Propane Explosion

New York City authorities say they found a potentially powerful bomb in a vehicle in Times Square late Saturday, 01 May 2010. Swift action by police and city residents averted what could have been a deadly car bombing attack. New York City officials say police, firefighters and bomb experts were notified of a suspicious sport utility vehicle after a t-shirt vendor noticed smoke coming out of it. Witnesses say they heard a loud "pop" from inside the vehicle, but that the car did not explode. investigators evacuated Times Square and removed propane tanks, gas containers, commercial-grade fireworks and timing devices from the vehicle. U.S. Attorney General Eric Holder said Monday it is too early to say whether the incident was of foreign or domestic origin and that it is also too early to designate it as a terrorist incident.

DHS has included propane on the list of Appendix A chemicals of interest because propane can produce significant consequences if used in a terrorist attack. And this is not hypothetical: propane has been successfully employed as a component of terrorist devices. The recent events in London and Glasgow - in which the terrorists attempted to attack using propane - illustrate how important it is to appropriately secure facilities that possess potentially dangerous chemicals.

On June 29, 2007 two attempted attacks in central London failed when two vehicles containing gas canisters and other incendiary materials were discovered and made safe. London Police thwarted an apparent terror attack when a car bomb was found shortly before 2 a.m. London time in The Haymarket near the famed Piccadilly Circus in the heart of central London's West End theater district. An ambulance crew attending an earlier incident reportedly had spotted smoke coming from the silver-green Mercedes. The bomb was made up of canisters containing a lethal mix of approximately 200 liters of gasoline, propane gas, and nails attached to a detonator, which was disabled by hand by Explosives Officers. In the second, a blue Mercedes with a similar explosive mix was left in Cockspur Street.

The definition for explosive is "a chemical that causes a sudden, almost instantaneous release of pressure, gas, and heat when subjected to sudden shock, pressure, or high temperature."Explosives are unstable materials and are of two types. One type consists of material capable of supersonic reactions (detonation), for example, nitroglycerine and TNT. The other type consists of materials (usually mixtures) that burn rapidly but at a subsonic rate. Examples of this type are gunpowder, rocket propellants, and pyrotechnic mixtures (fireworks). The difference between fire and explosion is the rate at which high temperature gases are produced and the physical containment of the burning gases. When high temperature gases build up extremely fast, there can be such a sudden release of energy from the gases that a shock wave or explosion is created. Confining the build-up of high pressure gases in a drum or vessel, which prevents venting of the gases, may promote an increase in the pressure within the restricted volume until an explosion occurs. Such is the principle behind some munitions, which confine high pressure gases until the pressure exceeds the strength of the casing.

All compressed gases are potentially hazardous since they are under great pressure in a container. Accidental rupture of the container and the rapid release of the pressurized gas can result in injury to persons and damage to objects in the vicinity. Not only can the gas be released with great force, but the force of the release may propel the container for a long distance. In addition to the mechanical hazard from the pressure or propelled container, other hazards may exist from the released gas. The hazard from some compressed gases may be strictly mechanical (e.g., compressed air), others may possess other types of hazards, such as being flammable (e.g., methane and propane) or toxic (e.g., ammonia and chlorine).

Propane is used extensively as a fuel for cooking and heating in residential, retail, and commercial applications.20 It is a gas at ambient temperature and pressure but is transported and stored as a liquid. Because propane is odorless and colorless, small quantities of an odorizing chemical (ethyl mercaptan) are added so leaks can be detected by smell. Unlike natural gas, propane is heavier than air. Consequently, propane releases tend to accumulate at ground level or in other low points such as pits and basements. Liquefied petroleum gas is the general term for mixtures of hydrocarbon gases liquefied by pressure and used for cooking, heating, and vehicle fuel. Liquefied petroleum gas can be propane, butane, propylene, butylene or any mixture of these compounds.

Propane-air mixtures can be explosive when the atmospheric concentration of propane is between 2.4 and 9.5 percent by volume. A propane emergency significant enough for fire department response is reported nearly everyday in the United States. Only gasoline and natural gas are involved in more hazardous materials emergencies. In 1984 in Mexico City a propane storage facility explosion killed more than 500. In 1978 in Spain a propane cargo tanker exploded, killing 200 and injuring 100 more.

On January 30, 2007, a propane explosion at the Little General Store in Ghent, West Virginia, killed two emergency responders and two propane service technicians, and injured six others. The explosion leveled the store, destroyed a responding ambulance, and damaged other nearby vehicles. On the day of the incident, a junior propane service technician employed by Appalachian Heating was preparing to transfer liquid propane from an existing tank to a newly installed replacement tank.

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