RAB/98-07

NATIONAL TRANSPORTATION SAFETY BOARD

WASHINGTON, D.C.

Railroad Accident Brief Report

LAX 96 FR 010

DERAILMENT AND HAZARDOUS MATERIALS RELEASE WITH FATALITY

MONTANA RAIL LINK

ALBERTON, MONTANA

APRIL 11, 1996

About 4:10 a.m., mountain daylight time, on April 11, 1996, 19 cars from

Montana Rail Link (MRL) freight train 01-196-10 derailed near Alberton,

Montana. Six of the derailed cars contained hazardous materials. One derailed

tank car containing chlorine (a poison gas) ruptured, releasing 130,000 pounds

of chlorine into the atmosphere; another tank car containing potassium hydroxide

solution (potassium cresylate, a corrosive liquid) lost 17,000 gallons of product;

and a covered hopper car containing sodium chlorate (an oxidizer) spilled 85 dry

gallons onto the ground.

About 1,000 people from the surrounding area were evacuated.

Approximately 350 people were treated for chlorine inhalation, 123 of whom

sustained injury. Nine people, including both members of the train crew, were

hospitalized. A transient riding the train died from acute chlorine toxicity.

U.S. Interstate Highway 90 (I-90) is roughly parallel and about 150 yards

north of the MRL tracks at the accident site. The hazardous material cloud

drifted across I-90 resulting in multiple highway traffic accidents. Several

motorists were stranded in the cloud after these accidents. I-90 was closed

following the accident requiring an 81-mile detour. Monetary damage was

estimated to be $3.9 million.

The Governor of Montana declared a state of emergency in Missoula and

Mineral County. On April 14, 1996 the evacuation area was reduced to 15

square miles; the residents were temporarily escorted into the area to feed and

water livestock animals, retrieve some personal possessions, and locate pets.

Chlorine from the derailed but nonruptured tank cars was transloaded at

the accident site. The operation began on April 14th and was concluded on April

28th. When the transloading was completed the evacuation was canceled,

residents were allowed to return to their homes, and I-90 was reopened.

The MRL train consisted of 3 locomotive units, 36 loaded and 35 empty

freight cars. Twenty-five of the loaded cars contained placarded hazardous
2

materials. It was traveling 40 mph just before the derailment when both train

crew members reported they felt the locomotive “dip to the left” and then come

back upright. The crew commented about the rough track and a few seconds

later the train brakes applied in emergency. When they looked back toward the

train they said they could see sparks flying and believed the train had derailed.

About 514 feet of rail was dislocated in the derailment. Approximately 444

feet of that total were recovered. Rail sections believed to have been located on

the outside of the curve at the point of derailment exhibited gage and head wear.

Additionally, a portion of rail recovered from the accident site displayed evidence

of a vertical split head. Rail sections were sent to a laboratory for metallurgical

analysis. The laboratory concluded that the “...level of wear rendered the rail

susceptible to fracture due to its diminished load bearing capacity,” and “these

rail fragments failed in a vertical split head mode with subsequent vertical

propagation to the surfaces in a progressive and rapid manner. Final separation

into the examined fragments next occurred during the derailment by rapid

cleavage overload along multiple transverse planes.”

Metallurgical analysis taken together with the wreckage dispersal pattern,

and the train crew’s statements revealed that a rail broke under the moving train

and that the failure mode was a vertical split head.

The visual rail inspection records did not indicate rail problems in this

area. An ultrasonic rail inspection vehicle traversed this area on March 1, 1996.

No defects were detected at the location of the vertical split head. The rail was

extensively covered with rail head checks (shelling) and other surface defects

throughout its length. Ultrasonic rail defect detection equipment is unable to

identify internal rail defects when rail surface defects are present in the same

location.

PROBABLE CAUSE

The National Transportation Safety Board determines that the probable

cause of this accident was a rail section that fractured in vertical split head mode

under the passing train induced by rail with reduced load bearing capacity

because of head and gage face wear. Contributing to the cause of the accident

was the inability of the ultrasonic rail defect detection equipment to readily

identify internal defects in rail with surface defects.

Adopted: August 18, 1998