LNG Carrier Polystyrene Foam Cargo Insulation Performance Under Fire Exposure
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The United States Government Accountability Office (GAO), in its February 2007 report &'Public Safety Consequences of a Terrorist Attack on a Tanker Carrying Liquefied Natural Gas Need Clarification&', stated that &'The leading unaddressed priority ... was the potential for cascading failure of LNG tanks&'. In 2006, the first author notified the Society of International Gas Tanker and Terminal Operators Ltd (SIGTTO) of his concerns that fire exposure of LNGC tanks insulated with foam plastic insulation following a terrorist attack could have the potential, as a result of loss of insulation efficacy due to heat damage, to lead to catastrophic rupture of remaining undamaged (in the attack) tanks on the carrier. In response, SIGTTO formed a Working Group (WG) to evaluate the effects of fire on LNGC Cargo Containment Systems in July of 2006, and the WG worked during the period 2006-2008, producing a report in March 2009 (available on the SIGTTO website) entitled &'Report on the Effects of Fire on LNG Carrier Containment Systems&'. The Working group agreed that given sufficient heat absorption by Polystyrene insulation in an external (to the tank) fire scenario, total insulation failure (melt-through) could result, depending on the intensity and duration of fire exposure. (Among others), the following conclusion was stated in the report: &'The response of the insulation system to heat, with time, is unclear; a detailed understanding of rates of insulation degradation and recession was not available for the structural arrangement of an LNG carrier. One dimensional CFD/heat transfer calculations made by the working group indicated time periods of 10 minutes for a complete degradation to a depth of 30 cm. Conversely, other studies in this report result in a degradation time of up to 29 minutes.... a detailed understanding of rates of insulation degradation and recession was not available for the structural arrangement of an LNG carrier. Additionally, reports from physical tests carried out in the 1970s indicate time periods of greater than 2 hours, although in these tests the conditions did not entirely accurately reflect actual LNG carrier dimensions.&' This paper presents experimental measurements of the degradation rates of polystyrene foam insulation as a function of applied heat intensity, augmented by mathematical simulations of the failure rates that could be expected under realistic fire exposure to the external weather cover, indicating that complete failure of the insulation (melt-through) might occur within 10 minutes of the start of a fire which enveloped the tank.
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