United States
Environmental Protection
Agency
Office of Solid Waste
and Emergency Response
(5104)
EPA 550-F99-004
August 1999
www.epa.gov/ceppo/
vvEPA
HOW TO PREVENT
RUNAWAY REACTIONS
CASE STUDY:
PHENOL-FORMALDEHYDE 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. Under CERCLA, section 104(e) and the Clean
Air Act (CAA), EPA has authority to conduct chemical accident investigations. EPA is striving
to learn the causes and contributing factors associated with chemical accidents to prevent
their recurrence. Major chemical accidents cannot be prevented solely through command and
control regulatory requirements, but by understanding the fundamental root causes, widely
disseminating the lessons learned, and integrating them into safe operations. EPA will
publish Case Studies and Alerts to increase awareness of possible hazards. It is important
that facilities, State Emergency Response commissions (SERCs), Local Emergency Planning
Committees (LEPCs), emergency responders and others review this information and take
appropriate steps to minimize risk.
PROBLEM: Many industrial chemical processes involve exothermic (heat
generating) reactions. Uncontrolled, or runaway, reactions can occur as a
result of various situations, such as mischarged raw materials, failure of a
reactor's cooling system or the presence of contaminants. If the heat
generation exceeds the reactor's ability to remove it, the reaction can
accelerate - or run away - and cause the temperature and pressure to
increase. A sudden energy release from such an uncontrolled reaction has
the potential to harm workers, the public, and the environment. The
following Case Study aims to increase awareness of possible hazards
connected with exothermic reactions.
explosion also resulted in the release of
a large quantity of liquid resin and
smaller quantities of other chemicals
within the facility. Three fire fighters
were injured during the response,
treated for first-degree chemical burns,
and released.
Columbus, Ohio
Sept. 10,1997
At approximately 10:42 a.m. on
Wednesday, Sept. 10, 1997, an
explosion occurred in a resins
production unit at Georgia-Pacific
Resins, Inc. in Columbus, Ohio. The
blast was reported to be felt at least 2
miles and possibly as far as 7 miles
away according to various news
accounts and other reports. As a result
of the explosion, one worker was killed
and four others injured. The explosion
extensively damaged the plant. Local
news reported that a vocational school
and several homes and businesses
within a 3/4-mile radius were
evacuated as a precaution by the local
fire department for several hours
(Dispatch, September 11, 1997). The
Accident Investigation
Under a 1997 Memorandum of
Understanding (MOU) to
investigate chemical accidents
and report on the lessons learned, EPA
and the Occupational Safety and Health
Administration (OSHA) collaborated to
analyze the evidence. The purpose of
this effort was to understand the
circumstances associated with the
accident to prevent a recurrence at this
and other facilities.
Chemical Emergency Preparedness and Prevention Office
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How to Prevent Runaway Reactions
August 1999
Phenol-formaldehyde reactions are common
industrial processes. The reaction of phenol or
substituted phenol with an aldehyde, such as
formaldehyde, in the presence of an acidic or basic
catalyst is used to prepare phenolic resins. Phenolic
resins are used in adhesives, coatings, and molding
compounds. The type of catalyst used, the ratio of
reactants, and the reaction conditions determine the
molecular structure and physical properties of the
resin produced. Typically, phenol-formaldehyde
reactions are highly exothermic and sensitive to a
variety of physical and chemical conditions. Once a
reaction is initiated, heat generated by the reaction
increases the reaction rate generating more heat.
Because the reaction rate is typically an exponential
function of temperature, the rate of heat generation
will accelerate. Without intervention, a thermal
runaway will occur, producing a large amount of heat
in a very short time. Once the reaction begins to
accelerate, the pressure of the system will typically
increase suddenly due to gas production and/or the
vigorous evaporation of liquid. If the reaction
continues to accelerate, the pressure buildup may
reach and exceed the ultimate strength of the reactor
and cause it to explode.
Typically, phenolic resin batch processes are
equipped with an agitator, heating/cooling jacket, a
water-cooled condenser, and a vacuum system
(Kirk-Othmer, p.614). The heat of reaction is
removed by the evaporation of water or other liquid
from the process, condensation of the liquid in the
overhead condensation system, and return of the
liquid to the reactor vessel. Emergency relief on the
reactor is usually provided by rupture disks. In a
conventional novalak process, molten phenol is
placed into the reactor, followed by a precise
amount of acid catalyst. The formaldehyde solution
is then added. For safety reasons, slow continuous
or stepwise addition of formaldehyde is preferred
over adding the entire charge at once (Kirk-Othmer,
p. 614).
The manufacture of phenolic resins has resulted in a
number of accidents dating back to 1957. A search
of accident databases and the literature reveals that
numerous incidents have resulted in worker fatalities
and injuries and significant property damage.
