The PEPCON disaster was an industrial
disaster that occurred in Henderson ,
Nevada Las Vegas Valley
Cloud from largest explosion
Background
The PEPCON plant, located in Henderson, Nevada, 10 miles (16 km) from Las Vegas, was one of only two American producers of ammonium perchlorate ("AP"), an oxidizer used in solid propellant rocket boosters, including the Space Shuttle, military weapons (SLBMs launched from nuclear submarines), and non-weaponized rocket programs (Atlas, Patriot, etc.). The other producer, Kerr-McGee, was located less than 1.5 mi (2.4 km) away from the PEPCON facility, within the area that suffered some blast damage. In addition to ammonium perchlorate, the plant produced other perchlorate chemicals including sodium perchlorate. The facility also had a 16-inch (41 cm) high-pressure gas transmission line running underneath it, carrying natural gas at 300 psi (2.1 MPa) gauge pressure. The invoice for this pipe, which was installed in 1956, characterized it as "limited service".
With the space shuttle fleet grounded as a result of the January 1986 Space Shuttle Challenger disaster, there was government instruction that the excess product — that was to be used to improve Shuttle launches and which was owned by the United States federal government or its prime contractors — would be stored in customer-owned aluminum bins as customer-owned material at the PEPCON plant. Ammonium perchlorate manufactured for otherUnited States
In addition to the PEPCON and Kerr-McGee facilities, there was also a large marshmallow factory, Kidd & Company, about 500 feet (150 m) away, and a gravel quarry in operation nearby (3,000 feet (900 m) to the west). The closest residential buildings were about 1 3⁄4 miles (2.8 km) away.
There are several theories about what caused the fire and explosions. TheClark
County (Nevada
The US Department of Labor (USDOL) working with the Division of Occupational Safety and Health (DOSH) issued a lengthy report on the accident that discounted the cause and origin findings of the CCFD. USDOL noted that the Arson Division of CCFD maintained control over the site for several weeks and that DOSH and PEPCON investigating teams were not permitted entry into the facility until 13 days after the event. The first significant DOSH inspection did not occur until 33 days after the fire. At that time, the damaged areas had been disturbed and key evidence had been either displaced or removed from the site.
According to the USFA report, the fire originated around a drying process structure at the plant between 11:30 a.m. and 11:40 a.m. that day. USDOL reported that at least one fire was burning in a barrel located at the west side of the southern portion of the building partition, which separated the batch dryer from the batch tanks in the process building. Fire was also reported on the north wall of the batch dryer section of the process building. A windstorm had damaged a fiberglass structure and employees were using a welding torch to repair the steel frame. The USFA report stated that this activity caused a fire that spread rapidly in the fiberglass material, accelerated by nearby ammonium perchlorate residue.
The USDOL report, however, discounted this theory while relying upon eyewitness testimony and scientific burn tests. There were ten individuals who provided testimony that indicated that they had observed the fire and/or participated in early fire-fighting activities. USDOL reported that testimony indicated that welding operations had taken place somewhere between 30 and 90 minutes prior to the discovery of the fire. These operations took place on the northwest wall of the building; and the vicinity was thoroughly washed down prior to and during this task. Furthermore, USDOL stated, the likelihood of transferring hot molten metal a distance of over 70 feet (20 m) through and around batch tanks to the batch dryer is considered extremely remote. USDOL stated that sparks from such operations would not present enough energy to ignite ordinary combustibles in close proximity, let alone at distances of up to 70 feet (20 m) and concluded that "the possibility of welding and cutting operations as a source of ignition is considered very low, in the author's professional opinion".
