially designed enclosures for either storage or process equipment do
not appear to be widely used for temporary containment of toxic materials.
The desirability of an enclosure depends partly on the frequency with which
personnel must be involved with the equipment. A common design rationale for
not having an enclosure where toxic materials are used is to prevent the
accumulation of toxic concentrations of a chemical within a work area. Where
flammable materials are involved, an additional concern is the accumulation of
flammable gases or vapors in the range of explosive limits. However, if the
issue is protecting the community from accidental releases, then total enclo-
sure may be appropriate. Enclosures should be equipped with continuous
monitoring equipment and alarms. Alarms should sound whenever lethal or
flammable concentrations are detected. Enclosures for flammable materials
should be equipped with adequate fire protection.
Care must be taken when an enclosure is built around pressurized equip-
ment. It would not be practical to design an enclosure to withstand the
pressures associated with the sudden failure of a pressurized vessel. An
enclosure would probably fail because of the pressure created from such a
release and could create- an additional hazard. If an enclosure is built
around pressurized equipment, it should be equipped with some type of
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explosion protection, such as rupture places designed Co fail before Che
encire structure fails.
Suitable containment structures might be concrete or corrugated metal
buildings. An enclosure would have a ventilation system designed to draw in
air when the building is vented to a scrubber or flare. The bottom section of
a building used for stationary storage containers should be liquid-tight to
retain any toxic material that might be spilled. Buildings around rail car
unloading stations do not lend themselves to effective liquid containment;
however, Che floor of Che building could be excavated several feet below the
track level while Che Cracks are supporced ac grade in Che center, creating a
contained space.
While the use of enclosures for secondary containment of spills or
releases of toxic material are not widely used, they can be considered as a
possible protection technology for areas near especially sensitive receptors.
Flares--
Flares are used in Che chemical process industries Co dispose of inter-
mittent emissions of some toxic waste gases from process upsets. The flare
burns Che waste gases, forming less toxic produce gases. Flares are distin-
guished from other process combustion devices, such as incinerators, by their
design to handle extreme flow race variations and their unenclosed combustion
zone.
The two common styles are elevated and enclosed ground flares. The
height of an elevated flare (often several hundred feed) is determined by
safety considerations for the surrounding areas because of Che high tempera-
tures and heat radiation at maximum gas rates. Enclosed ground flares consist
of stages of multiple burner assemblies surrounded by refractory walls and
acoustical insulation. They are generally used for small Co medium flow rate
applications. The elevated flare is used for larger gas flows. Often, an
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enclosed ground flare will be used In conjunction with an elevated flare for
optimum operation.
Several design characteristics of flare systems are important when
considering their use as protection against accidental chemical releases. The
design of flares is dictated by the desire to:
• Operate the flare safely over a wide range of gas flowrates; and
• Have acceptable emissions of radiant heat, toxic and flammable
materials, and noise.
A fundamental flare design variable is exit velocity. At maximum flow, the
flame should not leave the burner tip or be blown out. This is achieved by
limiting the exit velocity. EPA has published a set of flare requirements
calling for 98 percent destruction efficiency of flared chemicals using a
steam assisted flare (5). The addition of an accidental release discharge to
an existing flare must not cause the maximum flow to be exceeded, which is
especially of concern when venting toxic materials since exceeding the maximum
design flow could lead to flame-out and an uncontrolled toxic discharge.
Flares can be useful protection against accidental releases of some toxic
materials. However, because of potentially dangerous secondary hazards, their
use requires a thorough analysis of each application.
A flare system can be used to protect against accidental releases in two
ways. The first is to use an existing flare system. The second is to use a
dedicated "emergency" system. In essence, a flare system is a pipe transport-
ing flammable gases to a flame at the exit. As long as the flame remains at
the end of the pipe, the system operates safely. The flame can enter the pipe
if air or oxygen is present in the fuel above a certain concentration. In a
dedicated flare system, the entire collection network would have to be
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continually purged to prevent the risk of an explosion when an accidental
release occurred.
Since the flare collection system operates under a positive pressure
(above atmospheric), release rates through an emergency relief valve discharg-
ing to a flare may be less than direct discharge to -the atmosphere because of
the increased back pressure. In some instances, it is conceivable chat the
slight delay in reducing the pressure in a vessel may cause tank damage, which
may be especially important when rupture disks blow. A sudden overpres-
surization of the flare collection system because of a massive accidental
release could damage the pipes or potentially affect the venting of other
process units. Table 2-4 sunmarizes the factors thac should be considered to
prevent accidental chemical releases when using a flare system.
The rationale for using flares to protect against accidental chemical
releases is that flaring reduces the effects of -an atmospheric emission from a
process vessel. As long as the integrity.of the flare system is not compro-
mised, some lessening of the overall environmental impact would be expected.
It Is difficult to estimate the destruction and removal efficiency (DRE) of
flares because of the many variables associated with their operation. Numer-
ous studies have been conducted to determine the operational performance of
flares. Although EFA has published a set of flare requirements to ensure 98
percent or greater destruction of the gases (5), in an emergency condition
these conditions might not be met.
Because of the variable flow capacity, high temperature, high gas veloc-
ity, and usual remote location, using a flare as a protection measure for
accidental chemical releases of some toxic materials can be highly effective.
Small or isolated vessels that use a process that does not require normal
venting of a flammable gas, and that employ relief valves and rupture disks
that may have never been used, can be connected to a flare system to prevent
accidental releases.
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TABLE 2-4. IMPORTANT CONSIDERATIONS FOR USING FLARES TO PREVENT
ACCIDENTAL CHEMICAL RELEASES
Maximum flow rate - will it cause a flame blowout?
Possibility of air. oxygen, or other oxidant entering system?
Is gas combustible - will it smother the flare?
Will reactions occur in the collection system?
Can liquids enter the collection system?
Will liquids flash and freeze, overload knockout drum or cause rain
fire?
Is back pressure of collection system dangerous to releasing vessel?
Is releasing vessel gas pressure or temperature dangerous to
collection system?
Will acids or salts enter the collection system?
Will release go to an enclosed ground or elevated flare?
If toxic is not destroyed, what are the impacts on the surrounding
community?
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Scrubbers--
Scrubbers are a traditional method for absorbing toxic materials from
process streams. They can be used to control the release of the toxic
materials from vents and pressure relief discharges from storage equipment,
process equipment, or secondary containment enclosures, and they can be used
for many gases, vapors, or particulate matter.
A toxic material discharge can be contacted with an aqueous scrubbing
medium in any of several types of scrubbing devices. Depending on the toxic
material, an alkaline or acidic solution may be required for effective
absorption because absorption rates with water alone would require high
liquid-to-gas ratios. However, water scrubbing can be used in a make-shift
scrubber in an emergency.
Examples of scrubber types that might be appropriate include spray
towers, packed bed scrubbers, and Venturis. Other types of special designs
might be suitable. Whichever type pf scrubber is selected, a key considera-
tion for emergency systems is the design flow rate. A conservative design
would use the maximum rate expected from an emergency.
Whatever type of scrubber is selected, a complete system includes the
scrubber itself, a liquid feed system, and reagent makeup equipment. If such
a system is used to protect against emergency releases, how it would be
activated in time to respond to an emergency load must be considered. The
approach of some process facilities is to maintain a continuous circulation of
scrubbing liquor through the system, which may be practical where the emer-
gency scrubber also serves as a routine vent scrubber. For many facilities,
this would not be practical and the scrubber system might be tied into a trip
system that would turn it on when needed.
Venturi scrubbers have an advantage when the scrubbing system must be
activated by a trip system. A venturi scrubber can create its own draw of
vapor by the flow of the liquid. Thus a trip system need only turn on the
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flow of liquid to the scrubber, rather than turn on the flow of liquid and
start up a blower, as would be required by other types of scrubbing systems.
Another approach is the drowning tank, where the toxic material vent is
routed to the bottom of a large tank of uncirculating scrubbing medium. The
drowning tank does not have the high contact efficiency of the other scrubber
types; however, it provides substantial capacity on demand as long as the back
pressure of the hydrostatic head does not create a secondary hazard--by
impeding an overpressure relief discharge, for example.
2.2.3 Post-Release Mitigation
Post-release mitigation includes measures taken to reduce the severity of
the adverse effects of a hazardous chemical release. If, in spite of all
precautions, a toxic chemical release occurs, the first priorities are to
rescue workers in the immediate vicinity of the accident, to evacuate persons
from downwind ar«as, to determine the source of the release, and to stop the
release if possible. The next concern is to divert, limit, or disperse the
spilled or released chemical to reduce the atmospheric concentration and the
area affected by the chemical. The mitigation technology chosen for a
particular chemical depends on the specific properties of the chemical i.e.,
its flammability, toxicity, reactivity, and those properties that determine
its dispersion characteristics in the atmosphere.
A post-release mitigation effort requires that the source of the release
be accessible to trained plant personnel; therefore, the availability of
adequate personnel protection is essential. Personnel protection will typi-
cally include such items as portable breathing air and chemically resistant
protective clothing.
Mitigation technologies include such measures as physical barriers,
basins, water sprays and fogs, and foams. Table 2-5 lists typical mitigation
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TABLE 2-5. TYPICAL MITIGATION TECHNOLOGIES APPLICABLE TO
TOXIC CHEMICAL RELEASES
fhamVal
(physical state)8
Actylonitrile (L)
Benzenearsonic Acid (S)
Chloroacetic Acid (S)
Rydrazine (L)
Mechlorethamine (L)
Methiocarb (S)
Methyl Bromide (G)
Sodium Azide. (S)
Tetraethyl -Tin (L)
Trichloroacetyl Chloride CL)
Hydrogen Sulfide (6)
Fur an (L)
Benzotrichloride (L)
Mitigation
Technology
Flotation Water Sprays
Concainnent Devices and and/or
Dikes
X
X
X
X
X
X
X
X
X
X
X
X
X
Basin Foaas
X X
X X
X X
X X
X X
X X
X X
X X
X
Stean Curtains
X
X
X
X
X
X
X
Alkaline
Sprays
X
X
aPhysical state of 70°F. S = solid. L = liquid. G = gas.
The physical state of the chemical in the environment at the time of release
partly determines the applicability of the mitigation technology. For
example, while some materials may be solid at ambient conditions, if
discharged as a five particulate emission water sprayer might still be
applicable for water soluble materials.
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technologies chat may be applicable to releases of the various toxic chemicals
discussed in this manual.
In general, techniques used to disperse or control vapor emissions should
emphasize simplicity and reliability. In addition to the mitigation techni-
ques mentioned above, physical barriers such as buildings and rows of trees
will help control the vapor cloud and its movement. Additional information
can be found in other volumes in this series.
Physical Barriers and Basins--
Specific types of barriers and basins include excavated basins, natural
basins, earth, steel, or concrete dikes, and high impounding walls. These
measures are generally used in secondary containment systems which are de-
signed to prevent the accidental discharge of toxic material from spreading to
uncontrolled areas. The type of containment system best suited for a par-
ticular storage tank or process unit will depend on the risk associated with
an accidental release from that location. The inventory of toxic material and
its proximity to other portions of the plant and to the community should be
considered when selecting a secondary containment system. The secondary
containment system should be able to contain spills with a minimum of damage
to the facility and its surroundings and with a minimum potential for escalat-
ing the event.
Secondary containment systems for toxic chemical storage facilities
commonly consist of one of the following:
• The storage tank area drains to an impoundment basin with a capacity
equal to that of the largest tank served; or
• The storage tank area is surrounded by a dike, with the diked area
volume equal to that of the largest tank served.
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The most common type of containment system is a low-wall dike surrounding
one or more storage tanks. Generally, to reduce risk no more than one tank is
enclosed within a diked area. Dike heights usually range from three to twelve
feet, depending on the area available to achieve the required volumetric
capacity. The dike walls should be liquid-tight and able to withstand the
hydrostatic pressure and temperature of a spill. Low-wall dikes may be
constructed of steel or concrete. If earthen dikes are used, care must be
taken to ensure that the toxic material cannot leak through the dike. Piping
should be routed over dike walls, and penetrations through the walls should be
avoided if possible. Vapor fences may be situated on top of the dikes to
provide additional vapor containment. If more than one tank is in the diked
area, the tanks should be situated on beams above the maximum liquid level
attainable in the impoundment.
A low-wall dike can effectively contain the liquid portion of an acci-
dental release and keep the liquid from entering uncontrolled areas. By
preventing the liquid from spreading, the low-wall dike can reduce the surface
area of the spill. Reducing the surface area reduces the rate of evaporation.
The low-wall dike will partially protect the spill from wind; this can reduce
the rate of evaporation. A dike with a vapor fence provides extra protection
from wind and may be even more effective at reducing the rate of evaporation.
While a low-wall dike reduces the effects of an evaporating liquid, it does
not for a gaseous release.
A low-wall dike can also be used to surround areas where toxic solids are
stored to prevent contact with uncompatible materials in the event of a liquid
spill elsewhere in the facility. If materials that would react violently with
the toxic material are stored within the same diked area, the dike will
increase the potential for mixing the materials in the event of a simultaneous
leak. A dike also limits access to the tank during a spill.
A remote impoundment basin for capture of liquid spills is well-suited'
where a relatively large site is available. The flow from the spill is
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directed to the basin by dikes and channels. For materials with a high vapor
pressure and high acute toxicity, the trenches that lead to the remote basin
as well as the basin itself can be covered to reduce the rate of evaporation.
The spilled liquid is removed from the immediate tank area, allowing access to
the tank during the spill and reducing the probability that the spilled liquid
will damage the tank, piping, electrical equipment, pumps or other equipment.
In addition, the covered impoundment will reduce the rate of evaporation from
the spill by protecting the spill from wind or heating from sunlight.
High-wall impoundments are an alternative secondary containment system
"for selected situations. Circumstances that may warrant their use include
limited storage site area, the need to minimize vapor generation rates, and/or
a need to protect the tank from external hazards. Maximum vapor generation
rates will generally be lower for a high-wall impoundment than for low-wall
dikes or remote impoundments because of the reduced surface contact area.
These rates can be further reduced by using insulation on the wall and floor
in the annular space. High impounding walls may be constructed of steel,
reinforced concrete, or prestressed concrete. A weather.shield may be in-
stalled between the tank and wall with the annular space remaining open to the
atmosphere. The available area surrounding the storage tank will dictate the
minimum height of the wall. For high-wall impoundments, the walls may be
designed with a volumetric capacity greater than that of the tank to contain
the vapors. Increasing the height of the wall also raises the elevation of
any released vapor.
One disadvantage of these dikes is that the high walls around a tank may
hinder routine external observation. Furthermore, the closer the wall is to
the tank, the more difficult it becomes to reach the tank for inspection and
maintenance. As with low-wall dikes, piping should be routed over the wall if
possible. The proximity of the wall to the tank may require placing the pump
outside the wall, in which case the outlet (suction) line will have to pass
through the wall. In such a situation, a low dike encompassing the pipe
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penetration and pump may be provided, or a low dike may be placed around the
encire wall.
A further type of secondary containment system is one structurally
integrated with the primary system that forms a vapor-tight enclosure around
the primary container. Many types of arrangements are possible. A double
walled tank is an example of such an enclosure. These systems may be
considered where protection of the primary container and containment of vapor
are of greatest concern. Drawbacks of an integrated system are the greater
complexity of the structure, the difficulty of access to certain components,
and the fact that complete vapor containment cannot be guaranteed for all
potential events.
Flotation Devices and Foams--
Flotation devices and foams can be used to reduce the surface area of a
spilled toxic liquid, thereby minimizing the amount of toxic vapor released to
the environment.
Flotation Devices--Placing an impermeable flotation device over a spilled
chemical is a direct, highly percent efficient method for reducing evaporation
and containing toxic vapors. Deployment, however, may be difficult in all but
small spills.
Although such devices are potentially effective, no systems are currently
available for mitigating toxic spills. The primary deterrent to their use is
the cost associated with material and dispersal equipment. Such a system
would require the dispersal of a minimum of 280 particle per square foot of
spill surface (6).
£2203,--One approach to a toxic chemical spill is dilution with water.
However, many materials are only slightly soluble in water and a large
quantity would be required for dilution. Others react violently and result in
increased boil-off. Still other form highly corrosive material when contacted
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with water. Thus, while dilution with water may be applicable for some
materials, it is not applicable for all. A water-based foam, however, is
another way to dilute a toxic material.
The use of foams in vapor hazard control has been demonstrated for a
broad range of volatile chemicals. Unfortunately, it is difficult to accu-
rately quantify the benefits of foam systems because the effects will vary as
a function of the chemical spilled, foam type, spill size, and atmospheric
conditions.
Regardless of the type of foam used, the slower the drainage rate of the
foam, the better its performance will be. A slow-draining foam will collapse
more slowly. The initial cost of a slow-draining foam may be higher than that
of other foams, but a cost-effective system will be realized in superior
performance.
Sprays'and Steam Curtains--
Water sprays and steam curtains are two mitigation technologies that
might be used with some toxic gases or vapors.
Water Soravs--Water spray systems are routinely used in the chemical
process industries for a variety of fire protection purposes. However, they
can also be used to reduce the effects of toxic and/or flammable gas or vapor
releases. Theoretical studies and experimental research have shown that such
sprays can be effective in aiding the dispersion and dilution of gas or vapor
clouds resulting from an accidental release (7,8,9,10,11,12,13,14). However,
many of the results are based on specific systems operating under a specific
set of conditions. Details concerning the overall effectiveness of these
systems are limited in scope.
A spray is defined as a dispersion of liquid droplets in a gas. Sprays
can achieve a variety of objectives including, but not limited to, the forced
dispersion and dilution of a gas or vapor, absorption of water soluble
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materials, containment of released vapor or gas In a particular area, or
diversion away from a particular area.
The spray medium is typically applied to the vapor cloud by hand-held
hoses and/or.by stationary water-spray barriers. Important factors relating
to the effectiveness of spray systems are the distance of the nozzle from the
point of release, the fog pattern, nozzle gallonage, pressure, and nozzle
rotation. If water sprays are used to mitigate toxic vapors from a diked area
containing spilled water-reactive material, care must be taken not to be
direct water into the liquid itself.
The low solubility of some materials in water limits the effectiveness of
spray systems in some circumstances. An alternative is to use a reactive
spray system such as an ammonia-injected water spray to neutralize the
release.
sypflm Curtains--Steam curtains provide an alternative to water spray
systems for reducing the effects of toxic and/or flammable gas or vapor
releases. Steam curtains ace in a manner similar to water sprays in that the
primary dispersing mechanism is the dilution of the gas or vapor with air.
However, steam curtains provide enhanced buoyancy to the toxic and/or
flammable cloud by heating the gas or vapor passing through the steam curtain.
A steam curtain consists of a horizontal steam pipe with a row of small
holes in the top, mounted near the top of a wall. When operated, a wall of
steam approximately 15 to 20 feet high is produced. The steam pipe is
designed so that all of the individual jets combine to form a continuous
curtain of steam which entrains sufficient air to dilute the gas or vapor to
below its toxic and/or flammable limit. Additionally, the steam pipe is
usually divided into sections which are individually supplied with steam from
a distribution main. This allows plant operators or an automated activation
system to select which sections of the steam curtain will be activated in the
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event of a release. In practice, steam curtains are typically controlled
manually.
Steam curtains were initially designed to dilute and contain heavy
flammable vapors and indeed steam curtains are incorporated into several
installations to prevent highly flammable materials from reaching sources of
ignition in the event of an accidental release (12). In principle, steam
curtains can also be useful in mitigating toxic and/or flammable vapors which
are heavier than air. No commercial steam curtain installations for use in
mitigating toxic releases could be found at the time this manual was prepared.
One drawback of steam curtains is that they require large quantities of
steam, typically 0.15 ton/hr per foot of curtain. Thus, steam curtains must
often be limited to small scale uses. In addition, where steam is not
available or the supply of steam is not reliable, water spray systems may be
more applicable.
2.2.4 Operation and Maintenance Practices
Quality hardware, contained mechanical equipment, and protective devices
all increase plant safety; however, they must be supported by the safety
policies of management and by constraints on their operation and maintenance.
This section describes how management policy and training, operation, and
maintenance procedures relate to the prevention of accidental toxic chemical
releases. Within the chemical industry, such practices vary widely because of
differences in the size and nature of the processes and because any determina-
tion of their adequacy is inherently subjective. For this reason, the follow-
ing subsections focus primarily on fundamental principles and do not attempt
to define specific policies and procedures.
Management Policy--
Management is a key factor in controlling of industrial hazards and
preventing accidental releases. Management establishes the broad policies and
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procedures that influence the implementation and execution of specific hazard-
control measures. These management policies and procedures must be designed
to match the level of risk in the facilities where they will be used. Most
organizations have a formal safety policy. Many make policy statements to the
effect that safety must rank equally with other company functions such as
production and sales. The effectiveness of any safety program, however, is
determined by a company's commitment to its safety plan, as demonstrated
throughout the management structure. Specific goals must be derived from the
safety policy and supported by all levels of management. Ideally, management
should establish the specific safety performance measures, provide incentives
for attaining safety goals, and commit company resources to safety and hazard
control. The advantages of an explicit policy are that it sets the standard
by which existing programs can be judged, and it is evidence that management
views safety as a significant factor.
In the context of accident prevention, management is responsible for:
• Ensuring worker competency;
• Developing and enforcing standard operating procedures;
• Adequate documentation of policy and procedures;
• Communicating and promoting feedback on safety issues;
• Identification, assessment, and control of hazards; and
• Regular plant audits and provisions for independent checks.
More discussion of the responsibilities of management will be found in
the manual on Control Technologies, part of this manual series.
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Operator Training--
The performance of operating personnel is a key factor in preventing
accidental chemical releases. Many case studies documenting industrial
incidents note the contribution of human error to accidental releases (2).
Release incidents may be caused by improper routine operating procedures, by
insufficient knowledge of process variables and equipment, by lack of
knowledge about emergency or upset procedures, by failure to recognize criti-
cal situations, and in some cases by direct physical mistake (e.g., turning
the wrong valve). A comprehensive operator training program can decrease the
potential for accidents resulting from such causes.
Operator training can include a wide range of activities and a broad
spectrum of information. Training, however, is distinguished from education
in that it is specific to particular tasks. While general education is
important and beneficial, it is not a substitute for specific training. The
content of a specific training program depends on the type of industry, the
nature of the processes used, the operational skills required, the character-
istics of the plant management system, and tradition.
Some general characteristics of quality industrial training programs
include:
• Establishment of good working relations between management and
personnel;
• Definition of trainer responsibilities and training program goals;
• Use of documentation, classroom instruction, and field training (in
some cases supplemented by simulator training); and
• Frequent supplemental training and up-to-date training materials.
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In many instances, training is carried out jointly by plant managers and
a training staff selected by management. In others, management is solely
responsible for maintaining training programs. In either case, responsibili-
ties should be explicitly designated to ensure that the quality and quantity
of training provided is adequate. Training requirements and practices can be
expected to differ between small and large companies, partly because of
resource needs and availability, and partly because of differences in employee
turnover.
Table 2-6 lists the aspects typically involved in the training of process
operators for routine process operations.
Emergency training includes topics such as:
• Recognition of alarm signals;
• Performance-of specific functions (e.g., shutdown switches);
• Use of specific equipment;
• Actions to be taken on instruction to evacuate;
• Fire fighting; and
• Rehearsal of emergency situations.
Aspects specifically addressed in safety training include (2,3):
• Hazard recognition and communication;
• Actions to be taken in particular situations;
• Available safety equipment and locations;
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TABLE 2-6. ASPECTS OF TRAINING PROGRAMS FOR ROUTINE PROCESS OPERATIONS
Process goals, economics, constraints, and priorities
Process flow diagrams
Unit operations
Process reactions, thermal effects
Control systems
Process materials quality, yields
Process effluents and wastes
Plant equipment and instrumentation
Equipment identification
Equipment manipulation
Operating procedures
Equipment maintenance and cleaning
Use of tools
Permit systems
Equipment failure, services failure
Fault administration
Alarm monitoring
Fault diagnosis
Malfunction detection
Communications, record keeping, reporting
Source: Reference 2
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• When and how to use safety equipment;
• Use and familiarity with documentation such as
- plant design and operating manuals,
. company safety rules and procedures,
- procedures relevant to fire, explosion, accident,
and health hazards,
- chemical property and handling information; and
• First aid and CPR.
Although emergency and safety programs typically focus on incidents such
as fires, explosions, and personnel safety, it is important that prevention of
accidental chemical releases and release responses be addressed as part of
these programs.
Much of Che type of training discussed above is also important for
management personnel. Safety training gives management the perspective
necessary to formulate good policies and procedures, and to make changes that
will improve the quality of plant safety programs. Lees suggests that train-
ing programs applied to managers include or define the following (2):
• Overview of technical aspects of safety and loss prevention
approach;
• Company systems and procedures;
• Division of labor between safety personnel and managers with
respect to training; and
• Familiarity with documented materials used by workers.
