Second-hand smoke is more than a nuisance—it is a toxic mix of more than 4,000 chemicals. These chemicals can be roughly divided into three groups: particulate matter, volatile organic gases, and inorganic compounds, like heavy metals. In 1992 the U.S. Environmental Protection Agency (EPA) classified second-hand smoke as a “Group A” carcinogen. This category is reserved for the most dangerous compounds that have been proven to cause cancer in humans.

In 2006 the State of California added second-hand smoke to its toxic air contaminant list, putting it in the same category as the most toxic automotive and industrial air pollutants. Over fifty cancer-causing chemicals have been found in second-hand smoke, including arsenic, cadmium, benzene and vinyl chloride.

There is NO known safe level of exposure.

Second-hand smoke is actually composed of two kinds of smoke:

• mainstream smoke—what the smoker exhales after taking a puff, and
• sidestream smoke—the smoke emitted from the burning end of the cigarette.

Most of second-hand smoke is sidestream smoke, because per cigarette, more tobacco is consumed when it is smoldering between puffs. Sidestream smoke contains higher concentrations of certain chemicals than the smoke inhaled by the smoker, sometimes up to ten times higher, primarily because sidestream smoke is produced at lower temperatures than mainstream smoke.

Think of a lit cigarette as a small incinerator that operates at temperatures that are not high enough to completely burn the tobacco. The result of this incomplete combustion is thousands of harmful chemical by-products, both gases (including carbon monoxide, formaldehyde, ammonia, nitrogen oxides, hydrogen cyanide, and vinyl chloride) and solid particles (including “tar”).

Second-hand smoke is a serious problem for many Ontario residents living in multi-unit dwellings like co-ops, especially those who suffer from chronic health conditions such as heart disease, asthma, allergies, diabetes, and respiratory illnesses. For many forced to breathe their neighbour's smoke, the only remedy is to move. But moving is not always an option for the elderly, or for people with limited incomes or disabilities.

Because second-hand smoke particles are so small (less than 2.5 micrometres), they can actually penetrate the alveoli deep in the lungs where oxygen and carbon dioxide are exchanged. Each year in Canada, breathing second-hand smoke causes more than 1,000 deaths in non-smokers from lung cancer and heart disease and keeps thousands more from leading normal, healthy lives.

The most comprehensive scientific report on the health consequences of second-hand smoke was conducted by the US Surgeon General in 2006 and should be a wake-up call for non-smokers and smokers alike. The US Surgeon General’s Report warns that no amount of second-hand smoke exposure is safe.

Key conclusions from the report reveal that:

Second-hand smoke increases risk of heart disease and lung cancer

• Concentrations of many cancer-causing and toxic chemicals are potentially higher in second-hand smoke than in the smoke inhaled by smokers.
• Exposure to second-hand smoke at home or work increases a non-smoker’s risk of developing heart disease by 25 to 30 percent and lung cancer by 20 to 30 percent.
• Breathing second-hand smoke for even a short time can have immediate negative effects on the cardiovascular system and interferes with the normal functioning of the heart, blood, and vascular systems.
• Persons who already have heart disease are especially at high risk of suffering negative affects from breathing second-hand smoke. They should take extra precautions to avoid even brief exposure.

Second-hand smoke causes acute respiratory problems

• Second-hand smoke contains many chemicals that can quickly irritate and damage the lining of the airways.
• Even brief exposure can trigger respiratory symptoms, including cough, phlegm, wheezing, and breathlessness.
• Persons with asthma or other respiratory conditions are at especially high risk, and should take extra precautions to avoid breathing second-hand smoke.

Exposure to second-hand smoke harms children

• Babies exposed to second-hand smoke are at a greater risk for Sudden Infant Death Syndrome (SIDS).
• Babies exposed to second-hand smoke have weaker lungs than unexposed babies, which increases the risk for many health problems.
• Among infants and children, second-hand smoke cause bronchitis and pneumonia and increases the risk of ear infections.
• Second-hand smoke exposure can cause children with asthma to experience more frequent and severe attacks.

In addition, findings from a 2009 Canadian Expert Panel on Tobacco Smoke and Breast Cancer Risk confirm that exposure to second-hand smoke can cause breast cancer in younger, primarily pre-menopausal women.

Many people are under the impression that problems with second-hand smoke infiltration can be solved with ventilation. While ventilation and related methods (air purifiers, air filters) can help to clear some of the 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) is the world authority on ventilation, setting internationally-recognized standards that are widely adopted as industry norms. In 2010 ASHRAE issued a position statement on ventilation and environmental tobacco smoke (ETS), which stated in part:

• "No cognizant authorities have identified an acceptable level of ETS exposure, nor is there any expectation that further research will identify such a level;" and
• "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."

James Repace is an internationally recognized second-hand smoke physicist and former senior scientist at the U.S. Environmental Protection Agency (EPA). He describes how tornado-like levels of ventilation would be required to reach an acceptable risk level of exposure, based on the U.S. federal occupational and environmental health regulatory decision rules for assessing harm of environmental agents. However, this is a moot point, as no acceptable level of exposure to second-hand smoke has yet been determined.

The bottom line is that ventilation is the not the solution to pollution.

The short answer is days, weeks, months, or even years. The long answer is more complicated.

Second-hand smoke is a dynamic and heterogeneous mixture composed of 4,000 different compounds, all with their own physical and chemical properties. These compounds can be roughly divided into three categories: particulate matter, volatile organic gases, and inorganic compounds (like heavy metals).

After smoking has taken place, the heavier particles fall out of the air and land on surfaces, volatile organic gases react with sunlight and other compounds in the air to form new chemicals, and other compounds either adsorb (stick to surfaces) or absorb into surfaces. In a reverse process later on, these chemicals will then "off-gas" back into the indoor environment. Another term for this residual contamination is "third-hand smoke." Some of the chemical compounds in second-hand smoke are odourless but can be detected in the environment using sensitive equipment long after it can be seen or smelled.

How long second-hand smoke persists in an indoor environment depends on:

• Number of cigarettes smoked;
• Volume of air (depends on layout of the home);
• 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; and
• Rate of de-sorption and re-emission (off-gassing).

Studies have demonstrated that short-term adsorption and absorption reduced potential exposure to certain second-hand smoke chemicals while smoking was taking place, whereas later off-gassing increased concentrations hours after smoking ended. Other studies have shown this to be true regardless of ventilation rates.