United States
Environmental Protection
Agency
Office of Solid Waste
and Emergency Response
(5104)
EPA550-FOO-001
April 2000
www.epa.gov/ceppo/
SEPA
PREVENTION OF REACTIVE
CHEMICAL EXPLOSIONS
CASE STUDY: WASTE FUEL/OXIDIZER
REACTION HAZARDS
EPA is issuing this Case Study as part of its ongoing effort to protect human health and the environment by
preventing chemical accidents. EPA is striving to leam the causes and contributing factors associated with
chemical accidents and to prevent their recurrence. Major chemical accidents cannot be prevented solely
through command and control regulatory requirements; understanding the fundamental root causes of
accidents, widely disseminating the lessons learned, and integrating these lessons learned into safe operations
are also required. EPA will publish Case Studies and Alerts to increase awareness of possible hazards. It
is important that facilities, SERCs, LEPCs, emergency responders and others review this information and
take appropriate steps to minimize risk. This document does not substitute for EPA's regulations, nor is it
a regulation itself. It cannot impose legally binding requirements on EPA, states, or the regulated
community, and may not apply to a particular situation based upon circumstances. This guidance does not
represent final agency action, and may change in the future, as appropriate.
Problem: The mixing of organic fuels and oxidizers is generally recognized as
inherently dangerous. Accident histories reveal many examples of fires and explosions
triggered by improper mixing of these substances. The incident described here is an
example of the potential consequences associated with improper mixing of organic
solvents and oxidizers. This Case Study is designed to raise awareness about the
hazards associated with blending waste fuels and reactive chemicals and to offer
recommendations to reduce the potential for accidents.
HASKELL, OKLAHOMA (MARCH 26, 1997)
On March 26, 1997, at about 3 p.m. an
explosion occurred within a fuel
blending tank at Chief Supply
Corporation (Chief), in Haskell,
Oklahoma. One worker was killed and
two others injured. The explosion and
resulting fire caused extensive damage to
the facility. Several smaller explosions
occurred as over 1,000 drums containing
waste paints, oils, thinners, inks,
cleaning solvents, assorted acids, bases,
metal sludge, and four 5,000-gallon
tanks holding waste fuels became
involved in the fire. A highway next to
the site was closed; the facility and an
area 1.5 miles north and one mile east of
the facility in the path of a large smoke
plume were evacuated. The fire was
fully extinguished three days later.
FUEL BLENDING OPERATIONS
The waste fuel blending industry grew
from a need to provide large quantities
of fuel to cement production kilns while
providing a way to reuse flammable
hazardous waste. For years, cement
producers have burned flammable
hazardous waste liquids, such as
solvents, thereby reducing raw fuel
consumption and cost. Fuel demand for
cement production and availability of
flammable waste has increased the
amount of hazardous waste-derived fuels
being blended by smaller operations.
Fuel blenders process many types of
hazardous wastes, such as paints,
solvents, and used oil, into fuels with
sufficient heat value for use in cement
kilns. The specifications for the fuel
blend (e.g. BTU value and amount of
impurities) are normally established by
the cement kiln operator, dictated by the
emissions standards set for that kiln.
By 1996, over 140 U.S. companies were
blending and processing fuels derived
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Prevention of Reactive Chemical Explosions
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from hazardous wastes for use in cement kilns. These
facilities are subject to regulations under the Resource
Conservation and Recovery Act (RCRA) for the
treatment, storage, and disposal of hazardous waste.
The RCRA regulations establish general operating
practices and procedures for blending operations. For
example, "the owner or operator of a facility that treats,
stores or disposes ignitable or reactive waste, or mixes
incompatible waste or incompatible wastes and other
materials, must take precautions to prevent reactions
which: (1) Generate extreme heat or pressure, fire or
explosions, or violent reactions; ..." (US EPA, 40 CFR
264.17)
Although the regulations do not place extensive
requirements on the types of hazardous wastes that can
be blended, some states prohibit the blending of certain
wastes. "Beyond these restrictions, the specifications
for the hazardous wastes that are blended into fuels are
primarily determined by the cement producers, whose
operations must meet the regulations' standards for
emissions and other requirements." (US GAO, 1996)
ACCIDENT INVESTIGATION
Because of the severity of the consequences and the
opportunity for lessons learned, EPA conducted a
limited accident investigation to better understand and
communicate the major causal factors contributing to
this event. EPA's investigation focused on the fuel
blending operations and characteristics of the
substances involved.
