PEPCON disaster

The PEPCON disaster was an industrial disaster that occurred in Henderson, Nevada on May 4, 1988 at the Pacific Engineering and Production Company of Nevada (PEPCON) plant. The conflagration and subsequent explosions killed two people, injured 372 others, and caused an estimated US$100 million of damage. A large portion of the Las Vegas Valley within a 10-mile (16 km) radius of the plant was affected, and several agencies activated disaster plans.^[2]

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-weapons (Atlas, Patriot, etc.) programs.^[3] 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 (410 mm) high-pressure gas transmission line running underneath it, carrying natural gas at 300 psi (2.1 MPa) gauge pressure.^[4] The invoice for this pipe, which was installed in 1956, characterized it as "limited service." ^[5]

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.^[6] Ammonium perchlorate manufactured for other United States government programs was not held at the PEPCON plant during this period. High-density polyethylene (HDPE) plastic and steel drums were used for in-process and additional storage at the time of the accident, as they had been for many years prior to the Challenger accident.^[6] An estimated 4500 metric tons^[4] of the finished product were stored at the facility at the time of the disaster.^[6][7]

In addition to the PEPCON and Kerr-McGee facilities, there was also a large marshmallow factory, Kidd & Co.,^[8] 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 (3 km) away.^[4]

Fire and explosions

There are several theories about what caused the fire and explosions.^[9] The Clark County (Nevada) Fire Department (CCFD) did not issue a formal report but did issue a 2-page press release on July 15, 1988, describing what it believed to be the cause of the fire; this and other CCFD information was incorporated into a report by the United States Fire Administration (USFA).

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.^[9] The first significant DOSH inspection did not occur until 33 days after the fire.^[9] At that time, the damaged areas had been disturbed and key evidence had been either displaced or removed from the site.^[9]

According to the USFA report,^[4] 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.^[9] Fire was also reported on the north wall of the batch dryer section of the process building.^[9] 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.^[4]

The USDOL report, however, discounted this theory while relying upon eyewitness testimony and scientific burn tests.^[9] There were ten individuals who provided testimony that indicated that they had observed the fire and/or participated in fire-fighting activities early on.^[9] USDOL reported that testimony indicated that welding operations had taken place somewhere between 30 and 90 minutes prior to the discovery of the fire.^[9] These operations took place on the northwest wall of the process building; however, and in the vicinity of this welding was thoroughly washed down prior to and during this task.^[9] 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.^[9] 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^[9]

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.^[4][9] USFA^[4] reported that the first of a series of explosions occurred in the 55 US gal (210 L) 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.^[9] 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.^[9] High winds blowing in a northeasterly direction were a contributing factor.^[9] 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.^[9]

The yield of this first detonation was estimated to be between 17 and 41 kg TNT equivalent.^[6]

USDOL reported that considerable evidence existed that suggests that natural gas leaks may have existed in the plant.^[9] The on-site investigation of the plant revealed the presence of carbonaceous deposits around the perimeter of the foundation of the batch dryer building.^[9] 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.^[9]

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.^[4] 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.^[9] 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.^[4]

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.^[9] The leading edge of this sandbar was located approximately 1,100 ft (340 m) from the batch dryer building.^[9]

USFA reported that there were a total of seven explosions during the accident.^[4] 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.^[6] The two largest produced waves measuring 3.0 and 3.5 on the Richter scale.^[10] 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.^[4] A significant quantity of AP remained on the ground after the incident and material was subsequently recovered and recycled within 1 year.^[6] The largest explosion released estimated energy of approximately 1.0 kilotons of TNT according to one source.^[2]

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.^[9]

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 Kidd & Co., the nearby marshmallow factory, heard the explosion and also evacuated.

Fire department response

The Fire Chief of the City of Henderson, who was leaving the main fire station about 1.5 miles (2.4 km) north of the PEPCON facility, spotted the huge smoke column and immediately ordered his units to the scene. As he approached the plant, he could see a massive white and orange fireball about 100 ft (30 m) in diameter and dozens of people fleeing the scene.

