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National 

Transportation

Safety Board

Washington, D.C.

Hazardous Materials 

Accident Report

Rupture of a Railroad Tank Car Containing 

Hazardous Waste 

Freeport, Texas

September 13, 2002

NTSB/HZM-04/02

PB2004-917003 National Transportation Safety Board

Notation 7661 490 L’Enfant Plaza, S.W.

Adopted December 1, 2004 Washington, D.C. 20594
National Transportation Safety Board. 2004. Rupture of a Railroad Tank Car Containing Hazardous

Waste, Freeport, Texas, September 13, 2002. Hazardous Materials Accident Report NTSB/HZM-04/

02. Washington, DC.

Abstract: About 9:30 a.m. central daylight time on September 13, 2002, a 24,000-gallon-capacity railroad

tank car, DBCX 9804, containing about 6,500 gallons of hazardous waste, catastrophically ruptured at a

transfer station at the BASF Corporation chemical facility in Freeport, Texas. The tank car had been steamheated to permit the transfer of the waste to a highway cargo tank for subsequent disposal. The waste was a

combination of cyclohexanone oxime, water, and cyclohexanone. As a result of the accident, 28 people

received minor injuries, and residents living within 1 mile of the accident site had to shelter in place for

5 1/2 hours. The tank car, highway cargo tank, and transfer station were destroyed. Two storage tanks near

the transfer station were damaged; they released about 660 gallons of the hazardous material oleum.

The National Transportation Safety Board identified one major safety issue, the adequacy of procedures

for heating hazardous materials cargoes in railroad tank cars before transfer.

As a result of its investigation of this accident, the Safety Board makes safety recommendations to the

Research and Special Programs Administration, the Occupational Safety and Health Administration, and

the Environmental Protection Agency.

The National Transportation Safety Board is an independent Federal agency dedicated to promoting aviation, railroad, highway, marine,

pipeline, and hazardous materials safety. Established in 1967, the agency is mandated by Congress through the Independent Safety Board

Act of 1974 to investigate transportation accidents, determine the probable causes of the accidents, issue safety recommendations, study

transportation safety issues, and evaluate the safety effectiveness of government agencies involved in transportation. The Safety Board

makes public its actions and decisions through accident reports, safety studies, special investigation reports, safety recommendations, and

statistical reviews.

Recent publications are available in their entirety on the Web at <http://www.ntsb.gov>. Other information about available publications also

may be obtained from the Web site or by contacting:

National Transportation Safety Board

Public Inquiries Section, RE-51

490 L’Enfant Plaza, S.W.

Washington, D.C. 20594

(800) 877-6799 or (202) 314-6551

Safety Board publications may be purchased, by individual copy or by subscription, from the National Technical Information Service. To

purchase this publication, order report number PB2004-917003 from:

National Technical Information Service

5285 Port Royal Road

Springfield, Virginia 22161

(800) 553-6847 or (703) 605-6000

The Independent Safety Board Act, as codified at 49 U.S.C. Section 1154(b), precludes the admission into evidence or use of Board reports

related to an incident or accident in a civil action for damages resulting from a matter mentioned in the report. 
iii Hazardous Materials Accident Report

Contents

Executive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv

Factual Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

The Accident . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Synopsis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Events Preceding the Accident . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Tank Car Rupture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Emergency Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Injuries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Railroad Tank Car Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Hazardous Materials Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

BASF Oxime Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Postaccident . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Preaccident . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

BASF Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Company and Facility Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Procedures for Heating and Unloading Hazardous Materials at Freeport . . . . . . . . . . 15

BASF Postaccident Actions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Exclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

The Accident . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Rupture of DBCX 9804 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Overpressure Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Procedures Used in Steam-Heating DBCX 9804 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

MFR Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

BASF Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Heating Hazardous Materials in Railroad Tank Cars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Findings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Probable Cause . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Appendix

A: Investigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

B: Summary of Significant Events Preceding the Freeport Accident . . . . . . . . . . . . . . . 30
iv Hazardous Materials Accident Report

Executive Summary

About 9:30 a.m. central daylight time on September 13, 2002, a

24,000-gallon-capacity railroad tank car, DBCX 9804, containing about 6,500 gallons of

hazardous waste, catastrophically ruptured at a transfer station at the BASF Corporation

chemical facility in Freeport, Texas. The tank car had been steam-heated to permit the

transfer of the waste to a highway cargo tank for subsequent disposal. The waste was a

combination of cyclohexanone oxime, water, and cyclohexanone. As a result of the

accident, 28 people received minor injuries, and residents living within 1 mile of the

accident site had to shelter in place for 5 1/2 hours. The tank car, highway cargo tank, and

transfer station were destroyed. The force of the explosion propelled a 300-pound tank car

dome housing about 1/3 mile away from the tank car. Two storage tanks near the transfer

station were damaged; they released about 660 gallons of the hazardous material oleum

(fuming sulfuric acid and sulfur trioxide).

The National Transportation Safety Board determines that the probable cause of

the rupture of railroad tank car DBCX 9804 was overpressurization resulting from a

runaway exothermic decomposition reaction initiated by excessive heating of a hazardous

waste material. Contributing to the accident was the BASF Corporation’s failure to

monitor the temperature and pressure inside the tank car during the heating of the

hazardous waste.

The Safety Board identified the following safety issue during this investigation:

• Adequacy of procedures for heating hazardous materials cargoes in railroad

tank cars before transfer.

As a result of its investigation, the Safety Board makes safety recommendations to

the Research and Special Programs Administration, the Occupational Safety and Health

Administration, and the Environmental Protection Agency.
1 Hazardous Materials Accident Report

Factual Information

The Accident

Synopsis

About 9:30 a.m. central daylight time1 on September 13, 2002, a

24,000-gallon-capacity railroad tank car, DBCX 9804, containing about 52,450 pounds

(6,500 gallons)2 of hazardous waste, catastrophically ruptured at the BASF Corporation

(BASF) chemical facility in Freeport, Texas. The tank car had been undergoing

steam-heating to permit the transfer of the waste to a highway cargo tank for subsequent

disposal. The waste was a combination of cyclohexanone oxime, water, and

cyclohexanone. The railroad tank car, the highway cargo tank, and the transfer station

were destroyed. (See figure 1 for a postaccident photo of the transfer area.) Two nearby

storage tanks containing oleum (fuming sulfuric acid and sulfur trioxide) were damaged

and released about 10,650 pounds (660 gallons)3

 of material. Twenty-eight people

received minor injuries, and residents living within 1 mile of the accident site had to

shelter in place for 5 1/2 hours.

Events Preceding the Accident4

Generation and Initial Storage of the Waste in Freeport. On June 1, 2001, a

process upset5 occurred at the caprolactam II6 process of the BASF facility in Freeport. On

June 5, 2001, as a result of the upset, about 90,875 pounds (11,261 gallons) of material,

consisting of about 94 percent cyclohexanone oxime, 4 percent water,7 and 2 percent

cyclohexanone, was temporarily transferred to four highway cargo tanks. On June 11,

2001, the material was to be transferred to railroad tank car DBCX 9804, but it had

solidified within the highway cargo tanks. (The material would solidify at temperatures

below 194° F.) BASF applied steam heat from a facility boiler to the four highway cargo

tanks to liquefy the material for transfer. On June 12, 2001, BASF transferred the contents

of the four highway cargo tanks to tank car DBCX 9804.

1 Unless otherwise specified, the times used in this report are central daylight time.

2 According to the BASF Corporation, the density of the waste material was about 8.07 pounds per

gallon.

3 The density of oleum is about 16.14 pounds per gallon.

4 See appendix B for a summary chronology of significant events preceding the accident.

5 A process is a facility area where hazardous materials are used, stored, manufactured, or handled. A

process upset is a condition outside of routine operating parameters in chemical manufacturing.

6 Caprolactam is used in the production of nylon. There are two caprolactam processes at the Freeport

facility, known as caprolactam I and caprolactam II.

