The most important reason for smoke-free housing is clean indoor air. Second-hand smoke is more than a nuisance—it is a toxic mix of more than 4,000 chemicals.

Second-hand smoke travels due to differences in air pressure between units, between floors and between the inside and outside of a building. Second-hand smoke can transfer from a neighbour’s patio or balcony; through open windows or doors; through electrical outlets, cable or phone jacks, or ceiling fixtures; through cracks and gaps around sinks, countertops, windows, doors, floors, walls or dropped ceilings; and through the ventilation or forced air system.

Research has shown that up to 65% of the air in a unit can come from other units in the building.

There is no known safe level of exposure to second-hand smoke. Second-hand smoke is a serious problem for many Ontario residents living in multi-unit housing, especially those who have chronic health conditions. Second-hand smoke increases risk of heart disease and lung cancer and causes acute respiratory problems. It is especially harmful to seniors and children.


While ventilation and systems such as air purifiers or air filters can help to clear some smoke from indoor air, there is no ventilation system that can remove enough toxins to effectively protect human health from the dangers of second-hand smoke.

The American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE), the authority who sets internationally-recognized ventilation standards, issued a position statement on ventilation and environmental tobacco smoke (ETS), which stated “At present, the only means of effectively eliminating health risk associated with indoor exposure is to ban smoking activity.” In 2006 the US Surgeon General’s report on second-hand smoke stated that “the typical heating, cooling and exhaust systems found in most American homes are not capable of removing second-hand smoke particles.”

Third-hand Smoke

Read about thirdhand smoke.

Thirdhand smoke (THS) refers to residual second-hand tobacco smoke that persists after smoking has stopped. Chemicals in the smoke that are oily or waxy may be more likely to stick to surfaces than be removed by ventilation. Scientists are starting to think that these THS residues can persist in the environment for weeks, months or even years, remaining on surfaces and in dust where they later off-gas.

How long thirdhand smoke persists in an indoor environment depends on:

  • Number of cigarettes smoked
  • Volume of air
  • Ventilation rate
  • Rate of emission of chemical constituents from sidestream and mainstream smoke
  • Furnishing level (material type and surface area)
  • Sorbency (how likely something will be absorbed or adsorbed) of surfaces
  • Rate of de-sorption and re-emission (off-gassing).

Very little is currently known about potential or actual health effects of exposure to THS. Not all constituents of THS have yet been identified, and it is premature to assess the health risks of exposure without evidence from clinical outcomes.