Smoke Component Yields from Bench-Scale Fire Tests

A standard procedure is needed for obtaining smoke toxic potency data for use in fire hazard and risk analyses. Room fire testing of finished products is impractical, directing attention to the use of apparatus that can obtain the needed data quickly and at affordable cost. This report presents examination of the second of a series bench-scale fire tests to produce data on the yields of toxic products in both pre-flashover and post-flashover flaming fires. The apparatus is the ISO/TS 19700 controlled equivalence ratio tube furnace. This apparatus uses a mechanical feed mechanism to supply solid fuel into a tube furnace at a pre-determined rate, so that the global equivalence ratio can be adjusted. The test specimens were cut from finished products that were also burned in room-scale tests: a sofa made of upholstered cushions on a steel frame, particleboard bookcases with a laminated finish, and household electric cable. Initially, the standard test procedure was followed for two fire stages, well ventilated flaming and post- flashover. Subsequent variation in the procedure included dicing the specimen, further decreasing the equivalence ratio (well ventilated flaming) or increasing it (post-flashover), increasing the mass loading while maintaining the equivalence ratio, and increasing the fuel feed rate while maintaining the equivalence ratio. The yields of CO2 CO, HCl, and HCN were determined. The yields of other toxicants (NO, NO2, formaldehyde, and acrolein) were below the detection limits, but volume fractions at the detection limits were shown to be of limited toxicological importance relative to the detected toxicants. In general, the largest effects were seen between the two fire stages. The other variations within the fire stage had minor effects on gas yields. Under post-flashover conditions, the sum of the CO2 and CO yields frequently accounted for half or less of the carbon originally in the specimen. As a result, the gaseous combustion products cannot be used to estimate the mass burning rate. Under post flashover conditions, the CO yield for the sofa approached the value of 0.2 found in real-scale postflashover fire tests. However, for the bookcase and cable it did not. Yields of HCl from the cables generally approached their notional yields under well- ventilated conditions, and HCN was most readily detected from the sofa under post-flashover conditions at toxicologically significant concentrations.