Fuel Production and Chemicals
Chief produced various fuels by blending different
wastes composed primarily of spent (used) solvents and
cleaners (liquid and sludge). Several months prior to
this incident, Chief instituted a practice of adding "lab
pack" materials, which had been left on-site by the
previous owners of the facility, to the fuel blending
process. "Lab packs" are containers that hold small
jars, bottles or other containers of assorted laboratory
chemicals destined for disposal. These lab packs
contained various oxidizers including perchlorates,
nitrites, and chlorates.
Compatibility tests performed by Chiefs lab personnel
on the lab pack oxidizers showed that mixing different
oxidizer groups caused reactions, ranging from simple
heat buildups to small detonations. The lab personnel
were concerned about these reactions; consequently
various types of oxidizers from the lab packs were
separated from each other. Five-gallon buckets were
used to store the segregated oxidizers for later addition
to the waste fuel blend.
Blending Process and Equipment
Chief blended wastes in two, 1,000 gallon vertical tanks
called "dispersers." The disperser involved in the
incident was equipped with a mixer (a blade mounted
on a shaft connected to a motor on top of the tank). The
blade was positioned about 11A feet from the bottom of
the tank. To avoid excessive splashing and generation
of vapors and fumes, the mixer was not supposed to be
started until the liquid level in the disperser fully
covered the blade; the amount needed to cover the blade
was 400-500 gallons (between seven to nine 5 5-gallon
drums of liquid), or about half of the tank capacity. The
disperser was open to the atmosphere; no nitrogen or
other inert gas blanketing was used to suppress
flammable vapors.
The disperser had two top openings: a large semi-
circular "half-moon" opening with a tray for adding
liquids from 55-gallon drums; and a one foot square
opening used for adding lab packs. A grate was
positioned across the large opening to keep any "large
chunks" in the waste from falling into the tank.
Typically, wastes of greater fuel value and lower
contamination were added to the disperser first followed
by lower grade materials to achieve a better quality fuel
blend.
Oxidizers were to be added to the fuel blend only after
ensuring that the disperser was 3/4 full and the mixer
running, according to an unwritten procedure used by
lab personnel. Chief employees stated that there was no
concern for adding the oxidizers to the liquid fuels, but
addition might be dangerous if the oxidizer powders
were mixed together without a large quantity of liquid
fuel in the disperser. The liquid fuel acted as a heat
sink for the oxidizers.
The Incident
On the day of the incident, two workers were on top of
the disperser pouring liquids from 55-gallon drums into
the disperser. They were starting a new batch and only
four drums of liquid had been added to the tank when a
lab employee at the top of the tank added one bucket of
chlorates, one bucket of perchlorates, and one bucket of
nitrites (about 3-4 inches of dry material in each 5-
gallon bucket) to the disperser. The mixer was not
running at this time.
Thirty-to-sixty seconds after the oxidizers were added
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and while waste from a fifth drum was being dumped
into the tank, liquid suddenly erupted back out of the
large tank opening, followed by an explosion and
fireball. The fireball fatally engulfed the employee who
was pouring the drums and started a large fire in the
building. The fire spread to other flammable materials
stored throughout the building.
Chemical Hazards - Oxidizers
As noted above, Chief attempted to dispose of a variety
of strong oxidizers including chlorates, nitrites, and
perchlorates. Strong oxidizers generally are considered
to be incompatible with many organic substances
because of the potential for dangerous reactions. EPA
indicates that chlorates, perchlorates, and other strong
oxidizers are potentially incompatible with alcohols,
halogenated hydrocarbons, other reactive organic
compounds and solvents, and other flammable and
combustible wastes. The potential consequences of
mixing such incompatible materials are fire, explosion,
or violent reaction. Although "It is possible for
potentially incompatible wastes to be mixed in a way
that precludes a reaction . . .," none of the examples
provided applies to mixing oxidizers with organic
substances. EPA knows of no method of mixing
oxidizers with oxidizable substances that would
preclude a reaction (US EPA).
