 If work is done for less than two hours the ACGIH recommends an exposure airborne limit of 0.20pmm averaged over an 8-hour work shift.It is important to note that engineering controls are the most effective way of reducing airborne exposure of ozone (unless the exposure is the result of chemical use, in which exposure can possibly be reduced by substituting a less hazardous chemical).These controls include proper ventilation systems, proper respirators and protective clothing.