The Kingman Rail Car BLEVE

July 1, 1998
Robert Burke revisits the Kingman, AZ, explosion involving a railroad tank car carrying propane and discusses what lessons were learned.

It was 25 years ago, on July 5, 1973, that a propane tank car being off-loaded in Kingman, AZ, caught fire, resulting in a BLEVE - boiling liquid expanding vapor explosion - that killed 11 Kingman firefighters and one civilian.

Captain Wayne Davis is the only firefighter in the area who was at the explosion and is still active in the fire department. Davis, who was a new volunteer firefighter at the time, recalls that he was riding on the tailboard of the second Kingman engine to reach the scene. The crew had responded to the fire and was stretching hoselines to a deluge gun when the blast occurred.

Davis ducked behind the hosebed but still received second-degree burns on his arm. The engine sustained distortion damage to plastic light covers on the top of the apparatus but was otherwise undamaged. The Kingman chief at the time, Charlie Potter, was in his pickup truck directing operations when the explosion occurred. He ducked in the seat of the truck but still sustained second- and third-degree burns on his arm and was hospitalized for several days. In addition to the 11 firefighters and one civilian killed, three other firefighters were burned by radiant heat from the blast - two from Kingman and one from the Hualapai Valley Fire District. Two police officers and 95 civilians also suffered burns from the radiant heat. More than $1 million in property damage was reported. (Many previous reports erroneously indicated that 12 firefighters were killed).

Except for a career firefighter/engineer who was severely burned but survived and the three firefighters and two police officers who sustained lesser burns, those injured were mostly spectators who had gathered along Highway 66 about 1,000 feet from the fire, ignoring police warnings to stay back.

Photographs of the spectacular BLEVE have appeared in countless articles, books and training programs over the years. Instructors often refer to the Kingman incident when warning emergency responders of the dangers of flame impingement on the vapor space of propane tanks. Within the past year, however, two deadly incidents occurred involving propane tank explosions.

On Oct. 8, 1997, two volunteer firefighters in Carthage, IL, were killed when a propane tank exploded. The call came in as a fire in a grain dryer on a farm outside of town. When firefighters arrived, the found a fire involving a 1,000-gallon propane tank. About 20 minutes later, the tank exploded. The firefighters who died were reported to have been hit by the fireball but not burned; it is thought the concussion from the blast killed them. Two other firefighters were injured.

Exactly six months later, on April 8, 1998, a similar incident occurred in Albert City, IA. This time, two firefighters were killed and six others, including the Albert City fire chief, were injured. Firefighters responded to an 11 P.M. report of a fire involving an 18,000-gallon propane tank at a turkey farm. It was reported that the tank contained 10,000 gallons of fuel when it exploded. Firefighters were positioned 60 feet from the tank, attempting to cool it, when the explosion occurred. The incident apparently was caused by teenagers riding an all-terrain vehicle who struck a two-inch vaporizer line connected to the propane tank. It is believed the pilot light on the vaporizer may have been the ignition source for the leaking propane. The burning propane impinging on the tank caused the relief valve to activate, sending burning propane 80 feet into the air. Firefighters thought that because the relief valve was activated it was safe to approach the tank.

Department Profile

Kingman, with a population of 7,500 in 1973, is a desert community along Route 66, some 80 miles southeast of Las Vegas,184 miles northwest of Phoenix and 147 miles west of Flagstaff. At the time of the incident, the Kingman Fire Department was a combination force of six career firefighters and 36 volunteers operating out of two stations. One career member was on duty in each station at all times.

Kingman's equipment in service at the time of the explosion included four engines and a rescue vehicle. Station 2 was located just a half mile west of the Doxol Gas Distribution Plant, the site of the explosion. Fire protection features of the Doxol facility consisted of portable dry chemical extinguishers near the storage tanks and in the office. The nearest public-water-supply fire hydrant was 1,200 feet north of the site on Hoover Street.