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Maintenance and Modification Practices--
Plant maintenance is necessary to ensure the structural integrity of
chemical processing equipment; modifications are often necessary to allow more
effective production. However, since these activities are also a primary
source of accidental release incidents, proper maintenance and modification
practices are an important part of accidental release prevention. Use of a
formal system of controls is perhaps the most effective way of ensuring that
maintenance and modification are conducted safely. In many cases, control
systems have had a marked effect on the level of failures experienced (2).
Permit systems and up-to-date maintenance procedures minimize the poten-
tial for accidents during maintenance operations. Permit-to-work systems
control maintenance activities by specifying the work to be done, defining
individual responsibilities, eliminating or protecting against hazards, and
ensuring that appropriate inspection and testing procedures are followed.
Maintenance permits originate with the operating staff. Permits may be
issued in one or two stages. In one-stage systems, the operations supervisor
issues permits to the maintenance supervisor, who is then responsible for his
staff. Two-stage systems involves a second permit issued by the maintenance
supervisor to his workforce (2).
Another form of maintenance control is the maintenance information
system. Ideally, these systems should log the entire maintenance history of
equipment, including preventative maintenance, inspection and testing, routine
servicing, and breakdown or failure maintenance. This type of system is also
used to track incidents caused by factors such as human error, leaks, and
fires, including identification and quantification of failures responsible for
hazardous conditions, failures responsible for downtime, and failures re-
sponsible for direct repair costs.
Accidental releases are frequently the result of some aspect of plant
modification. Accidents result when equipment integrity and operation are not
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properly assessed following modification, or when modifications are made
without updating corresponding operation and maintenance instructions. In
these situations, it is important that careful assessment of the modification
results be of equal priority to setting the plant on-line.
For effective modification control, there must be established procedures
for authorization, work activities, inspection, and assessment, complete
documentation of changes, including the updating of manuals, and additional
training to familiarize operators with new equipment and procedures, (2,3).
Formal procedures and checks on maintenance and modification practices
must be established to ensure that such practices enhance rather than adverse-
ly affect plant safety. As with other plant practices, procedure development
and complete documentation are necessary. However, training, attitude, and
the degree to which the procedures are followed also significantly influence
plant safety and release prevention.
The use and availability of clearly defined procedures collected in
maintenance and operating manuals is crucial for preventing accidental
releases. Veil-written instructions should give enough information about a
process that the worker with hands-on responsibility for operating or main- .
taining the process can do so safely, effectively, and economically. These
instructions not only document the path to the desired results, but also are
the basis for most industrial training programs (2,3). In the chemical
industry, operating and maintenance manuals vary in content and detail. To
some extent, this variation is a function of process type and complexity;
however, in many cases it is a function of management policy. Because of
their importance to the safe operation of a chemical process, these manuals
must be as clear, straightforward, and as complete as possible. In addition,
standard procedures should be developed and documented before plant startup,
and appropriate revisions should be made throughout plant operations.
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Operation and maintenance may be combined or documented separately.
Procedures should include startup, shutdown, hazard identification, upset
conditions, emergency situations, inspection and testing, and modifications
(2). Several authors think industrial plant operating manuals should include
(2,3,15,16):
• Process descriptions;
• A comprehensive safety and occupational health section;
• Information regarding environmental controls;
• Detailed operating instructions, including startup and shutdown
procedures;
• Upset and emergency procedures;
• Sampling Instructions;
• Operating documents (e.g., logs, standard calculations);
• Procedures related to hazard identification;
• Information regarding safety equipment;
• Descriptions of Job responsibilities; and
• Reference materials.
Plant maintenance manuals typically contain procedures not only for
routine maintenance, but also for inspection and testing, preventive main-
tenance, and plant or process modifications. These procedures include spec-
ific items such as codes and supporting documentation for maintenance and
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modifications such as codes and supporting documentation for maintenance and
modifications (e.g., permits to vork, clearance certificates), equipment
identification and location guides, inspection and lubrication schedules,
information on lubricants, gaskets, valve packings and seals, maintenance
stock requirements, standard repair times, equipment turnaround schedules, and
specific inspection codes (e.g.. for vessels and pressure systems) (2). Full
documentation of the maintenance required for protective devices is a parti-
cularly important aspect of formal maintenance systems.
The preparation of operating and maintenance manuals, their availability,
and the familiarity of workers with their contents are all important to safe
plant operations. The objective, however, is to maintain this safe practice
throughout the life of the plant. Therefore, as processes and conditions are
modified, documented procedures must also be modified.
2.2.5 Control Effectiveness
It is difficult to quantify the control effectiveness of preventive and
protective measures to reduce the probability and magnitude of accidental
releases. Preventive measures, which may involve numerous combinations of
process design, and operational measures, are especially difficult to quantify
because they reduce the probability of a release rather than a physical
quantity of chemical. Protective measures are more analogous to traditional
pollution control technologies. Thus they may be easier to quantify in terms
of their efficiency in reducing the quantity of released chemical.
Preventive measures reduce the probability of an accidental release by
increasing the reliability of process systems operations and equipment.
Control effectiveness can thus be expressed for both the qualitative and
quantitative improvements achieved. Table 2-7 summarizes what appear to be
major design, equipment, and operational measures applicable to the some
primary hazards identified for various toxic chemical applications in the U.S.
The items listed in Table 2-7 are for illustration only and do not necessarily
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TABLE 2-7. EXAMPLES OF MAJOR PREVENTION AND PROTECTION MEASURES FOR TOXIC
CHEMICAL RELEASES
Process Hazard
Prevention/Protection
External fire
Flexible connection
failures
Fusible plug failure
Human error
Container failure
Vehicular collisions
Water intrusion
Excess flow rates
Temperature control of
reactor
Heating media flow control
Cooling media flow control
Direct relief discharges
to atmosphere
Water sprays to cool exposed chemical
storage vessels; siting away from flam-
mables; refrigeration systems; heat
shield.
Minimize use; higher quality components;
operator training in proper assembly.
Inspection/certification; storage in a
containment building.
Increased training and supervision; use
of automatic systems.
Adequate pressure relief; inspection and
maintenance: corrosion monitoring; siting
away from fire and mechanical damage.
Location; physical barriers; warning
signs; training.
Pad gas drying; backflow prevention;
equipment purging with dry gas.
Enhanced flow control; limited over-
design of feed systems; fail-shut control
valves.
Redundant temperature sensing and alarms;
interlocked feed shut-off.
Enhanced flow control; redundant tempera-
ture sensing and alarms.
Enhanced flow control; redundant tempera-
ture sensing and alarms.
Emergency scrubber system; tank enclo-
sures.
Includes controls, monitors, design, layout, and training.
(Continued)
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TABLE 2-7. (Continued)
Process Hazard
Prevention/Protection
Major tank or line rupture
Failure of mixing
Overfilling
Overpressure
Corrosion
Diking; enclosure with scrubber; corro-
sion monitoring: overpressure protection;
siting away from flammables and mechani-
cal damage; inspection and non-
destructive testing; foams; water sprays.
Interlock feed shut-off on loss of mixing
power.
Redundant level sensing, alarms and
interlocks; training of operators.
Redundant pressure relief; not i'so-
latable; adequate size; discharge not
restricted.
Increased monitoring with more frequent
inspections; use of pH sensing on cool-
ing water and steam condensate loops;
use of corrosion coupons; visual
inspections; non-destructive testing.
Includes controls, monitors design, layout, and training.
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represent a satisfactory option for all cases. These control options appear
to reduce the risk associated with an accidental release when viewed from a
broad perspective. However, there are undoubtedly specific cases where these
control options will not be appropriate. Each case must be evaluated
individually.
2.2.6 Estimating Costs of Release Prevention. Protection, and Mitigation
Prevention and Protection Measures--
Preventive measures reduce the probability of an accidental release from
a process or storage facility by increasing the reliability of both process
systems operations and equipment. Along with an increase in the reliability
of a system is an increase in the capital and annual costs associated with
incorporating prevention and protection measures into a system. Costs associ-
ated with increased reliability for prevention measures are not always easy to
determine because of complex interactions between design, construction,
operation, and maintenance decisions concerning such measures. Allocation of
costs specifically to release prevention are n6t always readily separated from
costs for enhancing process operability or other improvements.
Costs for protection measures such as flares or scrubbers are easier to
determine since they are clearly add-ons to a basic process system.
For both categories of control measures, and for mitigation also, there
can be varying degrees of probability (prevention and protection) and
consequences reduction (mitigation) related to how many and what types of
control measures are part of a system. The concept of "Levels of Control"
emerges.
Levels of Control--
Prevention of accidental releases relies on a combination of technolo-
gical, administrative, and operational practices as they apply to the design,
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construction, operation, and maintenance of facilities where hazardous
chemicals are used and stored. Inherent in determining the degree to which
these practices are carried out is their cost. At a minimum, equipment and
procedures should be in accordance with applicable codes, standards, and
regulations; however, additional protection measures can be applied.
The levels of control concept is one way of assigning costs to increased
levels of prevention and protection. The minimum level is referred to as the
"Baseline" system. This system consists of the elements required for normal
safe operation and for basic prevention of an accidental hazardous release.
The second level of control is "Level 1", which includes the baseline
system plus modifications such as improved materials of construction,
additional controls, and generally more extensive release prevention measures.
The costs associated with this level are higher than the baseline system
costs.
The third level of control is "Level 2", which incorporates both the
"Baseline" and "Level 1" systems plus additional modifications such as alarm
and interlock systems designed specifically for the prevention of an
accidental release. The extra accidental release prevention measures incor-
porated into "Level 2" are reflected in its cost, which is much higher than
that of the baseline system.
At the present time there are not universally accepted levels of control;
these levels are relative attributes of a system or facility only.
When comparing the costs of the various levels of control, it is impor-
tant to realize that higher costs do not necessarily imply improved safety.
The measures must be applied correctly. Inappropriate modifications or
add-ons may not make a system safer. Each added control option increases the
complexity of a system. In some cases, the hazards associated with the in-
creased complexity may outweigh the benefits derived from the particular
2-46
-------
control option. Proper design and construction and proper operational
practices are needed to ensure safe operation.
Some examples were developed for which cost estimates were prepared to
provide some indication of how control costs might vary by level. Various
possible control measures applied to a generic "typical" storage tank system
are presented in Table 2-8. An actual system is likely to incorporate some
items from each of the levels of control.
A summary of cost estimates for the tank at the different control levels
is presented in Table 2-9. From the table it can be seen that significant
cost differences can occur from different levels of control. Selection of an
appropriate control level would involve an evaluation of the cost
effectiveness or how much probability and consequences reduction could be
achieved for each cost increment of additional controls. Further examination
of this topic is. beyond the scope of this study. The example is provided only
to make the user aware that there can be varying economic implications of
various' levels of release prevention in a manner analogous to pollution
controls.
2-47
-------
TABLE 2-8. EXAMPLE OF LEVELS OF CONTROL FOR GENERIC TOXIC CHEMICAL
STORAGE TANK3
Process: Fixed storage tank
10.000 gal capacity
Controls
Baseline
Level No. 1
Level No. 2
Flow:
Temperature:
Pressure:
Quantity:
Location:
Single check-
valve on tank-
process feed line
Add second check
valve.
Temperature indi- Add remote indica-
cator and alarm. tor
Single pressure
relief valve,
vent to atmos-
phere, provide
local pressure
indicator.
Local level
indicator and
alarm.
Away from traf-
fic, flammables,
and other hazard-
ous processes.
Add second relief
valve, secure
non-isolatable
installation; vent
to scrubber.
Add remote level
indicator.
Same
Add a reduced-pressure
device with internal
air gap and relief
vent to scrubber.
Add redundant sensors
and alarms.
Add rupture disks
under relief valves;
provide local pressure
indication on space
between disk and
valves; vent to
scrubber.
Add level alarm. Add
high-low level inter-
lock shut-off for both
inlet and outlet
lines.
Same
Materials of
Construction:
Vessel:
Carbon steel.
Tank pressure
specification
225 psig.
Carbon steel with
increased corrosion
allowances. (1/8
inch)
Tank pressure
specification
300 psig.
Monel*
Tank pressure
specification
375 psig.
(Continued)
2-48
-------
TABLE 2-8 (Continued)
Process: Fixed storage tank
10.000 gal capacity
Controls
Baseline
Level No. 1
Level No. 2
Piping:
Process
Machinery:
Enclosures;
Sch. 40 carbon
steel
Sch. 80 carbon
steel.
Centrifugal pump. Centrifugal pump,
carbon steel.
stuffing box
seal.
None
Monel* double
mechanical seal.
None
Sch. 80 Monel®.
Magnetically-coupled
centrifugal pump
Monel*.
Steel building.
Diking:
Scrubbers!
Mitigation:
3 ft high dike.
None
None
3 ft. high dike.
Top of tank
height. 10 ft.
Water scrubber for Alkaline scrubber for
relief and building relief and building
vents. vents.
Water sprays.
Alkaline water sprays
and barriers.
a The examples in this table are appropriate for many, but not all applica-
tions. This is only an example system. The design must be suited to fit
the specific service.
A reduced pressure device is a modified double check valve.
2-49
-------
TABLE 2-9. SUMMARY COST ESTIMATES OF POTENTIAL LEVELS OF CONTROLS FOR TOXIC
CHEMICAL STORAGE TANK
Storage Tank;
Fixed Tank with
10.000 Gallon Capacity
Level of
Control
Baseline
Level No. 1
Level No. 2
Total
Capital Cost
(1986 $)
210.000
506.000
767.000
Total
Annual Cost
(1986 $/yr)
25.000
60.000
91.000
2-50
-------
SECTION 3
INDIVIDUAL CHEMICAL SUMMARIES
This section examines the specific hazards associated with the manufac-
ture, use, and storage of 13 toxic chemicals selected from the SARA Section
302(a) list of "extremely hazardous substances." Chemicals discussed in this
section are: acrylonitrile, benzenearsonic acid, benzotrichloride,
chloroacetic acid, furan, hydrazine, hydrogen sulfide, mechlorethamine,
methiocarb, methyl bromide, sodium azide, tetraethyl tin, and trichloroacetyl
chloride. Physical properties, chemical properties, toxicological and health
effects, manufacturing processes, and hazards during manufacturing, use, and
storage are presented for each chemical. Each chemical summary is an overview
of major characteristics of each chemical and its processes that have a
bearing on accidental releases. Most of the chemicals can be manufactured by
more than one process, and have multiple uses, also involving numerous
processes. Scope limitations for this study precluded examination of all
processes, but the basic principles discussed in Section 2 as well as the
chemical specific examples given here should be sufficient for a qualified
individual to extend these principles to new situations that might be
encountered. A table, shoving examples of potential hazard locations,
hazardous conditions, and process controls which can be used to reduce the
hazard is presented for each chemical.
The individual chemical summaries of this section are to be used in
conjunction with Section 2 of this manual for the evaluation of a facility
manufacturing, using or storing one of the 13 chemicals. The information in
Section 2 was presented there in order to minimize repetition in each chemical
summary of generic considerations for release prevention, protection, and
mitigation.
3-1
-------
AcryLonicrile
3.1 ACRYLONITRILE
Acrylonitrile is an important chemical raw material in the plastics
industry. It is used primarily to manufacture fibers, but also resins,
elastomers, and intermediates for other polymeric materials.
All current U.S. manufacture of acrylonitrile is based on the Sohio
ammonidation process. In 1983, 2,146 million pounds of acrylonicrile were
manufactured at five sites ranging in capacity from 300 to 460 million pounds
per year (17). At that time, the projected demand for 1987 was 1,590 million
pounds (18).
3.1.1 Chemical Characteristics
Physical Properties and Hazards--
Arcylonitrile is a colorless liquid at common room temperatures (65-75"F)
with'a characteristic odor described sometimes as similar to peach seeds.
Table 3*1 lists the physical properties of acrylonitrile.- Acrylonitrile is
soluble in water up to 7.3Z by weight at 68'F (19). It is miscible with
numerous solvents including acetone, benzene, carbon tetrachloride, toluene,
diethy1 ether, ethyl acetate, and methanol. Acrylonitrile vapor is more dense
than air at the same temperature and will tend to stay close to the ground
when released to the atmosphere. Liquid acrylonitrile expands slightly with
heating. Liquid-full equipment with little or no vapor space above the liquid
poses a containment failure hazard from thermal expansion of the liquid.
Chemical Properties and Hazards--
Acrylonitrile is a relatively reactive chemical because of both an
unsaturated carbon bond and an active nitrile group in the molecule. The most
striking chemical characteristic of acrylonitrile is its ability to spontane-
ously polymerize in storage. Commercial acrylonitrile usually contains
polymerization inhibitors.
3-2
-------
Acrylonitrile
TABLE 3-1. PHYSICAL PROPERTIES OF ACRYLONITRILE
Reference
CAS Registry Number 107-13-1
Chemical Formula C,H,N
Odor faintly pungent 19
Molecular Weight 53.06
Normal Boiling Point 171.14 °F & 14.7 psia 20
Melting Point -118.4 «F 20
Liquid Specific Gravity (H.0=l) 0.807 S 68 °F 19
Vapor Specific Gravity (air=l) 1.83 19
Vapor Pressure 1.75 psia S 68 °F 21
Vapor Pressure Equation8': 21
Where: Pv = vapor pressure, mm Hg
T = temperature. °C
A = 7.03855. a constant
B = 1.232.53. a constant
C = 222.47. a constant
Liquid Viscosity 0.34 centipoise S 77 °F 19
Solubility in Water 7.3% by weight 19
Specific Heat at Constant Pressure 0.50 Btu/(lb-°F) 19
Latent Heat of Vaporization 262 Btu/lb 21
Liquid Surface Tension 27.3 dynes/cm 9 75.2 °F 20
Heat of Combustion 759.000 Btu/lbmole 20
Autoignition Temperature 896 °F 20
(Continued)
3-3
-------
Acrylonitrile
TABLE 3-1 (Continued)
Reference
Explosive Range. Volume Z in 22
air e 1 atm and 77 °F 2.6 min.
17.5 max.
Flashpoint, TCC (ASTM D-56) 32 °F 22
Properties useful in determining other properties from physical property
correlations.
Critical Temperature 475 °F 20
Critical Pressure 513 psia 20
Critical Density 16.44 lb/ft3 19
aThis equation yields a vapor pressure of 16.3 psia rather than 14.7 psia at
the. boiling point. No explanation of this discrepancy was provided in the
reference for vapor pressure but may be due to curve fit averaging of
experimental data.
3-4
-------
Aerylonicrile
Chemical characteristics of acrylonitrile that could contribute to an
accidental release hazard include:
• Flammability • Acrylonitrile ignites readily and can form
explosive mixtures in air at concentrations from 2.6 to 17.5
percent by volume of acrylonitrile.
• Polymerization - Pure acrylonitrile can undergo spontaneous
polymerization, especially in the absence of oxygen or on
exposure to light. The self-polymerization reaction is
exothermic and the heat released will promote further polymer-
ization. The polymerization reaction occurs violently in the
presence of strong bases.
• Formation of toxic combustion products - When acrylonitrile is
heated or burned, highly toxic hydrogen cyanide gas and nitro-
gen oxides are formed.
Acrylonitrile is reported to be especially reactive when exposed to
strong acids, amines, alkalis, strong oxidizers, copper, and copper alloys
(23).
Toxicological and Health Effects--
Acrylonitrile is highly toxic and may be fatal by ingestion, inhalation,
and skin absorption. The Occupational Safety and Health Administration (OSHA)
regulates acrylonitrile as a carcinogen, and proper use of acrylonitrile must
be in conformance with Sec. 1045, Part 1910 of Title 29 of the Code of Federal
Regulations. Appendices to these regulations detail recommended safety
equipment and procedures. Acute acrylonitrile poisoning results in symptoms
similar to cyanide poisoning, which include: irritation of the eyes and nose,
limb weakness, breathing difficulty, dizziness, impaired Judgement, nausea,
collapse, irregular breathing, convulsions, and possible death by cardiac
arrest. Prolonged exposure can result in collapse, irregular breathing,
convulsions and death as a result of tissue anoxia (lack of oxygen) and
cardiac arrest. The IDLH (immediate danger to life and health) concentration
3-5
-------
Acrylonicrile
for acrylonicrile is 4,000 ppm. The oral lethal dose for humans is approxi-
mately 50-500 mg/kg (between 1 teaspoon and 1 ounces) for a ISO pound person)
(24). The LD_0 for racs via ingescion is 78 mgAg (25). Table 3-2 summarizes
of some additional exposure limits for acrylonitrile.
3.1.2 Facility Descriptions
This subsection briefly describes the manufacture and uses of acrylo-
nitrile in the United States. Major process hazards associated with acciden-
tal releases are discussed in Section 3.1.4.
Acrylonitrile Manufacture--
All of the acrylonitrile in the United States is manufactured by the
Sohio process. Other processes used worldwide resemble the Sohio process in
their basic configuration.
The Sohio process uses the vapor-phase catalytic air oxidation of
propylene and ammonia in a fluidized bed. Figure 3-1 illustrates a typical
manufacturing process. A mixture of ammonia, propylene. and air are fed in
stoichiometric amounts to a reactor operating at 750-900 *F and 1 to 3 atmos-
pheres of pressure (19). The residence time is usually a few seconds. The
reaction typically yields about 0.8 pounds of acrylonitrile per pound of
propylene fed. Acetonitrile and hydrogen cyanide are by-products (19).
(These are also toxic chemicals.) The heat of reaction is recovered as steam.
The product stream from the reactor is sent to a countercurrent absorber.
Water in the absorber cools and scrubs acrylonitrile and byproducts from the
product stream, leaving a nitrogen off-gas which is vented from the absorber.
The aqueous stream from the absorber is fed to a recovery column. The
column removes acetonitrile and water by extractive distillation and sends the
acrylonitrile-hydrogen cyanide stream overhead to the lights column. The
acetonitrile is removed from the water in the acetonitrile fractionator.
Crude hydrogen cyanide is removed from the crude acrylonitrile as the overhead
3-6
-------
Acrylonitrile
TABLE 3-2. EXPOSURE LIMITS FOR ACRYLONITRILa
Concentration
Limit (ppm) Description Reference
IDLH 4.000 The concentration defined as posing an 23
immediate danger to life and health (i.e.
causes irreversible toxic effects for a
30-minute exposure).
PEL 2 A time-weighted 8-hour exposure to this 23
concentration, as set by the Occupational
Safety and Health Administration (OSHA).
should result in no adverse effects for
the average worker.
TC-. 16 This concentration is the lowest published 20
concentration causing toxic effects (irrita-
tion) for a 20-minute exposure.
LC_O 570 This concentration is the lowest published 20
lethal concentration for a human over a
1-hour exposure.
3-7
-------
By-product
«f Propytene »
Ammonia »
High Pressure
Steam
|
Reactor
I 4
J I
i
Baler
Feed
Water
van
t>Atm
Water
|
Scrubber
1
1
IQl
osp
1
IS
here
Reco
Colu
1
1
Wa
very
mn
ler
(
•— i
hslil
Col
Cyanide
•a"0" Ac rv Ion it rile
j Product
Product
Column
| Heavy
"~ Impurities
Crude
IAceioniinle
Acetoniinle
"*" Fractionalor
_J
Figure 3-1. Conceptual flow diagram of Sohio aerylonltrlle manuf.icLurinn process.
Adapted from: Reference 19
o
H-
n
H.
h-
ID
-------
Acrylonicrile
in Che lights column. The crude acrylonitrile bottoms is sent to the product
column where purified acrylonitrile is recovered as the overhead. A heavy
impurities stream is sent to waste.
By-products such as hydrogen cyanide and acetonitrile are sometimes
incinerated after recovery if there is a commercial oversupply of these
chemicals. Excess ammonia is vented or may be converted to ammonium sulfate
for disposal. Aqueous wastes containing cyanides and sulfates are often
disposed of by incineration or deepwell injection.
Acrylonitrile Consumption--
The major use of acrylonitrile in the United States is for the manu-
facture of acrylic fibers, which accounts for about half of the U.S. consump-
tion. Table 3-3 presents a breakdown of typical end uses of acrylonitrile.
TABLE 3-3. ESTIMATED END USE PATTERN OF ACRYLONITRILE
End Use Percent
Acrylic Fibers 51
ABS/SAN Resins 18
Adiponitrile 14
Acrylamide 5
Nitrile Elastomers 3
Other 9
Source: Reference 18
Release hazards exist with each of the end-use processes just as they do
with the fundamental manufacturing processes.
3-9
-------
Acrylonicrile
Acrvltc Fibers--In fiber produccion, acrylonicrlle is polymerized by
three processes: aqueous heterogeneous polymerization, solution polymeriza-
tion, and mass or bulk polymerization. A typical aqueous heterogenous poly-
merization process is shown in Figure 3-2. In this process, acrylonitrile
monomer, water and an initiator are fed to a continuously stirred overflow
reactor that operates at one atmosphere and 85-160 °F (19). A separation
process removes the polymer from the mixture before it is spun into fiber.