Both the USFA and USDOL reports noted that the flames spread to 55 US gal (210 L) plastic drums containing the product that were stored next to the building as employees tried in vain to put the fire out inside the building with water hoses. USFA reported that the first of a series of explosions occurred in the drums about 10–20 minutes after ignition, and employees had begun fleeing on foot or in cars. USDOL reported this differently, stating that the fire spread rapidly to the north side of the partition, northeast and south walls by radiative and convective heat transfer. The extremely rapid fire spread in the process building and subsequent growth to other buildings was primarily due to the highly combustible fiberglass reinforced siding panels and close spacing of adjacent buildings. High winds blowing in a northeasterly direction were a contributing factor. Product stored in an area north of the process building heated up and approximately 7 minutes later at 11:51 a.m., an aluminum econobin containing approximately 4,000 pounds (1,800 kg) of AP, located about 30 feet (9 m) west of the northwest corner of the building detonated causing damage to the surrounding structures and batch dryer.
The yield of this first detonation was estimated to be between 17 and 41 kg TNT equivalent. USDOL reported that considerable evidence existed that suggests that natural gas leaks may have existed in the plant. The on-site investigation of the plant revealed the presence of carbonaceous deposits around the perimeter of the foundation of the batch dryer building. Other visual evidence of burning, possibly natural gas, from the ground was discovered in various portions of the plant including beneath the gas and telephone vaults and portions of the asphalt paving.
USFA reported that the fire continued to spread in the stacks of drums creating a large fireball and leading to the first of four explosions in the drum storage area. USFA reported that the fire then made its way into the storage area for the filled aluminum shipping containers, resulting in two small explosions there, and a massive explosion about four minutes after the first. USDOL reported that six or seven detonations occurred solely in areas where aluminum econo bins or steel drums were utilized to store the product of nominal 200 micron size. USFA reported that little fuel remained after that, causing the flame to diminish rapidly, except for a fireball that was supplied by the high-pressure natural gas line underneath the plant, which had been ruptured by one of the explosions. That gas line was shut off at about 1:00 p.m. by the gas company at a valve about a mile away.
USDOL also reported that there was strong evidence of a natural gas fire prior to the second explosion at the northeast edge of the plant within a 6 ft × 200 ft (2 m × 61 m) narrow band of soft sand. The leading edge of this sandbar was located approximately 1,100 ft (340 m) from the batch dryer building.
USFA reported that there were a total of seven explosions during the accident. Eyewitness testimony and the Dennis Todd video which began after the first detonation and other resources indicated there were five high order detonations, one north of the batch dryer, one in the storage area south of the administration building, two on the loading dock and the final largest detonation in the eastern storage area, where the gas line burned after the detonations occurred. The two largest produced waves measuring 3.0 and 3.5 on the Richter scale. Much of the approximately 4,500 metric tons of AP either burned/decomposed in combination with a fuel or exploded, with the final detonation creating a crater 15 feet (4.6 m) deep and 200 feet (61 m) long in the eastern storage area. A significant quantity of AP remained on the ground after the incident and material was subsequently recovered and recycled within 1 year. The largest explosion released estimated energy of approximately 1.0 kilotons of TNT according to one source.
USDOL concluded that the initiation mode of the fire was undetermined. It stated that smoking, sparking of electrical equipment, or frictionally ignited gas are among the probable igniting sources.
About 75 escaped successfully, but two were killed in the last two larger explosions: Roy Westerfield, PEPCON's Controller, who stayed behind to call the Clark County Fire Department; and Bruce Halker, the Plant Manager, who stood near his car when the first major detonation occurred. Employees at the nearby Kidd marshmallow factory heard the explosion and also evacuated.
The Fire Chief of the City ofHenderson
At about 11:54, as he approached the site, the first of the two major explosions sent a shock wave that shattered the windows of his car and showered him and his passenger with glass. The driver of a heavily damaged vehicle coming away from the plant then advised the chief about the danger of subsequent larger explosions, which prompted the chief to turn around and head back toward his station. The other units also stopped heading toward the site after the explosion.
The second major explosion nearly destroyed the chief's car; after he and his passenger were cut by flying glass, he was able to drive the damaged vehicle to a hospital. The windshields of a responding Henderson Fire Department vehicle were blown in, injuring the driver and firefighters with shattered glass.