Table 1 is a summary of the incidents that have
occurred during the past 10 years.
Table 1 Phenol-Formaldehyde Reaction Incidents at Various Companies
Date of incident
September 10, 1997
August 18, 1994
February 29, 1992
November 11, 1991
October 16, 1989
August 28, 1989
July 25, 1989
State
OH
OH
GA
OH
Wl
NY
VA
Description
A 8,000 gallon reactor exploded during production of a
phenol-formaldehyde resin.
Pressure buildup during manufacture of phenolic resin,
pressure increased, rupture disks popped. Product was
released through emergency vent. The cause of accident
was reported as failure to open condensate return line.
A 13,000 gallon reactor exploded during production of a
phenol-formaldehyde resin. Explosion occurred during
initial stages of catalyst addition.
Temperature increased in chemical reactor, releasing
phenol formaldehyde resin.
Manufacture of phenolic resins and thermoset plastics;
release of phenol and formaldehyde from process vessel.
Manufacture of phenolic resins; release of phenol and
phenolic resin from process vessel; "operator error" cited
as cause.
Specialty paper manufacturing; release of phenolic resin
and methanol from process vessel.
Effects
1 worker fatality, 4 employees
injured, 3 firefighters treated for
chemical burns. Evacuation of
residents for several hours.
Residents evacuated for 5 hours.
4 employees injured, 1 seriously. 1
firefighter treated for chemical
burns. Evacuation of 200 residents
for 3 hours.
None reported.
None reported.
1 injured.
None reported.
Chemical Emergency Preparedness and Prevention Office
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How to Prevent Runaway Reactions
August 1999
Georgia-Pacific was manufacturing a phenolic resin
in an 8,000-gallon batch reactor when the incident
occurred. An operator charged raw materials and
catalyst to the reactor and turned on steam to heat
the contents. A high temperature alarm sounded
and the operator turned off the steam. Shortly after,
there was a large, highly energetic explosion that
separated the top of the reactor from the shell. The
top landed 400 feet away. The shell of the reactor
split and unrolled, and impacted against other
vessels. A nearby holding tank was destroyed and
another reactor was partially damaged. The
explosion killed the operator and left four other
workers injured.
The investigation revealed that the reactor explosion
was caused by excessive pressure generated by a
runaway reaction. The runaway was triggered
when, contrary to standard operating procedures, all
the raw materials and catalyst were charged to the
reactor at once followed by the addition of heat.
Under the runaway conditions, heat generated
exceeded the cooling capacity of the system and the
pressure generated could not be vented through the
emergency relief system causing the reactor to
explode.
Lessons Learned
Controlling an exothermic reaction depends on
the interaction among the kinetics and
reaction chemistry; the plant equipment
design; and the operating environment. Facilities
must consider the following factors to better
understand and address the potential hazards and
consequences of reactive systems:
# Thorough hazard assessment - The
chemical and process hazards and the
consequences of deviations must be
thoroughly understood, evaluated,
documented, and appropriately addressed
through preventive measures. The adequacy
of safety systems to prevent deviations must
be carefully evaluated, including
consideration of worst case situations.
Several layers of safely systems, whether
complementary or redundant should be
considered to enhance reliability. One way
that facilities can carry out this evaluation is
to use formal process hazard analysis (PHA)
techniques, such as what-if or fault tree
analysis. The Center for Chemical Process
Safety (CCPS) of the American Institute of
Chemical Engineers (AIChE) has prepared
guidance on PHA methodologies. (See
CCPS, 1992)
# Complete identification of reaction
chemistry and thermochemistry - For
some exothermic reactions, the time to
runaway is very short. Overpressurization
can occur when gas or vapor is produced as
a byproduct of the reaction or any
decomposition reactions. The kinetics of the
runaway reaction will be reaction specific
and may differ in various runaway situations.
While general studies found in the literature
can be useful for screening thermal hazards,
the characteristics of the particular reactions
must be determined experimentally.
Experimental data should be used to define
process boundaries in terms of the pressure,
temperature, concentration, and other
parameters as well as the consequences of
operating outside of these boundaries.
# Administrative controls- If administrative
controls, such as training and standard
operating procedures, are used as a
safeguard against process deviation and
accidental release, consideration must be
given to human factors to ensure reliability,
especially if an administrative control is the
sole layer of protection. Humans make
mistakes; the consequences of a human error
should not lead to a catastrophic release.
Processes, equipment and procedures must
be designed with potential for human error in
mind. For manual operations, preventive
measures should be considered to minimize
the likelihood of human error, for example,
interlocks. SOP's must be understandable,
periodically reviewed, and kept up-to-date.
Employees must be trained on the SOP's and
mechanisms set up to ensure that SOP's are
followed at all times. The consequences of
deviation from SOP's must be well
understood by all employees.
