United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S8-87/034a Sept. 1987
&EPA Project Summary
Prevention Reference Manual:
Chemical Specific, Volume I:
Control of Accidental Releases of
Hydrogen Fluoride (SCAQMD)
D. S. Davis, G. B. DeWolf, and J. D. Quass
The South Coast Air Quality Manage-
ment District (SCAQMD) of southern
California has developed a strategy for
reducing the risk of a major accidental
air release of toxic chemicals. This
strategy involves monitoring and guiding
communities and industry in the storage,
handling, and use of certain chemicals,
including hydrogen fluoride. The
SCAQMD contracted for the prepara-
tion of a manual that would aid in
identifying and controlling release
hazards specific to the SCAQMD as-
sociated with hydrogen fluoride.
Anhydrous hydrogen fluoride is a
corrosive liquid that boils at room
temperature and rapidly absorbs mois-
ture to form a highly corrosive hydro-
fluoric acid. Hydrogen fluoride gas has
an IDLH (Immediately Dangerous to
Life and Health) concentration of 20
ppm, making it an acute toxic hazard.
To reduce the risks associated with
an accidental release of hydrogen
fluoride, the potential causes of such a
release from processes using hydrogen
fluoride in the SCAQMD must be identi-
fied. Examples of potential causes and
specific measures that may be taken to
reduce the risk of an accidental release
are identified. Such measures include:
certain plant designs; prevention, pro-
tection, and mitigation technologies;
and operation and maintenance prac-
tices. Prevention, protection, and miti-
gation costs are also estimated for some
example systems.
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
In 1985, the South Coast Air Quality
Management District (SCAQMD) con-
ducted a study to determine the presence,
quantities, and uses of hazardous chemi-
cals in the SCAQMD, which comprises
Los Angeles, Orange, San Bernadino,
and Riverside Counties. The resulting
report, "South Coast Air Basin Accidental
Toxic Air Emissions Study," outlined an
overall strategy for decreasing the
potential for a major toxic chemical re-
lease incident.
The hydrogen fluoride volume, one of a
Prevention Reference Manual series, dis-
cusses storage and handling practice and
process operations that relate to the pre-
vention of accidental releases of hydrogen
fluoride as it is used in the SCAQMD.
Hydrogen fluoride has a number of
industrial uses throughout the country.
In the SCAQMD specifically, hydrogen
fluoride is used primarily to manufacture
chlorofluorocarbons, as a catalyst in
petroleum products alkylation process,
and in repackaging. Hydrogen fluoride is
a highly toxic, highly corrosive irritant to
the skin, eyes, and respiratory system.
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
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the atmosphere, hydrogen fluoride
vaporizes readily and combines with
moisture in air to form hydrofluoric acid.
Liquid hydrogen fluoride spills can occur
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 tempera-
ture 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: 1) the process or system
of chemical production, 2) the equipment,
and 3) operation or maintenance proce-
dures, including human error.
Possible process causes of hydrogen
fluoride releases include'
Excess olefin feed to an alkylation
reactor leading to an exothermic re-
action, combined with failure of the
cooling system;
Backflow of alkylation process
reactants to a hydrogen fluoride feed
tank;
Inadequate water and sulfur removal
from hydrocarbon feeds to the alkyla-
tion process leading to progressive
corrosion in downstream processing
equipment;
Excess feeds in any part of a system
handling hydrogen fluoride leading
to overfilling or overpressure
equipment;
Loss of condenser cooling in distilla-
tion units; and
Overpressure in hydrogen fluoride
storage vessels due to overheating
or overfilling. This may be caused by
fire exposure, unrelieved overfilling,
or exothermic reactions from
contamination.
Equipment causes result from hard-
ware failures, including:
Excessive stress caused by improper
construction or installation;
Failure of vessels at normal operating
conditions caused by excessive
stress, external loadings, corrosion,
or overheating;
Mechanical fatigue and shock re-
sulting from age, vibration, stress
cycling, or collisions with moving
equipment such as cranes;
Thermal fatigue or shock in alkylation
reactors, heat exchangers, and distil-
lation columns;
Brittle fracture, especially in carbon
steel equipment subjected to exten-
sive corrosion;
Creep failure in equipment subject
to extreme operational upsets,
especially excess temperatures; and
All forms of corrosion.
Incorrect operating and maintenance
procedures include:
Overfilled storage vessels;
Improper process system operation;
Errors in loading and unloading
procedures;
Inadequate maintenance, especially
on water-removal unit operations
and pressure relief systems; and
Lack of inspection and nondestruc-
tive testing of vessels and piping to
detect corrosion weakening.
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
design 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 con-
trolled. Most importantly, the overheating
and overpressuring of systems containing
hydrogen fluoride must be prevented.
Equipment failure can occur in the
absence of overpressure if corrosion has
weakened process equipment. Also,
temperature monitoring is important be-
cause 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, valves,
process machinery, and instrumentation
must resist corrosion. For example, for
anhydrous hydrogen fluoride or concen-
trated hydrofluoric acid solutions, carbon
steel pipe is commonly used. However,
carbon steel is not appropriate for wet
hydrogen fluoride or dilute hydrofluoric
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 I
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, fogs, and foams. Secondary con-
tainment systems for hydrogen fluoride
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 success-
fully in vapor hazard control for many
volatile chemicals, no foam systems ap-
pear to be currently available for hydrogen
fluoride.
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D. S. Davis, G. B. DeWolf. and J. 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
SpecificVolume 1: Control of Accidental Releases of Hydrogen Fluoride
(SCAQMD)," (Order No. PB 87-227 047/AS; Cost: $18.95, subject to change)
will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Officer can be contacted at:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
:, Q '
Official Business
Penalty for Private Use $300
EPA/600/S8-87/034a
0000329 PS
U S gKVIR PROTECTION
CHICAGO
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