7 Because cyclohexanone oxime is produced in water within the process, some water accompanies it.
Factual Information 2 Hazardous Materials Accident Report

Sometime between June 12, 2001, and April 26, 2002, BASF applied steam heat to

the tank car to liquefy the waste mixture so water could be removed and disposed of

on-site.8

 BASF was unable to provide information on how many times the tank car was

heated, the specific dates of the heating, the pressures at which the steam heat was applied,

or the amount of water removed. According to BASF, no additional materials were added

to the tank car during this period.

On February 12, 2002, a BASF contractor took samples of the material in

DBCX 9804. The samples were sent to several waste disposal companies, which provided

BASF with disposal cost estimates. BASF subsequently contracted with Missouri Fuel

Recycling Environmental Services (MFR) in Hannibal, Missouri, to dispose of the hazardous

waste. (MFR conducted tests on its sample, which determined the material’s heating value

[13,600 British thermal units per pound] and the fact that it contained no metals.)

On or about April 2, 2002 (exact date unknown), BASF removed about

90,875 pounds (11,261 gallons) of waste material, consisting of about 94 percent

cyclohexanone oxime, 4 percent water, and 2 percent cyclohexanone, from a second

Figure 1. Damage to transfer area caused by catastrophic rupture of tank car DBCX 9804.

8 Environmental regulations allow facilities to dispose of some types of waste materials, such as the

water from DBCX 9804, on-site.

Location of

DBCX-9804
Factual Information 3 Hazardous Materials Accident Report

process upset of the caprolactam II process and loaded it into four highway cargo tanks.

According to BASF, the second batch of material had essentially the same chemical

composition as the material from the June 1, 2001, process upset.

On April 26, April 29, and May 10, 2002, BASF transferred the second batch of

material from the highway cargo tanks to DBCX 9804, which still contained the material

from the June 1, 2001, caprolactam II process upset. According to BASF, after the second

batch of material was added to DBCX 9804, nothing more was added to or removed from

the tank car while it remained at the Freeport facility.

On June 21, 2002, BASF released railroad tank car DBCX 9804, containing the

material from both process upsets, to the Union Pacific Railroad for transportation to MFR

in Hannibal, where the waste was to be unloaded and incinerated. According to BASF,

when the tank car departed Freeport, it contained about 181,750 pounds (22,522 gallons)

of the waste material.

Heating and Unloading the Waste in Hannibal. On the morning of July 7, 2002,

tank car DBCX 9804 arrived at the Continental Cement facility in Hannibal. MFR, a

division of the Continental Cement Company, procures hazardous wastes as supplemental

fuels for the cement production process at the facility. Each year, MFR unloads about 350

railroad tank car loads of such waste at Continental’s Hannibal plant. MFR had never

before heated or unloaded the waste material contained in DBCX 9804.

On July 8, MFR began preparing DBCX 9804 for unloading by moving the tank

car to a boiler station, where the waste material within the tank car was to be heated to

liquefy it. An MFR liquid fuel supervisor who oversaw most of the unloading stated that

when the tank car arrived at the boiler station, he looked through a 6-inch-diameter access

opening in one of the two dome housings on the top of the tank car. The liquid fuel

supervisor said he saw a white, solid material in the tank car. He attempted to take a

sample using a 7-foot-long sampling tube but was unable to do so because the material

was too hard. He said the material’s hardness was comparable to steel.

The liquid fuel supervisor decided to try to take a sample from a different location.

After inserting the sampling tube through a 3-inch-diameter eduction (liquid or product)

line valve, the liquid fuel supervisor extracted a sample through the eduction line, which

extended almost to the bottom of the tank car. The liquid fuel supervisor described the

sample material extracted as “flaky, gooey, very thick, black, and the consistency of

oatmeal.”

On the morning of July 9, MFR began to steam-heat DBCX 9804 using a natural

gas boiler to generate steam. The steam was applied to the tank car at a pressure of

115 pounds per square inch, gauge (psig). MFR inserted a pressure/temperature gauge

(attached to a 4-foot probe) into the 3-inch valve opening on top of the tank car. The gauge

was connected to an automatic shutdown mechanism on the boiler that would stop the

heating if the pressure within the tank car exceeded 15 psig.

MFR employees documented heating, unloading, and other daily activities in an

operations logbook. According to the logbook, at 9:00 a.m. on July 9, the temperature of
Factual Information 4 Hazardous Materials Accident Report

the material in the tank car was 107° F. At 2:00 p.m., the temperature was 119° F and the

pressure within the tank car was 3.5 psig. The heating continued until the boiler was shut

off at 9:30 p.m. on July 9.9 According to the logbook, when the boiler was shut off, the

temperature of the material was 131° F and the pressure within the tank car was 0.3 psig.

At 5:00 a.m. on July 10, MFR restarted the boiler and resumed the heating process.

According to logbook notes, at 9:00 a.m., the temperature of the material was 146° F, and

the material was “still chunky.” At 12:00 p.m., the temperature of the material was 150° F.

At 1:00 p.m., the liquid fuel supervisor, finding that the 4-foot probe attached to the

gauging device did not extend to the bottom of the tank car and so was not providing an

accurate reading of the material’s overall temperature, temporarily removed the probe and

replaced it with a 10-foot metal rod.

The liquid fuel supervisor stated that, after leaving the rod in place for about

5 minutes, the rod’s temperature was 129° F (21° F lower than the most recent reading

obtained using the 4-foot probe attached to the gauging device). When the liquid fuel

supervisor removed the rod, he could see the material was less viscous, but he also noted

that the material hardened very quickly when exposed to the ambient temperature. The

pressure/temperature gauge was reinserted into the tank car, and the heating continued

until 11:00 p.m. on July 10, when the heating was discontinued for the night. At this time,

the temperature of the material was 195° F.

At 5:00 a.m. on July 11, the temperature of the material in the tank car was

215° F.10 The liquid fuel supervisor visually checked the material’s viscosity and

determined that the material could be unloaded. MFR moved the tank car to a transfer

station about 200 yards from the boiler station. When the tank car arrived at the transfer

station, MFR employees used a vacuum truck to prime the pump to start the flow of

product from the tank car to a highway cargo tank. The transfer continued until the

highway cargo tank was full, at which time it was weighed. The highway cargo tank

contained about 57,840 pounds (7,167 gallons) of waste material.

The highway cargo tank was moved to another area where its contents were

unloaded into a storage tank; then it was returned to the transfer station, and the transfer of

material from the tank car resumed. The liquid fuel supervisor stated that while material

was being unloaded from the tank car to the highway cargo tank for the second time, the

pump began to “suck air,” which indicated to him that all the material that could be

pumped from the tank car had been removed. The vacuum truck was used to suck out any

additional material in the transfer hoses. Then, the pump was turned off, the hoses were

disconnected, and the transfer process was terminated.

The highway cargo tank and the vacuum truck were driven to the storage tank area,

where they were weighed, and the waste was transferred to the storage tank. The second

9 MFR did not operate a third shift at the Hannibal facility, so the boiler was shut down overnight,

when no employees were on duty.

10 In an insulated tank car, the temperature of heated material can continue to rise even after heating has

been discontinued.
Factual Information 5 Hazardous Materials Accident Report

load in the highway cargo tank contained about 36,540 pounds (4,528 gallons) of waste,

and the vacuum truck contained about 6,220 pounds (771 gallons) of waste. According to

the load receipt, MFR unloaded 100,600 pounds (12,466 gallons) of material from

DBCX 9804. The unloading procedure was completed about 4:00 p.m. on July 11.

According to the secondary liquid fuel supervisor, shortly after 4:00 p.m., he closed all the

valves and access ways on DBCX 9804 and applied new security seals to the tank car’s

two dome housings.11 DBCX 9804 left Hannibal on July 12. While traveling from

Hannibal to Freeport, DBCX 9804 encountered no unusual delays or routing.

