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In addition, Humphries said Cryogenic trailers are equipped with one more safety device called a fire valve or block valve. The valve can be tripped manually in the event of a fire. It is also connected to a spring-loaded fusible link system that will melt in the event of a fire and allow the valve to close on its own, stopping any flow of liquid from the inner tank to any external piping.
Humphries maintains that because of the safety features built into the trailers, and contrary to what Hora was told at the incident scene, pressure of the liquid oxygen inside the tank was not an issue because of the safety system regardless of the position of the trailer. Had firefighters not vented the trailer manually, the bursting disc would have ruptured eventually and vented the trailer as designed. There was no danger associated with pressure in this accident. As it was, pressure in the tank never rose above 38 psi because firefighters opened the manual vent valve. The tankers normally travel with the product at 28 psi.
Hora said there was some concern about the integrity of the tank because of the damage it sustained in the accident and also whether any of the safety features such as the bursting disc had been damaged.
Humphries also said, to calm fears of a trailer carrying LOX exploding or starting on fire, that because of safety systems on a liquefied oxygen trailer, it could not erupt in a fireball. In addition, erupting in a fireball is not a property of oxygen - even in it's concentrated refrigerated liquid state. Oxygen itself will not burn; it is a non-flammable, but it readily supports combustion.
Going back to basic firefighting 101, two other elements need to be present for fire to occur: a combustible material and an ignition source. Hence, the oxygen would have to come into contact with both before a fire would occur. Anything LOX may come into contact with outside the trailer would, though, undoubtedly burn with more vigor, and as in the case already mentioned of asphalt and other products with explosive intensity. Consequently, the utmost of caution in dealing with the hazard is still advised.
Hora observed that at this incident there was in addition to the blacktop hazard, spilled diesel fuel from the wreck and also the hazards of potential spilled oil and oil on the truck tires. He also believes that static electricity in the firefighters protective clothing may have been enough to provide an ignition source in the right situation.
Looking back on the incident, Hora recounts one lesson learned and something he would have done differently. That was to establish a safe zone earlier and farther back from the accident. LOX has numerous medical and industrial applications. Trucks towing tankers full of the product routinely pass through many communities. Any emergency response agency could be faced with the same situation faced by emergency responders to the Oxford incident.
Like any of the many hazards a small rural fire department may face, education and awareness are the key to keeping yourself on the safe side of misfortune.
Steve Meyer, a Firehouse® contributing editor, has been a member of the Garrison, IA, Volunteer Fire Department since 1981 and has served as chief for 16 years. He is a graduate of the National Fire Academy Executive Fire Officer Program and is a contract instructor for Leadership and Administration with the NFA. Meyer was the 1998 State of Iowa Firefighter of the Year.