Accident at Tobar, Nevada
RAILROAD ACCIDENT INVESTIGATION
REPORT NO. 4153
WESTERN PACIFIC RAILROAD COMPANY
JUNE 29, 1969
FEDERAL RAILROAD ADMINISTRATION
BUREAU OF RAILROAD SAFETY
WASHINGTON, D. C. 20591
DATE: June 29, 1969
RAILROAD: Western Pacific
LOCATION: Tobar, Nevada
ACCIDENT TYPE: Explosions
TRAIN INVOLVED: Freight
TRAIN NUMBER: Extra 765 West
LOCOMOTIVE UNITS: Diesel-electric units 765, 759, 3005, 755
CONSIST: 70 cars, caboose
SPEED: 50-55 m.p.h.
OPERATION: Signal indications
TRACK: Single; 1°00' curve; 0.23% ascending grade westward
TIME: 4:00 p.m.
CASUALTIES: 4 injured
DEPARTMENT OF TRANSPORTATION
FEDERAL RAILROAD ADMINISTRATION
BUREAU OF RAILROAD SAFETY
RAILROAD ACCIDENT INVESTIGATION REPORT NO. 4153 WESTERN PACIFIC RAILROAD COMPANY JUNE 29, 1969
On June 29, 1969, bombs in cars of a Western Pacific Railroad freight train exploded at Tobar, Nevada, resulting in destruction of several cars and in injury to two train employees and two unauthorized transients riding the train.
The cause of the explosions could not be determined.
Location and Method of Operation
The accident occurred on that part of the Western Pacific Railroad
extending westward from Salt Lake City, Utah, to Wells, Nevada, a
distance of 210.3 miles. This is a single-track line over which
trains operate by signal indications of a traffic control system.
At Tobar, Nevada, 194.5 miles west of Salt Lake City, a siding about 2800 feet long parallels the main track on the south. Tobar is unpopulated. It is in open rolling terrain with sparse vegetation.
The initial explosion occurred about 1800 feet west of the east siding-switch at Tobar. The subsequent explosions occurred 4200 feet farther westward.
Time and Weather
The initial explosion took place about 4:00 p.m., in clear weather. The subsequent explosions occurred four or five minutes later.
Authorized Train Speed
The maximum authorized speed for freight trains in the Tobar area is 65 m.p.h.
From the east on the main track there are, successively, a tangent
4623 feet long, a 1000' curve to the right 675 feet to the initial
explosion point and 796 feet westward, and a tangent about 3400 feet
to the point of the subsequent explosions. The tangent extends
several miles westward beyond the latter point.
The main-track structure in the Tobar area consists of 100-pound rail laid new in 1937. It has an average of 24 treated ties per rail length and is ballasted with crushed, rock.
Circumstances Prior to Accident
Extra 765 West, a westbound freight train, consisted of 4
diesel-electric units, 36 cars of general merchandise, 6 gondola
cars loaded with coiled steel, 22 box cars loaded with 750-pound
unfused demolition bombs, 6 gondola cars loaded with coiled steel,
and a caboose, in that order. It left Roper Yard, Salt Lake City, at
10:50 a.m. the day of the accident, after receiving a brake test and
an inspection by car inspectors that included lubrication of the
journals on the cars.
At Aragonite, Utah, 66.5 miles west of Salt Lake City, the train passed a hot-box detector. No overheated journal (hot box) on the cars was detected. At 1:30 p.m., the train arrived at Wendover, Utah, 121.7 miles west of Salt Lake City, and stopped on the main track for a crew change. The conductor and flagman of the outgoing crew visually inspected the cars as they rolled by during the arrival of the train, and noticed nothing unusual. The train left Wendover at 1:50 p.m. As it departed the front brakeman of the crew that had been relieved watched the cars rolled by and noticed nothing unusual.
About, 2 hours 10 minutes after leaving Wendover, Extra 765 West neared Tobar while moving at a speed of 50 to 55 m.p.h. The engineer, front brakeman, and a student brakeman were in the control compartment of the first diesel-electric unit. The conductor was seated next to the bay window on the south side of the caboose, and the flagman was seated next to the bay window on the north side. According to their statements, the crew members made frequent observations of the cars while enroute from Wendover, and saw nothing unusual. Two of the observations were made as the train moved on curves in approach to Tobar.
About 4:00 p.m., Extra 765 West began to pass the siding at Tobar while moving onto tangent track from a 1°00' curve to the right. The flagman stated that he was looking ahead along the right side of the cars as the train moved onto the tangent track, and that he noticed nothing unusual before hearing a loud explosion and seeing a large ball of flame, followed by black smoke, erupt from the upper portion of the 61st car, which was then moving on the curve at a point 796 feet east of the tangent track. He immediately opened the air brake valve in the caboose, applying the brakes in emergency and stopping the train 4200 feet farther westward. While the train was coming to a stop, another explosion occurred in the 61st car. Shortly after stopping a series of low and high order explosions occurred in the 60th to 64th cars, inclusive, resulting in debris from the cars and track structure being propelled over the surrounding terrain within a radius of about 1200 feet. In addition, large fires broke out throughout the wreckage.