When BASF sent tank car DBCX 9804 to MFR for unloading, it had provided

MFR a State of Missouri hazardous waste manifest for the shipment. The manifest from

BASF did not record the total quantity of material sent in the tank car. When MFR

returned the manifest to BASF, it was signed by an MFR secondary liquid fuel supervisor

and dated July 11, 2002. The manifest returned from MFR stated that 91,013 pounds

(11,278 gallons) of material had been in the tank car when MFR received it. Neither the

primary nor secondary liquid fuel supervisor, nor any other MFR employee, could tell

investigators how MFR had derived the figure for total quantity received from BASF that

appeared on the manifest. The manifest also stated that MFR had unloaded 90,973 pounds

(11,273 gallons) of material at Hannibal.

Heating and Unloading the Waste in Freeport. Tank car DBCX 9804 arrived at

the BASF Freeport facility on July 22. Facility personnel conducted a routine inspection

of the tank car and found no security seals on the dome housings or anywhere else on the

tank car. Aside from the missing seals, they found no indications of tampering with the

tank car or its contents. Also as part of the inspection, they removed the 6-inch access

plate and examined the interior of the tank car. A BASF contract employee who looked

into the tank car observed that it was still about one-third full of material. BASF accepted

the tank car. BASF did not contact MFR concerning the material remaining in the tank car

or the absence of security seals.

Facility personnel determined that the tank car could not be cleaned (in the typical

manner) because it contained too much material. They decided to transfer the material

remaining in DBCX 9804 to highway cargo tanks for disposal. Between July 22 and

September 11, no action was taken to unload the tank car. At some time during this

interval, a BASF employee and a Mundy Industrial Services (Mundy)12 employee looked

into the tank car through the 6-inch access opening and found that the tank car was about

one-third full of material. Both employees stated that they saw liquid in the tank.

On September 11, DBCX 9804 was moved to the caprolactam II process area so it

could be prepared for heating and unloading. A 7,000-gallon-capacity highway cargo tank

was brought to serve as a receiving vehicle for the waste. The highway cargo tank was

already about half full of a similar waste material.

11 There is no Federal requirement that security seals be attached; generally, companies establish their

own practices with respect to security seals. MFR practice was to attach security seals to all outgoing tank

cars, even those MFR believed were empty.

12 The contractor Mundy Industrial Services of Houston, Texas, provides chemical loaders, a track

repair crew, clerical support for truck shipments, and security inspections for BASF.
Factual Information 6 Hazardous Materials Accident Report

In the afternoon of September 11, two Mundy employees⎯a primary unloader and

a secondary unloader⎯connected the heating and unloading hoses to the railroad tank car.

They threaded one end of a 3-inch-diameter hose into the 3-inch eduction line valve on top

of the tank car; they inserted the other (open) end of the hose into the manway opening on

the top of the highway cargo tank. They connected a second hose from a facility nitrogen

supply to a 2-inch-diameter vapor line valve13 on top of the tank car. The nitrogen was

available to provide additional pressure to the tank car, if needed, to assist in unloading the

waste. The nitrogen was not turned on; the eduction and vapor line valves on the tank car

were not opened.

Unloaders ran a steam hose between a facility boiler and the inlet for the tank car’s

heating coil. They placed no pressure or temperature gauges in the tank car to monitor the

interior conditions, nor did they employ any automatic shutdown mechanism. Later in the

afternoon of September 11, steam was applied to the tank car at 60 psig. After about

1 hour of heating, facility personnel decided to adjust the car’s position. They

disconnected the unloading and heating lines, repositioned the tank car, and reconnected

the unloading and heating lines. They did not resume heating the tank that day. (See

figure 2 for a diagram showing the layout of the Freeport transfer area.)

13 A vapor line valve opens to the vapor space within the tank car.

Figure 2. Schematic drawing of Freeport facility transfer area showing the highway cargo 

tank, railroad tank car DBCX 9804, unloading hose, and oleum tanks.

OLEUM OLEUM

UNLOADING STRUCTURE

DBCX-9804

Hose

Road Road

N

Highway Cargo Tank
Factual Information 7 Hazardous Materials Accident Report

On September 12, about 7:00 a.m., unloaders again applied 60-psig steam to the

tank car. The steam-heating continued until 12:00 p.m., when a transfer was attempted.

The material did not transfer. All transfer hose connections were left in place. The primary

unloader told a BASF operations coordinator that the product was too thick to unload and

suggested continuing the application of steam heat until the next morning. The operations

coordinator agreed. According to the primary unloader, about 2:00 p.m., a steam trap14

was added to the tank car’s outlet coil, and the steam pressure was reduced to about

20 psig. The heating of the tank car continued uninterrupted for 17 hours, until 7:00 a.m.

the following morning. No one monitored the temperature of the material or the pressure

within the tank car during the overnight heating, although workers were in the area

through the night.

On September 13, about 7:00 a.m., the primary unloader stopped heating the tank

car. He was able to transfer product from the tank car to the highway cargo tank at this

time. About 7 minutes after the transfer began, the primary unloader saw a splash from the

highway cargo tank’s manway opening, indicating that the level of the material in the

highway cargo tank had reached the transfer hose. The transfer was stopped, and the

3-inch valve on top of the tank car was closed. The BASF operations coordinator climbed

on top of the highway cargo tank, looked in its manway opening, and decided that the

highway cargo tank was full.

Tank Car Rupture

About 7:45 a.m., the primary unloader and a secondary unloader (who had been

present during the unloading) left the area to do other tasks. About 8:40 a.m., the

secondary unloader returned to the unloading area. He noticed that the tank car’s pressure

relief valve had opened and then reset itself. He called the primary unloader and asked

what should be done. The primary unloader said the tank car just needed to vent and that it

should be left alone.

According to the secondary unloader, the pressure relief valve opened and reset

one or two more times. The first time, the valve opened for 3 or 4 minutes and then closed

for about 5 minutes. The following time(s), the valve closed for several minutes between

openings. Numerous workers noticed an ammonia smell coming from the car.

About 9:00 a.m., the tank car’s pressure relief valve began to continuously vent

white vapor. (The continuous venting persisted until the tank rupture occurred.) Facility

personnel called the Dow Chemicals fire department for assistance.15 Witnesses reported

hearing a high-pitched whistle sound coming from the relief valve around this time. BASF

activated a “seek shelter” horn in an adjacent process.

14 A steam trap recirculates the steam within the heating coils while allowing the condensate to flow

out of the coils. A steam trap increases the efficiency of the steam-heating process.

15 A Dow Chemicals facility is adjacent to the BASF facility in Freeport. BASF had contracted with the

Dow facility for Dow to provide BASF some limited emergency services.
Factual Information 8 Hazardous Materials Accident Report

At 9:05 a.m., BASF personnel began to apply water to the tank car to knock down

the venting vapors and to cool the tank car. At 9:10 a.m., evacuation horns within the

caprolactam II process sounded, and all nonessential employees were ordered to evacuate

the area. At 9:15 a.m., Dow Chemicals fire department personnel arrived and began

applying water to the tank car using their fire truck. At 9:25 a.m., unmanned fire hoses

were positioned to apply water to the tank car while on-scene personnel moved away from

the area to discuss further actions. About 9:30 a.m., while water was being applied, the

tank car catastrophically ruptured.

Emergency Response

Eleven emergency response agencies responded to the accident, including local

fire departments, law enforcement agencies, emergency medical services organizations, a

public safety agency, and an emergency management department. After the accident,

residents living within 1 mile of the accident site were ordered to shelter in place. About

5 1/2 hours later, the shelter-in-place order was lifted. The area immediately surrounding

the accident site (including several facility processes) at the BASF facility remained

evacuated, except for essential emergency responders, for about 10 days after the accident

due to a continuing leak of the hazardous material oleum from damaged storage tanks and

the danger from structural damage to the transfer station.

Injuries

No fatalities were caused by the accident. According to a BASF nurse from the

Freeport facility, 28 people reported minor injuries and all these individuals were treated

and released from medical supervision.

Damage

Tank car DBCX 9804 split longitudinally near its top. The split ran the length of

the tank car. Two circumferential tears on opposite sides of the car ran from the area where

the dome housings had been to about halfway down the sides of the tank car. The tank’s

fracture surfaces were consistent with overstress fracturing. The sides of the tank car had

unfolded into a flattened position. (See figure 3.) The pressure relief valve was not found.

