Contaminant Concentration

The relevant occupational exposure limits (OEL), Workplace Exposure Standard (WES) or Workplace Exposure Limit (WEL) safe exposure levels should be identified for contaminant/s associated with the task/application.

Knowing the exposure contaminant concentration is the key piece of information for the adequacy assessment to determine the minimum protection required from the Respiratory Protective Device (RPD) for adequate protection against the identified hazardous substance and/or oxygen deficiency. In estimating the required minimum protection factor, evaluation of the likely range of contaminant concentration in the atmosphere must be made.

In selecting a specific RPD for use, the RPD protection level should be sufficient to reduce the exposure to less than the OEL/WES/WEL. The minimum protection level required is determined by firstly calculating the hazard ratio (HR). To calculate the HR, it is necessary to know the foreseeable worst-case concentration(s) of the airborne contaminant(s) and the relevant occupational health regulatory requirements, exposure limits or the safe exposure levels applying to these contaminant(s). RPD with a protection level greater than the hazard ratio should be selected in order to reduce the wearer’s exposure to below the OEL/WES/WEL. Refer Step 3.9 and select Hazard ratio measurement option.

Where no OEL/WES/WEL is published for the contaminant and there are no national or local regulations that relate to the contaminant, then control-banding method may offer a solution. Refer Step 3.8 or 3.9 and select control banding calculation option. If the control banding method cannot be used, then select an RPD with the highest protection class/factor level.

Contact an Occupational Hygienist or similar qualified/skilled professional to assist with measurement or estimation of contaminant levels. The assessed levels of contaminants, taking into account peak levels, can then be used to determine the required protection both on a routine basis and for emergencies.  You can find an Occupational Hygiene Consultant in the following organisation’s directory:

Reference/s for further information and detail:

  • AS/NZS 1715:2009 – Selection, use and maintenance – Section 4.2.2.3
  • SA/SNZ TS ISO 16975.1:2023 – Selection, use and maintenance – Section 7.3.2 and Annex C