Chemical Emergency Preparedness and Prevention Office v Printed on Recycled Paper

CHEMICAL 

SAFETY

CASE STUDY

United States 

Environmental Protection

Agency

Office of Solid Waste

and Emergency Response

(5104)

EPA 550-F99-004

August 1999

www.epa.gov/ceppo/

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.

Columbus, Ohio 

Sept. 10, 1997

A

t 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

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.

Accident Investigation

U

nder 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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Chemical Emergency Preparedness and Prevention Office v Printed on Recycled Paper

Date of incident State Description Effects

September 10, 1997 OH A 8,000 gallon reactor exploded during production of a

phenol-formaldehyde resin.

1 worker fatality, 4 employees

injured, 3 firefighters treated for

chemical burns. Evacuation of

residents for several hours.

August 18, 1994 OH 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.

Residents evacuated for 5 hours.

February 29, 1992 GA A 13,000 gallon reactor exploded during production of a

phenol-formaldehyde resin. Explosion occurred during

initial stages of catalyst addition.

4 employees injured, 1 seriously. 1

firefighter treated for chemical

burns. Evacuation of 200 residents

for 3 hours.

November 11, 1991 OH Temperature increased in chemical reactor, releasing

phenol formaldehyde resin.

None reported.

October 16, 1989 WI Manufacture of phenolic resins and thermoset plastics;

release of phenol and formaldehyde from process vessel.

None reported.

August 28, 1989 NY Manufacture of phenolic resins; release of phenol and

phenolic resin from process vessel; “operator error” cited

as cause.

1 injured.

July 25, 1989 VA Specialty paper manufacturing; release of phenolic resin

and methanol from process vessel.

None reported. 

Table 1 Phenol-Formaldehyde Reaction Incidents at Various Companies

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.
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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

C

ontrolling 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 safety 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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# 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

T

he 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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Chemical Emergency Preparedness and Prevention Office v Printed on Recycled Paper

# 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

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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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Chemical Emergency Preparedness and Prevention Office v Printed on Recycled Paper

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 phenolformaldehyde 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 phenolformaldehyde 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.G. Redpath. “Incidents resulting from

process design and operating deficiencies,” I. 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.

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