One dome housing (without the cover) that contained the valves and fittings was found on

the adjacent Dow Chemicals facility property about 1/3 mile south of the accident site. The

second dome housing (containing the 6-inch access opening) was not found. Both tank car

heads were separated from the tank car shell. The B-end head was found about 25 feet west

of the flattened tank car, and the A-end head was found about 125 feet to the east.
Factual Information 9 Hazardous Materials Accident Report

The transfer station where DBCX 9804 had been, the highway cargo tank that had

been receiving the waste, and a second tank car in the vicinity were destroyed. The station

structure east and west of the blast site was severely damaged. Two storage tanks

containing oleum immediately to the north/northwest of the accident scene were damaged

by flying debris, leading to the oleum release.

Railroad Tank Car Information

DBCX 9804 was a U.S. Department of Transportation (DOT) specification

111A100W6 railroad tank car manufactured by Trinity Industries in June 1998. The tank

car was manufactured for BASF and was intended to transport acrylic acid. (DBCX 9804

had transported 26 shipments of acrylic acid before it began to be used to store waste. The

last shipment of acrylic acid made in DBCX 9804 took place on May 10, 2001.) The tank

car’s capacity was 23,589 gallons.

DBCX 9804 was a jacketed, stainless steel, general-purpose tank car equipped

with exterior heating coils. The tank was manufactured of 7/16-inch

ASTM A240-type 316L stainless steel. The tank car had glass wool and ceramic fiber

blanket insulation covered by a steel jacket. (See figure 4 to view a comparable tank car.)

Figure 3. Postaccident photo showing a Safety Board investigator standing on flattened 

portion of railroad tank car DBCX 9804.
Factual Information 10 Hazardous Materials Accident Report

According to postaccident estimates calculated by Trinity Industries, the burst

pressure of DBCX 9804 was about 595 psig. When the tank car was manufactured, its

tank and pressure relief valve were pressure-tested to 100 psig and 75 psig, respectively.

The valves, gauging devices, and tank access points were inside the two dome

cover housings on the top of the tank car. (See figure 5.) One housing contained a

20-inch-diameter cover assembly. A 6-inch-diameter access plate was secured to the top

of the 20-inch cover assembly. The opening through the 6-inch flange extended through

the 20-inch cover assembly, which allowed for visual inspection of the tank interior

through the 6-inch access plate opening.

Figure 4. Undamaged tank car comparable to DBCX 9804.
Factual Information 11 Hazardous Materials Accident Report

Product transfer took place by way of the valves and fittings located within the

second dome cover housing. (See figure 6.) The second dome housing contained the

eduction line valve, which was used for loading and unloading the tank car. A

3-inch-diameter eduction line extended from the eduction valve to near the bottom of the

tank car. The dome housing also contained the 2-inch-diameter vapor line valve, which

could be used to pressurize the tank car with nitrogen.

Figure 5. Photo showing interiors of two dome housings of tank 

car comparable to DBCX 9804. Housing to the right contains 6-inch 

access opening and 20-inch access opening.
Factual Information 12 Hazardous Materials Accident Report

The pressure relief valve was mounted on top of the tank car, outside of the dome

cover housings. The pressure relief valve, a Midland Manufacturing model

A-1779-P-MO-CZ, had a set pressure of 75 psig and a flow rating of 1,340 standard feet

per minute, air, at 75 psig.

During postaccident examination of the tank car, investigators found no

indications of corrosion or unusual wear. Since the tank car’s manufacture, only its brakes

had undergone repairs. No repairs to the tank or its attachments were recorded.

DBCX 9804 had last been cleaned on June 9, 2001. The cleaning consisted of

water-rinsing the tank for 4 1/2 hours and then removing the water by vacuum.

Hazardous Materials Information

The waste material in DBCX 9804 was a combination of cyclohexanone oxime

(oxime),16 water, and cyclohexanone. The majority of the waste material (94 percent) was

Figure 6. Housing of second dome on tank car comparable to DBCX 9804.

16 BASF typically referred to this material as “oxime,” so from this point onward, this report will

generally use this term to refer to cyclohexanone oxime.
Factual Information 13 Hazardous Materials Accident Report

oxime, which is a white, solid material under normal atmospheric conditions at

temperatures below 194° F. When solid, oxime is not classified as a hazardous material by

the DOT but, when liquid, oxime is flammable. The material safety data sheet for oxime

produced by BASF in 1994 describes the material as stable under normal temperatures

and pressures but states that temperatures above 212° F should be avoided.

About 4 percent of the waste material was water.

About 2 percent of the waste material was cyclohexanone, which is a flammable

liquid with a flashpoint of 111° F. Its flammable limits are 1.1 percent to 8.1 percent in air.

The BASF material safety data sheet for cyclohexanone describes the material as stable.

Oxime and cyclohexanone are maintained between 180° F and 204° F within the

caprolactam production process. The process operates at atmospheric pressure.

BASF Oxime Testing

Postaccident

BASF’s postaccident analysis of the material from the tank car showed that its

chemical constituents were consistent with the oxime waste material from the Freeport

process upsets. BASF found no additional constituents in the material.

Because the events preceding the accident (the heating of the tank car and the

continuous venting of the tank car’s pressure relief valve) suggested that

overpressurization from a chemical reaction might have brought about the accident, BASF

conducted postaccident Automatic Pressure Tracking Adiabatic Calorimeter tests on

residual oxime material from the accident scene to determine why the tank car ruptured.17

For comparison purposes, BASF ran the same tests on pure oxime from several different

sources. The tests measured changes in the oxime’s temperature and pressure as it was

heated.

The BASF test results showed that untempered oxime had a significantly higher

onset temperature18 and a longer induction time19 than tempered20 oxime. In effect, BASF

found that tempering oxime reduced its stability.

17 A Safety Board chemist reviewed the testing methodology and parameters used by BASF during its

postaccident testing and found them reasonable and appropriate.

18 The onset temperature is the lowest temperature at which exothermic (heat-releasing) behavior is

exhibited.

19 The induction time is the time required, at a given temperature above the onset temperature, for the

decomposition reaction to accelerate to an uncontrolled runaway condition.

20 Oxime is tempered by putting it through cycles of heating and cooling.
Factual Information 14 Hazardous Materials Accident Report

BASF tested one sample of untempered oxime obtained from a common chemical

supplier. Water was added to bring the percentage of water in the sample to 4.5 percent.

When the sample was heated,21 exothermic reactions were first observed at 338° F, about

590 minutes into the experiment. A second spike in exothermic reactions was recorded

after 895 minutes.

BASF also tested a sample of tempered oxime material (containing about

2.8 percent water) recovered from the highway cargo tank at the accident scene. When

heated, the sample first showed exothermic reaction at 282° F, about 503 minutes into the

experiment. More exothermic activity was recorded after about 665 minutes.

To confirm the lower onset temperature for tempered oxime, BASF conducted a

further test. BASF took a sample of oxime22 from the caprolactam process at the Freeport

facility, tempered the material at 230° F for 840 minutes, and then allowed it to cool.

When this sample was heated as the previous two samples had been, BASF recorded two

episodes of exothermic activity–the first at 258° F and the second starting at 381° F.

On the basis of its testing, BASF determined that the following reactions occurred

when oxime was heated:

1) Cyclohexanone Oxime + Heat + H2O -----→ Cyclohexanone + NH2OH 

(hydroxylamine).

Then, 

2) 4NH2OH + Heat -----→ N2O (nitrous oxide gas) + 2NH3 (ammonia gas) + 

3H2O.

BASF further determined that the second reaction is essentially irreversible

because two of the products of the reaction are gases and a state of equilibrium is never

attained. BASF found that once the first reaction started, both reactions would continue

until the reactants were consumed.

BASF also conducted five analyses of the gases that evolved during the heating of

the oxime. The results of all five tests showed the presence of ammonia and nitrous oxide.

