S. Department of Health and Human Services, 2006). SHS-related disease and financial burden are fundamental public health concerns reflected in the Framework Convention on Tobacco Control, advocated by 168 countries under the World Health Organization (WHO) sponsorship (WHO, nothing 2003). SHS exposure elimination is considered an attainable primary prevention goal to reduce morbidity and mortality (WHO, 2008). Efforts to eliminate the health risks associated to SHS can be classified into two categories. First, some countries have allowed mechanical systems, such as area separation, ventilation, and air extraction, in an attempt to reduce SHS exposure while still allowing smoking (WHO, 2009). These types of mechanical systems are advocated by tobacco companies and the hospitality sector as effective means to reduce SHS (Drope, Bialous, & Glantz, 2004).

Some experimental research partially supports this claim. For instance, working under ideal circumstances, the most sophisticated smoking rooms, which combine several mechanical systems, are capable of eliminating 90% of SHS (Wagner et al., 2004). The remaining 10%, however, is still transferred to nonsmoking areas. Thus, while mechanical systems may significantly reduce SHS, they can not completely eliminate it. Second, legislative action against tobacco smoke has increasingly gained public support and has led to substantial changes in policies around the world (WHO, 2008). Currently, 17 countries have followed 100% smoke-free environment policies, advocating complete smoking bans in all public places (WHO, 2009).

The WHO position is grounded on evidence showing that no safe levels of exposure to SHS exist (U.S. Department of Health and Human Services, 2006); therefore, all residuals and leakage resulting from the insufficient capability of mechanical systems represent a significant health risk (WHO, 2007). Complete smoking bans have received support from the American Society of Heating, Refrigerating, and Air Conditioning Engineers, who state that no engineering approach is capable of eliminating the health risks associated with SHS once the smoke has been released to the environment (Samet et al., 2005). While a vast body of literature has been dedicated to discussing mechanical systems versus smoking bans (Akbar-Khanzadeh, 2003; Cenko, Pisaniello, & Esterman, 2004; Dearlove, Bialous, & Glantz, 2002; Drope et al.

, 2004; Samet et al., 2005; WHO, 2008), no systematic attempt has been conducted to quantify the effectiveness of each approach under nonexperimental conditions. In February 2008, a total smoking ban in all public places, including restaurants and bars, was GSK-3 enforced in Mexico City (Gaceta Oficial del Distrito Federal, 2008). The rest of the country, however, still allowed indoor smoking.