Secondhand smoke transfer and reductions by air sealing and ventilation in multiunit buildings: PFT and nicotine verification

Abstract

Surveys suggest that transfer of secondhand smoke (SHS) between units in multiunit residential buildings is common, but measured data are rare. This study was undertaken to quantify bulk air transfer between units and document transfer of SHS species before and after treatments that sealed boundaries between units and provided a minimum amount of continuous exhaust ventilation of each unit. Six buildings in Minnesota were studied. Treatments were performed in clusters of up to eight units in each building, including zero to two units occupied by smokers. Bulk air transfer was quantified through passive perfluorocarbon tracer (PFT) gas tests. SHS transfer was evaluated using passive nicotine sampling. The median fraction of air entering a unit that came from other units tagged with PFTs ranged from 0.021 in a new condominium building to 0.353 in a 1930s duplex, with an overall median of 0.041. Treatments provided a median decrease of 29% in the fraction of transferred air and reduced PFT concentrations by about 40%, because of increased ventilation of both source and target apartments. Nicotine was transferred at only one-sixth the rate of PFTs. Involuntary exposure to SHS can be reduced but not eliminated by modifying existing, occupied multiunit buildings. Recent studies of secondhand smoke exposure in multiunit housing indicate transmission of SHS constituents from smokers' units to those occupied by nonsmokers. A straightforward solution for this problem is to eliminate air leakage transfer between these units. This study describes a 2-year investigation of air sealing and ventilation improvements in six multiunit buildings located in a heating-dominated climate region of the US. The results quantify the reduction in interunit transfer of air between smokers' and nonsmokers' units. While it is possible to reduce the transfer when done with care, it is extremely difficult to eliminate these flows unless the buildings are vacated and extensively rebuilt. Eliminating air leakage between smokers' and nonsmokers' units is not a practical means of solving SHS transmission in an existing building.