Preaccident

From 1989 to 1991, the BASF parent plant in Ludwigshafen, Germany, conducted

analytical tests of oxime. The data generated by the tests included information concerning

onset temperature and induction time. The data showed that the onset temperatures for

oxime ranged from 248° F to 338° F. The induction times for oxime ranged from

480 minutes at 311° F to 1,320 minutes at 275° F. Data from the tests were discussed at a

21 In the postaccident testing BASF conducted to determine when exothermic reactions would occur for

the various oxime samples, the samples were initially heated to 212o F, the maximum safe temperature for

oxime, before the test heating process was begun.

22 The sample was about 4.5 percent water.
Factual Information 15 Hazardous Materials Accident Report

1991 BASF caprolactam technology exchange meeting in Belgium, which personnel from

the Freeport facility attended. Some of the data appeared in an appendix of the BASF

Technical Exchange Packet for 1991, which was distributed at the meeting. The stated

goal of the appendix was to “prevent an out of control reaction resulting in emissions of

anone, hydroxylamine and/or oxime.” The appendix stated, “To avoid uncontrolled

rearrangement, temperature in oxime tank should not exceed 194° F. Proper attention is

given to the explosion limits of oxime in air.”

BASF Information

Company and Facility Information

The BASF Group comprises a parent plant in Ludwigshafen and 164 wholly

owned subsidiaries. The BASF Group has production facilities in 38 countries and

manufactures a wide range of products, including chemicals, polymers, automotive and

industrial coatings, colorants, vitamins, nylon fibers, and agricultural products. The BASF

Corporation is the North American affiliate of the BASF Group.

More than 700 employees and 350 contractors work at the 406-acre Freeport

BASF facility. The facility produces 23 different products in 16 processes. Raw materials

arrive at the facility by rail, highway, barge, and pipeline. Intermediate chemicals

produced at the facility are shipped out by rail, highway, and barge.

Procedures for Heating and Unloading Hazardous Materials at Freeport

According to BASF officials, the Freeport facility had no written procedures for

heating and unloading the specific waste material contained in tank car DBCX 9804. The

oxime mixture is an intermediate material in the production process for caprolactam, and

it is not typically removed from the process or shipped for disposal from the Freeport

facility. Consequently, the Freeport unloaders did not routinely handle this material.

According to BASF, the last shipment of oxime from Freeport had taken place more than

10 years before the accident, and the material had never before been shipped from the

facility in a railroad tank car.

The BASF Freeport facility had general operating procedures for transferring

material from a highway cargo tank to a railroad tank car and for using pressure to transfer

material from a tank car to a plant receiving tank. The facility also provided

product-specific unloading and heating procedures for the two materials that are routinely

steam-heated in tank cars at the Freeport facility⎯caprolactam and formaldehyde.

Of the written procedures provided by the BASF Freeport facility, only the general

operating procedure for transferring material from a tank car to a receiving tank required

that the material be sampled and tested by lab personnel before the transfer could begin.

Only the product-specific procedures for steam-heating formaldehyde required that the

pressure within the tank car be monitored during the steam-heating process. Those
Factual Information 16 Hazardous Materials Accident Report

procedures specified that the pressure within the tank car be checked every 30 minutes.

Neither the procedures for steam-heating formaldehyde nor those for steam-heating

caprolactam specified the pressure or temperature of the steam to be applied. The Freeport

facility did not provide the unloaders with additional or specific procedures for unloading

DBCX 9804.

BASF Postaccident Actions

Since the accident, the BASF Freeport facility has made several changes to its

facility procedures. It has developed and implemented written procedures specifically

addressing the safe handling of oxime waste material. The procedures prohibit the transfer

of oxime waste to railroad tank cars and the heating of closed containers of oxime. The

Freeport facility now requires that hot water, rather than steam, be used to heat oxime

waste. Additionally, BASF changed its material safety data sheet for oxime to specify that

the material must not be heated above 212° F.
17 Hazardous Materials Accident Report

Analysis

This analysis has three main sections. First, it identifies factors that can be readily

excluded as causal or contributory to the accident. Next, the analysis addresses the

accident and its possible causes. The remainder of the analysis discusses the following

safety issue arising from this investigation:

• Adequacy of procedures for heating hazardous materials cargoes in railroad

tank cars before transfer.

Exclusions

Before the Freeport accident, railroad tank car DBCX 9804 had not been in any

accidents, and the past repairs to this tank car involved only its brakes. Postaccident

examination of the tank car showed no evidence of corrosion or other signs of

deterioration. Postaccident evaluation of the tank car’s fracture surfaces indicated that

they were consistent with overstress failure. Therefore, the Safety Board concludes that

railroad tank car DBCX 9804 had no structural or material defects that caused or

contributed to the rupture of the tank.

The Accident

Rupture of DBCX 9804

Although the pressure relief valve for DBCX 9804 was not recovered after the

accident, the events described by the witnesses at the scene on September 13, 2002,

indicate that the pressure relief valve was functioning and venting vapors up to the time

the tank car ruptured. Witnesses recalled that the pressure relief valve opened and reset

itself two or three times between about 8:40 a.m. and 9:00 a.m., began to constantly vent

about 9:00 a.m., and continued to constantly vent until the rupture occurred about

9:30 a.m. Witnesses also reported hearing a high-pitched whistle around 9:00 a.m. and

seeing a stream of white vapor come from the pressure relief valve as it constantly vented.

During postaccident inspection of the tank car, investigators found a longitudinal tear

along the top of the tank car and circumferential tears near the dome housings.

The initial cycling of the pressure relief valve’s opening and closing, followed by

its continuous venting up to the time the tank car ruptured, indicates that the gas within the

tank car was being produced more rapidly than it could be vented. Further, this activity of

the pressure relief valve and the postaccident condition of the tank car—including the

flattened and torn tank shell, the damage to the tank heads, and the projection of one dome

housing a substantial distance from the tank car—strongly indicate that an overpressure
Analysis 18 Hazardous Materials Accident Report

condition developed due to the rapid generation of gas or vapor within the tank from a

chemical reaction involving the hazardous waste in the tank car.

The DOT hazardous materials regulations (49 CFR, Subchapter C) require that

tank car tanks have a pressure relief device with a sufficient flow capacity to prevent

pressure in the tank from exceeding a maximum pressure under specified fire conditions.

The regulations do not specifically require that pressure relief devices have the flow

capacity to relieve pressure generated from a chemical reaction within the tank. Rather,

the regulations include requirements that are intended to prevent chemical reactions from

occurring. For example, all components of a tank car must be chemically compatible with

the chemical cargoes authorized for carriage. Hazardous materials that self-react or are

highly reactive must have chemical stabilizers added to prevent these adverse reactions

from occurring during transportation. The Safety Board considers that this approach is

reasonable, and it has proven to be effective. Therefore, the Safety Board concludes that

the pressure relief valve on tank car DBCX 9804 functioned as designed and vented

vapors continuously once it activated, but the rapid generation of gas within the tank

exceeded the valve’s capacity to relieve the tank’s internal pressure sufficiently to prevent

the catastrophic rupture of the tank car.

Overpressure Condition

The Safety Board considered several possible causes for the overpressurization

that led to the tank car’s rupture, including 1) instability of the waste material,

2) introduction of chemically incompatible material to the waste material within the tank,

and 3) an adverse reaction resulting from the heating of the waste in the tank car.

Instability of the Waste Material. BASF material safety data sheets for oxime

and cyclohexanone state that both materials are stable. In addition, the waste had been

in the tank car for more than a year—experiencing significant changes in ambient

temperatures and humidity—and had arrived at the MFR plant in Hannibal, Missouri,

without any reported abnormalities, such as elevated tank pressure or material

temperature. Further, the tank car was shipped back from Hannibal to Freeport without

incident, and it remained in Freeport without unusual developments for 2 months before

the accident. Thus, instability of the material did not appear to be the cause of the

overpressurization.

