Rats were exposed for 30 minutes at the approximate LC50 of Douglas fir (DF), polyvinyl chloride (PVC) or polyisocyanurate foam (PI) smokes produced in a radiant furnace at 2.5 w/cm2. They were sacrificed and examined for respira tory tissue changes at 24 hours following exposure. All smokes produced air way injury. The more extensive airway injury produced by PVC smoke and, in some instances, by PI smoke, involved the entire epithelial surface area of the trachea and the surfaces of lobar and first division sublobar bronchi. The injury produced by DF smoke was concentrated in the proximal one-half of the trachea. The injuries are discussed with respect to potential chemical toxicants.

An approximate lethal exposure (ALE) method for acute inhalation toxicity testing of thermal decomposition products was developed and evaluated. In comparison to "traditional" LC 50 calculation methods, the ALE method required 70% fewer animals and 50% fewer test runs. The ALE procedure relied on analysis of combustion gases and their limited animal testing (F-344 rats). The procedure was used to evaluate eight materials under flaming (5.0 W/cm 2 ) and nonflaming (2.5 W/cm 2 ) conditions. The complete 30-minute L(Ct) 50's were also calculated for five of those eight materials and compared to the ALE's. The ALE's were within eleven percent of the calculated L(Ct) 50's at 5.0 W/cm 2 and ranged within thirteen to fifty-five percent of the L(Ct) 50's at 2.5 W/cm 2 . A microcomputer data acquisition and control system to improve data collection and Ct product calculation is also described for the radiant furnace test method for improved data collection and concentration-time product calculation.