July 5, 1973, was a typical summer day in Arizona. The temperature topped 100 degrees Fahrenheit and a light westerly wind was blowing in at 12 mph. Workers at the Doxol plant, located on the east side of Kingman two miles from the downtown area, were preparing to off-load a 33,500-gallon water-capacity rail car containing liquefied propane gas (LPG).

The Doxol Plant consisted of an office and two above-ground LPG storage tanks - one 30,000 gallons and the other 18,000 gallons. Located on the southwest side of Route 66, the office was approximately 70 feet from the highway. The two storage tanks were located at the rear of the office about 200 feet from the highway. (Stationary propane tanks are generally not insulated, and flame impingement on the vapor space can cause metal failure in much the same way as the rail car did in the Kingman incident.) Usually, four employees were present at the small facility - a clerk, the manager and two delivery personnel. At the time of the explosion, there were just three employees on duty at the plant. Just east of the Doxol plant were the Double G Tire Co., 600 feet away; the Country Kitchen restaurant; 800 feet away; and the Phillips Truck Stop, 900 feet away.

Racks to off-load rail cars were located on the south side of the rail siding with underground piping running to the storage tanks. Kingman was serviced by the Santa Fe Railroad, which had delivered the tank car to the Doxol plant exactly a month earlier. The delay in off-loading the rail car is believed to have occurred because the fuel demand during the summer is low and the bulk storage tanks were full.

The loading rack where the tank car was resting is 30 feet across the Santa Fe's main line southeast of the main Doxol facility, 450 feet from the highway. LPG tank cars at that time were not insulated and all of the valves were located within the dome cover at the top of the tank. This tank was constructed of 11/16-inch carbon steel with a hydrostatic test pressure of 340 psi and a rupture pressure of 500 psi. The pressure relief valve was set to expel excess pressure from the tank at 280 psi.

At 1:30 P.M., workers began to connect the hoses to the rail car to start the off-loading process. During such an off-loading procedure, liquid lines are attached to the two liquid valves in the dome cover housing at the top of the rail car. Vapors are collected and routed into the vapor space of the tank. After all connections are made, the valves are opened slowly at first so as not to trip the excess flow valves. Connections are routinely checked for leakage and the valves fully opened when no leaks are present.

Two men were involved in the off-loading operation that day. As the off-loading proceeded, one of the men detected a small leak in one of the connections. Connections were typically tightened by striking them with a non-sparking brass-alloy wrench. These workers, however, used an aluminum-alloy wrench.

Despite their efforts to tighten the connection, the leak continued. The liquid connection was once again struck with the wrench. That's when a fire erupted. It is thought that a spark was created as the wrench struck the steel fitting, because of magnesium being present in the alloy of the wrench.

Both men fell from the top of the tank car, their clothing on fire, resulting in severe burns from the fire and extreme heat. One of them later died of his burn injuries. The other man ran back to the office building where he was driven to a Arizona Depart-ment of Public Safety Office a quarter mile away to report the fire. It is believed that an ambulance was called for the injured man before a call was made to the fire department.

Kingman firefighters received the first call for help at 1:57 P.M. and arrived on scene three minutes later. Initially, a call went out to the Troxton Canyon and Hualapai fire districts for mutual aid assistance. The fire spread quickly and was impinging on the top of the rail car where the vapor space is located.

Every liquefied gas container has an approximate 20% vapor space above the liquid in the tank to allow for expansion of the liquid to vapor within the tank during shipping and storage. This is the most dangerous place for flame impingement to occur because there is nothing to absorb the heat but the metal itself. Steel does not absorb heat well so when temperatures reach above 400F, the integrity of the tank is quickly in jeopardy.