Solution polymerization is similar to aqueous heterogenous polymerization
except it eliminates the separation step by producing a polymer suitable for
wet or dry spinning. Solvents used include dimethyl formamide and dimethyl
sulfoxide.
Mass or bulk polymerization is also used to prepare acrylic polymers.
The rate of polymerization is carefully controlled so that an easily stirred
solution is maintained, thus preventing overheating that may lead to poten-
tially explosive auto-catalytic polymerization.
ABS Resins--ABS resins are produced using emulsion, suspension, or bulk
processes. Emulsion and suspension processes have historically been the
dominant routes for ABS resins. However, bulk processes are also used.
A typical emulsion process is illustrated in Figure 3-3. In this pro-
cess, a batch reactor operating at 40-160 *F produces a polybutadiene latex.
In the next two reactors, styrene and acrylonitrile are grafted onto the
polybutadiene latex as a styrene-acrylonitrile (SAN) copolymer. The grafted
polymer may be blended with emulsion SAN copolymer to produce an ABS resin
with the desired rubber content. The emulsion resins are recovered by coagu-
lation procedures.
The suspension process differs from the emulsion process in that it
starts with a "pre-poly" step in which lightly linked polybutadiene rubber is
dissolved in monomers to produce a solution free of cross-linked rubber gels.
3-10
-------
*
Polymerization ~|
Monomor >— - Reactor |
t
X,
CM
Wa
1 Slurry
1 Tank
lef . _ » Monomer n
Recovery * °'»«"
1
Product Polymer
Figure 3-2. Conceptual flow diagram of typical acrylic fiber manufacturing process.
Adapted from: Reference 19
o
H-
H-
(-•
n
-------
Slyrane.
acrytonitrile.
AmioxKtani.
coagulant.
•learn
w
I
•-•
10
Buladiena
emutailiera,
initiators.
water
emutoihera, — —
initiators
Polytauiadiene
Latex Reactor
1
ABS Latex
Reactor
CO&QUl&tOf
Additional
Finishing
Processes
Figure 3-3. Conceptual flow diagram of typical emulsion acryloniirile-
butadlene-styrene (ABS) resin manufacturing process.
Adapted from: Reference 19
>
n
o
9
H-
-------
Acrylonicrile
Figure 3-4 Illustrates a typical suspension process. After some mass polymer-
ization (converting 25-35 percent of monomer to polymer) and phase inversion
have taken place, the polymer syrup goes to a suspension reactor, where it is
dispersed in water and agitated, when the batch is complete, it is cooled and
dewatered.
The bulk process consists of similar "pre-poly" and reactor steps. The
polymer syrup is pumped into a specially designed bulk polymerizer operating
at 250-350*F (19). The residence time may be one to five hours. After
polymerization, the polymer goes to the devolatilizer, where unreacted monomer
is removed and recycled. The bulk process does not require dewatering, which
saves energy and avoids the need for wastewater treatment.
SAN Resins--SAN resins are produced by emulsion, suspension, or continu-
ous mass processes similar to those used in ABS resin production. The emul-
sion process produces SAN copolymers in a batch or continuous reactor system
from a mixture-of initiator-emulsifier and monomer solutions. The copolymer
is recovered by coagulation of the emulsion latex.
The suspension process for SAN resins does not contain the "pre-poly"
step, but otherwise it is similar to that for the ABS resins. The reaction
system contains monomers, chain-transfer agents, initiators, suspending
agents, and water. It produces a small polymer sphere, and the mixture is
centrifuged during dewatering.
In the continuous mass process, the feed goes to a screw reactor, where
the reaction is initiated thermally or catalytically. The highly viscous
polymeric melt has impurities removed in a devolatilizer. Instead of a screw
reactor, a stirred tank reactor may be used, but the high viscosity of the
mixture can be a problem. One option for handling the mixture would be adding
a solvent that could be removed in the devolatilizer. Although the viscous
mixture is a problem, an advantage of the continuous mass process is that it
is self-contained because it requires no wastewater treatment and minimizes
other environmental effects. From an accidental release perspective, the
3-13
-------
Acrylonllrile.
Initiators
Waler.
Suspending Agent
Slyrene
Rubber
Rubber
Dissolver
PreporynwriMr
Reactor
Suspension
Reactor
Additional
Finishing
Processes
I
*••
*•
Figure 3-4. Conceptual flow diagram ot typical suspension acrylonitrlle-
butadiene-styrene (ADS) manufacturing process.
Adapted from: Reference 19
O
p-
rt
n
H-
-------
Acrylonitrile
smaller inventory of in-process material in a screw reactor appears to be
advantageous, but temperature control with viscous materials can sometimes be
troublesome. The relative risks for acrylonitrile releases associated with
the different types of reactors depends also on the relative quantities of
acrylonitrile required in the respective systems.
ABS and SAN resins are used to make components for automobiles, recrea-
tional vehicles, pipe fittings, appliances, instrument panels, instrument
lenses, houseware items, packaging, business machines, and telephones.
Nitrile Elastomers--Nitrile elastomer (nitrile rubber) is manufactured by
emulsion polymerization techniques. Both batch or continuous processes are
used. In the batch process, measured amounts of reaction ingredients are
charged to an agitated, pressurized autoclave. The temperature is controlled
by cooling water circulating through a jacket or internal coils. The reaction
time is typically 5 to 12 hours, depending on the system (19). At the end of
the reaction tine, an inhibitor is added to the reaction vessel to stop the
reaction, which is then transferred to a stripper to remove unreacted acrylo-
nitrile. The continuous process is similar except a series of stirred tank
reactors are used to carry out the reaction.
Acrylamide--Aerylamide is manufactured by the catalytic hydrolysis of
acrylonitrile. In a typical process, an aqueous solution of acrylonitrile and
water is passed at 70-400 °F through a fixed bed catalytic reactor (19). The
reactor products, containing acrylamide and unreacted acrylonitrile, are sent
to a stripping column. Acrylonitrile and some water in the overhead are
recycled to the reactor. Acrylamide is used in paper manufacturing, waste
treatment, and some mining applications.
Adioonitrtle--Adlponierlle is manufactured principally to use as an
intermediate in the production of hexamethylenediamine. One adiponitrile
manufacturing process involves the dimerization of acrylonitrile. In electro-
lytic cell, a mixture of acrylonitrile, water, and tetralkylammonium salt
3-15
-------
Acrylonicrile
serves as Che catholyte, while sulfuric acid serves as Che anolyte. A quan-
tity of catholyte is continuously removed and adiponicrile and unreacted
acrylonitrile are recovered. The acrylonicrile is recycled back to the cell.
The cell typically operates at approximately 120-140 -F. The catholyte is
extracted with water and acrylonitrile. The extract, containing acrylonitrile
and adiponitrile, is sent to a distillation column where acrylonitrile is
removed overhead. The crude adiponitrile product is redistilled to remove
impurities and sent to storage.
3.1.3 Summary of Major Process Hazards and Control Technologies
For all processes, the accidental release risk can be reduced by applying
specific measures broadly classified as prevention, protection or mitigation
measures. The general features of these measures applicable to acrylonitrile .
or any toxic chemical, were summarily discussed in Section 2 of this manual,
and are discussed in other technical literature.
The two most significant chemical properties of acrylonitrile that
contribute to the risk of an acrylonitrile release are its ability to self
polymerize and its flammability. In addition to generic prevention measures,
specific measures for acrylonitrile are to prevent conditions that could lead
to self-polymerization, or fires and explosions.
In the processes that use acrylonitrile, the concerns parallel those for
acrylonitrile manufacture. For all of these processes, the reactor area to
which acrylonitrile is fed is a high hazard area because of the potential
relatively large inventory, especially if there is a feed control failure, and
the exothermicity of polymerization reactions. Below is a summary of hazard
areas in acrylonitrile manufacturing, use and storage processes.
Acrylonitrile Hanufacturing--
The reactor and the two product distillation columns appear to be the
highest hazard areas for potential accidental releases of acrylonitrile in the
manufacturing process. The reactor has a low inventory of acrylonitrile;
3-16
-------
Acrylonltrile
however, the reaction is exothermic and heat must be removed. This is typi-
cally accomplished by the production of steam. A loss of water flow to the
reactor could cause a loss of temperature control that could overpressure the
reactor. This in turn could cause a release through a relief valve or equip-
ment failure. The feed to the reactor includes propylene which is a highly
flammable material. A loss of composition control could cause excess feed
proportions of propylene and air. Flammable mixtures could be formed in the
reactor and/or downstream of the reactor, which could result in a fire and/or
explosion. Water leakage through heat exchanger tubes could lead to corrosion
in the reactor which could lead to equipment failure and an acrylonitrile re-
lease. Reactor failures of these types could damage other portions of the
process and could lead to an accidental release of acrylonitrile.
The product distillation columns are high-hazard locations because of the
high inventories of acrylonitrile. Loss of temperature control could result
in an overpressure of a column and a release through a relief valve or
equipment failure. A loss of temperature or composition control could cause
self polymerization, which could result in an overpressure, a relief discharge
or equipment failure and an accidental release. Another toxic release hazard
of the distillation column is hydrogen cyanide. While the scope of this
section is acrylonitrile releases, this hazard is significant enough to be
worthy of mention.
Acrylic Fiber Manufacturing--
The primary acrylonitrile accidental release hazard in acrylic fiber
production is the potential for overheating and corresponding overpressure
that could lead to a release through pressure relief or containment failure.
Overheating of a polymerization reaction could be caused by a variety of
process upsets or failures. Examples include the following: a loss of
adequate mixing resulting in uneven heat distribution with localized hot
spots; a loss of composition control resulting in a feed that has inadequate
solvent to absorb the heat of reaction and maintain the fluid level in the
3-17
-------
Acrylonicrile
reactor Co ensure adequate agitation; a loss of composition control resulting
in an excess of initiator that could result in excessive reaction rates and
heat generation; and a loss of cooling to the reactor which could also result
directly in reactor overheating.
Because of their large inventories and cyclic operation, batch
polymerization reactors may present a greater hazard than stirred tank,
tubular, or other continuous reactors which generally have a smaller inventory
for a given production rate.
ABS Resin Production--
The primary acrylonitrile release hazard for the ABS resin production
process is the same as for the polymerization processes discussed above--a
loss of temperature control. The potential for such a loss of control will be
closely tied to the particular polymer's tendency to undergo auto-catalytic
polymerization. The temperature at which such polymerization will begin, as
well as the sensitivity off this reaction to impurities, depends on specific
temperature and pressure operating conditions.
SAN Resin Production--
See Acrylonitrile Manufacturing.
Nitrile Elastomers•-
See Acrylonitrile Manufacturing.
Acrylamide--
See Acrylonitrile Manufacturing.
Adiponitrile Production--
The release hazard area for the adiponitrile process is the electrolytic
cell and acrylonitrile recovery operation. A loss of composition control
could result in a high concentration of acrylonitrile, which could result in
an overheating with auto-catalytic polymerization. The recovery operation is
3-18
-------
Acrylonicrile
a high-hazard area because of the high concentrations of acrylonitrile. Pump
or piping failures or a loss of temperature or flow control could result in an
accidental release.
Table 3-4 gives examples of possible locations, conditions, and process
hazards which could potentially lead to an acrylonitrile release, as well as
example controls for reducing the risk of such a release. The examples are
intended to be illustrative, not exhaustive. A more detailed discussion of
potential causes of releases appears in other portions of the Prevention
Reference Manual series.
3.1.4 Storage and Handling
In the United States, acrylonitrile is classified as a flammable liquid
and poison. It can be fatal if absorbed through the skin, inhaled or in-
gested. Acrylonitrile vapors can form an explosive mixture with air. Thus,
acrylonitrile should be stored in closed systems. Static electricity is a
significant hazard which requires careful attention to equipment grounding and
the use of non-sparking tools.
Table 3-5 presents a listing of materials of construction suitable for
use in acrylonitrile related processes. Carbon steel is typically used for
piping and storage vessels at ambient conditions (19). In more severe condi-
tions, stainless steel is desirable. Storage tanks should be electrically
grounded because of the flammability hazards with acrylonitrile. Any vent
lines discharging to the atmosphere should be routed through scrubbers or venc
condensers to prevent releases of toxic vapor to the atmosphere.
Because of its ability to undergo auto-catalytic polymerization, acrylo-
nitrile storage vessels should be equipped with a number of special safety
features. Some examples include:
• Continuous local and remote temperature monitors with high
temperature alarms;
3-19
-------
TABLE 3-4. EXAMPLE CONDITIONS, PROCESS HAZARDS AND HAZARD CONTROLS IN
ACRYLONITRILE MANUFACTURING AND USE
Location
Condition
Process Hazard
Leading to Release
Examples of Hazard Controls
CJ
o
Acrylonitrile
production and
polymerization
reactors
Loss of cooling
Polymerization
reactors
Acrylonitrile
storage vessels.
or polymeriza-
tion reactors
Water leakage
through heat ex-
changer tubes
Inadequate mixing
Excess acryloni-
trile
Excessive exothermic
reaction causing
overheating or over-
pressurization and
equipment -failure
Corrosion in reactor;
equipment failure and
release
Localized or general
overheating and over-
pressurization
leading to equip-
ment failure and a
release
Overfilling or over-
pressurization lead-
ing to a release
Redundant temperature sensing with
alarms and/or interlocks
Backup emergency cooling system with
redundant controls
Strict high safety maintenance, and
inspection procedures
Proper materials of construction;
increased maintenance inspection of
tubes
Agitation monitoring with alarms
Interlock feed with agitation
Emergency cooling capacity
Redundant high level alarms interlocked
to feed control
Strict high quality operating procedures
and operator training
o
9
(Continued)
-------
TABLE 3-4. (Continued)
Location
Condition
Process Hazard
Leading to Release
Hazard Controls or Monitors
Acrylonitrile pro-
cess or storage
vessel
Acrylonitrile pro-
cess or storage
vessel
Backflow of alkaline
or strongly acidic
materials
Fire or explosion
Ul
IsJ
Distillation
units for acryloni-
trile separation
and purification
Loss of condenser
cooling
Exothermic reaction;
causing overheating;
or overpressuriza-
tion with equipment
failure and release
Equipment damage
causing release
Overpressurization
equipment failure
or release through
relief valve self-
polymerization
with exothermic
reaction leading
to overheating or
ove rpressurizat ion
causing equipment
failure and release
Redundant check valves or feed tank in
line between storage vessels and
incompatible materials
Adequate fire protection and isolation of
process and storage vessles from poten-
tial sources of ignition
Inert the atmosphere in vessels
Flammable gas monitors in large quantity
storage areas
Backup temperature sensors with alarms
Interlock to shut off reboiler heat if
condenser cooling fails
Adequate relief valve sizing
o
i
H-
l->
ID
-------
Acrylonitrile
TABLE 3-5. CHEMICAL RESISTANCE OF VARIOUS METALS
TO ACRYLONITRILE
Average Penetration Per Year
Material (inch/year) Temperature
<0.002 <0.02
Aluminum X 210
Brass X 210
Bronze X 80
Carbon Steel X 100
Hastelloy-B« X 200
Hastelloy-C« X 200
Inconel* X 200
Monel* X. 200
Nickel* X 200
Stainless Steel 304 X 210
Stainless Steel 316 X 210
Tantalum X 210
Titanium X 210
Zirconium X 200
Source: Reference 26
3-22
-------
Acrylonitrile
• An emergency cooling system, typically composed of a heat
exchanger on a recirculation loop;
• An emergency stabilizer addition system ; and
• Where possible, dedicated inert gas and vent systems for the
tank. This will help prevent cross contamination with poly-
merization initiating impurities.
Samples should be routinely drawn from acrylonitrile storage tanks to
monitor the formation of polymer.
Specific features of acrylonitrile storage tanks, piping, and other
equipment are cited by one vendor of acrylonitrile (22). These include:
electrical grounding of the tanks, all welded construction, provision for
scrubbers or vent condensers for vapors, and diking to contain the full
contents of the tank if spilled. Piping should also be electrically grounded,
and butt welded or flanged connections used for piping diameters over one
inch. Pumps should be electrically grounded with explosion-proof motors. A
special note on pumps is that centrifugal pumps are preferred because acrylo-
nitrile may affect the lubricant in positive displacement pumps. Canned or
covered pumps are suggested to minimize fugitive vapor emissions.
Since acrylonitrile has recognized carcinogenic or co-carcinogenic poten-
tial, acrylonitrile-resistant protective clothing should be worn when it is
handled. Safety equipment typically includes full-face, self-contained
respirators.
Acrylonitrile is shipped by tank cars, tank truck, barges, steel drums,
and pipelines.
aAcrylonitrile suppliers should be able to recommend specific inhibitors.
3-23
-------
Benzenearsonic Acid
3.2 BENZENEARSONIC ACID
Benzenearsonic acid is reported Co be an analytical reagent for tin (24).
A review of several other technical literature sources revealed no other
information on its uses. Other common names include phenyl arsenic acid and
phenylarsonic acid (24).
3.2.1 Chemical Characteristics
Physical Properties and Hazards--
Benzenearsonic acid is a toxic, colorless, crystalline solid. It is
somewhat soluble in water and alcohol. Table 3-6 lists some physical proper-
ties of benzenearsonic acid. It is a solid at ambient conditions. From an
accidental release perspective, the hazard as a toxic dust, is a chief
concern. As a solid, the contamination of soil is possible. Its moderate
solubility in water makes, water contamination also a possibility.
Chemical Properties and Hazards--
Little information is available concerning the chemical properties and
reactivity of benzenearsonic acid; however, it is known that benzenearsonic
acid decomposes when heated to its boiling point of 320 °F, releasing highly
toxic fumes of arsenic (24). It has been reported that no information was
found in the open technical literature on stability, incompatibility with
other materials, hazardous polymerization potential, or special conditions to
avoid (24). It is also reported that this material does not burn or burns
with difficulty, and that no information was found on flash point or lower or
upper explosive limits (24). This implies that even dust explosions do not
appear to be likely with this material. The decomposition of this material to
toxic fumes on heating, however, suggests an air toxic hazard if a facility
containing this material were involved in a fire.
Toxicological and Health Effects--
Benzenearsonic acid is regarded as a deadly poison. Little information
is currently available, however, on the toxicological effects of accidental
3-24
-------
Benzenearsonic Acid
TABLE 3-6. PHYSICAL PROPERTIES OF BENZENEARSONIC ACID
CAS Registry Number
Chemical Formula
Molecular Weight
Melting Point
Specific Gravity (H_0=l)
Solubility in Water
Reference
98-05-5
202.05
320 °F. decomposes
1.760
3.3 lb/100 Ib H_0 ® 82 °F
24
24
24
3-25
-------
Benzenearsonic Acid
exposure Co benzenearsonic acid. The LD.. for rats by the oral route is 50
mg/kg' (25). Since it is an arsenic compound, some of the toxicological
effects of arsenic are likely for benzenearsonic acid. It is known that
symptoms of arsenic poisoning do not appear immediately and may be delayed for
many hours. These symptoms include a metallic taste and garlic -like odor,
skin disorders, difficulty in breathing, abdominal pain, vomiting, diarrhea,
dizziness, delirium, rapid heart beat, headache, and coma. Acute exposure can
result in death. The Occupational Safety and Health Administration (OSHA) has
set a permissible exposure limit for arsenic (PEL) of 0.5 mg/m in air (19).
3.2.2 Facility Descriptions
Benzenearsonic Acid Manufacture --
No information was found in the technical literature on the manufacture
of benzenearsonic acid.
Benzenearsonic Acid Consumption- -
Little information is available concerning Che use of benzenearsonic
acid. However, it has been reported that it is used as an analytical reagent
for tin (21). From this it can be inferred that it is probably packaged,
transported, and used in relatively small quantity containers.
3.2.3 fltmmip^v of Major Process Hazards and Control Technologies
The primary hazard of a significant accidental release of this material
appears to be from an accidental spill during handling. During manufacture,
if a crystallization or filtration step were used, it would be in these
operations that the material is likely to be present in its most concentrated
form. Generic equipment or operating failures of the type discussed in
Section 2 of this manual would be likely causes. Controls would like-wise be
generic .
3-26
-------
Benzenearsonic Acid
3.2.4 Storage and Handling
Although no specific literature information was found on storage and
handling, and direct contacts with manufacturers was explicitly prohibited in
this study, appropriate procedures would be expected to be those for any
toxic, solid chemical, which could be subject to decomposition to a toxic
vapor or fume in a fire.
Considering its toxicity, preferred handling of this material is likely
to be on a relatively small scale. As a solid it would likely be conveyed
using screw type conveyors or even manual transfer. In either case an
enclosed conveyance would prevent or reduce fugitive dust emissions, and any
venting routed to well sealed dust collection equipment would prevent or
reduce process emissions. Vent systems operating under a slight negative
pressure would be preferable to positive pressure systems.
Veil ventilated storage areas for bins, drums, or other containers can be
provided with appropriate dust collection equipment. A special consideration
is to ensure that storage areas have especially good fire protection because
of. the hazard of toxic fumes from thermal decomposition.
3-27
-------
Benzocri.chlori.de
3.3 BENZOTRICHLORIDE
Benzotrichlori.de is an inporcanc chemical intermediace used primarily co
produce another chemical intermediate, benzoyl chloride. Among other end
uses, benzoyl chloride is used in the plastics industry to produce UV light
absorbers and to initiate polymerization. Benzotrichloride is also used in
dye manufacturing processes. It is estimated that in 1982, over seventeen
thousand tons of benzotrichloride were produced in the United States (27).
3.3.1 Chemical Characteristics
Physical Properties and Hazards--
Benzotrichloride is a colorless to slightly yellow liquid at room temper-
ature (65-75 °F). It has a pungent odor and fumes (forming hydrogen chloride
vapors) when exposed to air. The physical properties of benzotrichloride are
listed in Table 3-7. Benzotrichloride is not soluble in water but is soluble
in most organic solvents such as benzene. Benzotrichloride has-a relatively
high boiling'point (417 *F) and a very low vapor pressure at room temperatures
(less than 0.01 psia at 68 *F), (27). Benzotrichloride vapor is nearly seven
times as dense as air and will tend to stay close to the ground when released
to the atmosphere.
Chemical Properties and Hazards--
The chemical properties of benzotrichloride that contribute to an
accidental release hazard include:
• Flammability - Although not classified as a flammable liquid.
benzotrichloride will autoignite in the presence of air near
its boiling point (417 *F). This means that near ambient
temperatures benzotrichloride is not likely to burn by itself,
but it will fuel a hot fire.
3-28
-------
Benzotrichloride
TABLE 3-7. PHYSICAL PROPERTIES OF BENZOTRICHLORIDE
Reference
CAS Registry Number
Chemical Formula
Molecular Weight
Normal Boiling Point
Melting Point
Liquid Specific Gravity (H.0=l)
Vapor Specific Gravity (air=l)
Vapor Pressure Equation
Solubility in Water
Latent Heat of Vaporization
Heat of Combustion
Autoignition Temperature
Flashpoint (Cleveland open cup)
98-07-7
C7H5d3
195.5
417°F ® 14.7 psia 28
22°F 28
1.370 28
6.8 28
log P = A - B 29
V T+C
where: P vapor pressure, mm Hg
T = temperature. °C (45.8C - 213.5°C)
A = 7.70437. a constant
B = 2166.280. a constant
C = 235.451. a constant
Insoluble (decomposes)
112 Btu/lb
7980 Btu/lb
412°F
260°F
30
27
30
30
30
3-29
-------
Benzotrichloride
• Reactivity with water - Benzotrichloride will react with water
to form benzole acid and hydrochloric acid. The rate of
hydrolization is enhanced in the presence of metals or their
salts. Hydrolysis will also occur when benzotrichloride is
exposed to acids or alcohols. Hydrolysis by water will occur
slowly at ambient temperatures. However, the reaction is
exothermic and will increase in speed as the benzotrichloride
is warmed.
• Polymerization - Benzotrichloride can undergo
self-polymerization when in contact with metals or cettain
acids. This reaction is exothermic.
• Corrosivity - Benzotrichloride is corrosive to most metals and
is especially corrosive when moisture is present.
Toxicological and Health Effeets--
Benzoerichloride is highly toxic by inhalation and when ingested. It is
also irritating to the eyes and skin. Death can result from exposure by
inhalation (31). No exposure limits have been established for benzotrichlor-
ide; however, one manufacturer has suggested an eight-hour time-weighted
inhalation exposure limit of 0.25 parts per million by volume in air (31).
The International Agency for Research on Cancer (IARC) has determined that
there is sufficient animal evidence and limited human evidence that benzotri-
chloride is a carcinogen (25). The LDen for rats via ingestion is 6 gin/kg
(25). Table 3-8 summarizes the reported toxicicy data.
3.3.2 Facility Descriptions
This subsection provides brief descriptions of the manufacture and uses
of benzotrichloride in the United States. Major accidental release hazards of
these processes are discussed in Section 3.3.4.
3-30
-------
Benzotrichloride
TABLE 3-8. TOXICITY DATA FOR BENZOTRICHLORIDE
Exposure
Effect
19 ppm for 2 hours
8 ppm for 2 hours
6 gm/kg
LC-_ - lethal by inhalation for rats
LC-. - lethal by inhalation for mice
LD-. - lethal by ingestion for rats
Source: Reference 25
3-31
-------
Benzotrichloride
Benzotrichloride Manufacture--
Benzotrichloride is manufactured by the thermal or photochemical chlori-
nation of toluene at 212 to 320 °F (33,34). This reaction may be carried out
either in batches or continuously. The toluene feed must be heated to near
212 °F before chlorine is introduced. Once chlorine addition has begun,
however, the reaction is exothermic and requires no additional heat to go to
completion. The chlorination efficiency in batch reactors is low and requires
several hours to go to completion (35). Efficiencies can be improved by using
multistage continuous reactors. The reaction is catalyzed with UV light, or
with a chemical catalyst such as phosphorus trichloride, or both (34).
Figure 3-5 shows a batch process for the production of benzotrichloride.
This figure also shows the subsequent batch production of benzoyl chloride,
which will be discussed later in this section. In this process, toluene is
fed to a reactor and heated with steam to its boiling point. The steam is
shut off and chlorine is added; benzotrichloride is produced. Unreacted
toluene is allowed to'boil and recondense into the reactor. The crude reac-
tion product mixture is purified by distillation.
Benzotrichloride Consumption--
The major use of benzotrichloride is for the production of benzoyl
chloride. Table 3-9 presents a breakdown of typical end uses of benzotri-
chloride, as well as some end uses of benzoyl chloride.
Benzovl Chloride--Benzovl chloride is produced by the reaction between
benzotrichloride and benzole acid. The reaction can be carried out in batches
or continuously and is chemically catalyzed using, for example, zinc chloride.
The reaction is carried out in the liquid phase, above the melting point of
benzoic acid (about 250 *F) (35). Hydrogen chloride gas is a by-product of
the reaction. The hydrogen chloride can be condensed and recovered. The
crude benzoyl chloride may be purified by vacuum distillation. Figure 3-5
illustrates a batch benzoyl chloride production process downstream of a
benzotrichloride batch production process.
3-32
-------
Benzotrichloride
TABLE 3-9. TYPICAL USES OF BENZOTRICHLORIDE
Primary Uses
Dyes
Benzoyl Chloride
Uses of Benzoyl Chloride
Herbicides
Benzoyl Peroxide (used in plastics manufacture)
Benzophenone (used in perfumes. UV light absorbers)
Glycol Dibenzoate Plasticizers (used in plastics manufacture)
Source: Reference 36
3-33
-------
Toluene A Catalyst
Followed by Chlorine
Steam
or
Water
Toluena
Redux
Condenser
__ Steam
» or
Water
UV Lights
Benzotrichlcr
Benzotrlchlorlde
Purification Column
Crude Benzotnchlonde
Benzotrlchlorlde Photoehlorinatlon
Reactor
Benzotrichloride
Product
Holding
Tank
Benzotrichloride Batch Production Process
Benzotrlchtorlde
Benzole Add
ft
Catalyst
Steam.
HCI
Condenser
Benzoyl Chloride
Purification Column
• Steam
Crude Benzoyl Chloride
Benzoyl
Chloride
Benzoyl Chloride
Production Reactor
Beuzoyl Chloride Batch Production Process
Figure 3-5. Conceptual flow diagram of benzotrichloride and benzoyl chloride
batch production processes.
Adapted from: Reference 35
3-34
-------
Benzotrichloride
3.3.3 Summary of Major Process Hazards and Control Technologies
To reduce Che risk of an accidental release specific measures broadly
classified as prevention, protection or mitigation measures may be applied.
These measures are discussed generally in Section 2 and are described in
detail elsewhere in the technical literature.
The properties of benzotrichloride chat can promote equipment failure are
its corrosivity, flammability and reactivity with water or acids. Below is a
summary of hazard areas in the benzotrichloride manufacturing, use, and
storage processes.
Benzotrichloride Manufacture--
The reactor and product distillation columns appear to have the highest
potential for an accidental release. The final product storage vessel is also
potentially Che site of an accidental benzotrichloride release.
The reaction to produce benzotrichloride is exothermic. Often, the heat
of reaction is removed by allowing some of the coluene to boil off and recon-
dense. A loss of condenser cooling, however, could result in a loss of .
temperature control followed by a runaway reaction. The reaction between
toluene and chlorine is very slow at temperatures below 140-*F. Below this
temperature, chlorine is fairly soluble in toluene; therefore, feeding chlo-
rine to toluene that has not been adequately warmed will result in an accumu-
lation of unreacted chlorine. Once the chlorine begins to react, the solution
will warm and a runaway reaction can follow (35). This runaway reaction can
result in an accidental release because of reactor overpressure.
The product distillation columns are high-hazard areas because of the
quantity and concentration of benzotrichloride present at elevated tempera-
tures. A loss of condenser cooling could lead to overpressure and a
benzotrichloride release. Internal corrosion could also result in vessel
failure and release.
3-35
-------
Benzocrichloride
Product storage is a potential hazard area because of the large quantity
of benzotrichloride; however, because of its low vapor pressure at ambient
temperatures, a release of liquid benzotrichloride from an ambient temperature
storage vessel is not likely to result in a serious risk of exposure to
off-site locations. A source of heat would probably be required before
sufficient quantities of benzotrichloride vapor could threaten off-site
locations. For example, the accidental introduction of water to a storage
vessel could create sufficient heat and pressure to result in a containment
failure and a release of benzotrichloride vapor. Another example would be a
spill of benzotrichloride into water, which could produce enough heat to
evaporate some benzotrichloride before it reacted with the water.
Benzoyl Chloride Production--
The reaction feed tanks and the benzoyl chloride production reactors are
the locations of greatest accidental release risk. Although this reaction is
run under relatively mild conditions (250 to 270 °F and atmospheric pres-
sures) , it is conceivable that a loss of temperature control or a failure to.
provide adequate vent capacity for the hydrogen chloride could lead to over-
pressure and an accidental release of benzotrichloride.
Table 3-10 presents examples of possible locations, conditions and
process hazards which could potentially lead to a benzotrichloride release,
and example control options for reducing the risk of such a release. The
examples are intended to be illustrative, not exhaustive.
3.3.4 Storage and Handling
The Department of Transportation classifies benzotrichloride as a corro-
sive liquid. The presence of moisture will enhance its corrosivity. It can
be fatal if inhaled and is an irritant to the skin and eyes; therefore, it
should be stored in closed systems.
3-36
-------
TABLE 3-10. EXAMPLE CONDITIONS. PROCESS HAZARDS AND HAZARD CONTROLS IN
BENZOTRICHLORIDE MANUFACTURING. USE AND STORAGE
Location
Condition
Process Hazard
Leading to Release
Examples of
Hazard Controls
Reactor
Inadequate preheat- Chlorine accumula-
ing of toluene feed tion. runaway
reaction and over-
pressurize tion
Improved operating procedures
Interlock feed temperature to chlorine
feed
Overpressure protection vented to a
scrubber
u>
^ Process or storage
~j vessel
Undetected corrosion Self-polymerization Regular inspection of lining
with overheating and
possible equipment
failure
Distillation column Loss of cooling
Overpressurizatibn
and loss of con-
tainment
Backup cooling system
Redundant temperature controls with
alarms
Process or storage
vessels
Back-flow of water
or acidic materials
into vessels with
benzotrichloride
Exothermic
hydrolysis and
overpressurization
Overpressure protection vented to a
scrubber
Interlock to shut off reboiler heat if
condenser cooling fails
Redundant check valves or blinds in lines
leading to possible contamination
CD
n
3
N
o
0
1
H-
O
H-
O.
m
(Continued)
-------
TABLE 3-10. (Continued)
Location
Condition
Process Hazard
Leading to Release
Examples of
Hazard Controls
Process or storage
vessel
Transfer of benzo- Corrosion or self-
trichloride to steel polymerization
container
Improved operator training
Piping configurations that prohibit
improper transfer
Reactor used in
benzoyl chloride
production
Loss of temperature Overpreasurization Adequate vent capacity
control
Redundant temperature sensors with alarms
LJ
OO
CO
0>
3
N
o
o.
ID
-------
Benzocrichloride
The preferred materials of construction for systems handling benzotri-
chloride are nickel, glass, or fluoroplastics (41). However, phenolic or
polyethylene linings are acceptable for storage or shipping containers. Lined
equipment should be inspected regularly, since imperfections in the lining can
expose the underlying metal to benzotrichloride. If the underlying metal has
poor corrosion resistance to benzotrichloride (as is typical for lined equip-
ment) , then the metal will corrode. If undetected, corrosion may result in
structural failure. Since most metals (apparently not nickel since it is
reported as a material of construction) can catalyze self polymerization of
benzotrichloride, care must be taken to ensure that benzotrichloride is never
incorrectly stored in metal tanks. Fittings on storage vessels should be
constructed of materials compatible with benzotrichloride. The addition of a
polymerization inhibitor is usually not required for benzotrichloride storage;
however, benzotrichloride stored for weeks at a time should be sampled period-
ically for changes in color. A change in color-(darkening) can indicate thac
polymerization and/or internal tank corrosion is occurring.
Benzotrichloride storage vessels should be grounded and diked. Vents
from storage or process vessels should be routed to an alkaline scrubber (such
as sodium hydroxide) or to an incinerator.
Storage and Handling--
Extreme caution should be taken to ensure that water or acids are not
allowed to enter vessels containing benzotrichloride. The resulting reaction
is exothermic and can produce two moles of hydrogen chloride vapor per mole of
water introduced. This combination of heat generation and gas evolution could
lead to a substantial pressure rise in the vessel, followed by containment
failure and accidental release. Precautions to prevent water or acid contami-
nation could include blinds in all water lines that connect to the process.
redundant check valves in lines that connect the vessel to potential sources
of contamination, or stringent drying procedures whenever a tank is washed
with water.
3-39
-------
Benzotrichloride
Spills of benzotcichloride should either be pumped back into a storage
vessel or absorbed onto clay or some ocher absorbing medium. Water should
never be added to a benzotrichloride spill since the heat of reaction will
only exacerbate the rate of vapor generation.
Benzotrichloride is shipped in fifty-five-gallon drums and four thousand-
gallon tank trailers
3-40
-------
Chloroacecic Acid
3.4 CHLOROACETIC ACID
Chloroacetic acid is a commercially important halogenated acetic acid
used primarily to make cellulose ethers and herbicides. It is also used in
the manufacture of a variety of other chemicals listed in Subsection 3.4.2.
In 1983, 40 million pounds of chloroacetic acid were manufactured (18).
At that time, the projected demand for 1987 was 68 million pounds (18).
Currently it is being produced in the United States at two sites with
estimated capacities of 25 and 30 million pounds each (37).
The major use of chloroacetic acid in the United States is for the manu-
facture of cellulose ethers (e.g., carboxymethyl cellulose), which in 1986,
accounted for approximately 45 percent of the U.S. consumption (37). Chloro-
acetic acid is used to manufacture a .variety of chemicals, including herbi-
cides (40 percent); and thioglycolic acid and glycine (15 percent) (37).
3.4.1 Chemical Characteristics
Physical Properties and Hazards--
At room temperature, chloroacetic acid is a colorless, hygroscopic,
crystalline solid. The physical properties of chloroacetic acid are listed in
Table 3-11. Chloroacetic acid exists in four crystalline forms, with the
alpha structure being the most stable and industrially important. It is
soluble in water, methanol, acetone, diethyl ether, and ethanol.
Chemical Properties and Hazards--
The chemical properties of chloroacetic acid that contribute to the
potential for an accidental release of the chemical include:
• Flammability - Chloroacetic acid is flammable at high tempera-
tures and can form explosive mixtures in air at concentrations
greater than 8 percent by volume chloroacetic acid.
3-41
-------
Chloroacetic Acid
TABLE 3-11. PHYSICAL PROPERTIES OF CHLOROACETIC ACID
Reference
CAS Registry Number
Chemical Formula
Molecular Weight
Normal Boiling Point
Melting Point
Solid Specific Gravity (H,0=l)
Vapor Specific Gravity (air=l)
Vapor Pressure
Vapor Pressure Equation3:
Log Pv-A
79-11-8
94.50
356 °E & 14.7 psia
145.4 °F
1.4043 8 104 °F
3.26
0.065 mm Hg ® 77 °F
Where: Pv = vapor pressure, mm Hg
T = temperature, °C
A = 7.55016. a constant
B = 1.723.365. a constant
C = 179.96. a constant
Liquid Viscosity
Solubility in Water
Specific Heat at Constant Pressure
Latent Heat of Vaporization
Latent Heat of Fusion
Liquid Surface Tension
Heat of Combustion
Ignition Temperature
2.16 centipoise 3 158 °F
421 lb/100 Ib H20 @ 68 °F
0.364 Btu/lb-°F @ 68 °F
228 Btu/lb
88 Btu/lb
35.17 dynes/cm 6 212 °F
308.000 Btu/lb mole
878 °F
33
33
39
24
33
22
39
39
39
39
39
39
39
39
(Continued)
3-42
-------
Chloroacetic Acid
TABLE 3-11 (Continued)
Reference
Explosive Range, Volume X in 8 mini mum; no mngiirmm 39
air @ 1 atm found reported
Flashpoint 258.8 °F 39
This equation yields a vapor pressure of 11.2 psia rather than 14.7 psia at
the boiling point. No explanation of this discrepancy was provided in the
reference for vapor pressure but may be due to curve fit averaging of
experimental data.
3-43
-------
Chloroacecic Acid
• Corrosivity - Chloroacetic acid is highly corrosive to most
common metals.
• Decomposition - When heated to decomposition, chloroacetic acid
may release highly toxic phosgene and hydrogen chloride vapor
(38).
Toxicological and Health Effects —
Chloroacetic acid is highly toxic by ingestion and skin absorption. It
is irritating to the skin, eyes, and respiratory tract, resulting in persis-
tent burns. Ingestion can interfere with body enzyme systems and cause
digestive tract perforation and peritonitis. More acute exposure can result
in central nervous system and respiratory system depression. The probable
lethal oral dose is between one teaspoon and one ounce for a ISO-pound person
(24). Death may also occur if more than 3 percent of the skin is exposed.
The only exposure limit which has been set is an eight-hour time-weighted
average of 0.13 ppm (20). The !£,_ is 180 mg/m for rats by inhalation (25).
3.4.2 Facility Descriptions
Chloroacetic Acid Manufacture--
Host chloroacetic acid is produced in the United States by the chlorina-
tion of acetic acid. Figure 3-6 illustrates a typical manufacturing process.
The process consists of sparging dry chlorine gas into liquid glacial
acetic acid in a reactor. The reaction is carried out in the presence of
catalytic quantities of sulfur or red phosphorous at temperatures between 185
and 250 *F (18,33). As the chloroacetic acid is formed, hydrogen chloride gas
is evolved and recovered as hydrochloric acid by water scrubbing. The reactor
contents are cooled to form chloroacetic acid crystals. A solvent is added,
and dichloroacetic acid and unreacted acetic acid are extracted from the
reaction mixture. An alternative purification process involves selective
dechlorination of the dichloroacetic acid in the presence of hydrogen and a
palladium catalyst at temperatures between 250 and 300 °F to form chloroacetic
3-44
-------
Catalyst
l*>
i Arollr Arid fc
tn
Chlorine _
j
<
J
Chtorinallor
Reactor
i
1
Scrubt
Solve
tot
\
nl •
^«%J«
Hys
Acetic Acid Recycle
-ta. MuHmrhkvlr ArM i n .
I ,
i Hydrogen •
^U ^ Hvdroaenatlon ^ Vacuum Additional Recovered
""""" ' Reactor Oistillalion Chloroacetw Acid
, ChtoroacetK
Product
Figure 3-6. Conceptual flow diagram of typical chloroacetic acid manufacturing process
Adapted from: Reference 39
o
0)
n
H-
n
r?
H-
O.
-------
Chloroacecic Acid
acid and acetic acid (39). The resulting stream is then separated by vacuum
distillation to produce a product that is more than 99 percent chloroacetic
acid (33,39).
Because of the highly corrosive nature of chloroacetic acid, the chlori-
nation reaction is carried out.in ceramic-lined, lead-coated steel, or glass-
lined vessels (33,39).
Chloroacetic Acid Consumption--
The primary uses of chloroacetic acid in the United States are for the
manufacture of cellulose ethers and herbicides. Additional uses of chloro-
acetic acid are for the manufacture of thiogycolic acid, glycine, ethyl
acetate, and synthetic caffeine.
Cellulose Ethers--The largest end use of chloroacetic acid is for the
manufacture of carboxymethyl cellulose. Figure 3-7 is a flow diagram of a
typical manufacturing process.
In a typical continuous process, powered cellulose is fed to a rotary
drum reactor. Chloroacetic acid and sodium hydroxide are added to the reactor
through spray nozzles. The three materials react to form carboxymethyl
cellulose. The reaction is exothermic, and cooling is required to maintain
the reaction temperature between 77 and 160 °F (29). The crude product
mixture is neutralized by adding acid and purified by extracting with methanol
or methanol-water mixtures. The purified product is then dried and packaged.
The efficiency of the reaction is approximately 60 to 80 percent (39). The
remainder is transformed into sodium glycolate by hydrolysis of the chloro-
acetic acid.
Herbicides--The other major use of chloroacetic acid is for the manufac-
ture of dichlorophenoxy and trichlorophenoxy acetic acid herbicides (i.e.,
2,4-D and 2,4,5-T). These herbicides are manufactured by reacting aqueous
chloroacetic acid with 2,4-dichlorphenol or 2,4,5-trichlorophenol in aqueous
sodium Hydroxide to form a sodium salt. The reaction is carried out at
3-46
-------
w
i
PjlllllkKA -
A
Hydrochloric
Acid
I
Reactor
Neutralization
Purification
Product
Processing
CarbOMymelhyt
Cellulose Product
Figure 3-7. Conceptual flow diagram of carboxymethyl cellulose manufacturing process.
Adapted from: Reference 39
g
o
n
ID
H-
n
fr
o.
-------
Chloroacecic Acid
approximately 212 *F. The resultant salt is hydrolyzed to the free acid by
adding hydrochloric acid. The corresponding acid is purified by recrystal-
lizacion, filtered, and recovered as a final product.
3.4.3 Summary of Maior Process Hazards and Control Technologies
For all processes, the accidental release risk can be reduced by applying
specific measures broadly classified as prevention, protection or mitigation
measures. These measures are discussed genetically in Section 2 of this
manual and are discussed in other technical literature.
The most significant property of chloroacetic acid that contributes to
the risk of a release is its corrosivity.
Proper materials of construction must be used throughout the manufactur-
ing, use, and storage systems. Particular attention should be paid to materi-
al selection for smaller equipment items such as pipe fittings- because such
items are frequently replaced, and proper material selection may be overlooked
when repairs are made.
Below is a summary of hazard areas associated with chloroacetic acid
manufacture, use and storage processes.
Cellulose Ethers Production- -
Since the reaction during cellulose production is exothermic, a loss of
cooling or reactant flow control could result in overheating and overpressure
in the reactor; this, in turn, could lead to an accidental release of
chloroacetic acid.
Herbicides--
In this production process, the chloroacetic and storage and feed systems
are the locations with the greatest potential for an accidental release of
chloroacetic acid. Probably the risk of a chloroacetic acid release from the
reactor is low; however, a loss of flow control to the reactor could result in
a release.
3-48
-------
Chloroacecic Acid
Table 3-12 presents examples of possible locations, conditions, and
process hazards which could potentially lead to a chloroacetic acid release,
as well as example controls for reducing the risk of such an event. The
examples are intended to be illustrative, not exhaustive.
3.4.4 Storage and Handling
Table 3-13 lists materials of construction suitable and unsuitable for
chloroacetic acid. Chloroacetic acid, which is highly corrosive to the
metals commonly used as materials of construction for storage and process
vessels, is stored as crystallized flakes, in molten form, or as an 80 percent
aqueous solution. In molten form, it is transported in glass-lined tank cars
and titanium-lined tank trucks and is stored in glass-lined containers (39).
Aqueous solutions are handled in special stainless steel or rubber-lined
containers below 100 °F and in iron containers with a baked phenolic resin
coating below 212 °F (39). Flaked crystals are stored in polyethylene-lined
fiber packs contained in fiberboard or iron drums. In addition, pipelines are
commonly constructed of glass-lined steel or steel lined with polytetrafluoro-
ethylene or perfluoroalkoxy polymers.
All Storage and Piping Systems--
Since most chloroacetic acid storage vessels and piping systems are
constructed of lined materials, there is the potential for lining failure and
a subsequent release because of corrosion. Linings should be routinely
inspected. Some linings are particularly sensitive to failure by thermal
cycling and shock, especially glass. While not generally a problem with
plastics, it should not be completely disregarded. Linings are also subject
to damage by mechanical shock. A perforation or crack in a lining will expose
the underlying metal to attack by the chloroacetic acid. A small leak can
lead to protracted corrosion ultimately leading to equipment failure and a
release.
3-49
-------
TABLE 3-12. EXAMPLE CONDITIONS. PROCESS HAZARDS AND HAZARD CONTROLS IN
CHLOROACETIC ACID MANUFACTURING AND USE
Location
Condition
Process Hazard
Leading to Release
Examples of Hazard Controls
Carboxymethyl
cellulose reactor
or chlorination
reactor
Excessively high
chloroacetic acid
feed rate; failure
of cooling system
Excessive exother-
mic reaction
High temperature alarm interlocked to
flow control
cauaing overheating
or overpressuriza- Limit maximum feed rates by flow limiting
tion with equipment orifices or line sizes
failure and release
Backup cooling
in
O
Excessive chloro-
acetic acid feed
Overfilling or over- Redundant level sensing with alarm and
pressurization interlock.to feed
leading to release
Overflow catch tank
Strict high quality operating procedures
and operator training
Process equipment
handling chloro-
acetic acid
Formation of solid
chloroacetic acid
Equipment plugging Flow sensors with alarms
leading to overpres-
suriza tion. over- Protection for pumps to prevent
filling, or backflow overpressure or overheating when flow is
leading to release stopped
Heat traced lines to prevent or melt
plugs
o
ft
o
n
n
>
o
(Continued)
-------
TABLE 3-12. (Continued)
Location
Condition
Process Hazard
Leading to Release
Examples of Hazard Controls
Process equipment
Undetected corrosion Equipment failure
leading to release
Frequent equipment inspections
Use of proper materials of construction
Validation of materials of construction
before equipment is installed
Process and storage
vessels
Sparks or flame
near vessels
to
1/1
Fire or explosion
from overheating
cbloroacetic acid
vessel or from ig-
nition of leakage
from vessel; fire
or explosion could
cause larger release
Improve fire protection
Isolate chloroacetic acid storage from
large concentrations of flammable
materials and sources of ignition
Pressure relief sized for fire
n
o
o>
o
to
n
-------
Chloroacetic Acid
TABLE 3-13. ACCEPTABILITY OF VARIOUS METALS AND ALLOYS
FOR CHLOROACETIC SERVICE
Material
Aluminum
Brass
Carbon Steel
Copper
Hastelloy-B«
Hastelloy-C*
Inconel®
Lead
Monel*
Nickel
Silver
Stainless Steel 316*
Tantalum
Titanium
Zirconium
Acceptable Unacceptable
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Source: Adapted from Reference 40
Reported in Reference 40. May only apply in special circumstances.
Decomposition or reaction of chloroacetic acid to produce chlorides would
appear to preclude use for some applications due to chloride stress corrosion
cracking.
3-52
-------
Furan
3.5 FURAN
Furan Is a chemical intermediate used Co manufacture Pharmaceuticals,
pesticides, herbicides, and fine chemicals. It is made commercially by
decarbonylation of furfural and appears to be manufactured at a single site in
the United States. Its use as a pesticide intermediate accounts for
approximately 95 percent of the U.S. consumption.
3.5.1 Chemical Characteristics
Physical Properties and Hazards--
Furan is a clear, colorless, flammable liquid. The liquid turns brown on
standing and has a strong odor similar to ether. It boils at 88.4 °F and one
atmosphere of pressure to form a colorless, flammable, toxic gas. Table 3-14
lists the physical properties of furan. The combination of flammability and
toxicity is especially hazardous since ignition of a leak could cause a fire
or explosion that could result in a larger release.
Furan is only slightly soluble in water. It is miscible, however, in
most common organic solvents. Furan vapor is 2.4 times more dense than air
and will tend to stay close to the ground when released into the atmosphere.
