Effects of Expansion Foam on Controlling LNG Vaporization Rate

With increasing consumption of natural gas, the safety of liquefied natural gas (LNG) utilization has become a challenge that requires comprehensive studies on risk assessment in the LNG facilities with mitigation measures.  The rapid vaporization after an LNG spill generates a vapor cloud, which is flammable at the concentration roughly between 5-15%v/v in the air (4.4 to 17%v/v for pure methane).  The LNG vapor is heavier than air and may migrate at the ground level to a long distance in downwind direction, which increases the possibility of ignition resulting in fires.  High expansion foam has been proved to be effective for mitigating vapor hazard and reducing a pool fire.  With respect to vapor hazard mitigation, high expansion foam reduces vaporization rate and increases vapor buoyancy.  These effects have not been fully analyzed yet.  In this work, a small-scale field experiment was performed to study the effect of high expansion foam on the vaporization rate of liquid nitrogen, used as a safe analog of LNG.  It has been found that foam blanket reduces convective and radiative heat flux to the pool.  At the same time, the water drainage from collapsing foam adds additional heat to the pool; however, it was found small and negligible with the long lasting pools.