In 1998, the Occupational Safety and Health Administration (OSHA) updated its general industry respiratory protection standard, 29 CF.R. § 1910.134. The use of airpurifying respirators (APR) was affected by a significant policy change that requires employers to provide respirators equipped with a NIOSH certified end-of-service-life indicator (ESLI) for the expected contaminant, or to implement a change schedule for canisters and cartridges based on objective data showing that the cartridges are effective in preventing exposure to the contaminant, and have an adequate service life.
However, questions continue to be raised about the permissibility of using APR in certain industrial applications where workers may be exposed above allowable limits to substances with poor warning properties. This paper outlines some of the important considerations such as: what data are necessary to demonstrate that the respirator cartridge/filter is quantitatively effective at removing the contaminant of interest, and what data are needed to demonstrate that employee exposures to a contaminant are within the range that the respirator can effectively remove it from the inhaled air stream. These considerations must be taken into account to assure that APR are properly selected and used to provide protection against substances with poor warning properties. Methylenediphenyl diisocyanate (MDI) and polymeric products made from MDI will be used as an example in this discussion.