Liquid furan will expand slightly with heating. As a result, liquid-full
equipment can pose a hazard.
Chemical Properties and Hazards--
The most significant chemical properties that may contribute to the
potential for an accidental release of furan are:
• Furan is dangerous when exposed to heat or flame. Liquid furan
has a low flash point, -32 "F, and high flammability. It is
flammable in air at concentrations from 2.3 to 14.3 percent
furan by volume.
3-53
-------
Furan
TABLE 3-14. PHYSICAL PROPERTIES OF FURAN
Reference
CAS Registry Number 110-00-9
Chemical Formula C4H4°
Molecular Weight 68.08
Normal Boiling Point 88.4 °F @ 14.7 psia 33
Melting Point -122.08 °F 33
Liquid Specific Gravity (H20=l) 0.9371 0 67 °F 21
Vapor Specific Gravity (air=l) 2.36 33
Vapor Pressure 9.54 psia ® 68 °F 21
Vapor Pressure Equation: 21
log Pv = A-JL
Where: Pv = vapor pressure, mm Hg
T = temperature. °C
A = 6.97527, a constant
B = 1.060-.87. a constant
C = 227.74. a constant
Liquid Viscosity 0.38 centipoise 21
Solubility in Water 1.0 lb/100 Ib HjO Q 77 °F 33
Specific Heat at Constant Pressure 0.406 Btu/(lb-°F) @ 77 °F 33
Latent Heat of Vaporization 171.2 Btu/lb 33
Liquid Surface Tension 24.10 dyne/cm 0 68 °F 21
Heat of Combustion 900.000 Btu/lb mole 33
(Continued)
3-54
-------
Fur an
TABLE 3-14. (Continued)
Reference
Explosive Range, Volume X in 33
air 2.3 min
14.3 max
Flashpoint. TCC (ASTM D-56) -31.9 °F 33
Properties useful in determining other properties from physical property
correlations.
Critical Temperature 417.2 °F 33
Critical Pressure 772 psia 33
3-55
-------
Fur an
• Furan decomposes at 1,200 °F in the absence of catalyst and at
680 °F in the presence of nickel, to form a mixture consisting
of carbon monoxide, hydrogen, and hydrocarbons (33).
• On exposure to air, furan can form unstable peroxides.
Decomposition of these peroxides in furan equipment where
unintentional exposure to air has lead to their formation could
cause equipment failure and cause an accidental furan release.
• Furan is incompatible with strong acids and oxidizing agents.
Contact with these materials can result in violent, exothermic
reactions or corresponding overheating or overpressuring of
equipment with containment failure and furan release.
Toxicological and Health Effects--
Little information is available on the toxological effects of accidental
exposure to furan. Furan.vapors are a central nervous system depressant.
Exposure to furan can cause irritation and burning of the eyes and skin,
dizziness, and suffocation. Furan is highly toxic by ingestion, inhalation.
and skin absorption. No exposure limits have been determined for furan,
although human exposures are routinely controlled to less than 10 ppm (33).
The LD.Q for mice via inhalation is 3500 ppm over 1 hour (41).
3.5.2 Facility Descriptions
Furan Manufacture--
Furan is manufactured commercially by the decarbonylation of furfural.
Several furan manufacture reaction schemes have been patented (42). In all
cases, the starting material for the manufacture of furan is furfural. The
reaction can be carried out under catalytic or noncatalytic conditions, in the
liquid or vapor phase. Figure 3-8 is a flow diagram of a typical manufacturing
process.
3-56
-------
u>
01
Furfural
Hydrogen
Reactor
Condenser
Distillation
Column
Furlural Recycle
Noncondensibles
lo \ton\
Furan lo
Product Storage
Figure 3-8. Conceptual flow diagram of typical furan manufacturing process.
Adapted from: Reference 42
H
01
-------
Furan
A typical noncatalycic process is the pyrolysis of furfural at
approximately 1,300 °F (33). The major drawback of noncatalytic processes is
that they generate low yields of furan.
A typical catalytic process consists of passing furfural and hydrogen
over a nickel or cobalt catalyst at approximately 540 °F to yield furan and
carbon monoxide (42).
Whichever reaction type is used, the reaction products are fed to a
distillation column that refluxes unreacted furfural to the reactor while
allowing furan vapor to pass on to a condenser for product recovery. Any
noncondensibles formed during the reaction, including carbon monoxide, are
vented from the condenser.
Furan Consumption--
Furan is used as a chemical building block in the manufacture of a
variety of chemical products, including: Pharmaceuticals, herbicides, pesti-
cides, stabilizers, and fine chemicals.
One such chemical is tetrahydrofuran. Tetrahydrofuran can be manufac-
tured by the catalytic hydrogenation of furan in either the liquid or vapor
phase (42). Figure 3-9 illustrates a typical vapor phase process. In this
process, furan is vaporized and combined with a stream of hydrogen gas. The
resulting gaseous mixture is then passed through a packed bed reactor
containing a nickel catalyst. The reactor operates at a temperature of
approximately 185 "F and a pressure of 1-2 pounds per square inch gauge (32).
The vapor stream from the reactor contains essentially pure tetrahydrofuran,
which is routed to a condenser for recovery of liquid product.
Thiophene can be manufactured by passing hydrogen sulfide and furan over
an alumina catalyst at approximately 750 "F (33), as shown in Figure 3-10,
producing thiophene and water. The water and thiophene are separated and the
crude product is continuously distilled to the required purity. Pyrrole can
be manufactured by passing furan, steam, and excess ammonia over an alumina
3-58
-------
ui
Liquid
Furan
Furan
Vaporizer
Hydrogen
Packed Bed
Reactor
Condenser
Furan lo
Product Storage
Figure 3-9. Conceptual flow diagram of typical tetrahydrofuran manufacturing process.
Adapted from: Reference 42
M
01
-------
Furan
Hydrogen
Sulhde
Reactor
Liquid
Separation
*• Water
Crude
Thiophene
Thiophene to
Product Storage
Distillation
Waste to Disposal
Figure 3-10. Conceptual flow diagram of typical thiophene manufacturing process.
Adapted from: Reference 33
-------
Furan
catalyst at approximately 750-850 °F (29). The separation sequence is similar
to that for thiophene.
Furan is also used in a variety of other organic syntheses, including the
synthesis of polymeric compounds with ethylene for use as flocculants,
pesticides, and Pharmaceuticals.
3.5.3 Summary of Maior Process Hazards and Control Technologies
To reduce the risk of an accidental release specific measures broadly
classified as prevention, protection or mitigation measures may be applied.
These measures are discussed generically in Section 2 and in greater detail
elsewhere in the technical literature.
The properties of furan that contribute to the risk of a release are its
low boiling point and flammability.
Below is a summary of hazard areas in the furan manufacturing, use and
storage processes.
Furan Production--
Within this process, an accidental release of furan could result from a
variety of sources. Three are mentioned below:
• Furan could thermally decompose if the temperature in the
packed bed reactor exceeds 680 "F. This decomposition would
cause the formation of two or more moles of gas per mole of
furan, which could lead to overpressurization and accidental
release.
• Lack of sufficient cooling in the distillation column condenser
could cause overpressurization and release from the
distillation column.
3-61
-------
Furan
• Catalyst poisoning could result in an accumulation of unreacted
furfural, which could lead to overpressurization and an
accidental release.
Another hazard associated with this process is the potential for explo-
sion since hydrogen is involved in a high-temperature reaction. Hydrogen is
extremely explosive, and leaks of hydrogen can travel near the ground for long
distances. The presence of trace quantities of oxygen in the reactor could
cause an explosion. A hydrogen explosion could damage equipment that contains
furan and result in a furan release.
Tetrahydrofuran Production--
The hazards associated with this process are similar to those associated
with the furan production process. However, the temperature of this reaction
is lower and the potential for thermal decomposition of the furan is less
severe.
Thiophene and Pyrrole Production--
For both processes, a loss of flow or temperature control could result in
thermal decomposition of furan, which could lead to an accidental release. In
addition, the presence of oxygen in either of these reactions could cause a
fire or explosion.
Storage and Handling--
Furan must be stored in the strict absence of oxygen. A reliable, and
preferably dedicated inert gas system should be used for all storage vessels.
Table 3-15 presents examples of possible locations, conditions and
process hazards which could potentially lead to a furan release, and example
controls for reducing the risk of such a release. The examples are intended
to be illustrative, not exhaustive.
3-62
-------
TABLE 3-15. EXAMPLE CONDITIONS. PROCESS HAZARDS AND HAZARD CONTROLS
FOR ACCIDENTAL FURAN RELEASES
Location
Condition
Process Hazard
Leading to Release
Examples of Hazard Controls
Packed bed reactor
Distillation column
condenser
u>
Catalyst
Reactor
Temperature exceeds
680° F
Losa of cooling
Overpressurization
of equipment and
relief valve dis-
charge or equipment
failure
Overpressurization
and relief valve
discharge
Catalyst poisoning
Presence of trace
quantities of oxygen
Distillation column Loss of flow control
Overpressure and
relieve valve
discharge
Release of hydrogen
and explosion.
damaging furan-
containing equipment
ing release
Formation of per-
oxide and subsequent
explosion
Redundant temperature sensors and
alarms
Redundant temperature sensors and
and alarms; backup cooling system
Adequate pressure relief
Interlock to shut off reboiler feed
if condenser cooling fails
Oxygen monitoring of reactor streams;
oxygen alarm
Redundant flow and temperature sensors
with alarms
Periodic cleaning of vessels where
peroxide formation is possible
Stringent inert gas system with oxygen
monitoring
01
(Continued)
-------
TABLE 3-15. (Continued)
Location
Condition
Process Hazard
Leading to Release
Examples of Hazard Controls
Distillation column
Loss of flow control Formation of per- Redundant flow and temperature sensors
oxide and subsequent with alarms
explosions
Periodic cleaning of vessels where
peroxide formation is possible
Storage and process
vessels
Nearby fire or
explosion
Damage to furan
containing equip-
ment
Stringent inert gas system with oxygen
monitoring
Inert gas system for storage or process
vessels
Storage or process vessels isolated from
potential sources of ignition
Flammable gas detectors located
throughout process or storage areas
Adequate fire protection
Pressure relief sized for heating due
to fire
fa
-------
Fur an
3.5.4 Storage and Handling
Furan must be stared In the stzict absence of oxygen. A reliable, and
preferably dedicated inert gas system sbould be used for all storage vessels.
Inventories of furan should be rotated regularly and should be kept to a
minimum. Long-term storage should never be attempted. Tanks should be
emptied and cleaned routinely to remove any peroxide crystals that may form.
However, extreme care should be taken to ensure an inert atmosphere before
refilling such vessels with furan.
3-65
-------
Hydrazine
3.6 HYDRAZINE
Hydrazine has traditionally been recognized as a high-energy fuel for
rockets and Jets. Today, however, it is used primarily as a raw material in
the manufacture of blowing agents for foamed plastics and in the production of
pesticides. Hydrazine and derivatives are also used in water treatment.
All manufacture of hydrazine in the United States is currently based on
the ketaztne process. In 1983, approximately 18 million pounds of hydrazine
were produced at two sites, each of which has a capacity of 14 million tons
(18). These production data are based on non-fuel production because the
production of hydrazine for fuel is erratic. However, it has been estimated
that one million pounds of hydrazine were used as fuel in 1983 (18). In 1983,
the non-fuel uses of hydrazine were as follows: herbicides, 53 percent;
blowing agents for plastics, 27 percent; water treatment, 13 percent; other
uses, 7 percent .(18).
3.6.1 Chemical Characteristics
Physical Properties--
Hydrazine is a colorless, oily, fuming liquid at ambient conditions with
an odor similar to ammonia. Table 3-16 lists the physical properties of
anhydrous hydrazine.
Hydrazine is a strong reducing agent, weakly alkaline, and is very
hygroscopic. It contracts upon freezing, so there is little danger of equip-
ment rupture from formation of the solid. Hydrazine is soluble in water and
other polar solvents such as alcohols, amines, and ammonia. The vapor is
slightly more dense than air and will tend to stay close to the ground when
released into the atmosphere.
Because liquid hydrazine will expand slightly when heated, liquid-full
equipment can pose a hazard. A liquid-full vessel is an unvented vessel
filled with liquid with little or no vapor space present above the liquid.
3-66
-------
Hydrazine
TABLE 3-16. PHYSICAL PROPERTIES OF HYDRAZINE
Reference
CAS Registry Number 302-01-2
Chemical Formula N?HA
Molecular Weight 32.05
Normal Boiling Point 236.3 °F ® 14.7 psia 21
Melting Point 34.8 °F 21
Liquid Specific Gravity (H,0=l) 1.008 « 68 °F 43
Vapor Specific Gravity (air=l) 1.04 6 68 °F 43
Vapor Pressure 0.28 psia @ 77 °F 33
Vapor Pressure Equation: 21
log Pv = A - B
t+C
where: Pv = vapor pressure, mm Hg
T = temperature.- °C
A = 7.8019. a constant
B = 1.679.07. a constant
C = 227.7. a constant
Liquid Viscosity 0.90 centipoise 33
Solubility in Water Complete 33
Specific Heat at Constant Pressure 0.7358 Btu/(lb-°F) @ 68 °F 43
Latent Heat of Vaporization 602 Btu/lb S 77 °F 43
Liquid Surface tension 66.67 dynes/cm 9 77 °F 33
Heat of Combustion 270.000 Btu/lbmole 33
Autoignition Temperature 518 °F 43
Explosive Range. Volume % in air 4.7 min. 43
(Continued)
3-67
-------
Kydrazine
TABLE 3-16. (Continued)
Reference
Flashpoint. COG 126 °F 43
Properties useful in determining other properties from physical property
correlations.
Critical Temperature 716 °F 43
Critical Pressure 2.130 psia 43
Critical Density 14.21 lb/ft3 43
3-68
-------
Hydrazine
A liquid-full line is a section of pipe sealed off at both ends and full of
liquid, with little or no vapor space. When there is no room for thermal
expansion of the liquid, temperature increases can lead to containment
failure.
Chemical Properties and Reactivity--
The most significant chemical properties contributing to the potential
for an accidental release of hydrazine include:
• Flammability - Hydrazine is flammable in air at concentrations
over 4.7 percent by volume and can decompose violently (see
•Decomposition") (43).
• Reactivity - Hydrazine reacts exothermically with oxygen to
form nitrogen and water. If a large liquid surface of
hydrazine is exposed to air, spontaneous ignition can occur
because, of Che heat evolved by oxidation with atmospheric
oxygen. Hydrazine reacts with sodium or calcium hypochlorite
to form nitrogen, water, and the corresponding salt. However,
if both reactants are present in high enough concentrations,
the reaction may occur violently.
• Decomposition - Thermal decomposition of hydrazine occurs at
temperatures above approximately 320 "F (33). However, the
decomposition temperature is significantly lowered in the
presence of catalysts, including copper, cobalt, molybdenum,
and iron oxides (rust) (33). At temperatures approaching the
boiling point of hydrazine, certain metals such as copper and
molybdenum act as catalysts, leading to the decomposition of
hydrazine. This can result in overpressure of storage and
process vessels.
• Instability - Liquid hydrazine is stable to shock. However,
sudden violent movement can cause hydrazine vapor to detonate
when it is within the flammable limits (43,44).
3-69
-------
Hydrazine
Toxicological and Health Effects--
Hydrazine is highly toxic by ingestion, inhalation, and skin absorption.
Symptoms of exposure to hydrazine include eye, nose, and throat irritation,
temporary blindness, dizziness, nausea, dermatitis, and skin and eye burns
(38). Inhalation may cause nausea, headache, facial numbness, twitching, sore
throat, and pulmonary edema (24). In addition, since prolonged exposure to
hydrazine vapors causes a deadening of the sense of smell, detection of
hydrazine by odor can be used only as an initial warning. According to the
International Agency for Research on Cancer (IARC), there is sufficient animal
evidence that hydrazine is a carcinogen (25). The Occupational Safety and
Health Administration (OSHA) standard in air for hydrazine is a time-weighted
average of 0.1 ppm over an 8-hour day. Hydrazine is especially hazardous by
dermal exposure (25). Table 3-17 summarizes some of the relevant exposure
data for hydrazine.
3.6.2 Facility Descriptions
Hydrazine Manufacture--
Hydrazine is manufactured by the partial oxidation of ammonia with
chlorine, hypochlorite, or hydrogen peroxide. Current U.S. production is
based on the ketazine process (18). Figure 3-11 is a flow diagram of a
typical ketazine process. In this process, sodium hypochlorite, aqueous
ammonia, and acetone are fed to a reactor that operates under slight pressure
and at a temperature of 85-100 °F (33). The reactor product stream,
containing 1-2 percent hydrazine, is sent to an ammonia recovery system where
the unreacted ammonia is stripped, absorbed in water and returned to the
reactor. The bottoms stream from the ammonia recovery system consisting of
hydrazine, ketazine, water and sodium chloride salt, is fed along with
additional acetone to a distillation column, where the sodium chloride is
removed.
The remaining materials (water, hydrazine and ketazine) are taken over-
head and fed to a pressure hydrolysis column. In the hydrolysis column, the
ketazine reacts with water to form acetone and hydrazine. The column operates
at approximately 10 atm (33). Acetone is taken overhead and is recycled to
3-70
-------
Hydrazine
TABLE 3-17. LC5Q OR LD5Q DATA FOR HYDRAZINE
Route of
Exposure
oral
inhalation
inhalation
intr aper itoneal
intravenous
dermal
dermal
Species
Rat
Rate
Mouse
Rat
Rabbit
Rabbit
Guinea pig
LC50 or "'SO
60 mg/kg
570 ppm
252 ppm
59 mg/kg
26 mg/kg
93 mg/kg
190 mg/kg
No. of
Doses or
Duration
of Dosage
Once
4 hr
4 hr
Once
Once
Once
Once
Source: Reference 25
3-71
-------
u>
to
Acetone
Sodium
Hypochtorrte
Excess
Amine
t[
•Water
Ammonia
Absorber
Aqueous
Ammonia
Kelazine
Reactor
Acetone
Recycle
Ammonia
Recovery
Column
Aceione
Pressure
Hydrolysis
Column
Waiei
Recycle
Concentrating
Column
Hydranne
Hydrate
Kelazine
Column
Brine
Waste
Figure 3-11. Conceptual flow diagram of typical ketazine-based hydrazii.f hydiale
manufacturing process.
Adapted from: Reference 33
ID
-------
Hydrazine
the ketazine reactor. The bottom stream, consisting of a 10 to 12 percent
hydrazine solution, is sent to a concentrating column where water is taken
overhead and recycled to the ketazine reactor while hydrazine hydrate is
withdrawn from the bottom as product. The concentration of the hydrazine
hydrate can be varied to produce the several aqueous grades available commer-
cially: 64, 54.4, and 35 percent hydrazine (33).
In addition to hydrazine hydrate, anhydrous hydrazine is also produced.
As shown in Figure 3-12, the hydrate and aniline are fed to an azeotrope
column. The bottoms from the azeotrope column, consisting of aniline and
hydrazine, are sent to a final hydrazine column where anhydrous hydrazine is
taken as an overhead product.
Hydrazine Consumption--
The primary uses of hydrazine in the United States are for manufacturing
agricultural chemicals and chemical blowing agents for foamed plastics, as a
high energy fuel (e.g., rocket fuel), and for boiler water treatment. Table
3-18 lists some additional end uses of hydrazine. Host commercial applica-
tions use hydrazine hydrate in various concentrations. One exception is for
high energy fuel consumption, in which anhydrous hydrazine is used.
Agricultural Chemicals--
Hundreds of hydrazine derivatives have been patented for use in
agriculture. Table 3-19 lists some of the most common. The reader can refer
to the patent literature for specific process information on a specific
chemical.
Blowing Agents--
Chemical blowing agents refer to substances that create a foaming action
in polymers to form foamed plastics. The bloving agent decomposes during
extrusion to form the foam. Several hydrazine-based blowing agents are
currently used. The blowing agent produced in the largest volume is azodicar-
bonamide.
3-73
-------
Decanter
Hydrazine
Hydrate
^4
Aniline
Water
Azeolrope
Column
Ambna
Anhydrous
Hydrazme
Hydrate
Column
Aniline Recycle
Figure 3-12. Conceptual flow diagram of typical anhydrous hydrazine separation process.
Adapted from: Reference 33
H-
n
-------
Hydrazine
TABLE 3-18. TYPICAL END USES OF HYDRAZINE
Agricultural Chemicals
Bloving Agents for Foamed Plastics
Food-Grade Hydrochloric Acid Manufacture
Fuel for Fuel Cells
Oxygen Scavenger for Boiler Water
Rocket Fuel
Spandex* Fibers
Soldering Fluxes
Tetracene
Source: Reference 17
3-75
-------
Hydrazine
TABLE 3-19. COMMON HYDRAZINE-BASED BIOCIDES AND GROWTH REGULATORS
Common Name
Use
Aminocide
Amitrole
Azinphosethyl
Benquinox
Credazine
Difenzoquat
Drazozolon
Maleic hydrazide
Methidathion
Metribuzin
Norflurazone
Oxadiazon
Pyrazon
Pyrazophos
Tebuthiuron
Plant growth regulator
Herbicide
Insecticide
Fungicide
Herbicide
Herbicide
Fungicide
Plant growth regulator
Insecticide
Herbicide-
Herbicide
Herbicide
Herbicide
Fungicide
Herbicide
Source: Reference 28
3-76
-------
Hydrazine
Hydrazine and urea are the starting materials for azodicarbonamide. An
intermediate, hydrazodicarboxamide, is prepared by refluxing an aqueous
solution of urea and hydrazine. Azodicarbonamide is then formed by the
oxidation of this intermediate. Additional information on hydrazine-based
blowing agents can be obtained from the technical literature.
Water Treatment--
Hydrazine is used by public utilities, pulp and paper, textile and
chemical processing plants for corrosion protection in boilers, hot-water
heating systems and waste steams (33).
Hydrazine is useful for controlling corrosion because it reacts with
oxygen to form nitrogen and water. Hydrazine also reacts with iron to form
magnetite on metal surfaces, which provides a protective coating against
additional corrosive attack. Generally, less than 0.1 ppm hydrazine is
required for full corrosion protection of equipment (33).
Propellents--
The first use of anhydrous hydrazine was as a rocket fuel (33), because
when hydrazine contacts certain oxidizers (e.g., nitrogen tetroxide), the
mixture ignites with instantaneous total conversion of all reactants. Today,
hydrazine is still used as a high-energy fuel, although its use has declined.
3.6.3 Summary of Major Process Hazards and Control Technologies
To reduce the risk of an accidental release, specific measures broadly
classified as prevention, protection or mitigation measures may be applied.
These measures are discussed generally in Section 2 in this manual and are
discussed in more detail in other technical literature.
The properties of hydrazine that contribute to the risk of a release are
its explosivity and flammability. Below is a summary of hazard areas in Che
hydrazine manufacturing, use and storage processes.
3-77
-------
Hydrazine
Hydrazine Manufacture--
Since the hydrazine in Che ketazine process is almost always present Ln
low concentrations, the potential for a hydrazine accidental release is low.
The highest hydrazine release hazard area is probably the concentrating
column. A loss of cooling to the condenser or a loss of temperature control
in the reboiler could result in an overpressure and an accidental release.
Handling anhydrous hydrazine at elevated temperatures creates a potential
for an accidental hydrazine release. A loss of temperature control in the
final hydrate column could lead to hydrazine decomposition and an accidental
release. The presence of oxygen could cause an explosion.
A small leak of hydrazine is likely to result in a fire, which could Lead
to a large hydrazine release. However, the released hydrazine would probably
burn; therefore, the greatest danger is probably the destruction associated
with a fire or explosion rather than the toxicological effects of exposure to
hydrazine.
Agricultural Chemical Production--
For all the agricultural chemical production processes, the greatest
hazard is the potential for a hydrazine-induced fire or explosion rather than
acute hydrazine exposure. The use of hydrazine in an aqueous solution
substantially reduces the risk. Fires or explosion are most likely to occur
whenever hydrazine vapors are present and wherever oxygen is allowed to
contact the hydrazine.
Blowing Agents Production--
The accidental release hazard for this process, which is similar to those
for agricultural chemical manufacturing processes, is that if unreacted
hydrazine comes in contact with the oxidizer in the second reaction, a poten-
tially explosive reaction could result.
Water Treatment Facilities--
The hydrazine accidental release potential is very low in facilities that
use the chemical for water treatment because the hydrazine inventories at
3-78
-------
Hydrazine
chese facilities are small. However, a small inventory should still be
created with caution since a small release could result in a fire that could
lead to a larger process upset.
Table 3-20 presents examples of possible locations, conditions and
process hazards which could potentially lead to a hydrazine release, and
example controls for reducing the risk of such a release. The examples are
intended to be illustrative, not exhaustive.
