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Sunday
Jul182010

Flaring Tank Cars

     Flaring Tank Cars is serious business for the Haz-Mat Responder. Since this is done on the basis of a “last resort”, experienced personnel who have performed this technique are far and few between. Equipment is exacting and specialized. Site constraints and accessibility requires pipe fitting and innovation at your incident site.

     Over zealous media coverage dappled with incorrect information and hysteria has often tended to exaggerate the danger to people living in the area of a derailment. Such reports have not only caused concern about the destructive capability of rail cars and their cargo, but many reports have initiated evacuations before the scene has been evaluated by rail and hazardous materials personnel.

     When railcars carrying hazardous materials or flammable materials derail, it is essential to determine 1] are there any leaks? And 2] locate them and stop if possible. Since LP {Liquefied Petroleum} is the most prevalent shipment, I have oriented this discussion on the theory and practice concerning flammable gas. Most flammable gases have five {5} basic behaviors. 1] They are usually liquids that are held in this state by the railcars restriction of its vapor pressure. These tanks are never loaded full, to allow for vapor expansion when exterior temperatures rise. This term is called “outage”. Full conditions occur between 105 and 130 degrees F depending on tank specifications. 2] When released, flammable gases can only become a fire hazard when mixed in the proper proportions with air. In this vaporous state, it presents a hazard comparable to natural gas. 3] Since these vapors are frequently heavier than air, they will sink to low lying areas and present a ventilation problem. In thick vegetation, generally found near rail tracks, some flammable vapors disperse at a much slower rate. Due to this problem, ignition sources from over 600 feet have been reported. 4] Most but not all gases contain an odorant which assists in detection of the flammable when improperly released. 5] Since most of these gases are refrigerants, when released, the temperature of the gas and liquid will drop fast, while the pressure inside the damaged railcar

equalizes at the BP {Boiling Point} of the liquefied gas. This property makes it possible to create a “pressure recession” inside the damaged car, which will contain the remaining material while hazardous materials responders evaluate which tactic to implement for this scenario.

     If the damage to the car is severe, and the location remote, and there is no chance to upright the car for removal or pump transfer of its contents, piping the contents away from the damaged car and deliberately igniting them may be an option. This is called a “flare-off”. This procedure should ONLY be attempted with the approval, personnel and expertise of the railroad personnel involved. As you can see by the drawings, ANY position you choose for the burning flare can be problematic. The Emergency Response Compressed Gas Accident Flare Pipe schematic demonstrates the size and type of equipment you will need, if you are involved with this type of incident.

     The Railroad Specialists technique consists of piping connecting the damaged car 75’ {or more} away to the 10’ Flare tower in the drawing. A swing check valve is installed to prevent flashback to the damaged railcar. Operator 1 opens the vapor valve to feed the flare tower, beginning the burn. Operator 2 ignites the flare tower with a "fusee" while both remain in position through out the burn. Operator 3 remains downwind with a flammable gas detector, marking the edge of the contaminated gas area to direct valve opening or closing, accordingly. Pipe size has proven important in the past. In like instances, tanks operating at 40 psi a 1” pipe lowered “recession” at the rate of 4psi/hr. A 2” pipe caused “recession” to atmospheric in 1 hr.

     A second suggested method, for Hazardous Materials Responders, is more controllable and functional if specialized equipment is not available. Here piping is extended approximately 100’ {or more} from the vapor line of the damaged car to the bottom of a 55 gallon steel drum filled with water. Operator 1 opens and monitors the vapor valve, operator 2 ignites the flammable vapors as they bubble through the water and reach the waters surface. Keep the transfer line warm with Engine hand-line water until the bubbling ceases and the fire extinguishes. At this point, you have burned off all the flammable vapors, and or, created a “vapor recession” inside the tank slowing, and or, hopefully halting the discharge flow. Either way, you have mitigated the immediate emergency and given yourself time to plan the next step of mitigation.

 

                                             Haz Mat Mike



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