Air Purifying Respirators (APRs) are negative-pressure respirators that draw air into the face piece via the negative pressure created by user inhalation and utilize ambient air, which is purified through a filtering element or chemical cartridge prior to inhalation.
APRs protect only against specific contaminants depending on the filter or chemical cartridge used. APR filters or chemical cartridges filter out contamination for a limited amount of time depending on the contaminant concentration, type of work to be performed, and amount of time in work area.
APRs cannot be used in work areas where the exposure conditions have not been characterized. This is because unknown contaminants may be present. Also, the concentrations of contaminants may be unknown and may exceed maximum use concentration(s).