Evaluation of the Cooling Effect of an Outdoor Misting Fan for Workers in Hot Environments Wearing Personal Protective Equipment (PPE)

Heat stress on workers wearing PPE(Personal protective equipment) in hot outdoor environments is of rising concern, especially in cases when rest breaks and clothing changes are impractical. Mist fan evaporative cooling could provide low-energy continuous cooling even during work activity. The cooling effect of a misting fan was compared to that of a fan alone, as well as natural convection. A thermal mannequin with heat flux sensors at 8 body locations was exposed to an outdoor misting fan while clothed in typical work clothes and PPE. Work clothes were dry or saturated with water to simulate sweat. The distance from the misting fan ranged from 4m (wetting common) to 7m (wetting unlikely). On average, the misting fan had a cooling effect of 0.31met (18.3W/m2) higher than natural convection when PPE with wet work clothes are worn, and 0.35met (10.63W/m2) higher when dry work clothes with PPE were worn. This equates to reducing thermal metabolic load from light industrial work to walking about in office work, or from standing to reclining. Under international standards for workers in hot environments based on metabolic rate and WBGT(wet bulb globe temperature), such as ISO 7243, this equate to an average of about a 0.35ºC (dry clothes with PPE) to 0.61ºC (wet clothes with PPE) increase in acceptable WBGT.