The NIOSH Respirator Selection Logic (RSL) relies entirely on whether the airborne concentration of a contaminant exceeds a defined exposure limit (such as the NIOSH Recommended Exposure Limit [REL] or OSHA Permissible Exposure Limit [PEL]), regardless of what the chemical’s vapor pressure is. However, vapor pressure plays a decisive role in selecting a respirator, particularly in determining the contaminant’s physical state and whether chemical cartridges can be safely used. Here is how vapor pressure impacts the NIOSH selection framework: