A review of the criteria for people exposure to radiant heat flux from fires

Abstract

The NFPA 59A Standard and the Federal Regulation, 49 CFR Part 193, stipulate a level of 5 kW/m 2 as the criterion for determining the hazard distance to people exposure from a LNG fire. Another regulation (24CFR, Section 51.204) while stipulating a lower exposure limit of 1.42 kW/m 2 provides administrative relief from the regulation if mitigation measures are provided. Several countries in Europe and the Far East have adopted both a specified heat flux value (generally, 5 kW/m 2) as well as modified dose criteria for human exposure hazard calculation in risk assessments. In some cases, the regulations in Europe require the use of lower values for children and physically challenged persons. This paper reviews the available literature on the phenomenon of skin burn caused by radiant heat exposure. The associated thermal and spectral properties of human skin are reviewed. The basis for regulatory setting, of 5 kW/m 2 and other exposure criteria (as a part of hazard and risk calculations) for evaluating distances to hazards from the exposure of people to radiant heat effects of large fires, is evaluated. An example calculation is provided to show the extent of reduction in the hazard distance to specified radiant heat flux from a fire when the spectral reflection and absorption properties of skin are considered with and without the inclusion of the mitigating effects of clothing. The results indicate that hazard distances calculated including the reflective and band absorptive properties (in IR wavelength) of skin results in a reduction of between 30 and 50% in the hazard distances obtained with current methodology, which ignores these effects. Unfortunately, there are no test results, from full-scale human-exposure-to-IR radiation, with which these predictions can be compared.