Residual tobacco smoke: measurement of its washout time in the lung and of its contribution to environmental tobacco smoke.

BACKGROUND: Tobacco smoking entails inhaling millions of fine particles with each puff, and it is intuitive that after smoking a cigarette it will take a certain time to washout residual tobacco smoke (RTS) from the lungs with subsequent breaths.
OBJECTIVES: To study the washout time of 0.3-1.0 microm particles after the last puff in 10 volunteer smokers by using equipment capable of measuring particle concentration in real time in the exhaled air. RESULT: Mean (standard deviation (SD)) lung RTS washout time was 58.6 (23.6) s, range 18-90 s, and corresponded to 8.7 (4.6) subsequent breathings. The contribution of individual and overall RTS to indoor pollution was calculated by subtracting incremental background particle concentration from room concentration after 10 consecutive re-entries of smokers after the last puff into a room of 33.2 m3, with an air exchange rate per hour in the range of 0.2-0.4. Mean (SD) individual RTS contribution consisted of 1402 (1490) million particles (range 51-3611 million), whereas RTS increased room 0.3-1.0 microm particle concentration from a baseline of 22,283 particles/l to a final room concentration of 341,956 particles/l, corresponding to a total increase in particulate matter (2.5) from a background of 0.56 up to 3.32 microg/m3.
CONCLUSION: These data reveal a definite although marginal, role of RTS as a source of hidden indoor pollution. Further studies are needed to understand the relevance of this contribution in smoke-free premises in terms of risk exposure; however, waiting for about 2 min before re-entry after the last puff would be enough to avoid an unwanted additional exposure for non-smokers.