Several nearby fire departments responded to the accident.Clark
County
The PEPCON plant, located in Henderson, Nevada, 10 miles (16 km) from Las Vegas, was one of only two American producers of ammonium perchlorate ("AP"), an oxidizer used in solid propellant rocket boosters, including the Space Shuttle, military weapons (SLBMs launched from nuclear submarines), and non-weaponized rocket programs (Atlas, Patriot, etc.). The other producer, Kerr-McGee, was located less than 1.5 mi (2.4 km) away from the PEPCON facility, within the area that suffered some blast damage. In addition to ammonium perchlorate, the plant produced other perchlorate chemicals including sodium perchlorate. The facility also had a 16-inch (41 cm) high-pressure gas transmission line running underneath it, carrying natural gas at 300 psi (2.1 MPa) gauge pressure. The invoice for this pipe, which was installed in 1956, characterized it as "limited service".
With the space shuttle fleet grounded as a result of the January 1986 Space Shuttle Challenger disaster, there was government instruction that the excess product — that was to be used to improve Shuttle launches and which was owned by the United States federal government or its prime contractors — would be stored in customer-owned aluminum bins as customer-owned material at the PEPCON plant. Ammonium perchlorate manufactured for other
In addition to the PEPCON and Kerr-McGee facilities, there was also a large marshmallow factory, Kidd & Company, about 500 feet (150 m) away, and a gravel quarry in operation nearby (3,000 feet (900 m) to the west). The closest residential buildings were about 1 3⁄4 miles (2.8 km) away.
Fire and Explosions
There are several theories about what caused the fire and explosions. The
The US Department of Labor (USDOL) working with the Division of Occupational Safety and Health (DOSH) issued a lengthy report on the accident that discounted the cause and origin findings of the CCFD. USDOL noted that the Arson Division of CCFD maintained control over the site for several weeks and that DOSH and PEPCON investigating teams were not permitted entry into the facility until 13 days after the event. The first significant DOSH inspection did not occur until 33 days after the fire. At that time, the damaged areas had been disturbed and key evidence had been either displaced or removed from the site.
According to the USFA report, the fire originated around a drying process structure at the plant between 11:30 a.m. and 11:40 a.m. that day. USDOL reported that at least one fire was burning in a barrel located at the west side of the southern portion of the building partition, which separated the batch dryer from the batch tanks in the process building. Fire was also reported on the north wall of the batch dryer section of the process building. A windstorm had damaged a fiberglass structure and employees were using a welding torch to repair the steel frame. The USFA report stated that this activity caused a fire that spread rapidly in the fiberglass material, accelerated by nearby ammonium perchlorate residue.
The USDOL report, however, discounted this theory while relying upon eyewitness testimony and scientific burn tests. There were ten individuals who provided testimony that indicated that they had observed the fire and/or participated in early fire-fighting activities. USDOL reported that testimony indicated that welding operations had taken place somewhere between 30 and 90 minutes prior to the discovery of the fire. These operations took place on the northwest wall of the building; and the vicinity was thoroughly washed down prior to and during this task. Furthermore, USDOL stated, the likelihood of transferring hot molten metal a distance of over 70 feet (20 m) through and around batch tanks to the batch dryer is considered extremely remote. USDOL stated that sparks from such operations would not present enough energy to ignite ordinary combustibles in close proximity, let alone at distances of up to 70 feet (20 m) and concluded that "the possibility of welding and cutting operations as a source of ignition is considered very low, in the author's professional opinion".