Perchlorates in particular may undergo hazardous
reactions with organic substances and have been
involved in a number of hazardous incidents. "Mixtures
of any perchlorates with oxidizable substances are . . .
highly explosive and must be treated accordingly . . .
avoid friction, heating, sparks, or shock from any
source, and provide suitable isolation, barricades, and
protective clothing for personnel." (Schumacher, 1960)
Further, methyl, ethyl, benzyl, and propyl perchlorate
are readily formed by reaction of perchloric acid with
the corresponding alcohol (Schumacher, 1960 and
Bretherick, 1985); ethyl perchlorate formed from
ethanol and perchloric acid is "reputedly the most
explosive substance known" (Bretherick 1985). In
addition, the above alcohols can also react violently or
explosively with perchlorates (Kirk-Othmer, 1995).
Chemical Analysis
EPA collected residue samples at various locations after
the incident to determine what chemical substances may
have been present and what may have triggered the
explosion. Exhibit 1 lists the substances and
concentrations found in samples taken from the
disperser where the accident originated. The exhibit
also notes potential reactions of each substance with
oxidizers and perchlorates or perchloric acid.
Most of the substances present after the explosion are
flammable or combustible. The phenols and benzyl
alcohol are readily oxidizable and could have
participated in reactions (possibly violent) with the
oxidizers added to the mixture. In addition, the phenols
and the alcohol are hydroxyl compounds and potentially
could have reacted with perchlorates to form
perchlorate esters (which are generally very explosive),
particularly if free perchloric acid was present along
with the perchlorate salt or formed when the perchlorate
salt was added to the solvent mixture.
Although more extreme conditions are required than for
phenols and alcohols, the ketones and aromatic
hydrocarbons could have been oxidized under some
conditions by the oxidizers added to the mixture (e.g.,
other reactions could have provided enough heat to
initiate oxidation; materials that might act as a catalyst
could have been present). The ketones and two of the
aromatic hydrocarbons (toluene and xylenes) are
commonly used in printing ink solvents handled by
Chief (Kirk-Othmer, 1995).
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Exhibit 1: Substances Detected in Samples Collected From Top of Disperser
Chemical
Cone.
(mg/L)
Potential Reaction with Oxidizers
Potential Reaction with Perchlorates
(Other than Oxidation)
Ketones - Solvent for rotogravure inks; limited use for flexographic inks. (Flammable)
Acetone
Methyl ethyl ketone
7,000
2,700
Oxidized by strong oxidizers under vigorous conditions
to carboxylic acids (not found in residues). Could be
oxidation product of isopropyl alcohol.
Oxidized by strong oxidizers under vigorous conditions
to carboxylic acids (not found in residues). Could be
oxidation product of alcohol.
None reported.
None reported.
Phenols Not commonly used as solvent. Phenolic resins are used in certain types of inks. (Combustible)
4-Methyl phenol
(p-Cresol)
Phenol
32
276
Phenols readily oxidize to a variety of products
Same as above.
Not reported - might expect formation of
perchlorate esters with perchloric acid, by analogy
with alcohols.
Same as above.
Aromatic Alcohol - Not commonly used as solvent in printing ink. (Combustible)
Benzyl alcohol
353
Oxidized by strong oxidizers to benzoic acid.
Potentially could form benzyl perchlorate (reported
to be explosive) in reaction with perchloric acid.
Aromatic Hydrocarbons - Some solvent use for rotogravure inks. (Flammable)
Ethyl benzene (Not
commonly used as solvent in
printing ink)
Toluene (Solvent for
rotogravure inks.)
Xylenes (Solvent for
rotogravure inks.)
370
14,000
2,400
Side-chain oxidation by strong oxidizers under vigorous
conditions.
Side-chain oxidation by strong oxidizers under vigorous
conditions to benzoic acid, other products.
Side-chain oxidation by strong oxidizers under vigorous
conditions.
None reported.
None reported.
None reported.