Introduction of Incompatible Material. Another possible cause of the

overpressurization in the tank was the introduction of a chemically incompatible material,

either intentionally or unintentionally, which caused the reaction in the tank that led to the

overpressurization. Given that the tank car arrived in Freeport without the security seals

that MFR said it had applied in Hannibal, the introduction of an incompatible material

during the transport period may have been possible. However, the routing of the tank car

from Hannibal to Freeport was traced, and no unusual delays were found. Further, no

indications of product tampering were found.

The waste mixture was not reactive with steels or metals, and postaccident

analysis of the material from the tank car showed that the chemical constituents were
Analysis 19 Hazardous Materials Accident Report

consistent with the waste material from the process upsets in Freeport. Therefore, it

appears that the overpressurization was not caused by the introduction of incompatible

chemical contaminants.

Heating the Tank Car. BASF’s postaccident tests of oxime materials showed that

heat-tempered oxime like the material in DBCX 9804 has a lower onset temperature than

untempered oxime. Consequently, less heat would have been needed to initiate an

exothermic (heat-releasing) reaction of the tempered material in DBCX 9804 than would

have been necessary for untempered material. Specifically, the tests showed that

untempered oxime required heating to about 338° F to show the first signs of exothermic

reaction. In contrast, the tempered oxime from the accident scene, as well as another

sample of tempered oxime, required heating only to about 282° F to show the first signs of

exothermic reaction. Thermodynamic tables show that, for the heating conducted at the

BASF facility, 60-psig steam would have had a minimum temperature of 308° F and

20-psig steam a minimum temperature of 260° F. (BASF applied 60-psig steam to the tank

for about 1 hour on September 11 and about 7 hours on September 12. BASF applied

20-psig steam to the tank for about 17 hours from September 12 through the early morning

of September 13.)

According to the results of BASF postaccident testing, given the amount of waste

material in DBCX 9804 at the time of the accident and the steam pressures used by BASF

to heat the material in Freeport, 23 hours of heating would have been required to raise the

temperature of the material in the tank car to 284° F, surpassing the estimated onset

temperature of 282° F. In fact, BASF heated the material for about 24 hours on

September 12 and 13. The use of the steam trap during the heating would have increased

the efficiency of the steam-heating process.

Further testing showed that when heated, tempered oxime broke down into

cyclohexanone and hydroxylamine. The heat released from this breakdown reaction was

sufficient to initiate a second exothermic reaction, the decomposition of hydroxylamine

into nitrous oxide and ammonia gases. The generation of ammonia from such a reaction is

consistent with the witness reports of ammonia odors as DBCX 9804 vented before the

accident.

Therefore, the steam heat that BASF applied to DBCX 9804 in the hours

preceding the accident at Freeport was sufficient to initiate two exothermic reactions of

the waste material. Both reactions released heat in an insulated tank, the insulation of

which likely prevented the heat’s dissipation. This resulted in the generation and retention

of heat at a rate that led to a runaway reaction and build-up of pressure within the tank.

Given the runaway nature of the reaction, the capacity of the pressure relief valve to vent

the gases and relieve the pressure in the tank was exceeded, so the pressure increased until

the tank ruptured. The Safety Board concludes that the overpressurization and rupture of

the tank car was caused by a runaway exothermic decomposition reaction that resulted

when the oxime waste material the tank car contained was steam-heated to an excessive

temperature for an extended period of time.
Analysis 20 Hazardous Materials Accident Report

Procedures Used in Steam-Heating DBCX 9804

In the months preceding the accident, both MFR and BASF had steam-heated tank

car DBCX 9804 to liquefy the hardened waste material within it so that the waste could be

transferred from the tank car. However, MFR and BASF followed different procedures

while performing these operations.

MFR Procedures

Different waste materials may have widely dissimilar chemical make-ups and

properties. As might be expected of a company that unloads many different waste

materials of diverse compositions, MFR was not familiar with the specific chemical

properties of the oxime waste material in DBCX 9804. (MFR had never previously

unloaded this particular waste material from a tank car.) MFR knew only the waste’s

heating value and that it did not contain metals.

Because MFR did not have detailed information about the chemical properties of

the waste, it was concerned about the potential for an increase in vapor pressure that could

result from heating the tank car. Consequently, MFR took precautions to monitor the

interior conditions of the tank car during heating. MFR used a gauging device to keep

track of the temperature and pressure within the tank car, employed a safety mechanism to

automatically stop the heating of the tank car if the pressure reached a preset limit

(15 psig), periodically conducted visual inspections of the material, and halted the

application of heat when no employees were present (at night) to monitor the process.

MFR records show that the pressure within the tank car never exceeded 3.5 psig while the

tank car was being heated at the Hannibal facility. However, had a significant increase in

the internal tank pressure developed, the MFR procedures for monitoring the heating

process probably would have alerted MFR employees before the pressure reached critical

levels. In such a situation, MFR would most likely have had sufficient time to take

appropriate measures to relieve the pressure within the tank car (such as by opening the

6-inch access plate) before the pressure could reach a level that would rupture the tank.

It should be noted that although MFR used appropriate safety procedures when

heating DBCX 9804, MFR’s lack of procedures for ensuring that the tank car had been

emptied of all waste material after the unloading process at Hannibal was terminated

allowed the tank car to be sent back to BASF containing about 8,000 to 10,000 gallons of

waste. Had MFR taken steps to ensure that the tank car was truly empty before sending it

back to BASF (such as by visually inspecting the interior of the tank through the 6-inch

access opening), MFR would have learned that the tank car still contained a significant

amount of material. Then, MFR could have unloaded the remaining waste and sent

DBCX 9804 back to Freeport empty, in which case the Freeport facility would not have

had to deal with the disposal of the material.

BASF Procedures

Like the unloading personnel at MFR, the unloaders in Freeport did not routinely

heat oxime waste material for transfer. According to BASF, the Freeport facility had last
Analysis 21 Hazardous Materials Accident Report

shipped this material more than 10 years before the accident. And, although the oxime

material was an intermediate product from the Freeport facility, it had never before been

heated and transferred from a railroad tank car. Consequently, the BASF Freeport facility

had no specific written procedures for heating the waste mixture before unloading it from

the tank car. Perhaps the Freeport facility could not have been expected to have

predetermined procedures for heating this particular hazardous waste mixture, but the

facility’s lack of experience with the material should have indicated that special care

should be taken during the heating process.

Instead of adopting reasonable safety measures, the BASF Freeport facility treated

the material as if it posed little or no risk. Specifically, the unloaders in Freeport did not

use a gauge or other device to monitor the temperature and pressure within the tank; they

did not apply any safety mechanism that would stop the heating if the pressure inside the

tank reached a preset limit; and they did not periodically evaluate the tank’s interior

conditions.

The unloaders at the Freeport facility did not use any monitoring tools to help them

assess the internal conditions of the tank during the heating process. Because the facility

did not require its unloading personnel to use a pressure gauge to monitor the pressure in

the tank car during the heating process, the first indication the unloaders had of the rising

pressure in the tank car was the activation of the pressure relief valve when the pressure

exceeded 75 psig. This happened about 45 minutes before the tank car ruptured. By this

time, it was likely too late to stop the runaway chemical reaction.

Nor did the Freeport unloaders use a safety mechanism to automatically stop the

heating if the pressure reached a preset limit. Had they used an automatic shutdown

mechanism, the tank car heating would likely have been terminated much sooner, when

the tank pressure rose to the established safe limit.

Further, if the Freeport facility workers had monitored and evaluated the

conditions within the tank car (specifically, the temperature of the waste material and the

internal pressure of the tank car) by checking them periodically, they would have found

that the material was sufficiently liquid for successful transfer around 9:00 p.m. on

September 12—about 12 1/2 hours before the accident occurred. They also would have

had time to relieve the pressure within the tank car before it reached critical levels, by

taking such action as opening the 6-inch access plate.

Therefore, the Safety Board concludes that lack of experience in transferring the

oxime material should at least have led the BASF Freeport facility, like MFR, to take

precautions during the heating process.

