Objective To determine the impact on bar employee's health and exposure to secondhand smoke (SHS) before and after the implementation of Michigan's Dr Ron Davis smoke-free air law that went into effect on 1 May 2010, prohibiting smoking in places of work, including bars.

Methods This study used a pre/postintervention experimental design. The setting was bars in 12 Michigan counties. Subjects were bar employees, recruited through flyers and individual discussions with local health department staff. Participants completed a screening questionnaire to determine eligibility. A total of 40 eligible employees completed a demographic survey, provided urine samples for analysis of cotinine and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and completed questionnaires on respiratory and general health status 6 weeks before and 6–10 weeks after the law went into effect. The main outcome measures were urine samples for total cotinine and total NNAL and data from a self-administered respiratory and general health status questionnaire collected during the pre-law and post-law study periods.

Results There was a significant decrease in the mean cotinine levels from 35.9 ng/ml to a non-quantifiable value (p<0.001), and there was a significant reduction in the mean NNAL level from 0.086 pmol/ml to 0.034 pmol/ml (p<0.001) 2 months after implementation of the law. There was also a significant improvement in all six self-reported respiratory symptoms (p<0.001) and general health status (p<0.001).

Conclusions The reduction in the SHS biomarkers cotinine and NNAL and reported improvement in respiratory health demonstrates that the Michigan smoke-free workplace law is protecting bar employee health.