Chemical Emergency Preparedness and Prevention Office
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How to Prevent Runaway Reactions
August 1999
# Temperature control - The capability of the
cooling system to remove the heat generated
by the reaction is critical to the safe
operation of an exothermic process.
Facilities should evaluate capacity of cooling
system with respect to controlling
unexpected exotherms. Condensation
cooling of reflux is commonly used to cool
exothermic reactions that generate vapor as a
byproduct, but has several limitations to
control unexpected exotherms. Reflux
cooling is limited until the reaction mass
reaches the boiling point of the liquid and
cannot control exotherms that begin while
the reaction temperature is below the liquid's
boiling point. As a runaway reaction
proceeds, the increased generation rate of
vapor increases the vapor velocity, the mass
flow rate, and the inlet temperature in the
overhead condenser. The increased heat
load on the condenser results in only partial
condensation and reflux of water.
# Addition of raw materials - Frequently,
the reaction rate is controlled by the addition
rate of one reactant or the catalyst and
should be determined based on chemistry
studies. Facilities must pay attention to the
order of ingredients, the addition rates,
under- or over-charging, and loss of
agitation.
# Emergency relief - Runaway reactions may
lead to the rapid generation of gas or water
vapor. Under certain conditions, the vapor
generation rate may be large enough to cause
the vapor-liquid mixture to swell to the top
of the vessel, resulting in two-phase flow in
the relief venting system. Relief system
capacity should be evaluated in conjunction
with the hazard analysis to ensure that sizing
is based on an appropriate worst case
scenario.
# Learning from accident history and near
misses - Very few accidents occur without
any warning. As Table 1 shows, a search of
readily available sources found a number of
incidents involving phenol-formaldehyde
reactions. Accident history should be
included in the information evaluated as part
of the process hazard analysis. Additionally,
many accidents are preceded by one or more
near-miss incidents. Near misses should be
analyzed to determine if operating
procedures or other items need change.
Steps To Reduce Hazards
The consequences of a runaway reaction can be
severe. Therefore, facilities must focus on
prevention of conditions favorable to a
reaction excursion through process design control,
instrumentation, and interlocks to prevent
recurrence of similar events.
Facilities should take the following steps to prevent
runaway reactions:
# Modify processes to improve inherent
safety. Consider inherently safer processes
to reduce reliance on administrative controls.
(See CCPS, 1996)
# Minimize the potential for human error.
Anticipate possible human errors and
carefully evaluate scenarios where an error
could have catastrophic results. Managers
should implement various protective
measures, such as temperature control,
instrumentation, and interlocks to eliminate
opportunities for human error, especially in
critical manual operations.
# Understand events that may lead to an
overpressure and eventually to vessel
rupture.
Ensure that all chemical and process hazards
and consequences are understood, evaluated,
and appropriately addressed. Examine
scenarios that include the failure of
engineering and/or administrative controls.
Evaluating these hazards may require
detailed process hazard assessments. Use
techniques and available information to
minimize the chance of missing an important
potential accident scenario.
Chemical Emergency Preparedness and Prevention Office
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How to Prevent Runaway Reactions
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# Use lessons learned. Go beyond issues of
quality control and operator error and
identify true root causes. Learn from near
misses and similar incidents and foster an
environment where any deviation, no matter
how small, is raised and addressed. Identify
root causes and recommend changes to
prevent recurrence. Share your expertise
with all facilities in the corporate structure
and share your experience through regular
participation in safety forums sponsored by
trade associations or professional
organizations.
# Evaluate SOPs. SOP's should include
critical operating parameters and why they
are important. Each numbered step in the
SOP should include only one action.
Evaluate SOP's and modify when necessary
to minimize the likelihood of an undetected
human error. Supervisors should audit SOPs
regularly, including the direct observation of
employees and conducting employee
interviews to ensure the SOPs are fully
understood. This information will help
supervisors identify deviations from SOP's
and will help supervisors recommend and
ensure revision of SOPs.
# Evaluate employee training and oversight.
Ensure that operators are adequately trained
and supervised before assignment to critical
manual operations. Be aware that a
limitation of on-the-job training is that
trainees are prepared to handle only a limited
number of problems, primarily those
encountered before. To offset this limitation,
trainees should work alongside an
experienced operator and be supervised
when using new procedures. Operator
training can frequently be improved by
showing operators how to respond to upset
conditions or process deviations.
# Evaluate measures to inhibit a runaway
reaction. A runaway reaction, if caught
early, can sometimes be halted by adding
chemicals to cancel the effect of the catalyst.
Common measures include neutralization,
quenching with water or other diluent, or
dumping the contents into another vessel
which contains a quench liquid. Carefully
select the inhibitor or quench material,
determine the appropriate concentration and
rate of addition of inhibitor and understand
the inhibition reaction.
