How is a cartridge change out schedule calculated?

In the absence of an ESLI, a cartridge/canister change out schedule is required for gas- and vapor-removing respirators and should be based on objective information or data that will ensure that canisters and cartridges are changed before the end of their service life. Usually, manufacturers have software to estimate a change out schedule for their cartridges or canisters. Changeout schedules are not the same from one manufacturer’s cartridges or canisters to that of another manufacturer. This is because the volume and type of adsorbent varies between manufacturers. Additionally, the Occupational Safety and Health Administration (OSHA) has mandatory changeout schedules for cartridges for certain substances like acrylonitrile, benzene, butadiene, formaldehyde, vinyl chloride, and methylene chloride. Workers depending on respiratory protection who are exposed to any of these contaminants at or above the OSHA Permissible Exposure Limit (PEL) must change cartridges/canisters according to OSHA’s requirements. In any case, workers should consult their Respirator Program Administrator regarding when to change their cartridges/canisters.

OSHA provides guidance on using mathematical models to predict the service life of organic vapor respirator cartridges when used for protection against single contaminants. You can also find the service lives for respirator cartridges intended to protect against selected gases already calculated in a table. You can calculate others using a computer program called Advisor Genius. OSHA suggests that you reduce the service life estimate by some safety factor and document the change schedule in your written respiratory program.

OSHA has no accepted way to determine a cartridge’s service life when exposed to mixtures; computer models have been developed that can estimate service life if you know all the canister physical attributes, environmental factors, contaminants and levels, and work rates [Note: Other research has been conducted to develop models for contaminant mixtures, but they have not yet been adopted by OSHA.] NIOSH has developed a computer tool for estimating breakthrough times and service lives of air-purifying respirator cartridges manufactured to remove toxic organic vapors from breathed air that can be used with the cartridge/canister manufacturer’s recommendations for multi-gas use of the specific canister/cartridge being used.

If respirators are required in your workplace, OSHA mandates that your employer establish and maintain a respiratory protection program that must describe the information and data relied upon and the basis for the canister and cartridge change schedule. Because of the complexity of factors involved in determining canister changeout schedules, consult your Respirator Program Administrator.