United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S8-87/034h Feb. 1988
Project  Summary
Prevention  Reference  Manual:
Chemical  Specific, Volume 8:
Control of Accidental Releases  of
Hydrogen  Fluoride
D. S. Davis, G. B. DeWolf, and J. D. Quass
  The accidental release of  a  toxic
chemical at Bhopal, India, in 1984 was
a milestone in  creating an increased
public awareness of toxic release prob-
lems. As a result of other (perhaps less
dramatic) incidents in the past, portions
of the chemical  industry were aware of
this  problem long before this event.
These same portions of the industry
have made advances in this area. In-
terest in reducing the probability and
consequences  of accidental  toxic
chemical releases that  might  harm
workers within  a process facility and
people in the surrounding community
prompted the preparation of technical
manuals addressing accidental releases
of toxic chemicals. This chemical speci-
fic manual is for hydrogen fluoride. The
manual summarizes information to aid
regulators and  industry  personnel in
identifying and controlling release haz-
ards associated with hydrogen fluoride.
  Reducing the  risk associated with an
accidental release of hydrogen fluoride
involves identifying some of the poten-
tial causes of accidental  releases that
apply to the process facilities that handle
and  store hydrogen fluoride.  In this
manual, examples of  potential causes
are identified as are specific measures
that may be taken to reduce the ac-
cidental release risk.  Such measures
include recommendations on  plant
design practices; prevention, protection,
and mitigation technologies; and opera-
tion and maintenance practices. Con-
ceptual cost estimates of example pre-
vention,  protection,  and  mitigation
measures are provided.
  This Project Summary was developed
by EPA's Air and Energy Engineering
Research Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that Is fully docu-
mented In a separate report of the same
title (see Project Report ordering In-
formation at back).

Introduction
  The accidental release of a  toxic
chemical, methyl isocyanate, in Bhopal,
India, in 1984 was a milestone in creating
an increased public awareness of toxic
release problems. There have been other
less dramatic incidents of toxic chemical
releases in the  past, and the chemical
industry was aware of this problem long
before this event. Safety and loss preven-
tion have long been standard parts of
industrial activity  and,  over the years,
industry has made many advances in this
area. There is renewed interest, however,
in reviewing technology and procedures
for preventing, protecting against, and
mitigating accidental releases.
  As an aid to regulators and industry
personnel charged with  reducing the
probability and consequences of accident-
al toxic chemical releases,  technical
manuals have been prepared that address
prevention, protection, and mitigation
measures for releases. This chemical
specific manual  on hydrogen fluoride is
part of that series.
  Hydrogen fluoride is a major commodity
chemical in industry. The major industrial
uses of hydrogen fluoride are: petroleum
refinery alkylation (as a catalyst), chloro-
fluorocarbon manufacturing, sodium

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aluminum fluoride manufacturing, ura-
nium processing, glass  etching and
polishing, and repackaging for resale.

Potential Causes of Releases
  Both anhydrous hydrogen fluoride and
hydrofluoric acid can  be  used safely in
the appropriate processing and storage
equipment; however,  when  exposed to
the atmosphere, hydrogen fluoride vapor-
izes readily and combines with moisture
in air to form  hydrofluoric acid.
  Liquid hydrogen fluoride can spill when
anhydrous hydrogen fluoride is released
at or below its boiling point of  19.5°C
(67°F) or when a sudden  release  of
hydrogen fluoride above this temperature
results in vapor flashing, which cools the
remainder  of the  chemical to  19.5°C
(67°F). Direct releases of gaseous hydro-
gen fluoride can also occur.
  Hydrogen fluoride releases can origi-
nate from many sources, including leaks
or ruptures  in vessels, piping,  valves,
instrumentation connections, and process
machinery such as pumps and compres-
sors. The sources of accidental releases
may be broadly classified as failures in or
problems with: the process or system of
chemical production, the equipment, and
operation or maintenance procedures,
including human error.
  Process causes  of  hydrogen fluoride
releases include: (1) excess olefin feed to
an  alkylation  reactor leading  to  an
exothermic  reaction, combined  with
failure of the cooling system; (2) backf low
of alkylation  process reactants to a hy-
drogen fluoride feed tank; (3) inadequate
water and sulfur removal from hydrocar-
bon feeds to the alkylation process leading
to progressive corrosion in downstream
processing equipment; (4) excess feeds
to any part of a system handling hydrogen
fluoride  leading to overfilling or over-
pressuring equipment; (5) loss of con-
denser  cooling in distillation  units;  (6)
loss of temperature control  in  heating
and cooling units; and (7) overpressure in
hydrogen fluoride storage vessels due to
overheating  or  overfilling, perhaps
caused by exposure to fire,  unrelieved
overfilling, or exothermic reactions from
contamination.
  Equipment causes  of releases result
from hardware failure, including: (1)  ex-
cessive stress caused by improper con-
struction  or  installation;  (2) failure of
vessels at normal operating conditions
caused  by  excessive stress,  external
loadings, corrosion,  or overheating; (3)
mechanical fatigue and shock resulting
from age, vibration,  stress cycling, or
collisions with moving equipment (e.g.,
cranes); (4) thermal fatigue or shock in
alkylation reactors, heat exchangers, and
distillation columns;  (5) brittle fracture,
especially in carbon steel equipment sub-
jected to extensive corrosion;  (6) creep
failure in equipment subject to extreme
operational  upsets,  especially  excess
temperatures;  and  (7) all  forms  of
corrosion.
  Incorrect operating and maintenance
procedures include: (1) overfilled storage
vessels;  (2) improper  process system
operation; (3) errors in loading and  un-
loading procedures; (4) inadequate main-
tenance, especially on water-removal unit
operations and pressure relief systems;
and (5) lack of inspection and nondestruc-
tive testing of vessels and piping to detect
weakening by corrosion.

