Morton International Explosion 

Paterson, New Jersey April 8, 1998

To workers at the Morton International chemical plant

in Paterson the evening of April 8, the gathering noise

“sounded like a train rumbling through.”

The 2,000-gallon chemical reactor shook as the internal

temperature rose ever higher. Nearly four decades old, the

kettle was nine feet tall with carbon-steel walls an inch thick.

Inside were thousands of pounds of reacting chemicals.

Minutes earlier, everything had appeared to be normal.

At 7:40 p.m., workers turned on the steam supply to the

kettle, beginning what they assumed would be a routine sixto eight-hour production run of Automate Yellow 96, a dye

used to tint petroleum fuel products. But the lead operator

watched with concern as the kettle temperature began to

climb precipitously, reaching 212 ̊F less than half an hour

later, at 8:05 p.m. A vigorous heat-producing reaction was

underway, and it was warming the kettle much faster than

steam alone would do.

Many industrially useful reactions are heat-producing or

“exothermic.” A runaway can occur when a chemical reaction 

produces heat more rapidly than it can be removed from the system.

Excess heating further accelerates the reaction, causing the 

temperature to skyrocket. Components of the mixture may then boil

violently or decompose to form gases, and the resulting pressure

may cause a vessel rupture or explosion. Generally the larger a

reaction vessel is, the more difficult it is to cool effectively, and the

greater the risk of a runaway. Even reactions that require heating

for initiation are frequently exothermic and may be susceptible to a

runaway. Runaway reactions have been responsible for a number of

catastrophic chemicals accidents, including those in Seveso, Italy

(1976); Bhopal, India (1984); and Lodi, New Jersey (1995).

To control the reaction, the lead operator decided to cut

off the steam and turn on the cooling water. A couple of

minutes later, the kettle began to vibrate ominously as it

surpassed the intended maximum processing temperature 

of 300 ̊F. Liquid and gas began venting from the top of 

the kettle, as the internal pressure built. Unknown to the

workers, the chemicals inside the kettle would begin to

decompose at 380 ̊F. That would initiate an even more violent runaway reaction that could rip the steel vessel apart. 

Moments later, 

as the temperature

rocketed past 380 ̊F,

the rumbling grew

louder still. Workers

began rushing for the exits.

At about 8:18 p.m., the Morton plant shook as accumulated pressure blew off the 18-inch metal hatch that was

clamped to the top of the kettle. The kettle was lifted 

from its moorings and driven into the floor below. A fiery

stream of gas and liquid erupted through the roof of the

building, raining down chemicals onto the surrounding

community.

Residents in a 100 city-block area were confined to their

homes, voluntarily sheltering in place for up to three 

hours while officials evaluated health risks. Firefighters and

workers in neighboring businesses reported throat, eye, and

skin irritations consistent with chemical exposure.

Meanwhile, the last two fleeing workers had been

caught by the blast and were knocked down a flight of 

stairs before collapsing to the ground. In all, nine workers

were injured, including two with severe burns. As one of

the injured said later at a public meeting of the U.S.

Chemical Safety Board, “The pressure was so much on me, I

couldn’t move. It had pinned me against the wall. It seemed

like forever.” 

The CSB investigation found that Morton had not 

adequately evaluated or controlled the hazards of the

Yellow 96 production process. Neither the preliminary

assessment conducted in 1990 nor a subsequent hazard

analysis five years later considered the possibility of a 

runaway chemical reaction – one of the most common 

reactive hazards. As a result, the production kettle was 

not provided with sufficient cooling capacity or adequate

emergency shutdown or venting systems. Morton’s analyses

never considered possible scenarios – such as excessive 

heat input or inadequate cooling – that could trigger a 

runaway reaction.

Photo by Bill Tomkins

WHAT IS A RUNAWAY REACTION?

ANALYSIS OF PROCESS HAZARDS WAS DEFICIENT
U. S. Chemical Safety and Hazard Investigation Board Morton International Explosion

CSB investigators found that two critical decisions had

increased the chances of a runaway reaction in the Yellow

96 process. 