Although the workers immediately involved in the transfer operation may not have

been aware of the specific properties of the oxime waste they were unloading, BASF had

such information. The 1994 BASF material safety data sheet for oxime specifically stated

that temperatures above 212° F should be avoided for this material. Additionally, during a

1991 BASF meeting in Belgium, the variations in onset temperatures for oxime were

discussed. Guidance distributed to those attending the meeting (including representatives
Analysis 22 Hazardous Materials Accident Report

from the Freeport facility) advised that to avoid uncontrolled runaway reactions of

tempered oxime, the temperature within the tank should not exceed 194° F. The Safety

Board concludes that, before the accident, BASF had information concerning the dangers

associated with excessive heating of oxime that should have alerted the Freeport facility to

the need for developing and implementing safe procedures for heating and unloading this

material from railroad tank cars.

The BASF Freeport facility has changed its facility procedures to address

problems identified during the investigation of this accident. It has developed and

implemented written procedures designed to ensure the safe handling of oxime waste

material. The procedures prohibit the transfer of oxime waste to railroad tank cars, as well

as the heating of closed containers of oxime. Additionally, the Freeport facility now

requires that hot water be used, rather than steam, to heat oxime waste. BASF revised its

material safety data sheet for oxime to stipulate that oxime must not be heated above

212° F. The Safety Board considers that these actions will significantly reduce the

likelihood of incidence of an accident similar to the one discussed in this report.

Consequently, the Safety Board makes no recommendations to the BASF Freeport facility

concerning its oxime handling procedures.

Heating Hazardous Materials in Railroad Tank Cars

The Safety Board addressed issues involving the heating of hazardous materials

cargoes prior to unloading in its investigation of the rupture of a railroad tank car that took

place in Clymers, Indiana, on February 18, 1999.23 The Safety Board determined that the

tank car had overpressurized and catastrophically ruptured after a waste material had been

heated in it for more than 28 hours over several days. As in the Freeport accident, the

internal tank conditions were not monitored during the heating process. In the Clymers

investigation, the Safety Board determined that the failures in the procedures were

attributable to the companies involved with the shipment and heating. Consequently, the

Safety Board issued the following safety recommendations to the specific companies

involved with the generation and disposal of the waste material in the Clymers accident:

I-01-2 through -5

Collaborate with applicable producers, shippers, consignees, and end-users

in the development and implementation of specific and written procedures

for the loading or offloading of any chemical or waste material from a

railroad tank car, highway cargo tank, or other bulk transportation vessel

when the chemical or waste material exhibits properties that require special

handling or processing during the loading or offloading operation.

23 National Transportation Safety Board, Rupture of a Railroad Tank Car Containing Hazardous Waste

Near Clymers, Indiana, February 18, 1999, Hazardous Materials Accident Report NTSB/HZM-01/01

(Washington, DC: NTSB, 2001).
Analysis 23 Hazardous Materials Accident Report

Two of the four companies receiving the safety recommendations did not respond.

Safety Recommendations I-01-2 and -3 were therefore classified as “Closed—

Unacceptable Action—No Response Received” on July 31, 2003. The third company

responded that it considered the recommendation unwarranted. Consequently, Safety

Recommendation I-01-4 was classified as “Closed—Unacceptable Action” on

September 12, 2001. The fourth company ultimately determined not to implement Safety

Recommendation I-01-5, which was classified as “Closed—Unacceptable Action” on

September 16, 2004. Because of the lack of action by the companies involved in the

Clymers accident, as well as the circumstances of the Freeport accident, the Safety Board

is concerned that the heating of hazardous materials cargoes in railroad tank cars remains a

significant safety problem.

The DOT hazardous materials regulations24 do not specifically address the heating

of cargo in tank cars. On October 30, 2003, the Research and Special Programs

Administration (RSPA) published a final rule under docket HM-223 that was intended to

clarify the applicability of the hazardous materials regulations to the loading, unloading,

and storage of hazardous materials during transportation. Under this final rule, with

respect to tank cars and other bulk containers, RSPA has interpreted “unloading incidental

to movement,” which is subject to the DOT hazardous materials regulations, to take place

only when a hazardous material is emptied from its bulk packaging after the material has

been delivered to the consignee and prior to the delivering carrier’s departure from the

consignee’s facility or premises. Because virtually all tank cars are unloaded by the

consignee after the delivering rail carrier has departed, this rule in effect means that RSPA

no longer considers the unloading of a tank car to be a RSPA-regulated transportation

function.

The final rule under HM-223 was to have become effective on October 1, 2004. In

a Federal Register notice published on May 28, 2004, RSPA stated it was delaying the

effective date to January 1, 2005. In the notice, RSPA stated that it had received 14

appeals to the final rule. According to RSPA, the appellants raised a number of issues

concerning the consistency of the final rule with Federal hazardous materials

transportation law, State and local regulation of hazardous materials facilities, the

relationship of the DOT hazardous materials regulations to Occupational Safety and

Health Administration (OSHA) and Environmental Protection Agency (EPA) regulations,

the definition of “unloading incidental to movement,” and other aspects of the final rule.

Also, 11 industry associations filed a petition on December 29, 2003, in the U.S. Court of

Appeals for the District of Columbia to reverse the HM-223 final rule.

The Safety Board initially summarized its concerns in an October 29, 2001, response

to the Notice of Proposed Rulemaking for HM-223 by stating that the proposed rule may

result in the elimination of effective Federal oversight of hazardous materials

loading/unloading operations for bulk transportation containers. The Safety Board also

emphasized in its response that the Board has historically and consistently considered

loading and unloading operations, particularly of bulk containers such as tank cars, to be

24 The DOT’s Research and Special Programs Administration promulgates these regulations.
Analysis 24 Hazardous Materials Accident Report

transportation-related functions. The Board also expressed its belief that the DOT has both

the statutory mandate and the authority to regulate loading and unloading operations, and that

the DOT should strengthen its oversight of these operations rather than ignore these issues.

The Safety Board’s concerns were reinforced as a result of its investigation of the

July 14, 2001, accident at a chemical plant in Riverview, Michigan.25 In this accident,

methyl mercaptan, a poisonous and flammable gas, was released and ignited during the

offloading of a railroad tank car. Three plant employees were killed and about 2,000

residents were evacuated from their homes for 10 hours. Although the unloading

operations involving the accident tank car were subject to OSHA’s process safety

management and the EPA’s risk management programs, the Safety Board concluded that

effective oversight of hazardous materials loading and unloading operations from tank

cars and other bulk containers was not provided by the Federal Railroad Administration,

the EPA, or OSHA. As a result, the Safety Board issued the following safety

recommendations to the DOT:

I-02-1

Develop, with the assistance of the EPA and OSHA, safety requirements

that apply to the loading and unloading of railroad tank cars, highway

cargo tanks, and other bulk containers that address the inspection and

maintenance of cargo transfer equipment, emergency shutdown

procedures, and personal protection requirements.

I-02-2

Implement, after the adoption of safety requirements developed in response

to Safety Recommendation I-02-1, an oversight program to ensure

compliance with these requirements.

The Safety Board also issued Safety Recommendations I-02-3 and -4 to OSHA

and the EPA, respectively, to recommend that they assist the DOT in the development of

the safety requirements referred to in Safety Recommendations I-02-1 and -2.

In a November 25, 2002, response to Safety Recommendations I-02-1 and -2,

RSPA noted that it had worked closely with OSHA and the EPA on various hazardous

materials issues and that it was proceeding with the HM-223 rulemaking. In a

February 25, 2003, reply to RSPA’s response, the Safety Board again expressed its

concern that the rulemaking could have an adverse effect on the safety of loading and

unloading operations, and the Board classified both recommendations “Open—

Unacceptable Response.” OSHA and the EPA responded to Safety Recommendations

I-02-3 and -4 in August and October 2002, respectively. The two agencies pledged to

work with the DOT to develop the needed safety requirements. As a result, the Safety

Board classified Safety Recommendations I-02-3 and -4 “Open—Acceptable Response.”

