Fire Safety Improvements in the Combustion Toxicity Area: Is There a Role for LC_(50) Tests?

摘要

It is a well-known fact that the bulk of fire fatalities can be attributed to the inhalation of toxic combustion gases. This single fact has led regulators in Europe, the US, and other industrialized countries to consider (and in some cases to adopt) requirements for testing of products with various tests for toxic potency, commonly expressed as LC_(50). The regulators have more recently been joined by the International Organization for Standardization (ISO), which has been developing standards for LC_(50) and related variables. All of the standards considered so far have been limited to using only bench-scale test results. Engineers, however, have known for quite some time that the actual toxic effect from combustion gases must be viewed as a product of two factors: (a) the product's real-scale mass loss rate; and (b) its real-scale LC_(50). Thus, two issues can be seen to arise: (1) are real-scale values of LC_(50) adequately similar to the bench-scale ones; and (2) is the range of mass loss rates exhibited by various products small enough so that differences could be ignored and products ranked/rated solely by their LC_(50) values? This paper examines these questions by the use of a database of experimental results covering a wide range of building products. The analysis shows that far from being the dominant factor in the fire toxicity picture, LC_(50) is a minor constituent. For real products, LC_(50) values simply do not vary much. Mass loss rates, however, vary tremendously. Thus, it is demonstrated that the proper strategy for controlling fire toxicity hazard is by reducing the burning rate, not by attempting to make the effluent less toxic. These findings directly indicate that regulations based on controlling the LC_(50) cannot hope to address the proper concern of reducing fire fatalities.