3.6.4 Storage and Handling
In the United States, hydrazine is stored in drums, bulk storage tanks,
and railroad tank cars and tank trucks used for temporary stationary storage.
Table 3-21 lists materials of construction compatible with hydrazine for
storage and process vessels.
Large quantities of hydrazine are typically stored in pressure vessels.
Each tank is typically electrically grounded and fitt'ed with a level gauge,
pressure gauge, relief valve, and flame arrester on its top (44,45). Nitrogen
or another inert gas blanket is used to prevent the formation of flammable
mixtures. Hydrazine muse be stored away from sources of ignition and away
from oxidants. Carbon dioxide should not be used as a blanketing gas since
hydrazine reacts to form a carbazic acid salt (33). In addition, all transfer
and storage systems must be free of air, since hydrazine reacts violently with
oxygen.
Hydrazine is usually transferred by pressurizing the storage vessel with
dry inert gas (e.g., nitrogen), or by using a transfer pump constructed of
compatible materials.
Hydrazine fires can be controlled by deluging with water, which should
generally be applied as a spray rather than a fog (43).
3-79
-------
TABLE 3-20. EXAMPLE CONDITIONS. PROCESS HAZARDS AND HAZARD CONTROLS IN
HYDRAZINE MANUFACTURING AND USE
Location
Condition
Process Hazard
Leading to Release
Examples of Hazard Controls
Distillation columns
for anhydrous
hydrazine production
o,
o
Excess hydrazine
feed; loss of
condenser cooling
Overfilling leading
to release; over-
pressurization
causing equipment
failure and release
High level alarms interlocked to flow
control
Overflow catch tank
Adequate sizing of pressure relief to
handle maximum flow
Pressure relief discharge sent to flare
Redundant temperature sensors with
alarms
Interlock to shut off reboiler heat if
condenser cooling fails
Process or storage
areas
Spark or flame near Loss of containment
hydrazine facilities
Hydrazine storage isolated from sources
of flame
High quality fire protection
Explosion proof electrical equipment
Flammable gas detectore around process
and storage areas interlocked to a
sprinkler system
P>
N
(Continued)
-------
TABLE 3-20. (Continued)
Location
Condition
Process Hazard
Leading to Release
Examples of Hazard Controls
00
Process or storage
areas
Ketazine reactor
in hydrazine
manufacturing
process
Loss of inert gas
blanket
Loss of temperature
control
Formation of explo-
sive mixture
Thermal decomposi-
tion an'd overpres-
surization leading
to relief valve
discharge or equip-
ment failure and
release; possible
fire or explosion
Flammable gas detectors inside storage
vessels
Backup inert gas system
Flame arresters on any vent connections
Backup cooling system with redundant
control
Maximum feed rates limited by flow
restrictions to reduce the potential for
a runaway reaction
Blast shields around high hazard
equipment•
Concentrating
column in
hydrazine manu-
facturing process
Final hydrate
column in anhydrous
hydrazine manufac-
turing process
Loss of cooling in
condenser or temp-
erature control in
reboiler
Loss of temperature
control
Overpressurization
leading to relief
valve discharge or
equipment failure
and release
Hydrazine decompo-
sition leading to
Overpressurization
and relief valve
discharge or equip-
ment failure and
Relief valve; redundant temperature
sensors and alarms; high reliability
controls: interlock to shut off reboiler
heat if condenser cooling fails
High reliability heating controls;
redundant temperature sensing and
alarms; interlock to shut off heating
with excess temperature or failure of
condenser cooling
a
1-1
u
N
H-
re
-------
Hydrazine
TABLE 3-21. MATERIALS OF CONSTRUCTION REPORTED TO BE
COMPATIBLE WITH HYDRAZINE
Compatible with Hydrazine
Aluminum Alloy Nos. 356. B3S6, Inconel-X®
1100, 2014. 2024. 4043, 5052 Kel-F»
6061, 6066, and Tens 50 Polyethylene
Chromium plating Stainless Steel 304, 321,
Graphite 347. and 1707 pH
Inconel* Teflon*
Not Compatible with Hydrazine
Carbon Steel Nickel
Copper Stainless Steel AM-350
and AM-355
Hastelloys* Monel*
Magnesium Lead
Iron Zinc
Source: References 43 and 44
3-82
-------
Hydrogen Sulfide
3.7 HYDROGEN SULFIDE
Hydrogen sulfide is a colorless gas used in Che manufacture of numerous
sulfur compounds, especially various inorganic sulfides, and alkyl mercaptans.
A detailed discussion of uses appears in Subsection 3.7.2.
Little information is currently available concerning the size of the U.S.
market for hydrogen sulfide; however, it appears to be currently manufactured
at ten sites in the United States. It is used primarily in manufacturing
sulfur, sulfuric acid, sulfur dioxide, sodium sulfide, and miscellaneous
mercaptans (33).
3.7.1 Chemical Characteristics
Physical Properties and Hazards--
Hydrogen sulfide is a colorless, flammable, toxic gas at ambient
conditions, with a characteristic odor of rotten eggs. Table. 3-22 lists the
physical properties of hydrogen sulfide. Hydrogen sulfide is only slightly
soluble in water; however, it is soluble in some organic solvents and it is
very soluble in alkanolamines, which are often used as scrubbing solvents to
remove hydrogen sulfide from gas streams. Hydrogen sulfide is slightly more
dense than air- and will tend to stay close to the ground when released to the
atmosphere at ambient temperatures.
Because liquid hydrogen sulfide has a large coefficient of thermal
expansion, liquid-full equipment can pose a special hazard.
Chemical Properties and Hazards--
The chemical properties of hydrogen sulfide that contribute to the
potential for an accidental release include:
• Flammability - Hydrogen sulfide is flammable in air at
concentrations from 4.3 to 46 percent by volume of hydrogen
sulfide.
3-83
-------
Hydrogen Sulfide
TABLE 3-22. PHYSICAL PROPERTIES OF HYDROGEN SULFIDE
Reference
CAS Registry Number
Chemical Formula
Molecular Weight
Normal Boiling Point
Melting Point
Liquid Specific Gravity (H2O=D
Vapor Specific Gravity (air=l)
Vapor Pressure
Vapor Pressure Equation:
log Pv = A-
7783-06-4
H_S
34.08
-76.6 °F 8 14.7 psia
-117.2 °F
0.916 0 -76.6 °F
1.19
149.9 psia 8 68 °F
46
46
33
33
33
where: Pv = vapor pressure, mm Hg
T = temperature, °C
A = 6.99392. a constant
B = 768.130, a constant
C = 249.09. a constant
Liquid. Viscosity
Solubility in Water
Specific Heat at Constant Pressure
Latent Heat of Vaporization
Liquid Surface Tension
Heat of Combustion
Autoignition Temperature
Explosive Range. Volume % in
air 6 1 atm 3 68 °F
0.412 centipoise 6 32 °F
21
0.398 lb/100 Ib H20 @ 68 °F 33
0.2532 Btu/(lb-°F) e 70 °F 46
236.3 Btu/lb
59.6 dyne/cm 6 -76.6 "F
8.340 Btu/lb
500 °F
4.3 min.
46
46
21
46
33
33
(Continued)
3-84
-------
Hydrogen Sulfide
TABLE 3-22 (Continued)
Reference
Additional properties useful in determining other properties from physical
property correlations.
Critical Temperature 212.7 °F 46
Critical Pressure 89 atm 46
Critical Density 21.8 lb/ft3 46
3-85
-------
Hydrogen Sulfide
• Corrosivity - Dry, pure hydrogen sulfide does not react wich
common metals at ordinary temperatures. However, in the
presence of air or moisture, hydrogen sulfide is very corrosive
to metals.
• Reactivity - Hydrogen sulfide reacts rapidly with strong
oxidizing agents.
Toxicological and Health Effects--
Hydrogen sulfide is a highly toxic and asphyxiant gas that acts directly
on the central nervous system to cause paralysis of the respiratory system.
Hydrogen sulfide has a sweet odor at concentrations between 30 and 100 ppm and
deadens the sense of smell above this range (46). Relying on its rotten egg
odor can prove dangerous in certain situations.
The effects of hydrogen sulfide exposure vary, depending on the level of
exposure. Low level exposure may cause headache, nausea, fatigue, inflamma-
tion of the eyes and mucous membranes, labored breathing, digestive tract
disorders, vomiting, and diarrhea. More severe exposure can cause rapid heart
rate, weakness, sudden collapse, unconsciousness, and death. Acute exposure
can cause immediate death. Table 3-23 summarizes some of the relevant expo-
sure limits of hydrogen sulfide. Table 3-24 summarizes the human health
effects of exposure to various concentrations of hydrogen sulfide.
3.7.2 Facility Descriptions
This subsection provides brief descriptions of the manufacture and uses
of hydrogen sulfide in the United States. Major accidental release hazards of
these processes are discussed in Section 3.7.4.
Hydrogen Sulfide Manufacture--
Most hydrogen sulfide produced in the United States is either a by-
product of other processes or is obtained from natural gas contaminated with
hydrogen sulfide (33). Most hydrogen sulfide is sold as a liquified gas.
3-86
-------
Hydrogen Sulide
TABLE 3-23. EXPOSURE LIMITS FOR HYDROGEN SULFIDE
Concentration
Limit (ppm) Description Reference
IDLH 300 The concentration defined as posing an 23
immediate danger to life and health (i.e.
causes irreversible toxic effects for a
30-minute exposure).
PEL 20 A time-weighted 8-hour exposure to this 23
concentration, as set by the Occupational
Safety and Health Administration (OSHA),
should result in no adverse effects for
the average worker.
LC-. 600 This concentration is the lowest published 25
lethal concentration for a human over a
30-minute exposure.
3-87
-------
Hydrogen Sulfide
TABLE 3-24. EFFECTS OF HYDROGEN SULFIDE INHALATION
Concentration
(PPM)
Effect of Exposure
20-150
500
<600
Severe burning of eyes, headache, dizziness.
conjunctivitis
For 30 minutes, headache, dizziness.
excitement, staggering, bronchitis.
bronchial pneumonia.
For 30 minutes, fatal through respiratory
paralysis.
Source: Reference 46
3-88
-------
Hydrogen Sulfide
The natural gas industry produces the largest quantity of by-product
hydrogen sulfide. The natural gas processing units use an amine solution to
absorb the hydrogen sulfide to "sweeten" the natural gas. Figure 3-13
illustrates this type of process. The recovered hydrogen sulfide is usually
used either as a feedstock for commercial sulfur recovery or sulfuric acid
production, or is flared or incinerated.
In petroleum refining, 90 percent of the sulfur accumulates in the gas
oil and coke-distillate fractions. Sulfur is removed by passing the
sulfur-rich fractions through a fixed bed catalyst with hydrogen, which
converts 80-90 percent of the sulfur to hydrogen sulfide and increases
hydrocarbon saturation. Concentrated in this manner, the sulfur is then
recovered by converting the hydrogen sulfide to sulfur in a Glaus unit or
equivalent process.
Several commercial processes have been developed for the manufacture of
hydrogen sulfide from heavy fuel oils -and sulfur and from methane, water
vapor, and sulfur. One such process is carried out in two steps. The first
step reacts methane with sulfur to form carbon disulfide and hydrogen sulfide.
This is followed by the hydrolysis of carbon disulfide to hydrogen sulfide.
Hydrogen sulfide is also manufactured by directly combining hydrogen gas
with elemental sulfur. In this process, hydrogen and sulfur vapor react at
approximately 950 "F in the presence of an alumina catalyst (33). This
reaction can also be carried out at elevated temperature and pressure without
a catalyst (46).
Hydrogen Sulfide Consumption--
Hydrogen sulfide is captured primarily in acid gas recovery and sulfur
recovery processes. The acid gas recovery usually acts as a feed to the
sulfur recovery process. Host hydrogen sulfide recovered as a by-product is
converted to elemental sulfur. Hydrogen sulfide is also used to manufacture
sulfuric acid and inorganic sulfides, including sodium sulfide and sodium
hydrosulfide, and a variety of mercaptans. Table 3-25 lists some end uses of
hydrogen sulfide.
3-89
-------
Natural Gas
u>
±
o
Natural Gas
Containing
Hydrogen
Sulfide
Absorber
Heat
Exchanger
Hydrogen Sulfide
Stripper
mono- or di-
ethanolamine with
hydrogen sulfido
mono- or di-
ethanolamine
Figure 3-13. Conceptual flow Jj attain "t a process for absorbing hydrogen sultide.
Adapted from: Reference 33
o
00
ID
3
M
&
Hi
O.
n
-------
Hydrogen Sulfide
TABLE 3-25. TYPICAL END USES OF HYDROGEN SULFIDE
Alkyl Hercaptans:
Butyl Mercaptan
Dodecyl Mercaptan
Ethyl Mercaptan
Methyl Mercaptan
Fropyl Mercaptan
Ammonium Polysulfide
Ammonium Sulfide
Dimethyl Sulfide
Mercaptobenzothiazole
Mercaptoethanol
Mercuric Sulfide
Molybdenum Disulfide
Potassium Hydrosulfide
Sodium Hydrosulfide
Sodium Sulfide
Sulfur
Sulfur Dioxide
Sulfuric Acid
Source: Reference 47
3-91
-------
Hydrogen Sulfide
Sulfur Production--
The Glaus process is the most widely used process for converting hydrogen
sulfide into elemental sulfur. The Stretford process, a combination process
that sweetens the feed gas and produces elemental sulfur, is also prominent.
Figure 3-14 shows two configurations of the Glaus process.
The process consists of a combustion stage catalytic converter and a call
gas cleanup stage. After entering the combustion stage, a portion of the
hydrogen sulfide is converted to sulfur dioxide. The sulfur dioxide and
remaining hydrogen sulfide react (usually in a catalytic converter) to produce
elemental sulfur, which is removed as a liquid in the condenser. The process
stream enters a reheater, passes to another converter, and condenses again.
The reheater-converter-condenser stages are linked in series to enhance
removal of hydrogen sulfide. Because most Glaus plants are unable to meet new
air pollution regulations for sulfur dioxide, the tail gas often goes to an
additional treatment process where residual hydrogen sulfide is removed (33).
In the Stretford process, hydrogen sulfide is absorbed into an alkaline
solution. The absorber solution is sent to a reactor where the hydrogen
sulfide is oxidized by vanadium to produce elemental sulfur. The alkaline
mixture of sulfur and reduced vanadium is sent to a series of vessels where
the sulfur is removed and the vanadium is oxidized and recycled (49) .
When hydrogen sulfide is converted to sulfur, usually the hydrogen
sulfide is present in the initial gas stream in a dilute form.' If the initial
hydrogen sulfide extraction column failed to extract the chemical, then the
hydrogen sulfide would exit with the gas stream. The consequences of this
would depend on the concentration of hydrogen sulfide in the gas stream and on
the ultimate destination of the gas stream. In most cases, the hydrogen
sulfide would probably be released to the atmosphere with the gas stream. The
hydrogen sulfide absorption column could fail if it were contaminated with
acid or if the scrubber liquid circulation pump were to fail, or if the
scrubber was not kept at a low enough temperature.
3-92
-------
IUIW4IW
1/3
21
Reaction
3
WMM
HMI
Boiler
. ,
COIIYMIM
Condtnuf
"1
f 1
Converter
r
i
Condmiw
T«H Ou
Sullui
Split - How configuration
Sullur
R*hMlM
w 1
VO
Ul
AddOu • -RiMllon *ail*
Al, J *"""" B8lto' 1
f CondMiui
r l l
COOMIIW
CondniMf
r1 1
Comwrur
r
CondMMr
Sulluf
Tail GM TraiMMiU
I T
Sulluf Sullui Sullui
Straight - through configuration
Figure 3-14. Conceptual flow diagram of two confjgurationu ot the Ciaus process.
Adapted from: Re Terence 48
Q.
n
o
09
n
9
M
H)
H-
O.
(B
-------
Hydrogen Sulfide
Sodium Sulfide Production--
Hydrogen sulfide is used for the manufacture of sodium sulfide. In this
process, hydrogen sulfide is bubbled through an excess of sodium hydroxide in
water, where sodium sulfide and water are formed. The reaction is exothermic
and heat is removed either by evaporating water from the mixture or by
cooling. The product mixture is often concentrated by evaporation to 60
weight percent sodium sulfide (33).
Sulfuric Acid Production--
Occasionally, hydrogen sulfide is used to produce sulfuric acid. In this
process hydrogen sulfide is burned in air to produce sulfur dioxide. The
sulfur dioxide is then catalytically converted to sulfur trioxide, which is
hydrated to sulfuric acid by absorption into an aqueous sulfuric acid stream
(33).
Nercaptan Production--
Most mercaptans are made by reacting hydrogen sulfide with olefins or
alcohols <33). The details of the process will depend on the specific olefin
or alcohol used. For example, ethyl mercaptan can be manufactured by exposing
a continuous stream of ethylene and excess hydrogen sulfide vapors to
ultraviolet light. The excess hydrogen sulfide can be stripped from the
product ethyl mercaptan and recycled back to the reactor.
3.7.3 Summary of Major Process Hazards and Control Technologies
To reduce the risk of an accidental release, specific measures broadly
classified as prevention, protection or mitigation measures may be applied.
General features of these measures are discussed in Section 2 and are
presented in greater detail in other technical literature.
The properties of hydrogen sulfide that contribute to the risk of a
release are its corrosiveness and flammability. Hydrogen sulfide releases can
originate from many sources, including ruptures in process equipment,
3-94
-------
Hydrogen Sulfide
separated flanges, actuated relief valves or rupture disks, leaks at joints
and connections, and failed pumps.
Since hydrogen sulfide has a deceptively sweet smell at 30-100 ppm
concentrations and deadens the sense of smell above these levels, hydrogen
sulfide vapor detection devices should be located throughout facilities that
store and handle hydrogen sulfide. Enclosures for hydrogen sulfide storage
vessels or process facilities should be used with extreme caution because
toxic concentrations can accumulate.
Below is a summary of hazard areas in the hydrogen sulfide manufacturing,
use and storage processes.
Hydrogen Sulfide Production--
For all hydrogen production processes, the primary hydrogen sulfide
release hazards are in the final hydrogen sulfide purification steps. In all
cases, the reactors used to recover or produce hydrogen sulfide have low
inventories of dilute hydrogen sulfide and therefore a low risk of
accidentally releasing hydrogen sulfide.
Host of the processes incorporate a final distillation step where the
purified hydrogen sulfide is removed, and a large in-process inventory of
hydrogen sulfide is present during this step. A condenser coolant failure
could lead to an overpressure followed by an accidental release. Corrosion or
wear of pumps and piping systems could also result in a release.
Sodium Sulfide Production--
During sodium sulfide production, as long as there is an excess of sodium
hydroxide, there is little chance of an accidental release of hydrogen
sulfide. However, a loss of feed or composition control could result in
incomplete reaction and hydrogen sulfide pressure could build in the reaction
vessel and be accidentally released. In addition, a loss of temperature
control in the reactor could raise the temperature to a point where the
hydrogen sulfide escapes before reacting, which could lead to an accidental
3-95
-------
Hydrogen Sulfide
release as a result of hydrogen sulfide pressure in the reactor. Where
mechanical agitation is required, a loss of agitation could also result in
incomplete reaction and hydrogen sulfide overpressure.
Sulfuric Acid Production--
As long as sufficient air is available, there is little chance of a
hydrogen sulfide release from this process. However, a loss of air supply
could result in an accumulation of unreacted hydrogen sulfide, leading to an
accidental release.
Mercaptan Production--
Because mpst mercaptans are manufactured with an excess of hydrogen
sulfide, the potential exists for a hydrogen sulfide release from the hydrogen
sulfide recirculation equipment. Pumps, valves, and piping in the recircula-
tion system are all potential sources of a hydrogen sulfide release. Also.
all mercaptan manufacturing processes involve a catalyst. Deactivation of the
catalyst could result in an incomplete reaction, which would result in an
accumulation of unreacted hydrogen sulfide, excess pressure, and an accidental
release.
Table 3-26 presents examples of possible locations, conditions and
process hazards which could potentially lead to a hydrogen sulfide release,
and example controls for reducing the risk of such a release. The examples
are intended to be illustrative, not exhaustive.
3.7.4 Storage and Handling
Hydrogen sulfide is classified as a flammable gas and poison. As such,
it has several dangerous properties and should be handled and stored as any
flammable gas. Because it is heavier than air, hydrogen sulfide will collect
and concentrate in low-lying areas. It forms explosive mixtures with air over
a wide range of conditions and also reacts explosively with some halogenated
compounds. When heated to decomposition, it emits toxic fumes of oxides of
sulfur.
3-96
-------
TABLE 3-26. EXAMPLE CONDITIONS. PROCESS HAZARDS AND HAZARD CONTROLS IN
HYDROGEN SULFIDE MANUFACTURING AND USE
Location
Condition
Process Hazard
Leading to Release
Examples of Hazard Controls
Vessels, pumps.
piping
Corrosion including
stress corrosion
cracking, and
hydrogen embrittle-
ment
Equipment .failure
Proper construction material selection
Routine inspection and testing
Verify the materials of construction for
new equipment items by testing
ui
Sulfide manufacturing Loss of cooling
reactor
Combustion reactor or Loss of temperature
catalytic converter control
Excessive exother-
mic reaction
Overheating and
overpressurization
Redundant temperature sensors with alarms
Backup cooling system
Adequate pressure relief
Redundant flow control with automatic
shutoff during upset
Redundant temperature sensors with alarms
Backup cooling system
Adequate pressure relief
Redundant flow control with automatic
shutoff during upset
O
00
(D
W
c
(Continued)
a
n>
-------
TABLE 3-26. (Continued)
Location
Condition
Process Hazard
Leading to Release
Examples of Hazard Controls
Process or storage
vessels
Fire or explosion
nearby
Loss of contain-
ment
Where possible, inert the vapor space on
all process or storage vessels of flam-
mable materials
Hydrogen sulfide storage tanks isolated
from potential sources of ignition
Flammable gas detectors throughout process
or storage areas
Relief valves sized for heating due to
fire"
VO
00
Reactor
Reactor
Catalyst
Loss of feed or
composition control
Loss of temperature
control
Deactivation of
catalyst
Overpressuris ation
leading to pressure
relief discharge or
equipment failure
and release
Excess temperature
with overpressurei-
zation and same
result as above
Overpressurization
with results as
above
Pressure relief; pressure alarm and in-
terlocks with feed shutoff
Pressure relief; redundant temperature
measurement and alarms
Pressure relief; monitoring feedstock
specifications to prevent catalyst
poisoning
Sodium Sulfide Production rrocess
2
Hercaptan Production
«<
a
ft
o
oo
n
a
ID
-------
Hydrogen Sulfide
Anhydrous (dry) hydrogen sulfide is noncorrosive to many commonly used
materials of construction. However, moist or wet hydrogen sulfide is very
corrosive to most metals. Table 3-27 lists construction materials suitable
for hydrogen sulfide service. Hard steels, if highly stressed, are suscep-
tible to hydrogen embrittlement by hydrogen sulfide. Additionally, hydrogen
sulfide can produce severe sulfidation of metals at elevated temperatures and
high strength steels may suffer stress corrosion cracking in the presence of
moist hydrogen sulfide. Therefore, materials of construction must be care-
fully chosen to fit the service.
Steel or black iron pipe is commonly used for dry hydrogen sulfide (46).
For wet hydrogen sulfide, aluminum and certain stainless steels are commonly
used (46). Brass valves, although tarnished by hydrogen sulfide, hold up well
in service. However, all lines carrying hydrogen sulfide are subject to
corrosion and embrittlement and are prone to develop leaks.
Hydrogen sulfide may be shipped by rail, highway, water, or air. It can
only be shipped in cylinders and TMU (ton multi-unit) tanks and tank cars that
meet Department of Transportation (DOT) specifications (46). The cylinders
must be retested hydrostatically every five years, and each tank must be
equipped with a safety relief device of a fusible plug type that will yield at
temperatures of 157-170 degrees Fahrenheit (46). The tanks must be leak-tight
at 130 degrees Fahrenheit (46).
3-99
-------
Hydrogen Sulfide
TABLE 3-27. MATERIALS OF CONSTRUCTION REPORTED TO BE
ACCEPTABLE FOR HYDROGEN SULFIDE SERVICE
For Wet For Dry
Material or Dry H.S H.S Only
Aluminum X
Brass X
Carbon Steel X
Copper X
Copper-Nickel Alloys X
Hastelloys* X
Inconel* X
Lead X
Nickel X
Platinum X
Stainless Steel. Type 304 X
Stainless Steel. Type 310 X
Stainless Steel. Type 316 X
Tantalum X
Teflon* X
Titanium X
Source: Adapted from Reference 40
3-100
-------
Mechlorethamine
3.8 MECHLORETHAMINE
Mechlorechamine is reported to be a drug used in the treatment of cancer
and also a former chemical warfare agent under the name of nitrogen mustard
(24). .It is a toxic liquid.