Both the USFA and USDOL reports noted that the flames spread to 55 US gal (210 L) plastic drums containing the product that were stored next to the building as employees tried in vain to put the fire out inside the building with water hoses. USFA reported that the first of a series of explosions occurred in the drums about 10–20 minutes after ignition, and employees had begun fleeing on foot or in cars. USDOL reported this differently, stating that the fire spread rapidly to the north side of the partition, northeast and south walls by radiative and convective heat transfer. The extremely rapid fire spread in the process building and subsequent growth to other buildings was primarily due to the highly combustible fiberglass reinforced siding panels and close spacing of adjacent buildings. High winds blowing in a northeasterly direction were a contributing factor. Product stored in an area north of the process building heated up and approximately 7 minutes later at 11:51 a.m., an aluminum econobin containing approximately 4,000 pounds (1,800 kg) of AP, located about 30 feet (9 m) west of the northwest corner of the building detonated causing damage to the surrounding structures and batch dryer.
The yield of this first detonation was estimated to be between 17 and 41 kg TNT equivalent. USDOL reported that considerable evidence existed that suggests that natural gas leaks may have existed in the plant. The on-site investigation of the plant revealed the presence of carbonaceous deposits around the perimeter of the foundation of the batch dryer building. Other visual evidence of burning, possibly natural gas, from the ground was discovered in various portions of the plant including beneath the gas and telephone vaults and portions of the asphalt paving.
USFA reported that the fire continued to spread in the stacks of drums creating a large fireball and leading to the first of four explosions in the drum storage area. USFA reported that the fire then made its way into the storage area for the filled aluminum shipping containers, resulting in two small explosions there, and a massive explosion about four minutes after the first. USDOL reported that six or seven detonations occurred solely in areas where aluminum econo bins or steel drums were utilized to store the product of nominal 200 micron size. USFA reported that little fuel remained after that, causing the flame to diminish rapidly, except for a fireball that was supplied by the high-pressure natural gas line underneath the plant, which had been ruptured by one of the explosions. That gas line was shut off at about 1:00 p.m. by the gas company at a valve about a mile away.
USDOL also reported that there was strong evidence of a natural gas fire prior to the second explosion at the northeast edge of the plant within a 6 ft × 200 ft (2 m × 61 m) narrow band of soft sand. The leading edge of this sandbar was located approximately 1,100 ft (340 m) from the batch dryer building.
USFA reported that there were a total of seven explosions during the accident. Eyewitness testimony and the Dennis Todd video which began after the first detonation and other resources indicated there were five high order detonations, one north of the batch dryer, one in the storage area south of the administration building, two on the loading dock and the final largest detonation in the eastern storage area, where the gas line burned after the detonations occurred. The two largest produced waves measuring 3.0 and 3.5 on the Richter scale. Much of the approximately 4,500 metric tons of AP either burned/decomposed in combination with a fuel or exploded, with the final detonation creating a crater 15 feet (4.6 m) deep and 200 feet (61 m) long in the eastern storage area. A significant quantity of AP remained on the ground after the incident and material was subsequently recovered and recycled within 1 year. The largest explosion released estimated energy of approximately 1.0 kilotons of TNT according to one source.
USDOL concluded that the initiation mode of the fire was undetermined. It stated that smoking, sparking of electrical equipment, or frictionally ignited gas are among the probable igniting sources.
About 75 escaped successfully, but two were killed in the last two larger explosions: Roy Westerfield, PEPCON's Controller, who stayed behind to call the Clark County Fire Department; and Bruce Halker, the Plant Manager, who stood near his car when the first major detonation occurred. Employees at the nearby Kidd marshmallow factory heard the explosion and also evacuated.
Fire Department Response
The Fire Chief of the City of
At about 11:54, as he approached the site, the first of the two major explosions sent a shock wave that shattered the windows of his car and showered him and his passenger with glass. The driver of a heavily damaged vehicle coming away from the plant then advised the chief about the danger of subsequent larger explosions, which prompted the chief to turn around and head back toward his station. The other units also stopped heading toward the site after the explosion.
The second major explosion nearly destroyed the chief's car; after he and his passenger were cut by flying glass, he was able to drive the damaged vehicle to a hospital. The windshields of a responding Henderson Fire Department vehicle were blown in, injuring the driver and firefighters with shattered glass.
Several nearby fire departments responded to the accident.
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