The impact of implementation of a national smoke-free prisons policy on indoor air quality: results from the Tobacco in Prisons study

ObjectiveTo determine secondhand smoke (SHS) concentrations in prisons during the week of implementation of a new, national prisons smoke-free policy.DesignRepeated measurement of SHS concentrations immediately before and after implementation of smoke-free policies across all 15 prisons in Scotland, and comparison with previously gathered baseline data from 2016.MethodsFine particulate matter (PM2.5) measurements at a fixed location over a continuous 6-day period were undertaken at the same site in each prison as previously carried out in 2016. Outdoor air quality data from the nearest local authority measurement station were acquired to determine the contribution of outdoor air pollution to indoor prison measurement of PM2.5.ResultsAir quality improved in all prisons comparing 2016 data with the first full working day postimplementation (overall median reduction −81%, IQR −76% to −91%). Postimplementation indoor PM2.5 concentrations were broadly comparable with outdoor concentrations suggesting minimal smoking activity during the period of measurement.ConclusionsThis is the first evaluation of changes in SHS concentrations across all prisons within a country that has introduced nationwide prohibition of smoking in prisons. All prisons demonstrated immediate substantial reductions in PM2.5 following policy implementation. A smoke-free prisons policy reduces the exposure of prison staff and prisoners to SHS.