No information was found concerning the size of any U.S. market for
medical applications of mechlorethamine. Mechlorechamine is reported to be
produced at one site in Che United States for use in military research (25).
3.8.1 Chemical Characteristics
Physical Properties and Hazards--
Mechlorethamine is a liquid at ambient conditions with a faint odor of
herring. It is only slightly soluble in water. Table 3-28 lists a few of the
physical properties of mechlorethamine that were found reported in the
technical literature (24). As a liquid, the primary release hazard is liquid
spills. Its low vapor pressure indicates that it probably poses little threat
as an air toxic.
Chemical Properties and Reactivity and Hazards--
Little information has been reported concerning the chemical properties
and reactivity of mechlorethamine; however, it is known that pure
mechlorethamine decomposes on standing (24). Previous work has been unable to
locate even such basic information as vapor pressure data, although with a
reported boiling temperature of 189 °F at 18 mm Hg, the vapor pressure appears
to be quite low and the normal boiling point is quite high. It would not
appear, therefore, to pose a significant vapor threat if spilled at ambient
conditions. Its very slight solubility in water, and its specific gravity
slightly higher Chan water suggests that vapor emissions could be controlled
by covering a spill with vater. Of course, proper cleanup procedures would be
required to prevent land or water runoff contamination. No specific
information was found on whether or not this chemical is flammable.
3-101
-------
Mechlorethamine
TABLE 3-28. PHYSICAL PROPERTIES OF MECHLORETHAMINE
Reference
CAS Registry Number 51-75-2
Chemical Formula CgH-.Cl-N
Molecular Weight 156.07
Boiling Point 189°F 9 18 aim HG 24
Melting Point -76°F 24
Specific Gravity (H20=l) 1.118 ® 77°F 24
Solubility in Water Very slight 24
3-102
-------
Hechlorethamine
Toxicological and Health Effects--
Mechlorethamine is reported to be a chemotherapy drug used in treating
cancer (24). Toxic doses as Low as 0.4 mg/kg have been reported in humans
(20). The warning signs of mechlorethamine poisoning include: nausea,
vomiting, bleeding, and skin lesions. Delayed effects can include hair loss,
hearing loss, jaundice, impaired spermatogenesis and germinal aplasia, and
hypersensitivity. Severe exposure can result in death.
3.8.2 Facility Descriptions
Mechlorethamine Manufacture•-
No information on manufacture was found in the technical literature
including a search through Chemical Abstracts. The general nature of this
chemical suggests a batch chemical manufacturing procedure. As a result, no
specific process features significantly heightening the generic release
hazards of Section 2 can be identified.
Hechlorethamine Consumption--
Mechlorethamine is reported as currently used in research being conducted
by the U.S. military and as a drug to treat cancer. (24)
3.8.3 Summary of Hal or Process Hazards and Control Technologies
There appears to be no specific information on the process
characteristics of mechlorethamine manufacture or use in the open technical
literature. Its toxicity suggests that all procedures are in accord with
practices for other toxic substances which are covered in Section 2 of this
manual and other technical literature. Fundamentally, selection of proper
materials of construction, and special attention to the design, construction,
operation, and maintenance details of equipment and procedures is required to
minimize the chances for a release.
At ambient conditions, a release of mechlorethamine will result in a
liquid spill. Proper containment by curbing or dikes around process
3-103
-------
Hechlorethamine
equipment, and a method for absorbing or otherwise cleaning up a spill is
required. Adequate ventilation should be provided to minimize inhalation of
vapors. The toxicity of this chemical suggests that ultimate disposal of
spill residues should avoid possible water or land contamination.
3.8.4 Storaee and Handling
No information specific to the storage and handling of mechlorethamine
was found in the technical literature surveyed. Since mechlorethamine is a
liquid at room temperatures, storage and handling practices are expected to be
those generic practices common to any toxic liquid. These practices have been
discussed elsewhere in this manual. It has been reported that the undiluted
liquid decomposes on standing.
3-104
-------
Methiocarb
3.9 METHIOCARB
Methiocarb is a broad spectrum carbamate pesticide. Little information
is available concerning the size of the U.S. market for methiocarb. It is
used solely as a pesticide in the United States and is manufactured at only
one site in the United States.
3.9.1 Chemical Characteristics
Physical Properties--
Methiocarb is a white crystalline powder with a mild odor. It is soluble
in acetone and alcohol, but is only slightly soluble in water. Table 3-29
lists a few of the physical properties of methiocarb.
Chemical Properties and Reactivity--
Little information is available concerning the chemical properties of
methiocarb. However, it Is known that methiocarb decomposes when heated,
forming highly toxic nitrogen and sulfur oxides. In addition, methiocarb is
unstable in highly alkaline media.
Toxicological and Health Effects--
Methiocarb is a highly toxic carbamate insecticide. The probable oral
lethal dose for a human is approximately 50 to 500 ppm or between 1 teaspoon
and 1 ounce for a 150-pound adult (24). Exposure can result in slowed
heartbeat, blurred vision, slight paralysis, muscle twitching, nausea,
vomiting, diarrhea, and abdominal pain. Acute exposure can result in
unconsciousness, convulsions, and death.
3.9.2 Facility Descriptions
This subsection provides brief descriptions of the manufacture and uses
of methiocarb in the United States.
3-105
-------
Methiocarb
TABLE 3-29. PHYSICAL PROPERTIES OF METHIOCARB
Reference
CAS Registry Number
Chemical Formula
Molecular Weight
Melting Point
Vapor Pressure
Solubility in Water
2-32-65-7
C11H15N02S
225.3
243 °F
1 z 10~4mm Hg
0.0027 lb/100 Ib
24
17
17
3-106
-------
Methiocarb
Hechiocarb Manufacture--
Little information is available concerning the manufacture of methiocarb;
however, it is known that methiocarb can be manufactured by the reaction of
methyl isocyanate and 4-methylthio-3,5-xylenol, although details of the
process are confidential (45). A small-scale process has also been patented
for laboratory synthesis (45).
Methiocarb Consumption--
Methiocarb is used as an insecticide, acaricide, and molluscicide. It is
used for insect control on various types of fruits and vegetables and in baic
pellets to control slugs and snails. It is also used as a bird repellent on
corn seed, cherries, and blueberries.
3.9.3 Summary of Major Process Hazards and Control Technologies
The mosC important property of 'methiocarb that can promote equipment
• .
failure is its ability to decompose to nitrogen and toxic sulfur oxide gases
on heating. Thus, loss of temperature control to any process vessel con-
taining methiocarb could lead to overpressure and eventual equipment failure.
The capacity and integrity of temperature control and cooling systems must
therefore be carefully evaluated for systems that handle methiocarb. Redundant
temperature sensors with alarms and backup cooling systems may be in order for
some processes. Reaction feed flowrates should be limited so that a loss of
mixing or cooling will not lead to thermal decomposition. This discussion is
intended to be illustrative and not exhaustive. A discussion of hazard
prevention and control appears in Section 2.
3.9.4 Storage and Handling
Little information is available concerning the storage and handling of
methiocarb. It should be stored away from potential sources of fire since it
decomposes on heating. It should be kept dry since the liquid solutions are
also highly toxic.
3-107
-------
Methyl Bromide
3.10 METHYL BROMIDE
Methyl bromide is a colorless gas at typical room temperature and is a
soil and space fumigant and as a chemical intermediate. Methyl bromide is
produced by the esterification of methanol with hydrobromic acid. In 1983, it
was estimated that 35 million pounds of methyl bromide were manufactured in
the United States (18). At that time, the projected demand for 1987 was 25
million pounds (18). As of 1984, three manufacturers with capacities of 8,
30, and 35 million pounds of methyl bromide existed in the United States (18).
In 1984, the uses of methyl bromide manufactured in the United States
were as follows: soil fumigant, 80 percent; space fumigant, 15 percent; and
other uses, 5 percent.
3.10.1 Chemical Characteristics
Physical Properties and Hazards--
Methyl bromide is a colorless gas at ambient conditions, but it liquefies
at moderate pressures. Table 3-30 lists the physical properties of methyl
bromide.
Methyl bromide is only slightly soluble in water. The gas is 3.3 times
more dense than air and will tend to stay close to the ground when released
into the atmosphere. Because liquid methyl bromide has a large coefficient of
thermal expansion, liquid-full equipment can pose the hazard of rupture on
heating.
Chemical Properties and Hazards--
The most significant chemical properties of methyl bromide that can
contribute to the potential for an accidental release are as follows:
Flammability - Methyl bromide is flammable in air at
concentrations from 10 to 16 percent methyl bromide.
3-108
-------
Methyl Bromide
TABLE 3-30. PHYSICAL PROPERTIES OF METHYL BROMIDE
Reference
CAS Registry Number 74-83-9
Chemical Formula CH.Br
Molecular Weight 94.94
Normal Boiling Point 38.41 °F @ 14.7 psia 33
Melting Point -136.7 °F 33
Liquid Specific Gravity (H20=l) 1.732 3 32 °F 50
Vapor Specific Gravity (air=l) 3.3 6 68 °F 50
Vapor Pressure 27.5 psia 8 68 °F 50
Vapor Pressure Equation: 51
log Pv = A- -2g
where: Pv = vapor pressure, mm Hg
T = temperature. °C
A = 6.95965. a constant
B = 986.590. a constant
C = 238.32. a constant
Liquid Viscosity 0.324 Centipoise 6 77 °F 33
Solubility in Water 1.75 lb/100 Ib solution 50
3 68 °F
Specific Heat at Constant Pressure 0.107 Btu/(lb-°F) @ 77 °F 33
Latent Heat of Vaporization 108.4 Btu/lb @ 38.4 °F 33
Average Coefficient of Thermal 0.00163/°F 33
Expansion. 5-37°F
Liquid Surface Tension 25.5 dynes/cm 6 32 °F 51
Autoignition Temperature 998 °F 50
Explosive Range. Volume % in air 10 min. 50
16
(Continued)
3-109
-------
Methyl Bromide
TABLE 3-30. (Continued)
Reference
Properties useful in determining other properties from physical property
correlations.
Critical Temperature 318.2 °F 51
Critical Pressure 757 psia 51
Critical Density 38.09 lb/ft3 51
3-110
-------
Methyl Bromide
• Decomposition - Thermal decomposition of methyl bromide to
produce carbon monoxide, carbon dioxide, and highly toxic
bromides can occur above 750 °F (39).
• Decomposition - In aqueous solution, methyl bromide can undergo
hydrolysis to methanol and hydrobromic acid. The rate of
hydrolysis increases in the presence of alkaline materials.
• Corroslvity - Most metals commonly used as materials of
construction are inert to pure, dry methyl bromide. One
exception is aluminum. However, in the presence of moisture or
alcohols, corrosion of zinc, tin, and iron occurs.
Toxicological and Health Effects--
Methyl bromide is highly toxic by inhalation and skin absorption. It has
very little odor or irritating effects, even at high concentrations, and thus
gives no warning. It is a dangerous cumulative poison. Delayed symptoms that
may appear several hours after inhalation include dizziness, headache, nausea,
vomiting, abdominal pain, weakness, blurred vision, mental confusion, convul-
sions, collapse, and coma. Repeated exposure can cause central nervous system
depression, kidney damage, and permanent brain damage. Severe exposure can
result in fatal pulmonary edema. The International Agency for Research on
Cancer (IARC) has determined that there is limited animal evidence and
inadequate human evidence that methyl bromide is a carcinogen. The
Occupational Safety and Health Administration (OSHA) standard in air for
methyl bromide is a ceiling limit of 20 ppm. Workers should never be exposed
to a concentration higher than this limit. The OSHA standard also notes that
methyl bromide is harmful when absorbed through the skin (25). The LD__ for
rats via ingestion is 214 mg/kg (25). Table 3-31 summarizes some of the
relevant exposure data for methyl bromide.
3-111
-------
Methyl Bromide
TABLE 3-31. EXPOSURE LIMITS FOR METHYL BROMIDE
Concentration
Limit (ppm) Description Reference
IDLH 2.000 The concentration defined as posing an 23
immediate danger to life and health
(i.e., causes irreversible toxic
effects for a 30-minute exposure).
PEL 20 A time-weighted 8-hour exposure to 23
this concentration, as set by the
Occupational Safety and Health
Administration (OSHA), should result
in no adverse effects for the average
worker.
35 This concentration is the lowest pub- 20
lished concentration causing toxic
effects (irritation) for a 1-minute
exposure.
CTQ 60,000 This concentration is the lowest pub- 20
lished lethal concentration for a
human over a 2-hour exposure.
3-112
-------
Methyl Bromide
3.10.2 Facility Descriptions
This subsection provides brief descriptions of the manufacture and uses
of methyl bromide in the United States. Section 3.7.3 discusses major
accidental release hazards of these processes.
Methyl Bromide Manufacture--
Methyl bromide is manufactured primarily by the reaction of hydrobromic
acid with methanol. Figure 3-15 is a flow diagram of a typical manufacturing
process.
In this particular process, hydrobromic acid and methanol are fed to a
reactor. The reaction is carried out in the presence of concentrated sulfuric
acid (33).* The crude reaction products are sent to a distillation column
where methyl bromide is removed and methanol and hydrobromic acid are recycled
to the reactor. The product is dried to remove residual water and is redis-
tilled to remove impurities.
Processes also exist in which sulfuric acid is added to a solution of
sodium bromide and methanol in a reactor to produce methyl bromide. The
methyl bromide is then recovered in a manner similar to that discussed above.
Methyl Bromide Consumption--
Methyl bromide is used primarily as a soil fumigant, insecticide,
rodenticide, and nematocide (18). In 1984, agricultural and related applica-
tions accounted for approximately 9SZ of the U.S. consumption. In addition co
these agricultural uses, methyl bromide is used as an intermediate in the
manufacture of Pharmaceuticals and other agricultural chemicals, as a fire
extinguishing agent, and also as a selective solvent.
3.10.3 Summary of Major Process Hazards and Control Technologies
To reduce the risk of an accidental release, specific measures broadly
classified as prevention, protection or mitigation measures may be applied.
3-113
-------
aununc
Add
H
Drying
lower
L
^ Condenser
Dilute
"*" Sulfunc
Acid
1
Dislillalion
Column
' *• Imp
Bromide
Sulluric Acid
I
M
5
Hydrobromtc Add »
Re
actor
Dlsi
UttaUon
KBr * Methanol
Recycle
Figure 3-15. Conceptual flow diagram of typical methyl bromide manufacturing process.
Adapted from: Reference 33
H-
a
it
-------
Methyl Bromide
These measures are discussed generally in Section 2 in this manual and are
discussed in other technical literature. The properties of methyl bromide
that contribute to the risk of a release are its relatively low boiling point.
high vapor pressure, flannnability and corrosivity.
The highest hazard area for this process appears to be the methyl bromide
recovery column. An upset with this distillation column could lead to a
methyl bromide release. Corrosion of process equipment could also result in
an accidental release of methyl bromide from this process. The presence of
sulfuric and hydrobromic acids in the process can be expected to cause
corrosion problems. Inappropriate materials of construction could fail.
resulting in an accidental release of methyl bromide.
Table 3-32 presents examples of locations, conditions and process hazards
which could potentially lead to a methyl bromide release, as well as example
controls for reducing the risk of such a release. The examples are intended
to-be illustrative, not exhaustive.
3.10.4 Storage and Handling
Methyl bromide is stored as a liquefied gas in pressure vessels because
of its relatively low boiling point and high vapor pressure. Methyl bromide
is also stored in cylinders for small-scale use and is shipped by tank car.
Since no pressure relief devices are used on cylinders containing methyl
bromide (53), all sources of heat must be kept away from cylinders to prevent
hydrostatic pressure buildup from leading to overpressure (52).
Table 3-33 lists materials of construction reported to be suitable for
methyl bromide service. It is not particularly corrosive to most metals and
is noncorrosive when completely dry. However, when aluminum and aluminum
alloys are attacked by methyl bromide, aluminum trimethyl is formed, which is
spontaneously combustible.
3-115
-------
TABLE 3-32. EXAMPLE CONDITIONS. PROCESS HAZARDS. AND HAZARD CONTROLS IN
METHYL BROMIDE MANUFACTURING AND USE
Location
Condition
Process Hazard
Leading to Release
Examples of Hazard Controls
Methyl bromide
product distilla-
tion units
Loss of condenser
cooling
Overpressiirization Reboiler heating interlocked to temperature
sensors on condenser
Adequately-sized pressure relief
Relief discharge to a flare or scrubber
Excess methyl
bromide feed
Overfilling: High level sensor and alarm interlocked
overpreasurization with feed flow controller
Feed flow restrictors
Overflow catch tank
Improved operator training and operating
procedures
Process or storage
Fire or explosion
nearby
Overheating and
overpressurization
Flammable gas detectors around process and
storage areas
Adequate fire protection
Relief valve sized for heating due to fire
Tanks, vessles. and storage cylinders
isolated from flammable materials and
sources of ignition
oo
1
H-
o.
n
(Continued)
-------
TABLE 3-32. (Continued)
Location
Condition
Process Hazard
Leading to Release
Examples of Hazard Controls
Storage vessel lines Backflow of water Corrosion and
to storage vessels equipment failure
Rarely used or unnecessary water lines dis-
connected or blinded off
Check valves or feed tanks in essential water
lines
Routine corrosion inspection
Inadequate water
removal from
methyl bromide
product
Corrosion and
equipment failure
Routine corrosion inspection
Improved materials of construction for high
risk equipment.
00
3
3
H-
O.
ID
-------
Methyl Bromide
TABLE 3-33. MATERIALS OF CONSTRUCTION REPORTED TO BE SUITABLE
FOR METHYL BROMIDE SERVICE
Braes
Copper
Hastelloy-B*
Hastelloy-C«
Inconel*
Lead
Mild Steel
Monel*
Nickel
Silver
Stainless Steel
Titanium
Zirconium
Source: Adapted from Reference 26
3-118
-------
Sodium Azide
3.11 SODIUM AZIDE
Sodium azide is a chemical intermediate used in the manufacture of
Pharmaceuticals. It is also used as an explosive, herbicide, fungicide,
nematicide, and soil fumigant.
No information was found concerning the size of the U.S. market for
sodium azide; however, it is reported as not currently being manufactured at
any site in the United States (S3).
3.11.1 Chemical Characteristics
Physical Properties and Hazards--
Sodium azide is a colorless solid. It is soluble in water, slightly
soluble in ethyl alcohol and benzene, and insoluble in ether. Table 3-34
lists the physical properties of sodium azide. As a solid, dust or fumes from
prpcess operations present the major air release hazard.
Chemical Properties and Hazards--
Sodium azide is a combustible solid (54). It can decompose explosively
on heating, shock, concussion, or friction (54). Decomposition products
consist of nitrogen oxides, which are extremely explosive. Sodium azide
reacts with copper, silver, mercury, and lead to form explosive azides. It
can form highly toxic hydrazoic acid fumes in the event of a fire. In addi-
tion, sodium azide is incompatible with bromine, benzoyl chloride, potassium
hydroxide, carbon disulfide, sulfuric acid, and nitric acid (54). Its overall
reactivity and chemical instability contribute significantly to an accidental
release hazard, since these attributes could set off a chain of events leading
to a release.
Toxicological and Health Effects--
Sodium azide is highly toxic by ingestion, inhalation and skin absorp-
tion. Ingestion or inhalation can result in dizziness, weakness, blurred
vision, shortness of breath, hypertension, slowed heart rate, abdominal pain
3-119
-------
Sodium Azide
TABLE 3-34. PHYSICAL PROPERTIES OF SODIUM AZIDE
Reference
CAS Registry Number
Chemical Formula
Molecular Weight
Melting Point
Specific Gravity (H20=l)
Solubility in Water
26628-22-8
65.02
Decomposes at 572 °F
1.85 6 68 °F
42 lb/100 Ib H20 9 63 °F
54
24
24
3-120
-------
Sodium Azide
and reduced body temperature and pH. Acute exposure can result in convulsion,
unconsciousness, and death. Skin contact can result in redness and pain.
When sodium azide is absorbed through the skin, it produces symptoms similar
to those of inhalation or ingestion. The only exposure limit established for
sodium azide to date has been a Threshold Limit Value (TLV) of 0.1 ppm, as sec
by the American Conference of Governmental Industrial Hygienists (ACGIH) (24).
The LD_Q for rats via oral routes is 27 mgAg (25).
3.11.2 Facility Descriptions
This subsection provides brief descriptions of the manufacture and uses
of sodium azide in the United States. Major accidental release hazards of
these processes are discussed in Section 3.11.3.
Sodium Azide Manufacture--
Sodium azide has been manufactured by a liquid ammonia process in the
United States. Figure 3-16 is a flow diagram of a typical manufacturing
process.
In this process, sodium reacts with liquid ammonia in the presence of a
catalyst such as ferric nitrate, to form sodamide. The sodamide, along with
nitrous oxide, is fed to a reactor where sodium azide, sodium hydroxide, and
additional ammonia are produced. The reaction is typically carried out at a
temperature of approximately 86 *F (55). The ammonia produced during the
reaction is vented from the reactor. The sodium azide product is then sepa-
rated from the caustic solution by crystallization from water.
Sodium Azide Consumption--
Sodium azide is used primarily as an intermediate chemical in the manu-
facture of Pharmaceuticals. It is also used as an explosive, and has been
used as a herbicide, fungicide, nematicide, and soil fumigant. Other end uses
of sodium azide include: propellant for inflating automotive air bags,
retarder in the manufacture of sponge rubber, anticoagulant in styrene and
butadiene latexes, a reagent in water pollution analysis, and an intermediate
3-121
-------
10
(O
Slurry of
Sodambtein »
Liquid Ammonia
Nitrous
Oxide
Reactor
i
By-product
Ammonia
Recrysfattuer
I
Sodium
Hydroxide
^ Sodium
Azide
Figure 3-16. Conceptual flow diagram of typical sodium ezide manufacturing process.
Adapted from: Reference 33
o
o.
H-
O.
ID
-------
Sodium Azide
in organic synthesis. Limited information is available on the various uses of
sodium azide since most are small, limited-scale uses.
3.11.3 Summary of Maior Process Hazards and Control Technologies
To reduce the risk of an accidental release, specific measures broadly
classified as prevention, protection or mitigation measures may be applied.
These measures are discussed generally in Section 2 in this manual and are
described in other technical literature.
The most important property of sodium azide that can promote equipment
failure is its ability to decompose explosively on heating, shock, concussion,
or friction. Thus, loss of temperature control to any process vessel
containing sodium azide could result in explosion and equipment failure.
Redundant temperature sensor and controllers should be used in high-
temperature applications.
The product recrystallizer is the manufacturing process location with the
greatest potential for an accidental release. Spills or leaks of material
from the crystallizer would result in a solids contamination of the air by
dust or fumes, and of the surrounding area by solids deposition.
The primary release hazard in its use as an intermediate chemical is
careless storage and handling of the solid chemical.
Sodium azide must be stored away from heat sources since it is a
combustible solid and can explode on heating, shock, concussion, or friction.
Care must therefore be taken when sodium azide is transferred from a storage
container to a process. Large inventories of sodium azide should be located
away from other process areas. Blast shielding may be considered where sodium
azide must be routinely handled.
3-123
-------
Sodium Azide
A special hazard with sodium azide is the possible accumulation of Che
solid in inadequately cleaned equipment and facility areas. Proper employee
training and well•documented procedures are essential when handling sodium
azide. Inadequate fire protection in process or storage areas could also lead
to loss of containment. Process or storage areas should be protected with
sprinkler systems, and blast shields may be appropriate for some applications.
Table 3-35 presents examples of possible locations, conditions and
process hazards which could potentially lead to a sodium azide release, as
well as example controls for reducing the risk of such a release. This
discussion is intended to be illustrative, not exhaustive.
3.11.4 Storage and Handling
Limited information is available concerning the storage and handling of
sodium azide. It is stored in polyethylene or similar type drums (54), and it
is compatible with most common materials of construction, but as noted in
Section 3.11.1, it reacts with a number of metals to form extremely explosive
azides.
3-124
-------
Sodium Azide
TABLE 3-35. EXAMPLE CONDITIONS, PROCESS HAZARDS AND EXAMPLE HAZARD CONTROLS
IN SODIUM AZIDE MANUFACTURING AND USE
Location
Condition
Process Hazard
Leading or Release
Examples of
Hazard Controls
Sodium Azide
Product
Recrystallizer
Solids contamination
by dust or fumes
Accummulation of
solids on equip-
ment can lead to
conditions where
heating, shock,
concussion, or
friction could
lead to explosive
decomposition: the
resulting damage
can lead to an
accidental release
Storage and
Solids contamination (see above)
Fire
Handling Areas by dust
Heating of stored
solids leading to
explosion and
release of toxic
solids
Good
housekeeping;
employee
training;
locate large
inventories away
from other
process areas;
blast shielding
for routine
handling areas;
sprinkler
systems
(see above)
Adequate fire
protection
Process Vessel
Loss of temperature
control
Explosion and
equipment failure
Redundant
temperature
sensor and
controllers in
high-temperature
applications
3-125
-------
Tetraethyl Tin
3.12 TETRAETHYL TIN
Tetraethyl tin is reported to be used as a pesticide, and may have
applications as a catalyst, and preservative for wood, textiles, paper and
leather (24). It is reported as not being a registered pesticide in the U.S.