Note: The analytical results presented in this Exhibit may not provide an accurate representation of the composition of the solvent before the
explosion and fire for several reasons: (1) some substances, particularly those directly involved in the explosion, may have been decomposed by
the explosion or heat of the fire, or may have been completely combusted; and (2) analysis, conducted by the Oklahoma Department of
Environmental Quality, was not carried out for all possible substances present.
KEY FINDINGS
The immediate cause of the explosion and fire was
most likely a violent reaction of oxidizers in the
disperser in the presence of flammable liquid and
vapor. Since only four drums had been dumped into
the previously empty disperser, only about 9" of liquid
would be in the bottom of the tank, or about half of
the amount needed to reach the mixer. This allowed
the solid oxidizers to pile up at the bottom of the tank,
most likely right below the small tank opening, in
direct contact with each other and with flammable
solvent liquid and vapor. Although the exact chemical
mechanism is not precisely known, given the
chemicals present in the disperser residue (Exhibit 1),
a violent reaction could have occurred because:
• The waste printing ink solvents typically handled
by Chief could have violently reacted with the
perchlorates added to the disperser.
• The perchlorate salt could have contained free
perchloric acid, or perchloric acid possibly could
have formed when the salt was added to the
solvent mixture. If the solvent contained even a
small amount of ethanol (or other alcohols), and if
even a small amount of perchloric acid was
present, explosive ethyl perchlorate (or other
explosive organic perchlorate esters) could have
been formed.
• Waste printing ink solvents potentially could
contain a variety of pigment residues that could
react violently with strong oxidizers. Such a
reaction could have initiated or contributed to the
explosion.
Contributing Factors
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Several management and operational safety factors
contributed to the reaction, explosion and fire,
including, but not limited to:
• Although chemical compatibility tests were
conducted on the oxidizers and concern was raised
about the potential for an adverse reaction, the
reaction chemistry, potential for explosion and fire
in the blending operation, recognition of accident
history, and evaluation of hazards may not have
been completely examined, understood, or
documented prior to instituting the practice of
adding lab pack materials to the fuel blends.
• Lab results and concerns were not communicated
clearly to all other operators. No system for
instituting and documenting such communications
was in place at the facility.
• Although a procedure for adding the oxidizers to
the waste fuel blend was established, it was not
evaluated for safety or documented as a Standard
Operating Procedure (SOP). The consequences of
deviation from this procedure were not evaluated,
communicated or understood. It is not known if
any training on this procedure occurred or if the
company had a management system for SOPs.
• No controls, barriers, or layers of protection, other
than the unwritten procedure, were established to
ensure that the mixing procedure was always
followed, to minimize the consequences of human
error, or to preclude or minimize the possibility of
an abnormal reaction situation or its consequences
when the oxidizers were added to the solvent
mixture.
STEPS FOR ACCIDENT PREVENTION
Disposing of oxidizers by mixing them with organic
solvents is generally recognized as inherently
hazardous; common references warn against mixing
oxidizers with organic or combustible materials.
Perchlorates, which Chief added to the solvent
mixture, are recognized as a particularly severe
explosion hazard. Many past accidents have been
reported involving explosions and fires that have
resulted from reactions between oxidizers and organic
substances. Although the analysis presented here does
not identify the exact cause of the explosion and fire
at Chief, the analysis shows that the potential for such
an incident exists whenever strong oxidizers, such as
those used at Chief, are mixed with oxidizable and
combustible organic substances, like the solvent
mixture at Chief. When the oxidizer is a perchlorate,
as was one of the oxidizers mixed with solvents at
Chief, the danger increases.
Here are some steps that facilities should take to
address the hazards of reactions between oxidizers and
waste fuels. If these hazards are not well understood
and addressed, oxidizers and oxidizable substances
(fuels) must not be mixed because of the potential for
dangerous unknown reactions. These steps are based
on the findings associated with this incident and on
the recognition that most chemical accidents can be
successfully prevented if a management system is in
place that ensures that all chemical and process
hazards are well understood. Facilities should be
designed, constructed, maintained, and safely operated
day-after-day with those hazards under control. This
approach, and these steps, applies to any facility
handling any hazardous substance.
• The chemicals and reaction mechanisms
associated with the substances mixed or blended
must be well understood and documented.