25 National Transportation Safety Board, Hazardous Materials Release from Railroad Tank Car With

Subsequent Fire at Riverview, Michigan, July 14, 2001, Hazardous Materials Accident Report

NTSB/HZM-02/01 (Washington, DC: NTSB, 2002).
Analysis 25 Hazardous Materials Accident Report

The Safety Board’s investigation of the Riverview accident identified a lack of

effective oversight of hazardous materials loading and unloading operations with respect

to inspection and maintenance of equipment, emergency shutdown procedures, and

personal protection. Further, the accidents in Clymers and Freeport identify a lack of

Federal oversight when hazardous materials in railroad tank cars are heated prior to

unloading the materials. In the absence of any apparent Federal regulations addressing this

issue, and given the uncertainty over the eventual outcome of the appeals to HM-223, the

Safety Board concludes that Federal oversight of operations for heating hazardous

materials in railroad tank cars prior to unloading is inadequate. The Safety Board believes

that RSPA should, in cooperation with OSHA and the EPA, develop regulations that

require safe operating procedures to be established before hazardous materials are heated

in a railroad tank car for unloading; at a minimum, the procedures should include the

monitoring of internal tank pressure and cargo temperature.
26 Hazardous Materials Accident Report

Conclusions

Findings

1. Railroad tank car DBCX 9804 had no structural or material defects that caused or

contributed to the rupture of the tank.

2. The pressure relief valve on tank car DBCX 9804 functioned as designed and vented

vapors continuously once it activated, but the rapid generation of gas within the tank

exceeded the valve’s capacity to relieve the tank’s internal pressure sufficiently to

prevent the catastrophic rupture of the tank car.

3. The overpressurization and rupture of the tank car was caused by a runaway

exothermic decomposition reaction that resulted when the cyclohexanone oxime

waste material the tank car contained was steam-heated to an excessive temperature

for an extended period of time.

4. Lack of experience in transferring the cyclohexanone oxime material should at least

have led the BASF Freeport facility, like Missouri Fuel Recycling Environmental

Services, to take precautions during the heating process.

5. Before the accident, the BASF Corporation had information concerning the dangers

associated with excessive heating of cyclohexanone oxime that should have alerted

the Freeport facility to the need for developing and implementing safe procedures for

heating and unloading this material from railroad tank cars.

6. Federal oversight of operations for heating hazardous materials in railroad tank cars

prior to unloading is inadequate.

Probable Cause

The National Transportation Safety Board determines that the probable cause of

the rupture of railroad tank car DBCX 9804 was overpressurization resulting from a

runaway exothermic decomposition reaction initiated by excessive heating of a hazardous

waste material. Contributing to the accident was the BASF Corporation’s failure to

monitor the temperature and pressure inside the tank car during the heating of the

hazardous waste.
27 Hazardous Materials Accident Report

Recommendations

As a result of its investigation of the September 13, 2002, hazardous materials

accident at Freeport, Texas, the National Transportation Safety Board makes the following

safety recommendations:

To the Research and Special Programs Administration:

In cooperation with the Occupational Safety and Health Administration and the

Environmental Protection Agency, develop regulations that require safe operating

procedures to be established before hazardous materials are heated in a railroad

tank car for unloading; at a minimum, the procedures should include the

monitoring of internal tank pressure and cargo temperature. (R-04-10)

To the Occupational Safety and Health Administration:

In cooperation with the Research and Special Programs Administration and the

Environmental Protection Agency, develop regulations that require safe operating

procedures to be established before hazardous materials are heated in a railroad

tank car for unloading; at a minimum, the procedures should include the

monitoring of internal tank pressure and cargo temperature. (R-04-11)

To the Environmental Protection Agency:

In cooperation with the Research and Special Programs Administration and the

Occupational Safety and Health Administration, develop regulations that require

safe operating procedures to be established before hazardous materials are heated

in a railroad tank car for unloading; at a minimum, the procedures should include

the monitoring of internal tank pressure and cargo temperature. (R-04-12)

BY THE NATIONAL TRANSPORTATION SAFETY BOARD

MARK V. ROSENKER CAROL J. CARMODY

Vice Chairman Member

RICHARD F. HEALING

Member

DEBORAH A. P. HERSMAN

Member

Adopted: December 1, 2004

Chairman Ellen Engleman Conners did not participate in the adoption of this report.

29 Hazardous Materials Accident Report

Appendix A

Investigation

The National Transportation Safety Board was notified of the accident about

10:30 a.m. eastern daylight time on September 13, 2002. Two hazardous materials

investigators were dispatched from Washington, D.C., to Freeport, Texas. No Board

Member went with the team.

A single investigative group was established, comprising the following parties: the

BASF Corporation; Missouri Fuel Recycling Environmental Services; Trinity Industries,

Inc.; the Midland Manufacturing Corporation; the Federal Railroad Administration; and

the Railroad Commission of Texas.

The Safety Board did not conduct a public hearing concerning this investigation.
30 Hazardous Materials Accident Report

Appendix B

Summary of Significant Events Preceding the Freeport Accident

Date Event

June 1, 2001 Caprolactam II process upset in Freeport, Texas, BASF facility produces 

about 91,000 pounds of cyclohexanone oxime mixture waste material

June 5, 2001 BASF transfers the June 1, 2001, process upset waste to four highway cargo 

tanks at Freeport

June 12, 2001 After heating the waste to liquefy it, BASF transfers the contents of the four 

highway cargo tanks to railroad tank car DBCX 9804 at Freeport

Between June 12, 2001, 

and April 26, 2002

BASF applies steam heat to the tank car to liquefy the waste mixture so 

water can be removed and disposed of on-site

April 2, 2002 BASF loads about 91,000 pounds of cyclohexanone oxime waste from a 

second caprolactam II process upset at Freeport into four highway cargo 

tanks (Waste material is chemically indistinguishable from material from 

June 1, 2001, process upset)

April 26, April 29, and 

May 10, 2002

BASF transfers the second batch of material from the four highway cargo 

tanks to DBCX 9804, which still contains the material from the June 1, 2001, 

caprolactam II process upset

June 21, 2002 BASF sends tank car DBCX 9804, containing the material from both process 

upsets, to the Missouri Fuel Recycling Environmental Services (MFR) facility 

in Hannibal, Missouri, so the hazardous waste material can be incinerated 

July 7, 2002 DBCX 9804 arrives at the MFR facility in Hannibal

July 9, 2002 MFR steam-heats DBCX 9804 from 9:00 a.m. until 9:30 p.m.

July 10, 2002 MFR steam-heats DBCX 9804 from 5:00 a.m. until 11:00 p.m.

July 11, 2002 MFR unloads waste material from DBCX 9804; MFR mistakenly believes 

DBCX 9804 is empty

July 12, 2002 MFR sends the partially emptied DBCX 9804 back to the BASF Freeport 

facility

July 22, 2002 Tank car DBCX 9804 arrives back in Freeport; tank car is judged to be about 

1/3 full of waste material

September 11, 2002 BASF begins heating DBCX 9804 (for about 1 hour) so that the material left 

in the tank can be transferred to highway cargo tanks
Appendix B 31 Hazardous Materials Accident Report

Date Event

September 12, 2002 7:00 a.m. BASF heats DBCX 9804 for about 5 hours

12:00 p.m. BASF attempts to transfer the material from the tank car but is 

unsuccessful because the material is not sufficiently liquid

2:00 p.m. BASF continues to heat the tank car; heating continues till next 

morning

September 13, 2002 7:00 a.m. Heating of DBCX 9804 is stopped; transfer of material to highway 

cargo tanks is begun

7:45 a.m. Transfer of material to one highway cargo tank is completed

8:40 a.m. DBCX 9804 is seen to be venting

9:00 a.m. DBCX 9804 is seen to be continuously venting; fire emergency 

personnel are summoned from Dow Chemical; the “seek shelter” 

horn is activated

9:05 a.m. Water is applied to DBCX 9804 to knock down vapors and cool the 

tank car

9:10 a.m. Area around DBCX 9804 is evacuated

9:15-9:30 a.m. Water is applied to DBCX 9804

9:30 a.m. DBCX 9804 catastrophically ruptures