(24). Little information is available concerning the size of the U.S. market
for tetraethyl tin; it is not currently being manufactured in the United
States, although it can be manufactured on request at one site. It has also
been reported as having no commercial utility (33).
3.12.1 Chemical Characteristics
Physical Properties and Hazards--
Tetraethyl tin is a colorless liquid at ambient conditions. It is very
slightly soluble in water and is soluble in most organic solvents. Table 3-36
lists the physical properties of tetraethyl tin. Its boiling point is high,
so it does not represent a substantial air release hazard at typical ambient
conditions.
Chemical Properties and Hazards--
Little information is available concerning the chemical properties and
reactivity of tetraethyl tin; however, it is known that tetraethyl tin decom-
poses on heating, emitting acrid smoke and fumes (24). It is incompatible
with strong oxidizers.
Toxicological and Health Effects--
Tetraethyl tin is highly toxic by inhalation and ingestion. The warning
signs of exposure include: muscular weakness and paralysis leading to respir-
atory failure, convulsions, headaches, dizziness, physiological and neurologi-
cal disturbances, sore throat, cough, abdominal pain, nausea, and vomiting.
Acute exposure can cause swelling of the brain and spinal cord and eventual
death. The Occupational Health and Safety Administration (OSHA) has set a
short term exposure limit (STEL) of 0.1 mg (tin)/ m (25). The LD50 for rats
via ingestion is 16 mg/kg (25).
3-126
-------
Tetraethyl Tin
TABLE 3-36. PHYSICAL PROPERTIES OF TETRAETHYL TIN
Reference
CAS Registry Number
Chemical Formula
Molecular Weight
Boiling Point
Melting Point
Specific Gravity (H
597-64-8
C8H20Sn
234.97
357.8 °F 8 14.7 psia
-169.6 °F
1.199 ® 68 °F
24
24
24
3-127
-------
Tecraethyl Tin
3.12.2 Facility Descriptions
This subsection briefly describes the manufacture and uses of tetraethyl
tin in the United States. Major accidental release hazards of these processes
are discussed in Section 3.12.3.
Tetraethyl Tin Manufacture--
Limited information is available concerning the manufacture of tetraethyl
tin. Although it is not presently produced in the United States, several
processes have been patented for its manufacture (56,57).
In a typical process, finely divided tin and sodium tetraethylaluminum
dissolved in toluene are fed to a reactor equipped with an external heating
source (e.g., steam jacket), agitator, and a nitrogen pad system. The
reaction mixture is heated to approximately 120 to 140°F and ethyl chloride is
added (20). The reaction is carried out for a period of 1.5 hours. The
reaction mixture is then cooled to room temperature, -filtered to remove sodium
chloride by-product, and vacuum distilled to remove the toluene and triethyla-
luminum overhead. The residual liquid is the desired tetraethyl tin product.
Tetraethyl Tin Consumption--
Tetraethyl tin has no significant commercial uses (33). It has been used
as a biocide, bactericide, fungicide, insecticide, catalyst, and preservative
for wood, textile, paper, and leather in the past. It has also been used to
induce encephalopathy (a disease of the brain) and intracranial pressure in
laboratory animals for research purposes (33).
3.12.3 S"tm<|arv of Mai or Process Hazards and Control Technologies
The most important property of tetraethyl tin that can promote equipment
failure is its ability to decompose to acrid vapor on heating. Thus, loss of
temperature control in any process vessel containing tetraethyl tin could lead
to overpressure and eventual equipment failure. Redundant temperature sensors
and controllers should be used in any high-temperature processes where
3-128
-------
Tetraethyl Tin
teraethyl tin is used. A general discussion of hazard prevention and control
appears in Section 2 in this manual and are discussed in greater detail in
other technical literature.
3.12.4 Storage and Handling
No information is currently available on the storage and handling of
tetraechyl tin. As a hazardous liquid, standard storage practices for such
materials should be followed.
3-129
-------
Trichloroacetyl Chloride
3.13 TRICHLOROACETYL CHLORIDE
Trichloroacetyl chloride is an intermediate chemical used to manufacture
other chemicals. The chemical characteristics, storage, uses, and manufacture
of trichloroacetyl chloride are discussed in this section of the manual, as
well as the major hazards of these processes.
No information is currently available on the size of the U.S. market for
trichloroacetyl chloride.
3.13.1 Chemical Characteristics
This subsection describes the physical, chemical, and toxicological
properties of trichloroacetyl chloride as they relate to accidental releases.
Physical Properties and Hazards•-
Trichloroacetyl chloride is a colorless liquid at ambient conditions.
Table 3-37 lists the physical properties of trichloroacetyl chloride.
Chemical Properties and Hazards--
Two chemical properties of trichloroacetyl chloride contribute to the
potential for an accidental release of the chemical:
• Decomposition - Trichloroacetyl chloride decomposes on
contact with water to form highly corrosive chloroacetic
and chlorohydric acids (52). This hydrolysis reaction can
occur violently.
• Flammability - Trichloroacetyl chloride may burn but does
not ignite readily (24).
Toxicological and Health Effects--
Little information is available concerning the toxic effects of acciden-
tal exposure to trichloroacetyl chloride; however, trichloroacetyl chloride is
3-130
-------
Trichloroacetyl Chloride
TABLE 3-37. PHYSICAL PROPERTIES OF TRICHLOROACETYL CHLORIDE
Reference
CAS Registry Number 76-02-8
Chemical Formula CC1 COC1
Molecular Weight 181.83
Boiling Point 244°F 8 14.7 psia 21
Melting Point -70 °F 52
Liquid Specific Gravity (H20=l) 1.6202 fi 68 °F 58
Vapor Pressure 0.306 psia 6 68 °F 21
Vapor Pressure Equation:
log Pv = A - Jg
where: Pv = vapor pressure, mm Hg
T = temperature. °C
A = 6.99075, a constant
B = 1.390.47, a constant
C = 220.11, a constant
Solubility in Water Decomposes 21
3-131
-------
Trichloroacecyl Chloride
toxic by ingestion and inhalation. 1C is also a strong irritant to the skin
and may cause severe burns. The LD,Q for rats via ingestion is 600 mg/kg
(25).
3.13.2 Facility Descriptions
This subsection briefly describes the manufacture and uses of trichloro-
acetyl chloride in the United States. Major accidental release hazards of
these processes are discussed in Section 3.13.4.
Trichloroacecyl Chloride Manufacture--
Trichloroacetyl chloride is manufactured by the reaction of a polyhalome-
chane with carbon monoxide in the presence of a platinum or palladium triad
catalyst.
In a typical process, a mixture of palladium chloride catalyst and carbon
tetrachloride is fed to a reactor. Carbon monoxide is then fed to the
reactor. The reactor is operated at a temperature in the range of 300-400 "F
and at a pressure of approximately 100 atmospheres (59). On completion of the
reaction, the reactor is vented and the reaction products are filtered to
remove any residual solid catalyst. The filtrate is then distilled to remove
any unreacted carbon tetrachloride, leaving the desired trichloroacetyl
chloride product. The unreacted carbon tetrachloride is subsequently returned
to Che reactor.
Trichloroacecyl Chloride Consumption--
Little information is available on the use of trichloroacetyl chloride;
however, it used as an intermediate in the manufacture of other chemicals.
3.13.3 S"nm|arv of Malor Process Hazards and Control Technologies
To reduce the risk of an accidental release of specific measures broadly
classified as prevention, protection or mitigation measures may be applied.
3-132
-------
Trichloroacetyl Chloride
Section 2 discusses the general features of these measures and details are
presented elsewhere in the technical literature.
The properties of trichloroacetyl chloride that contribute to the risk of
a release are its corrosiveness and its reactivity with water. The primary
hazard areas in the manufacturing process appear to be the reactor and
distillation column where trichloroacetyl chloride is present at an elevated
temperature. The reactor is likely to be more hazardous than the distillation
column because it operates at very high pressure. Any failure in this system
could release large quantities of hot trichloroacetyl chloride vapor.
Table 3-38 presents examples of possible locations, conditions and
process hazards which could potentially lead to a trichloroacetyl chloride
release and example controls for reducing the risk of- such a release. The
examples are intended to be illustrative, not exhaustive.
3.13.4 Storage and Handling
Dry trichloroacetyl chloride is relatively noncorrosive to most metals.
However, in the presence of moisture, trichloroacetyl chloride is highly
corrosive and is similar to chloroacetic acid in its corrosive effects. Thus,
storage vessels and containers must be constructed of materials that take this
potential corrosion effect into account. Trichloroacetyl chloride is
typically shipped and stored in metallic drums lined with a polyethylene or
similar coating.
3-133
-------
TABLE 3-38. EXAMPLE CONDITIONS. PROCESS HAZARDS AND HAZARD CONTROLS IN
TRICHLOROACETYL CHLORIDE MANUFACTURING AND USE
Location
Condition
Process Hazard
Leading to Release
Examples of Hazard Controls
Trichloroacetyl
chloride reactor
Process or storage
vessels
Loss of temperature
control
Inadequate water
removal from feeds
to vessels
Equipment failure
Corrosion, exother-
mic reactions and
equipment failure
Temperature and pressure sensors with
alarms
Routine inspection and testing of high
pressure equipment.
Pressure relief system
Routine inspection and testing of all
equipment handling chloroacetyl chloride
Periodic or continuous monitoring for
water contamination
Process or storage
vessels
Backflow of water
into vessels
Exothermic reaction Blind or disconnect rarely used or
and overpresauriza- unnecessary water lines
tion
Redundant check valves in essential water
lines
Pressure relief on high risk piping
Relief sent to vent to a scrubber or
collection tank
H
n
i*
n
t->
O
3
(U
n
(Continued)
o
i
o.
n
-------
TABLE 3-38. (Continued)
Process Hazard
Location Condition Leading to Release Examples of Hazard Controls
Any process vessel Mixing of water vith Corrosion leading Non aqueous heating or cooling fluid
containing chloro- chloroacetyl chlo- to equipment fail-
acetyl chloride ride, due to leaking ure and release Routinely inspect and test all jacketed
process vessel jac- equipment
ket or steam-filled
heat exchanger tube Pressure relief on jackets and heat
exchangers that vent to a collection tank
or scrubber
u>
in
O
I-1
O
1
O
to
o
n>
o
i
-------
SECTION 4
REFERENCES
1. Battelle Columbus Division. Guidelines for Hazard Evaluation Procedures.
The Center for Chemical Process Safety, American Institute of Chemical
Engineers, New York. NY, 1985.
2. Lees, Frank P. Loss Prevention in the Process Industries, Volumes 1 and
2, Butterworths, London, England, 1983.
3. Process Safety Management, Control of Acute Hazards. Chemical
Manufacturer's Association, Washington, DC, May 1985.
4. Green, D.V. (ed.). Perry's Chemical Engineer's Handbook. Chemical
Manufacturers Association, Washington, DC, May 1985.
5. Federal Register. Volume 50. April 16, 1985. pp. 14,941-14.945.
6. Bennett, G.F.. F.S. Feates, and I. Wilder. Hazardous Materials Spills
Handbook. McGraw-Hill Book Company, New York, NY, 1982.
7. Eggleston, L.A., W.R. Herrera, and M.D. Pish. Water Spray to Reduce
Vapor Cloud Spray. Loss Prevention, Volume 10, American Institute of
Chemical Engineers, New York, NY, 1976.
8: Watts, J.W. Effects of Water Spray on Unconfined Flammable Gas. Loss
Prevention, Volume 10, American Institute of Chemical Engineers, New
York, NY, 1976.
9. Vincent, G.C., et al. Hydrocarbon Mist Explosions - Part II, Prevention
by Water Fog. Loss Prevention, Volume 10, American Institute of Chemical
Engineers, New York, NY, 1976.
10. Experiments With Chlorine. Ministry of Social Affairs, Voorburg,
Netherlands, 1975.
11. Martinsen, W.E. and S.P. Muhlenkamp. Disperse LNG Vapors With Water.
Hydrocarbon Processing, July 1977.
12. Moore, P.A.C. and W.D. Rees. Forced Dispersion of Gases by Water and
Steam. Inst. Chem. Engineers Symposium Proceedings. The Containment and
Dispersion of Gases by Water Sprays. Manchester, England, 1981.
13. Moodie, K. The Use of Water Spray Barriers to Disperse Spills of Heavy
Gases. Plant/Operations Progress, October 1985.
4-1
-------
14. Hoodie, K. Experimental Assessment of Full-Scale Water Spray Barters for
Dispersing Dense Gases. Inst. Chem. Engineers Symposium Proceedings.
The Containment and Dispersion of Gases by Water Sprays. Manchester.
England. 1981.
15. Stus, T.F. On Writing Operating Instructions. Chemical Engineering,
November 26, 1984.
16. Burk, A.F. Operating Procedures and Review. Presented at the Chemical
Manufacturers Association Process Safety Management Workshop. Arlington,
VA, May 7-8, 1985.
17. World Chemical Outlook. Chemical and Engineering News, December 15,
1986.
18. Chemical Products Synopsis. Manneville Chemical Products Corporation,
Cortland, NY, 1985.
19. McKetta, J. Encyclopedia of Chemical Processing and Design. Marcel
Dekker Publishing Company, New York, NY, 1985.
20. Lewis. R.J.S. and R.L. Tatken (ed.). Registry of Toxic Effects of
Chemical Substances. NIOSH (DHEW) Publication No. 79-100, January 1985.
21. Dean, J. (ed.). Lange's Handbook of Chemistry. Twelfth Edition,
McGraw-Hill Book Company, New York, NY, 1979.
22. Acrylontrile Data Sheet. E.Z. Dupont de Nemours & Company (Inc.),
Wilmington, DE, 1987.
23-. NIOSH/OSHA Pocket Guide to Chemical Hazards. DHEW (NIOSH) Publication
No. 78-210.
24. Chemical Emergency Preparedness Program Interim Guidance. Chemical
Profiles. 2 Volumes. U.S. Environmental Protection Agency, Washington.
DC, December 1985.
25. Lewis, R.J. and R.L. Tatken, (ed.). Registry of Toxic Effects of
Chemical Substances. Microfiche Ed. National Institute for Occupational
Safety and Health. Cincinnati, OH. April 1987.
26. Schweitzer, P.A. Corrosion Resistance Tables. Marcel Dekker, Inc., New
York, NY, 1976.
27. Hazardous Substances Databank. National Library of Medicine, Bethesda,
MD, July 1985.
28. Material Safety Data Sheet. Moby Corporation, Pittsburgh, PA, March
1986.
4-2
-------
29. Vapor Pressure Data Provided by Occidental Chemical Corporation, Niagara
Falls, NY, November 1983.
30. Benzotrichloride Data Sheet 728G 1284. Occidental Chemical Corporation,
Niagara Falls, NY, November 1983.
31. Sax, N.I. Dangerous Properties of Industrial Materials. Sixth Edition.
Van Nostrand Rienhold Company, New York, NY, 1984.
32. Material Safety Data Sheet. Occidental Chemical Corporation, Niagara
Falls, NY, October 1985.
33. Kirk, R.E. and Othmer, D.F. Encyclopedia of Chemical Technology. Third
Edition, John Wiley & Sons, Inc., New York, NY, 1980.
34. U.S. Patent 3,974,093.
35. Shearson, V.H., H.E. Hall, and J.E. Stevens, Fine Chemicals from Coal.
Ind. Eng. Chem. 41 (9), 1812-20 (1949).
36. Lawler, G.M. (ed.) Chemical Orgins and Markets. Fifth Edition.
Chemical Information Services, Stanford Research Institute, 1977.
37. Chemical Profile, Chloracetic Acid. Chemical Marketing Reporter.
Schnell Publishing Company, Inc., June 16, 1986.
38. U.S. Department of Health and Human Services. NIOSH Pocket Guide to
Chemical Hazards. National Institute for Occupational Safety and
Health. September 1985.
39. Gerhartz, V. (ed.). Ullmann's Encyclopedia of Industrial Chemistry.
Fifth Edition, VCH Publishers, New York, NY, 1986.
40. Hamner, N.E. Corrosion Data Survey. Fifth Edition, National Association
of Corrosion Engineers, 1974.
41. Terrill, James B., Ph.D., D.A.B.T. Acute Inhalation Toxicity Study with
Furan in the Rat. Final Report. Hazelton Laboratories America, Inc.,
April 24, 1987.
42. Williams, A. Furans - Synthesis and Applications. Noyes Data
Corporation, London, England, 1973.
43. Handling Hazardous Materials. Report No. NASA SP-5032. National Aero-
nautics and Space Administration, Greenbelt, MD, 1965.
44. The Handling and Storage of Liquid Propellants. Office of the Director
of Defense Research and Engineering. U.S. Advisory Panel on Fuels and
Lubricants, Washington, DC, 1961.
4-3
-------
45. Sittig, M. Pesticide Manufacturing and Toxic Materials Control
Encyclopedia. Noyes Data Corporation, NJ, 1980.
46. Handbook of Compressed Gases. Second Edition, Compressed Gas
Association, Inc., New York, NY, 1981.
47. Lawler, G.M. (ed.). Chemical Orgins and Markets. Fifth Edition Chemical
Information Services, Stanford Research Institute, 1977.
48. Paskall, Harold G. Capability of the Modified Glaus Process. Prepared
for Alberta Department of Energy and Natural Resources. Prepared by
Western Research, Calgary, Alberta, March 1979.
49. Trofe, T.W., Dalrymple, D.A., and Scheffel, F.A. Stretford Status and
R&D Needs. Gas Research Institute, Chicago, IL, February 1987.
50. Material Safety Data Sheet. Union Carbide Corporation, Danbury, CT,
1985.
51. Matheson Gas Book. Matheson Gas Products. Inc. Secaucus, NJ.
52. Material Safety Data Sheet. Rhone•Poulenc, Inc., Monmouth Junction, NJ,
1987.
53. 1986 Directory of Chemical Producers. Stanford Rese'arch Institute
International, Menlo Park, CA.
54. Material Safety Data Sheet. Mallinckrodt. Inc., Paris, ICY, 1985.
55. Filbert, V.F. and Acken, M.F. U.S. Patent No. 2.373,800.
56. U.S. Patent No. 3,057,894.
57. U.S. Patent No. 3,028,320.
58. Weast, R.C. (ed.). CRC Handbook of Chemistry and Physics. CRC Press.
Inc., Boca Raton, FL, 1983.
59. U.S. Patent No. 3,454,632.
4-4
-------
APPENDIX A
GLOSSARY
This glossary defines selected terms used in the text of this manual
which might be unfamiliar to some users or which might be used differently by
different authors.
Accidental Release: The unintentional spilling, leaking, pumping, purging,
emitting, emptying, discharging, escaping, dumping, or disposing of a toxic
material into the environment in a manner that is not in compliance with a
plant's federal, state, or local environmental permits and results in toxic
concentrations in the air that are a potential health threat to the
surrounding community.
Assessment: The process whereby the hazards which have been identified are
evaluated in order to provide an estimate of the level of risk.
Aucoeaealvtlc: A chemical reaction which is catalyzed by one of the products
of the reaction.
Carcinogen: A cancer causing substance.
Containment/Control: A system to which toxic emissions from safety relief
discharges are routed to be controlled. A caustic scrubber and/or flare can
be containment/control devices. These systems may serve the dual function of
destructing continuous process exhaust gas emissions.
Control System: A system designed to automatically maintain all controlled
process variables within a prescribed range.
A-l
-------
Emergency Response Plan: A plan of action to be followed by source operators
after a toxic substance has been accidentally released to the atmosphere. The
plan includes notification of authorities and impacted population zones,
minimizing the quantity of the discharge, etc.
Exothermic: A term used to characterize the evolution of heat. Specifically
refers to chemical reactions from which heat is evolved.
Facility: A location at which a process or set of processes are used to
produce, refine or repackage chemicals, or a location where a large enough
inventory of chemicals are stored so that a significant accidental release of
a toxic chemical is possible.
Fire Monitor: A mechanical device holding a rotating nozzle, which emits a
stream of water for use in firefighting. Fire monitors may be fixed in place
or may be portable. A fire monitor allows one person to direct water on a
fire whereas a hose of the same, flowrate would require more than one person.
Hazard: A source of danger. The potential for death, injury or other forms
of damage to life and property.
Hygroscopic: Readily taking up and retaining moisture (water).
Identification: The recognition of a situation, its causes and consequences
relating to a defined potential, e.g., Hazard Identification.
Lachrvmator: A substance which increases the flow of tears.
Mitigation: Any measure taken to reduce the severity of the adverse effects
associated with the accidental release of a hazardous chemical.
Mutagen: An agent that causes biological mutation.
A-2
-------
Plant: A location at which a process or set of processes are used to produce,
refine, or repackage chemicals.
Prevention: Design and operating measures applied to a process to ensure that
primary containment of toxic chemicals is maintained. Primary containment
means confinement of toxic chemicals vithin the equipment intended for normal
operating conditions.
Primary Containment: The containment provided by the piping, vessels and
machinery used in a facility for handling chemicals under normal operating
conditions.
Probability/Potential: A measure, either qualitative or quantitative, that an
event will occur within some unit of time.
Process: The sequence of physical and chemical operations for the production,
refining, repackaging or storage of chemicals.
Process Machinery: Process equipment, such as pumps, compressors, heaters, or
agitators, that would not be categorized as piping and vessels.
Protection: Measures taken to capture or destroy a toxic chemical that has
breached primary containment, but before an uncontrolled release to the
environment has occurred.
Pvrophorlc: A substance that spontaneously ignites in air at or below room
temperature without supply of heat, friction, or shock.
Qualitative Evaluation: Assessing the risk of an accidental release at a
facility in relative terms; the end result of the assessment being a verbal
description of the risk.
A-3
-------
Quantitative Evaluation: Assessing Che risk of an accidental release at a
facility In numerical terms; che end result of the assessment being some type
of number that reflects risk, such as faults per year or mean time between
failures.
Reactivity: The ability of one chemical to undergo a chemical reaction with
another chemical. Reactivity of one chemical is alvays measured in reference
to the potential for reaction with itself or with another chemical. A
chemical is sometimes said to be "reactive", or have high "reactivity",
without reference to another chemical. Usually this means that the chemical
has the ability to react with common materials such as water, or common
materials of construction such as carbon steel.
Redundancy: For control systems, redundancy is the presence-of a second piece
of control equipment where only one would be required. The second piece of
equipment is installed to act as a backup in the event that the primary piece
of equipment fails. Redundant equipment can be installed to back up all or
selected portions of a control system.
Risk: The probability that a hazard may be realized at any specified level in
a given span of time.
Secondary Containment: Process equipment specifically designed to contain
material that has breached primary containment before the material is released
to the environment and becomes an accidental release. A vent duct and
scrubber that are attached to the outlet of a pressure relief device are
examples of secondary containment.
Teratogenic: Causing anomalies of formation or development.
Toxicltrv: A measure of the adverse health effects of exposure to a chemical.
A-4
-------
APPENDIX B
TABLE B-l. METRIC (SI) CONVERSION FACTORS
Quantity
Length :
Area:
Volume:
Has s (weight):
Pressure :
Temperature:
Caloric Value:
Enthalpy :
Specific-Heat
Capacity :
Density:
Concentration:
Flovrate:
Velocity:
Viscosity:
To Convert From
in.
ft 2
in..
2
in..
ft 3
gal.
Ib
short ton (ton)
short ton (ton) metric
atm
mm Hg
psia
psig
°F
°C
Btu/lb
Btu/lbmol
kcal/gmol
Btu/lb-°F
lb/ft3
Ib/gal.
oz/gal.
qt/gal.
gal . /min
gal. /day
ft /min
ft/mia
ft/sec
centipose (CP)
To
cm
2
cm.
2
cm3.
"3
m3
kg
Mg
ton (t)
kPa
kPa
kPa
kPa*
OG*
K*
kj/kg
kj /kgmol
kj /kgmol
kj/kg—§
kg/m.
kg/m.
cf/wT
m /min
m^/day
m /min
m/min
m/sec
kg/m-s
Multiply By
2.54
0.3048
6.4516
0.0929
16.39
0.0283
0.0038
0.4536
0.9072
0.9072
101.3
0.133
6.895
(psig)+14.696)
x(6.895)
(5/9)x(°F-32)
•C+273.15
2.326
2.326
4.184
4.1868
16.02
119.8
25.000
0.0038
0.0038
0.0283
0.3048
0.3048
0.001
*Calculate as indicated.
B-l
------- |