# Evaluate the effectiveness of the
emergency relief system. Proper vent
sizing for potential runaway exothermic
reactions is complex and requires data on the
heat and pressure generation that may occur
during a runaway. The most recent
procedures used to calculate vent size were
developed by the Design for Emergency
Relief Systems (DIERS) program, a
consortium of companies chartered by the
American Institute of Chemical Engineers
(AIChE). For certain reaction systems, the
pressure rise due to a runaway may be so
quick that the calculated vent size will be
impractical and the only safety options are to
prevent or inhibit a runaway reaction.
Related Statutes and Regulations
EPA
\ General Duty Clause [Section 112(r) of the Clean
Air Act (CAA)]- Facilities have a general duty to
prevent and mitigate accidental releases of extremely
hazardous substances.
! Risk Management Program (RMP) Rule [40 CFR
68]- Facilities with listed substances in quantities
greater than the threshold planning quantity must
develop a hazard assessment, a prevention program,
and an emergency response program
OSHA
Process Safety Management (PSM) Standard [29
CFR 1910.119] - Facilities with listed substances at
or above the threshold planning quantity are subject
to a number of requirements for management of
hazards, including performing a process hazards
analysis and maintaining mechanical integrity of
equipment.
Chemical Emergency Preparedness and Prevention Office
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How to Prevent Runaway Reactions
August 1999
Information Resources
Booth, A.D. et. al. "Design of emergency venting system for
phenolic resin reactors - Part 1," Trans IChemE, vol. 58
(1980) 75-79.
Booth, A.D. et. al. "Design of emergency venting system for
phenolic resin reactors - Part 2," Trans IChemE, vol. 58
(1980) 80- 90.
Center for Chemical Process Safety (CCPS), Inherently Safer
Chemical Processes, AIChE, New York, NY (1996 ).
Center for Chemical Process Safety (CCPS), Guidelines for
Chemical Reactivity Evaluation and Application to Process
Design, AIChE, New York, NY (1995).
Center for Chemical Process Safety (CCPS), Guidelines for
Hazard Evaluation Procedures Second Edition with Worked
Examples. AIChE, New York, NY (1996 ).
Gustin, J.L. et. al. "The phenol + formaldehyde runaway
reaction. Vent sizing for reactor protection," J. Loss Prev.
Process Ind., vol. 6, no. 2 (1993) 103-113.
Jones, T.T. "Some preliminary investigations of the phenol-
formaldehyde reaction," J. Soc. Chem. Ind., vol. 65, (1946)
264-275.
Kirk-Othmer Encyclopedia of Chemical Technology,
Phenolic Resins, (1996) 603-644.
Knop, A. and L. A. Pilato, Phenolic Resins Chemistry,
Applications, and Performance, Springer-Verlag, Berlin,
1985.
Kumpinsky, E. "A study on resol-type phenol-formaldehyde
runaway reactions," Ind. Eng. Chem. Res., vol. 33 (1994)
285-291.
Kumpinsky, E. "pH effects on phenol-formaldehyde runaway
reactions" Ind. Eng. Chem. Res., vol. 34 (1995) 3096-3101.
Leung, J.C. and H.K. Fauske. "Thermal runaway reactions in
a low thermal inertia apparatus," Thermochimica Acta, vol.
104 (1986) 13-29.
Mau, K.Y. et. al. "The development of a real-time emergency
advisory system for batch reactors," Computers Chem. Engng,
vol. 20, supplement (1996) S593-S598.
Schaechtel, D. and D. Moore. "Using quantitative risk
analysis in decision making: an example from phenol-
formaldehyde resin manufacturing," Proceedings from the
International Conference and Workshop on Risk Analysis in
Process Safety, Oct. 21-24, 1997, Atlanta, GA, Sponsored by
CPS, EPA, H&SE, Eur. Fed. of Chem Engg., 285-297.
Taylor, H.D. and P.O. Redpath. "Incidents resulting from
process design and operating deficiencies," /. Chem. E.
Symposium Series No. 34 (1971: Instn Chem. Engrs,
London).
Waitkus, P.A. and Griffiths, G.R.,"Explosion venting of
phenolic reactors-- toward understanding optimum explosion
vent diameters," Safety and Health with Plastics, National
Technical Conference, Society of Plastics Engineers,
November 8-10, 1977, pp 161-186.
FOR MORE INFORMATION...
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AND COMMUNITY RIGHT-TO-KNOW
HOTLINE
(800) 424-9346 or (703) 412-9810
TDD (800) 553-7672
MONDAY-FRIDAY, 9 AM TO 6 PM, EASTERN TIME
VISIT THE CEPPO HOME PAGE:
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