This aspect of respiratory protection is a SAFETY CRITICAL path when using Air Purifying Respirators (APRs), and in my experience, it is rarely done correctly when it is done at all. I teach my program administrators to do precisely what NIOSH has been stating since 2004. When using the Change Out software, use 1 ppm below the IDLH of the chemical. The software will not allow us to establish a change-out schedule at or above the chemical’s IDLH, because we can only use a SAR/SCBA in an IDLH atmosphere. But I see businesses using something less than IDLH to base their changeout schedule on and this is NOT derived from IH sampling data. Here is what NIOSH says…
Employers must establish a cartridge/canister changeout schedule which is based on the service life of the cartridge/canister under the conditions of use. The changeout schedule can be determined with the assistance of the respirator manufacturer (changeout software or other tools) or by conducting service life tests. Information obtained on the service life of the cartridge/canister under conditions of intended use must be evaluated regardless of the odor warning properties of the chemicals. These evaluations must be based on all gases and vapors present at the temperature and relative humidity extremes (high and low) in the workplace. NIOSH recommends that when the employer or a representative of the employer conducts service life tests, the challenge concentrations of the gases and vapors should be at least the maximum use concentration (MUC) of the respirator and that a safety margin be applied when evaluating service life data. OSHA provides information on determining change schedules on their website (www.OSHA.gov/SLTC/etools/respiratory/change-schedules.html). In humid workplaces where organic vapor cartridges are used to protect workers from a single volatile source, software (CD-ROM) for predicting service life can be ordered from NIOSH by calling 1- 800-356-4674. The software can also be downloaded from the OSHA website at: http://www.osha.gov/SLTC/etools/respiratory/advisor_genius_wood/breakthrough.html. This information can be used to set up cartridge replacement schedules and should be used in conjunction with sensory warning properties.