Company researchers had originally called for controlling the process by introducing one of the raw materials

stepwise in four equal portions. But in 1990, Paterson 

managers adopted a new procedure whereby the full

amount of the chemical would be added to the reactor at

the outset. With all the reactive chemicals massed in the

kettle, a runaway reaction would become much harder to

prevent or control.

Similarly, a 1996 decision to increase the kettle size and

the batch volume made it harder for operators to cool the

reaction mixture effectively. The percentage of temperature

overruns rose significantly after the scale-up.

The CSB investigation found that Morton had not 

provided operators with adequate instruction to manage 

the Yellow 96 process safely. For example, operators were

directed to inject small shots of steam to raise the kettle

temperature in 4-5 ̊F increments, but they were not told

how much steam to let in or for how long. Nor did operators have a way to measure how much steam or cooling

water was actually reaching the kettle. Workers had to rely

largely on their own personal experience and intuition in 

trying to control the process.

Under these conditions, it was very difficult to keep 

the temperature of the Yellow 96 reaction within the 

narrow safe operating range. Temperature-control problems

occurred in eight of the 32 previous batches, according to

operator notes.

Supervisors and operators in Paterson were unaware 

of the potential for a runaway chemical reaction, despite

cautionary statements in early corporate research reports.

Years before the incident, company researchers had noted

possible hazards in the Yellow 96 reaction and recommended

testing to design emergency venting equipment and an

emergency shutdown system. This information never found

its way to Paterson personnel responsible for the safety of

the Yellow 96 production process.

Absent any knowledge of the hazard, Paterson operating

procedures did not discuss how to avoid or recover from

temperature deviations nor did they warn of the consequences if the kettle overheated.

Morton could still have corrected safety problems in the

process by launching investigations into any of the eight

prior instances when process temperatures exceeded the

normal range.

Process and design changes resulting from such investigations could have prevented the 1998 explosion.

Although investigating near-miss events and other safety

incidents is a recognized good practice, no investigations

were conducted in this case.

After analyzing the root causes of the Morton incident,

the U.S. Chemical Safety Board on August 16, 2000, made

a number of safety recommendations to reduce the risks of

similar incidents at Morton and elsewhere.

To Morton International:

The Board recommended that the Morton Paterson plant

revalidate its analyses of the hazards of all reactive chemical

processes. The Board also requested that the plant revise

operating procedures and training, install any needed pressure relief and emergency shutdown equipment, and establish

a program to investigate any unsafe process deviations in the

future. The Board also called for revision of Morton’s Yellow

96 Material Safety Data Sheet (MSDS) to include more

accurate information on the chemical’s reactive nature.

The Board further recommended that parent corporation Morton International, now a Rohm and Haas subsidiary, establish a program to share reactive chemical safety

information more widely within the company.

To OSHA and EPA:

The Board recommended that the U.S. Occupational

Safety and Health Administration (OSHA) and the U.S.

Environmental Protection Agency (EPA) issue joint guidelines on the management of reactive process hazards. The

Board also called on the two agencies to cooperate with

CSB in a special investigation on reactive hazards. 

NOTICE: 

The CSB is an independent federal agency charged with investigating industrial chemical accidents and hazards. The CSB

determines the root causes of accidents and issues safety recommendations to industry, labor, and other government agencies.

CSB Investigation Digests are not intended to substitute for the official, Board-approved reports, which can be obtained

from the agency’s web site, www.csb.gov. The web site also has complete, up-to-date information on the implementation

status of all CSB safety recommendations. Comments or suggestions, please write to info@csb.gov.

CSB Headquarters: 2175 K Street NW, Suite 400, Washington D.C. 20037 • Phone: (202) 261-7600 • www.csb.gov

PROCESS CHANGES EXACERBATED RISKS

OPERATORS LACKED NEEDED SAFETY INFORMATION

DANGER SIGNS WENT UNHEEDED

KEY RECOMMENDATIONS