Hazard  Prevention and Control
  Prevention of accidental  releases re-
quires careful consideration of the design,
construction,  operation,  and protective
systems  of facilities where  hydrogen
fluoride is stored and used.
  Deviations from expected process de-
sign or operation  can initiate a series of
events that result in an accidental release.
Process variables  such as flow, pressure,
temperature, composition, and quantity
must be  monitored and controlled. Most
importantly, the overheating and over-
pressuring of systems containing hydro-
gen  fluoride must be prevented. Equip-
ment can fail in  the absence of over-
pressure if corrosion has weakened pro-
cess equipment. Temperature monitoring
is also  important because  hydrogen
fluoride's corrosiveness  increases with
temperature.
  The  proper selection of  construction
materials for hydrogen fluoride service is
dictated  by conditions  that directly and
indirectly affect corrosion-(temperature,
pressure, moisture content, flow velocity,
aeration, and the presence of impurities
such as sulfur). Vessels, piping and valves,
process machinery, and instrumentation
must resist corrosion.  For example, for
anhydrous hydrogen  fluoride or con-
centrated  hydrofluoric acid  solutions,
carbon  steel pipe is  commonly used.
However, carbon  steel  is not appropriate
for wet hydrogen fluoride or dilute hydro-
fluoric acid solutions.
  The location of systems and equipment
must also be considered with  reference
to the proximity  of population centers,
prevailing winds, local terrain, and poten-
tial natural occurrences such as flooding
or  earthquakes.  Anhydrous  hydrogen
fluoride and  aqueous hydrofluoric acid
storage and handling equipment should
be located away from  other potentially
hazardous storage and handling facilities.
  Two types  of protective systems for
hydrogen fluoride facilities are enclosures
and scrubbers. Enclosures are structures
which would capture and contain  any
hydrogen fluoride spilled or vented from
storage or process equipment, thus pre-
venting  immediate  discharge  of  the
chemical to the environment.
  Scrubbers  absorb toxic gases from
process streams. These devices can be
used to control hydrogen fluoride releases
from vents and pressure relief discharges,
from process equipment, or from secon-
dary containment structures. Types of
scrubbers include spray towers, packed
bed scrubbers, and Venturis.
  Mitigation measures for minimizing the
effects of a  large release of hydrogen
fluoride should be  part of a  facility's
emergency  preparedness.  Mitigation
measures include physical barriers, water
sprays and fogs,  and foams. Secondary
containment  systems for hydrogen fluo-
ride storage facilities commonly consist
of an adequate drainage system that leads
to a lime-containing neutralization basin,
or a diked area. Water sprays  may not
always be suitable for hydrogen fluoride  |
spills, but soda ash or a strong soda ash
solution can  be used to neutralize the
chemical and prevent the release of toxic
vapors. Although foams have been used
successfully  in vapor hazard control for
many volatile chemicals, no foam systems
appear to be currently available for hy-
drogen fluoride.

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     D. S. Davis, G. B. DeWolf, andJ. D. Quass are with Radian Corporation, Austin,
       TX 78766.
     T. Kelly Janes is the EPA Project Officer (see below).
     The complete report, entitled "Prevention Reference Manual: Chemical Specific,
       Volume 8: Control of Accidental Releases of Hydrogen Fluoride," (Order No.
       PB 87-234 530/AS; Cost: $18.95, subject to change) will be available only
       from:
           National Technical Information Service
           5285 Port Royal Road
           Springfield. VA 22161
           Telephone: 703-487-4650
     The EPA Project Officer can be contacted at:
           Air and Energy Engineering Research Laboratory
           U.S. Environmental Protection Agency
           Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
                                                                                         U.S.OFFICIAL MAD
VA
U.S.POSTAGE
Official Business
Penalty for Private Use $300

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