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.
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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.
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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.
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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.
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                                        How to Prevent Runaway Reactions
                        August 1999
#     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.
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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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