Two unauthorized transients on the train were injured as a result of the explosions. Concussion from one of the high order explosions after the train stopped caused the flagman to be thrown about 30 feet from where he was standing behind the caboose. As a result, he sustained relatively minor injuries. The conductor was seated at the caboose desk, radioing instructions to the engineer, when this explosion occurred. He was seriously injured when the concussion threw him from his seat with considerable force.
The 43rd to 64th cars, inclusive, comprised the 22 box cars loaded
with bombs. Apparently none of those cars was derailed before the
train stopped as a result of the emergency brake application. A car
door found 25 feet from the main track at the scene of the first
explosion was identified as belonging to CBQ 34619, the 61st car,
indicating that the initial explosion occurred in this car. The
series of explosions that occurred after the train stopped
disintegrated the 61st to 64th cars, inclusive. Four craters, about
30 feet long, 20 feet wide, and 8 feet deep were blown into the
track structure and ground at the locations where those four cars
stopped. The 60th car stopped upright on the track structure with
both of its trucks derailed. Approximately one-half the bombs in
this car had exploded; heavily damaging the car. The remaining bombs
in the car had shifted to the extent that it was virtually
impossible to move them without risk of further explosions. The 59th
car stopped upright on the track structure with its front truck
derailed. Its roof was badly damaged and the doors were missing, as
a result of the explosions in the following cars. Both trucks of the
65th car and the front truck of the 66th car (gondola cars loaded
with coiled steel) were derailed. The 65th car was destroyed, having
been virtually blown apart by the explosions. In addition the 49th
to 58th cars, inclusive, and the 66th and 67th cars were damaged as
a result of the explosions. All the windows of the caboose were
blown inward, and partitions inside the caboose were torn loose.
According to the carrier's estimate, the total cost of damages to the train equipment was about $140,000.
Post-Accident Emergency Action
Due to the fire that broke out in the wreckage, unexploded bombs
remaining in cars and strewn about the wreckage area, the accident
scene was considered to be an extremely hazardous area. Employees of
various Nevada State agencies blockaded the area shortly after the
accident, and representatives of the railroad carrier, Federal
Bureau of Investigation, Federal Railroad Administration, AAR Bureau
of Explosives, Hill Air Force Base, Ogden, Utah, and an Army
demolition team from Fort Douglas, Salt Lake City, proceeded to the
scene. The next morning, after the situation was evaluated in
daylight, employees of the Nevada State Forestry Division proceeded
into the explosion area and extinguished the fires. About 4:55 p.m.,
after this was accomplished, a locomotive hauled the first 58 cars
of the train, including 16 cars loaded with bombs, westward to Elko,
Nevada. It was considered too hazardous to risk rerailing and moving
the 59th and 60th cars. Consequently, these cars were left standing
where they had stopped immediately west of the craters caused by
explosions in the following four cars.
The Army demolition team moved all unexploded bombs found strewn about the area to the craters in the track structure, fused them with the bombs remaining in the 59th and 60th cars and detonated the entire lot, completing the destruction of the two cars and eliminating the hazardous condition existing up to that time.
Repairs were then made to the main-track structure, and the track was restored to service during the morning of July 2nd.
Post-Accident Examination of Track
Examination of the main track for several miles westward to the explosion points revealed no evidence of a defective track condition or of dragging on the track structure having contributed to the accident.
Post-Accident Examination of Train Equipment
The equipment of Extra 765 West was examined to the fullest extent
possible after the accident in an effort to determine whether a
defective condition was a factor in the explosions. It found no
defective condition which could be attributable as a causal factor.
This finding is inconclusive, however, because of the disintegration
of the 61st to 64th cars, inclusive. All axles and journal boxes
found intact showed no evidence of an overheated journal (hot box).
Explosive Bomb Cargo in Train
The unfused bombs in the 43rd to 64th cars, inclusive, of Extra 765 West comprised a shipment from the Cornhusker Army Ammunition Plant, Coplant (Grand Island), Nebraska, to a Naval Weapons Station in the San Francisco Bay area. Each bomb weighed 750 pounds, and was classified as "Explosive Bomb, Class A Bomb". The bombs contained an explosive material identified as Minol II, which is subject to deflagration and low order explosion if exposed to heat exceeding 350°F.
The 22 cars in which the bombs were loaded were 40-foot box cars. Each car was loaded in the same manner, 56 wooden pallets containing two bombs each, laid in two longitudinal rows, two pallets high with the bombs crosswise in the car and facing the car centerline. The noses of the bombs in one row were interlaced with the bomb noses in the other row. Each pair of bombs was cradled and secured in its pallet by two steel bands.
The contents of each car weighed 88,974 pounds. Best information available indicates that the pallets of bombs were loaded in accordance with applicable specifications recommended by the Association of American Railroads and methods prescribed by the U. S. Army.
Car CBQ 34619
The explosions evidently originated in CBQ 34619, the 61st car in the train. This box car was built by the Chicago, Burlington and Quincy Railroad in August 1945. It was an all-steel 55-ton car, 40 feet 6 inches long, with 5½-inch by 10-inch friction journals. Its interior was provided with wooden wall lining and standard wooden flooring.
