Combustible liquids may self-heat in porous insulation yielding smoldering or flaming combustion. In Part I the problem is reviewed and practical measures discussed. Using two-inch cubes of insulation and a standardized procedure, Spontaneous Ignition Temperatures (SITs) ranging from 55-184 C are reported for a series of combustible liquids. The application of a self-heating parameter Z = (AIT)/(AIT-FP), where AIT is autoignition temperature and FP is closed cup flash-point (both in Celsius), is examined. The “Z” parameter gives some indication of materials that will self-heat and those that will evaporate. For Z > 1.61 ignition occurred for all the liquids tested. Evaporation usually occurred for materials with Z < 1.35. It was found that some water-reactive or peroxide-forming materials can ignite where only evaporation would be predicted from Z value considerations. An important example of a water-reactive material is ethylene oxide (EO); the importance of EO insulation fires is that under certain conditions explosive decomposition of EO contained in the equipment can be initiated.
It was previously determined that ethylene oxide reacts in porous, refractory insulations forming low molecular weight polyethylene glycols. The formation rate depends on temperature and the type and condition (particularly water content) of the insulation. Unlike EO the glycols have low volatility and may accumulate over time to several times the mass of some insulations. Under certain conditions the glycols can ignite spontaneously. In Part II experiments carried out to examine this phenomenon are discussed.
Where process temperatures are above the SIT (but below the AIT), cellular glass insulation will minimize the risk of insulation fires. One disadvantage, especially for thermally unstable materials such as EO, is that cellular glass has poor fire endurance properties. The use of a realistic fire endurance test to specify insulation thickness and additional measures such as stainless steel jackets are described.
Alternatives to the use of cellular glass are discussed. When selecting an insulation system, it should be determined whether an insulation fire might occur and the loss potential from such an event should be evaluated.