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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