On June 10, 1969, nineteen days before the accident, the car was released from the Chicago, Burlington and Quincy shops at Havelock, Nebraska, after undergoing heavy repairs which included repairs to the car floor and interior lining, replacement of journal lubricator pads; overhaul of the trucks, and installation of two new body bolsters. On June 16, (13 days before the accident) the car was certified for bomb loading and was dispatched to the Cornhusker Army Ammunition Plant, where it was inspected by CB6Q and U. S. Government car inspectors without any exception being taken. The car was loaded at the aforesaid ammunition depot on June 26, and was subsequently delivered to the Western Pacific Railroad, by the D&RGW, at Salt Lake City, June 29, the day of the accident.
Stability of Bombs Containing Minol II
From March 1968 to October 1969, according to a report of the
Department of the Army, 11,160 car loads totaling 1,250,000 unfused
bombs containing Minol II have been shipped by rail. Although some
have been involved in railroad accidents, none of these bombs have
exploded in railroad transit except in the Tobar, Nevada case.
Results of sled, drop, bump, bullet-impact, and aircraft jettison tests conducted by the U. S. Army, Navy, and Air Force have proven that unfused bombs containing Minol II are safe for transport by railroad insofar as risks from impacts are concerned.
Analysis of Accident
In the light of information developed in the investigation, it
appears the original explosion was caused by a bomb in the 61st car
(CB4 34619) being subjected to heat exceeding 350°F. The source of
this heat cannot be determined conclusively, however, because of the
lack of evidence caused by disintegration of the car and its cargo.
According to rumors circulating after the accident, the injured transients on the train allegedly reported to an FBI Agent that they had seen a hot box in the train before the original explosion. An interview with the FBI Agent later revealed the rumor was without foundation. If credence is given to the conductor's and flagman's statements, it is not likely the heat source was fire that had spread to the wooden flooring of the car from an overheated journal on the 61st car, as the conductor and flagman saw no flames or smoke emanating from that car, the 10th ahead of the caboose, when they made observations of the cars on curves in approach to Tobar. Because of the time element, it is further unlikely that the heat source was the result of something left smoldering inside the car after it was loaded at the Cornhusker Army Ammunition Plant.
Ruling out the aforesaid unlikely possibilities, and taking into consideration the stability of Minol II bombs insofar as impacts are concerned, one can surmise that the original explosion was caused by a bomb in the 61st car having been subjected to excessive heat from a source arising from some condition of the car or its lading.
While best information available indicates the pallets of bombs in the 61st car were loaded in accordance with applicable specifications, there is a possibility that they were not adequately blocked and braced, and that as a result they shifted while in transit. Such incidents are known to have occurred in other bomb shipments and to involve dislodged bombs breaking loose from their pallet bands and dropping with enough force to penetrate wooden flooring of cars. In a few incidents, the dislodged bombs were found resting on car wheels and/or axles. If shifted lading in the 61st car resulted in a bomb penetrating the wooden floor and lodging on or against a rotating axle or wheel, there is a real possibility the bomb was subjected to friction producing heat in excess of 350°F, causing the bomb to deflagrate and the resulting fire to trigger off the subsequent explosions.
It was learned during the investigation that eight C&O/ B&O box cars carrying Class A explosives were recently refused by the Southern Pacific Company in interchange at Ogden, Utah, because of broken floor stringers causing unsafe conditions. Those cars were eight in a series of 800 former CBQ cars sold to the Chicago Freight Car Company and subsequently leased to the C&O/B&O after reconditioning, which included alterations to floor stringers. Because of the unsafe floor-stringer problem, the Federal Railroad Administration arranged with the Association of American Railroads to have all of these 800 cars taken out of service for inspection and necessary modification of floor stringers.
The discovery of the floor-stringers problem suggests there is also a possibility that the floor at one end of the 61st car collapsed because of a floor-stringer failure, permitting a bomb pallet to drop in such manner that a bomb rested against a rotating axle and/or wheel, and subsequently exploded as a result of being subjected to friction heating in excess of 350°F.
To minimize the possibility of explosions, we recommend that
carriers and shippers take vigorous action to ensure that their
employees thoroughly inspect all cars before and after they are
loaded with explosive ordinance. Particularly close attention should
be given to the car floor and supporting stringers and the blocking
and bracing of lading.
Dated at Washington, D. C., this 28th, day of July 1970.
By the Federal Railroad Administration,
Mac E. Rogers,
Director Bureau of Railroad Safety
NOTE. The Federal Railroad Administration has no jurisdiction over railroad operating rules; track structures; bridges; rail-highway grade crossing protection; track clearances; consist of train crews; qualifications or physical condition of railroad employees; running and draft gear on cars, or the construction of cars except those appurtenances within jurisdiction of the Safety Appliance Acts and the Power Brake Law of 1958, and those cars used to transport hazardous materials as defined by the explosives and dangerous articles law of 1961 Public Law 86-710.