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...
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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
Photo by Robert Burke
A liquefied petroleum gas (LPG) or propane pressure railroad tank car like the one that exploded in Kingman.
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.
Robert Burke, a Firehouse® contributing editor, is the fire marshal for the University of Maryland and has served on state and county hazmat response teams. Burke is a veteran of over 16 years in career and volunteer fire departments, serving as assistant chief and deputy state fire marshal. He holds an associate's degree in fire protection technology and a bachelor's degree in fire science, and is pursuing a master's degree in public administration. Burke is an adjunct instructor at the National Fire Academy and Maryland Fire and Rescue Institute, and is the author of the textbook Hazardous Materials Chemistry For Emergency Responders. He can be reached on the Internet at email@example.com.