National Fire Protection Associa-tion (NFPA) statistics show that pressure tanks can fail from flame impingement within the first 15 to 20 minutes of the first flame exposure. It is estimated that the Kingman fire burned for eight minutes before firefighters arrived and an additional two minutes before the first water was applied from the engine booster tank to cool the propane rail car. The BLEVE occurred at 2:10 P.M., just 19 minutes after the first flame impingement on the top of the tank. (Flame impingement on the liquid level is a somewhat less dangerous situation because the liquid will absorb the heat and protect the integrity of the tank. However, the increased heat will cause the already boiling liquid to boil faster, causing the pressure inside the tank to increase.)

Firefighters' tactical objectives at Kingman were to provide water to cool the tank and prevent an explosion. An engine with a 1,000-gallon booster tank was positioned 75 feet from the rail car and two one-inch booster lines were put into service to cool the tank shell. (The water flow from a one-inch booster line is about 30 gpm.) If water is applied effectively to the point of flame impingement, the temperature of the shell cannot go above 212F, well below the failure temperature of the steel. This operation requires large quantities of water. The NFPA recommends that an uninterrupted water supply of 500 gpm be applied the surface of the tank for cooling.

While the first firefighters attempted to cool the rail car from the booster tank of the engine, others began laying two 2 1/2-inch lines to the hydrant 1,200 feet away to supply a deluge gun located 50 feet from the burning tank car. The first 2 1/2-inch hose lay was completed but the firefighters ran out of hose for the second supply line. The first line was being charged when the explosion occurred. Thirteen firefighters were within 150 feet of the burning rail car when the blast occurred. Eleven of them died from severe thermal burns - one career member and 10 volunteers. A 12th firefighter was taken to the hospital in critical condition but survived.

Protective equipment typical for firefighters at the time was cotton duck with wool linings and helmets made of polycarbonate plastic. This was the type of protection worn by the Kingman firefighters. It is reported that at the time of the explosion some firefighters had full protective gear, while others wore only coats and helmets or just coats. Those firefighters killed had the coats and their street clothes burned off of their bodies by the fire and radiant created from the explosion.

The tank broke into pieces from the force of the blast and one half of the tank bounced end over end westward down the tracks, landing 1,200 feet from its original location on the siding. The other portion of the tank tore along the welds and flattened out on the ground. A ground-level fireball ensued and extended 150 to 200 feet in all directions from the center of the blast. This was followed by a large mushroom cloud of flame extending several hundred feet into the air, measuring 800 to 1,000 feet in diameter.

Fireball flame temperatures can reach well over 3,500F. The fireball and radiant heat set five buildings on fire, including the tire company, restaurant, truck stop and gas company office building, and started several brushfires. Radiant heat was so intense that it caused the relief valve on the 30,000-gallon storage tank to activate. The released vapors, however, did not ignite; once the pressure was relieved, the valve closed and remained closed from that point on.

Following the explosion, calls for mutual aid went out to the Lake Havasu City, Mohave Valley and Bullhead City fire departments. There was a catastrophic-disaster clause in the county's mutual aid agreements and when the explosion occurred an all-hands call went out to the fire departments in the county. Chiefs of the Lake Havasu City and Bull Head City departments set up a command post at the Kingman Fire Station 2. Responding mutual aid companies were assigned to extinguish the numerous fires, the last of which was brought under control at 5:30 P.M.

On-The-Scene Photography

Many of the photos of the fire and explosion were taken by Hank Graham, a Santa Fe Railroad conductor. He was working on a short train servicing the industries along the railroad in Kingman when the incident occurred. Graham had been notified of the fire at the Doxol plant and was advised not to proceed into the area. While maneuvering several rail cars, he saw the smoke from the fire. Graham pulled out his camera and started taking photos of the incident. When the train stopped, he proceeded to a point on Route 66 where a police officer was blocking traffic access from the incident. He wanted to know how long the rail line would be blocked.

Graham then began photographing the burning tank car's relief valve and awaited the fireball that would be created when it opened. While he was preparing to take another photo of the flaming relief valve, the BLEVE occurred, burning the hair off of his arms.

