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Experiments were carried out to investigate the effect of burning conditions on combustion of Douglas fir wood in a proposed smoke toxicity test: a plastic 200 L exposure chamber with a radiant furnace. Research included effects of: incident heat flux, sample surface, initia1 oxygen 1eve1 and endpoint criteria. Wood board sample mass can vary broadly even at equal surface and thickness, suggesting that surface may not be an ideal surrogate for amount of material. The effect of carbon black on ignitability is erratic. Ignitability of blackened wood samples is higher than that of unblackened samples only if both are identical. Irreproducibility increases at low incident fluxes. Tests carried out with the IT50 concept are hazardous to the operator (oxygen addition can cause explosions) and lead to high irreproducibility (six fold variations of CO doses in identical tests). Yields of CO depend on exposure protocol and on sample size. At high initial oxygen levels, however, CO/C02 ratios are very low, unless big samples are burnt to completion. This leads to excessive smoke for toxicity purposes. The CO yields and CO/C02 ratios are adequate when using very low oxygen levels (0-5%) and high heat fluxes, conditions which simulate those in ventilation controlled fully developed fires.