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 units staged 1.5 miles (2.4 km) from the scene and assisted injured firefighters. The explosions and the raging fire were beyond their firefighting capabilities and they made no attempt to approach or fight the fire in recognition of the danger it posed.^[4]

Evacuation and overhaul of the scene

The Las Vegas Metropolitan Police Department, Nevada Highway Patrol and the National Guard evacuated a five-mile (8 km) radius around the plant, concentrating on areas downwind of the explosion. Roads in the area were clogged in both directions due to residents trying to leave and curious spectators headed toward the scene, creating a traffic jam that took over two hours to clear.

More than an hour after the first explosions, authorities concluded that the airborne products could be a respiratory irritant. However, it was not considered highly toxic. Nor was the danger of further explosions estimated as high. Authorities had considered expanding the evacuation zone to 10 miles (16 km), but the idea was dropped due to the new information, although a few cases of respiratory irritation were reported in a small community about 30 miles (50 km) downwind.

Crews in protective clothing headed to the scene to clean up, a slow process due to leaking tanks of anhydrous ammonia and residue from acids and other products. Several firefighters had to undergo treatment for respiratory irritation. Overhaul continued until dusk and resumed the following day. Authorities found the remains of Bruce Halker, the Plant Manager, but no trace of the other victim, the Controller Roy Westerfield, was ever found.^[6]

Emergency medical services treated and transported about 100 patients to five hospitals in the region, with the remaining 200 to 300 heading into hospitals on their own volition. Many of the injured had been struck by flying glass when windows were shattered.^[11] Fifteen firefighters were injured.

About four hours after the incident, hospitals were advised by the fire department that their disaster plans could be deactivated.^[4]

Damage assessment and aftermath

The explosions leveled the PEPCON plant and Kidd & Co marshmallow manufacturing facility. Damage within a 1.5-mile (2.4 km) radius was severe, including destroyed cars, damage to buildings and downed power lines. Damage to windows and moderate structure damage was recorded within three miles (5 km) of the incident. In the video of the incident, the resultant shockwave struck a nearby highway, where it blasted a car off its wheels, killing the driver within.

The damage reached a radius of up to 10 miles (16 km), including shattered windows, doors blown off their hinges, cracked windows and injuries from flying glass and debris. At McCarran International Airport, seven miles (11 km) away in Las Vegas, windows were cracked and doors were pushed open. The shock wave buffeted a Boeing 737 on final approach.^[4]

An investigation estimated that the larger explosion was equivalent to about one kiloton of TNT, approximately the same yield of a tactical nuclear weapon.^[12]

In 1991, the Nevada legislature passed the Chemical Catastrophe Prevention Act, which led to Nevada's Chemical Accident Prevention Program.^[13]

PEPCON had only $1 million in stated liability insurance, but costs paid by its insurer ultimately significantly exceeded this amount.^[6] A courtroom battle involving dozens of insurance companies and over 50 law firms resulted in a $71 million 1992 settlement with contributions from multiple parties including AMPAC/PEPCON and Southwest Gas Corporation that was divided among insurance companies on subrogation claims as well as the victims and their families.^[6][12]

After the incident, American Pacific Corporation changed the name of the perchlorate chemicals manufacturing subsidiary to PEPCON Production, Inc and within one year, to Western Electrochemical Co. (WECCO).^[6] It built a new ammonium perchlorate plant in an isolated area about 14 miles (23 km) outside of Cedar City, Utah with a substantial voluntary no-build buffer around it. Natural gas service to this WECCO facility is handled in a different manner (mostly above ground away from AP storage areas) than was the case at PEPCON.^[6] On July 30, 1997, an explosion at that plant killed one and injured four.^[14]

Today, the Henderson site is a commercial development near the Valley Auto Mall which is home to a number of dealerships and a university.^[6] Kidd & Co rebuilt their plant on their original location. This facility is now owned and operated by the Clark County School District Facilities Service Center.

References

External links

External image

The location of the disaster via Google Maps.

• Western Electrochemical – the company formerly known as PEPCON.
• Las Vegas Review-Journal – a special section on the 10th anniversary of PEPCON, including videos.