In the years since the Kingman explosion, rail cars have been manufactured with an outer layer of insulation and tank skin surrounding the inner tank to provide time before a fire can reach the inner tank. This insulation adds about one hour to the 15-to-20-minute time of flame impingement before a BLEVE is likely to occur.

A recent incident occurred in Weyuwega, WI, where 18 propane and LPG cars derailed and some experienced direct flame impingement. The insulation on the tank cars may have helped prevent a BLEVE from occurring during this 21-day incident. However, stationary and portable propane containers still have no protective insulation. Flame impingement on the vapor surface of these tanks will produce conditions that may lead to a BLEVE.

Others Inspired To Join

Today, the Kingman Fire Department is headed by career Chief Charles Osterman (who was just 16 years old when the explosion occurred) in command of four stations, five engines, a 55-foot TeleSqurt, a heavy support vehicle, an extrication truck, two brush engines and a reserve ambulance. The department's response area has grown to over 30 square miles and the population now exceeds 18,000. Each shift now has eight career firefighters on duty supported by Osterman, two assistant chiefs, an EMS coordinator and a training officer. The career force is complemented by 19 volunteers.

Osterman reports that the incident that occurred 25 years ago this month has led many relatives of the firefighters who were killed - including sons, nephews and uncles - to become career and volunteer firefighters in Kingman and other communities. Osterman's father was a volunteer firefighter in Kingman when the explosion occurred but was at work 22 miles away and missed the call - which may have saved his life.

What Is A BLEVE?

A BLEVE is a boiling liquid expanding vapor explosion. Gases are liquefied to allow the shipment of large volumes of product more economically. The process involves pressurization of the gas at its critical temperature and critical pressure.

Every gas has different critical temperatures and pressures. The boiling point of liquid propane is -40 degrees below zero Fahrenheit. It remains a liquid because of the pressure in the tank pressing down on the surface of the liquid. Liquefied gases other than cryogenics (refrigerated liquids) exist at what ever ambient temperature is present around the tank - if it is 70F outside, then the temperature of the liquid gas is 70F. Almost any ambient temperature encountered in this country is above -40F. Therefore, liquid propane is existing as a liquid above its boiling point. At 70F it is existing at 110 degrees above its boiling point!

When radiant heat, changes in ambient temperature or flame impingement increase the rate of boiling within the tank, the pressure also increases. Each tank has a pressure relief valve to remove the excess pressure. If, however, the pressure is being increased at a greater rate than it is being removed, or the tank is weakened as a result of flame impingement or mechanical damage to the tank, a BLEVE can occur.

As the tank fails, the liquid within the tank, which is above its boiling point (thus the term boiling liquid), is released and instantaneously converts to a gas all at once (expanding vapor), which results in a violent "explosion." The blast causes the container to break into pieces with some of them being rocketed over a half mile away. If the gas is flammable and an ignition source is present, a fireball may also develop.

Liquefied Propane Gas

Gases are liquefied because much more volume of the gas can be shipped and stored when the gas is in the liquid state. This is because one gallon of liquid propane can expand to over 250 gallons of propane gas.

Propane is primarily used as a fuel for vehicles and heating of homes and businesses. It is a colorless, odorless gas in its natural state; however, an odorant is added to detect leaks and it smells similar to natural gas. Propane is non-toxic but can displace the oxygen in the air and cause simple asphyxiation. The vapor density of propane is 1.53, which makes it heavier than air, so during a leak it will seek low areas such as storm sewers, manholes and basements. It is highly flammable with a explosive range of 2.4% to 9.5% in air.

Propane's boiling point is approximately -40 degrees Fahrenheit and it has an auto-ignition temperature of 874F. The National Fire Protection Association (NFPA) 704 Marking System lists the hazards of propane as Health-1, Flammability-4, Reactivity-0 and Special-0. The United Nations and U.S. Department of Transportation (UN/DOT) list propane as a Class 2.1 Flammable Gas. Its UN four-digit identification number is 1075.

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