United States
                    Environmental Protection
 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).

  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

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
  • Inadequate water and sulfur removal
     from hydrocarbon feeds to the alkyla-
     tion process leading to progressive
     corrosion in downstream processing
  • Excess feeds in any part of  a system
     handling hydrogen fluoride leading
     to  overfilling  or  overpressure
  • 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
   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
  • 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

     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
       Specific—Volume 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
Center for Environmental Research
Cincinnati OH 45268
                                                                                                         :, Q  '•
Official Business
Penalty for Private Use $300

              0000329    PS
              U S  gKVIR PROTECTION