Facilities need to conduct the necessary
information searches or laboratory tests to ensure
that all reaction mechanisms are known and
documented, especially those that may trigger
fires or explosions as a result of abnormal
situations or changes in chemicals mixed.
• Chemical and process hazards must be understood
and addressed. Once the reaction mechanisms are
well understood, facilities need to ensure that
process equipment, controls, and procedures are
designed, installed, and maintained to safely
operate the process. A formal hazard review using
techniques like 'What-If or 'Hazop' can help
identify opportunities for failure (e.g., human
error, mechanical failure) and layers of protection
to minimize the consequences of such failures,
based on established codes and standards, industry
practices, regulations (federal or state) and
common sense.
• All employees need to understand the chemical
and process hazards. All personnel should openly
communicate information about hazards and
process conditions and understand the
consequences of deviations and unusual
situations. Facilities should establish mechanisms
for documenting and sharing such information.
• Standard Operating Procedures (SOPs) are
essential to safe operations. Facilities should
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establish a system to develop and maintain written
SOPs and ensure that they are understood and
followed at all times. The SOPs must address all
phases of operation, safe limits for operation,
consequences of deviation, and identification of
corrective measures during emergency situations.
• Before starting a process or procedure that has
been changed or modified, the chemical and
process hazards must be evaluated. Abnormal or
non-routine circumstances are a leading factor in
chemical accidents. Facilities should make use of
management of change (MOC) and pre-startup
safety review techniques to ensure that modified
processes or procedures will function as intended
without unanticipated impacts on other operations.
• Employees must be properly trained in the
processes they work on using the SOPs for that
process or job tasks. Training must include
potential hazards, reduction of those hazards,
safety consequences if procedures are not
followed, and proper emergency response to
abnormal situations. Training should contain
clear and concise objectives that can easily be
evaluated for operator competence.
REFERENCES
Bretherick, L. Handbook of Reactive Chemical
Hazards, Third Edition. Boston: Butterworths, 1985.
Chase, M.W., Jr., et al. JANAF Thermochemical
Tables, Third Edition. Published by the American
Chemical Society and the American Institute of
Physics for the National Bureau of Standards, 1986.
Design Institute for Physical Property Data (DIPPR),
American Institute of Chemical Engineers. Physical
and Thermodynamic Properties of Pure Chemicals,
Data Compilation. Washington: Taylor & Francis,
1997.
Kirk-Othmer Encyclopedia of Chemical Technology,
4th Edition, Vol. 14. "Inks," page 483 ("Printing
Inks"). New York: John Wiley & Sons, 1995.
Kirk-Othmer Encyclopedia of Chemical Technology,
4th Edition, Vol. 18. "Perchloric Acid and
Perchlorates," page 157. New York: John Wiley &
Sons, 1996.
Lewis, Richard J. Sax's Dangerous Properties of
Industrial Materials, Ninth Edition. New York: Van
Nostrand Reinhold, 1996.
Lide, David R., ed. CRC Handbook of Chemistry and
Physics, 75th Edition. Boca Raton: CRC Press, 1994.
National Fire Protection Association (NFPA). NFPA
49, Hazardous Chemicals Data, 1994 Edition and
NFPA 325, Fire Hazard Properties of Flammable
Liquids, Gases, and Volatile Solids, 1994 Edition.
Quincy, MA: NFPA, 1994.
Schumacher, Joseph C., ed. Perchlorates, Their
Properties, Manufacture and Uses. American
Chemical Society Monograph Series. New York:
Reinhold, 1960.
US EPA; Standards for Owners and Operators of
Hazardous Waste Treatment, Storage, and Disposal
Facilities, 40 CFR 264; Appendix V to Part 264 -
Examples of Potentially Incompatible Waste.
US GAO; Inspections of Facilities Treating and Using
Hazardous Waste Fuels Show Some Noncompliance,
US General Accounting Office, Report to Congress,
GAO/RCED-96-211, August 1996.
For More Information.
Contact the Emergency Planning and
Community Right-to-Know Hotline:
800-424-9346 or 703-412-9810
TDD 800-553-7672
Monday-Friday, 9 AM to 6 PM (EDT)
Visit the CEPPO Home Page on
the World Wide Web at:
http ://www. gov/ceppo/
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