Environmental tobacco smoke (ETS) is a mixture of tobacco smoke and ambient air. ETS may be produced by cigarettes or other smoking devices, and is a combination of mainstream smoke (exhaled by the smoker) and sidestream smoke (emitted by the burning end of the tobacco product).[2,3] Approximately two thirds of the smoke from a burning cigarette enters the surrounding environment and may be inhaled by people in the area. ETS may also be referred to as “secondhand tobacco smoke,” “involuntary smoking,” or “passive smoking”.
ETS is comprised of more than 4000 chemicals emitted from burning tobacco, of which at least 250 are known to be carcinogenic or toxic. Some chemicals found in ETS include arsenic, benzene, beryllium, cadmium, chromium, ethylene oxide, nickel and vinyl chloride. Compared to the smoke that is inhaled by smokers, ETS has over twice the nicotine and tar, and five times the carbon monoxide.
The primary route of exposure to ETS is inhalation.[2,3] The complexity of ETS mixtures leads to difficulties in assessing exposure. As surrogate measures of ETS exposure, research and public health studies typically monitor levels of nicotine, carbon monoxide, benzene, and respirable particulates suspended in air, or biomarkers such as levels of nicotine metabolites in saliva, blood or urine.[3,6]
Environmental tobacco smoke is classified by IARC as a Group 1 agent, carcinogenic to humans, with a well-established link to lung cancer.[2,3] A recent IARC review of Group 1 agents reaffirmed the classification and included larynx and pharynx as "tumour sites for which there is limited evidence." 
Other adverse health effects associated with exposure to ETS include eye, nose and throat irritation, dizziness, and nausea. Children exposed to ETS may experience chronic respiratory illness, impaired lung function and middle ear infection. ETS can aggravate symptoms in people with allergies or asthma, and long-term exposure has been linked to heart disease.[2,32] Health Canada estimates that over 1,000 non-smokers die in Canada each year as a result of ETS exposure.
In Canada, regulations governing environmental or occupational protection from ETS are administered by federal, provincial, and municipal governments.  Federal regulations apply to federal lands and corporations, and federally regulated areas (i.e., transportation, communications, and banking). Provincial regulations can ban or restrict smoking in workplaces or public places, whereas municipalities have the authority to introduce additional restrictions within their geographic boundaries.
Non-Smokers' Health Act
Regulates smoking in federal workplaces and on common carriers; amends Hazardous Products Act's cigarette advertising regulations
Smoke-free Environment Act
Smoke-free Places Act
Smoke-free Places Act
Smoke-free Places Act
Smoke-free Ontario Act
The Non-Smokers' Health Protection Act The Highway Traffic Act
The Tobacco Control Act The Occupational Health and Safety Regulations (Under the Occupational Health and Safety Act)
Tobacco Reduction Act
Tobacco Control Act Motor Vehicle Act
Tobacco Control Act Environmental Tobacco Smoke Work Site Regulations (Under the Safety Act)
Tobacco Control Act
Environmental Tobacco Smoke Work Site Regulations (Under the Safety Act) Smoke-Free Places Act
Legislation banning smoking within each of the provincial and territorial jurisdictions is mostly consistent. Smoking is prohibited in enclosed places of employment and public places in nearly all provinces. However, not all First Nations territories have applied such bans to their communities. The majority of provincial legislation no longer permits smoking in separate designated smoking rooms or areas (DSRs/DSAs), although group living, long-term care facilities and designated smoking hotel rooms are common exceptions.[26, 27] Recent amendments to provincial smoking legislation ban smoking in vehicles when children are present. Depending on the province, the maximum age for “children” ranges between 16 and 19, inclusive. Legislation does not cover smoking in private homes. Some provinces prescribe additional areas where smoking is prohibited, including school grounds and outdoor patios. Other provinces continue to permit smoking on outdoor patios, with restrictions relating to the percentage of the patio that is enclosed.
Many municipalities have passed more restrictive bylaws to provide additional protection from ETS. Examples of municipal bylaws include smoking bans on outdoor patios, in public outdoor areas such as playgrounds and parks, hotel rooms and private vehicles, and may also include buffer zones around entranceways, air intakes and windows.[27,28]
Currently, the main occupations where workers are exposed to ETS are those taking place in environments where smoking is still permitted. The exposed workers include outdoor occupations such as farming, fishing, construction and landscaping; “in-house” workers including caregivers and tradespeople who enter private residences to provide a service; hospitality workers (i.e. in the service industry), emergency workers and law enforcement officers; and employees on First Nations' reservations.
Due to the recent introduction of a variety of smoking ban legislation into most Canadian jurisdictions, the prevalence and level of current ETS exposure in occupational settings are significantly different than they have been in the past. In 2001, a Canadian workplace study showed that 90% of workers surveyed reported some form of smoking restrictions and 82% reported being protected from ETS. A US survey shows secondhand smoke concentrations have declined by more than 90% following workplace smoking restrictions.
Prior to the introduction of the smoking ban legislation, occupational ETS exposure was high in workplaces such as bars, bowling alleys, billiard halls, bingo parlours and casinos. Nicotine concentrations measured in these workplaces were 2.4-18.5 times higher than in offices or residences with at least one smoker and 1.5-11.7 times higher than in restaurants.
Non-occupational exposures to ETS can occur in a variety of indoor and outdoor, private and public settings.
Health Canada's Canadian Tobacco Use Monitoring Survey (CTUMS) provides information on tobacco use trends and related issues. In early 2009, 34% of survey respondents indicated that they were being exposed to second-hand smoke at least once a week, with an additional 21% being exposed daily or almost every day. Reported sites of exposure were building entrances (54%), on a sidewalk or in a park (53%), inside a vehicle (20%) and at the workplace (20%).