LOX Vessel Fire Exposure
Portable liquid oxygen (LOX) vessels are commonly used in homes by patients requiring oxygen therapy. The sizes of the vessels vary from small LOX volumes of less than 1 L (which can be transported by individuals) to larger vessels, while still transportable, are normally utilized and stored in a patient's home or vehicle. These larger vessels may contain up to of 60 L of LOX.
Several hazards may exist in a house fire scenario when LOX vessels are present. The high liquid-to-gas expansion ratio generates the risk of oxygen enrichment due to gaseous venting. Oxygen enrichment of the fire environment leads to earlier ignition of materials, faster combustion, and higher temperatures resulting in a much more vigorous fire. Some metals can even ignite and burn with extreme temperatures in enriched oxygen environments at atmospheric pressure. Additionally, expulsion of LOX, when mixed with certain hydrocarbons and ignited, may lead to explosion or detonation. Finally, as with any cryogenic liquid exposed to a heat source, an overpressure risk exists if the vessel cannot vent the pressure build-up from the rapidly vaporizing liquid.
WHA developed a test system to evaluate the reaction effects of portable liquid oxygen vessels exposed to house fire conditions. The test approach uses a custom propane flame-heated furnace (See figure below) to expose LOX vessels to a standard temperature profile intended to simulate the thermal environment of a house fire. The reaction effect is documented by video surveillance during testing and by post-test analysis of the LOX vessel condition. This test could also be performed for oxygen concentrators and compressors that also could be subjected to a house fire.
The standard temperature profile used as a guideline from NFPA 251 Standard Methods of Tests of Fire Resistance of Building Construction and Materials is outlined below.
1000°F (538°C)...........at 5 minutes
1300°F (704°C)...........at 10 minutes
1550°F (843°C)...........at 30 minutes
1700°F (927°C)...........at 1 hour
1850°F (1010°C)...........at 2 hours
2000°F (1093°C)...........at 4 hours
2300°F (1260°C)...........at 8 hours or more