United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S8-87/034c Sept. 1987
x°/EPA Project Summary
Prevention Reference Manual:
Chemical Specific, Volume 3:
Control of Accidental Releases of
Hydrogen Cyanide (SCAQMD)
D. S. Davis, G. B. DeWolf, and J. 0. Quass
The South Coast Air Quality Manage-
ment District (SCAQMD) of Southern
California has been considering a
strategy for reducing the risk of a major
accidental air release of toxic chemicals.
This strategy, intended to guide both
industry and communities, consists of
monitoring activities associated with
the storage, handling, and use of certain
chemicals. The hydrogen cyanide (HCN)
manual summarizes technical informa-
tion that will aid in identifying and con-
trolling release hazards (specific to the
SCAQMD) associated with HCN.
Because HCN has an IDLH (immedi-
ately dangerous to life and health) con-
centration of 50 ppm, it is an acute
toxic hazard. The manual identifies the
potential causes of accidental releases
that apply to processes using cyanides
in the SCAQMD and also describes
measures that may be taken to reduce
the accidental release risk. Such mea-
sures include recommendations on
plant design practices; prevention, pro-
tection, and mitigation technologies;
and operation and maintenance prac-
tices. Conceptual cost estimates of
examples of these 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
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 consists of
Los Angeles, Orange, San Bernardino,
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
release.
The hydrogen cyanide (HCN) manual,
which contains technical information on
the prevention of accidental releases of
HCN, discusses storage and handling
practices and process operations involving
cyanides as they are used in the SCAQMD
that could result in an accidental release.
Although HCN itself is not used in the
SCAQMD, its salts are used in electro-
plating operations. In the electroplating
industry cyanides are used in plating
solutions for certain metals and in clean-
ing solutions used to prepare metal sur-
faces for plating. Here the cyanide is
present only in the salt form, most com-
monly as sodium cyanide. HCN is not
directly used in the SCAQMD in the
plating industry.
Potential Causes of Releases
Cyanide solutions can be used safely in
the plating industry, though the industry
has been moving away from their use
since substitutes are available for many
metals in certain applications. Though
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cyanide salts are toxic, since they have
very low vapor pressures in solution or in
the solid form, they are not as hazardous
as HCN. However, small amounts of HCN
will be present whenever a cyanide salt
or salt solution is used. Large amounts of
HCN could be generated if acid were
added to a cyanide salt solution, but an
accidental release of HCN from a cyanide-
based plating bath appears to require
adding a large amount of acid.
Failures in or problems with a chemical
process, equipment, or operating and
maintenance procedures can cause ac-
cidental releases. Since very little auto-
matic process control is used in typical
plating operations and since the solution
compositions within a process are
typically monitored and adjusted manual-
ly, any error in adjustment leading to an
HCN release would most likely be caused
by operator error.
An accidental release related to equip-
ment failure might occur if a spilled
cyanide solution came in contact with a
strong acid. Examples of equipment
failure that could cause spills are:
• Failure of a bath resulting in a spill
of cyanide-containing solution. The
failure could be caused by excessive
stress, external loadings, or cor-
rosion.
• A spill of cyanide-containing solution
from a bath caused by a pump or
pipe failure.
• A fire, resulting in an accidental
release of cyanide. Destruction of
cyanide salt containers by fire, com-
bined with water from a sprinkler
system, could result in a sodium
cyanide runoff. Sprinkler water could
also cause a tank overflow and
mixing of acid and cyanide baths.
Human error could lead to an ac-
cidental release; e.g.:
• Overfilling of baths resulting in an
improper mixture of acidic and
cyanide solutions.
• Incorrect addition of acidic raw
materials to a cyanide bath.
• Incorrect transfer of liquid from an
acid bath to a cyanide bath or vice
versa.
• Use of a carbon dioxide (C02) fire
extinguisher on a fire where cyanide
salt or solution is present, resulting
in an accidental release of HCN. CO2
is a weak acid, however, and large
quantities would be necessary to
create an accidental release of HCN.
Hazard Prevention and Control
Prevention of accidental releases re-
quires careful consideration of the design.
construction, operation, and protective
systems of facilities where HCN is stored
and used.
Few options appear to exist in process
design for reducing the potential of an
accidental release from plating processes.
One method would be to switch to a non-
cyanide-based process if economics allow
it and if the non-cyanide process is
adequate for the intended application.
The only control system in a plating
operation is likely to be temperature
control on some of the baths. Transfers,
monitoring, and composition adjustment
are typically done manually.
From the perspective of accidental re-
lease prevention, pH control of cyanide-
based plating solutions is very important,
and also typically accomplished manually.
Since plating solutions are highly buf-
fered, they are resistant to pH change. It
might be difficult to automate pH control,
but if such controls were incorporated
into the plating process, a backup system
should be used to protect the process
from control system failures that result in
low pH.
Physical plant design considerations
include equipment such as vessels, pipes,
valves, instrumentation, siting and layout,
and transfer/transport facilities. Founda-
tions, dikes, walls, flooring, and other
supports should be constructed from
materials resistant to attack by the
chemicals used in the plating process.
For example, "acid brick" combined with
chemically resistant mortar is a reliable
material to use for corrosion protection.
Tanks must be constructed of or lined
with a material resistant to chemical at-
tack such as plastic, stainless steel, lined
carbon steel, or lined precast or poured-
in-placs concrete.
Facilities and equipment should be
located so as to reduce plant and public
personnel exposure in the event of a
release. Inventories of solid cyanide salts
should be separated from inventories of
acid. Cyanide salts should be protected
from contact with moisture, and adequate
drainage or diking should be available to
prevent runoff or spills from leaving the
building. Overflows or leaks from one
bath should not be able to contaminate
another bath.
The two types of protection tech-
nologies for cyanide-based plating facili-
ties are enclosures and scrubbers.
Ventilation systems and individual hoods,
or a combination of these, are used to
capture vapors from areas where HCN
might be generated. For most cyanide
plating operations, scrubber systems may
be a level of protection out of proportion
to the hazard, but they could be used
when extreme precautions are needed.
Incineration or flaring may also be applic-
able to control HCN vapors.
Mitigation techniques, to reduce the
consequences if a release of HCN occurs,
include physical barriers, water sprays
and fogs, and foams. Secondary con-
tainment systems such as diking are used
to contain accidental liquid spills and
reduce the rate of evaporation by de-
creasing the surface area of the spilled
liquid. For plating facilities, diking could
be effective around acid storage tanks to
isolate spills from dry cyanide storage
areas.
Employees of plating facilities should
be trained in important aspects of
handling cyanide salts and solutions,
especially the dangers of excess acidifica-
tion of these solutions, and should
thoroughly understand maintenance and
emergency procedures.
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 3: Control of Accidental Releases of Hydrogen Cyanide
(SCAQMD),'1 (Order No. PB 87-227 062/AS; Cost: $13.95, 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
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