The National Institute for Occupational Safety and Health (NIOSH or the Institute) wishes to inform users of a recent investigation involving a dust/mist filter which was approved under Title 30, Code of Federal Regulations (CFR), Part 11. The Institute was recently asked to investigate a report involving the presence of a fine yellow-white dust on "packaged", unused dust/mist filters that were approximately four years old. Respirator manufacturers have not been able to produce filters, labeled as NIOSH Approved, under the requirements of 30 CFR Part 11 since July 10, 1998. Therefore, any dust/mist filters approved under 30 CFR Partll, remaining in the field, are at least four years old. The condition was observed in a limited number of dust/mist filters. However, it is possible that other filters (Dust, Fume, and Mist; Pesticide; Paint Spray Respirators and chemical cartridge respirators) which were processed using the same methods might also be affected. Examination of the sample filter received by maSH suggests that the zinc/calcium salt resin that is applied as a coating to the individual filter fibers can crumble, resulting in small particles of the resin being released. The Institute has been unsuccessful in its attempt to obtain additional samples of this filter in order to determine whether or not these filters would meet the performance requirements of 30 CFR Part 11. There are no known health risks associated with exposure to the zinc/calcium salt resin (CAS # 68188-23-8). The Institute recommends that any respirator user who is still using filters produced and approved under 30 CFR Part 11 should discontinue the use of these filters and replace them with filters approved under the enhanced filter penetration requirements of 42 CFR Part 84. Respirator users who have questions about the performance and/or useful shelf life of filter respirators approved under 30 CFR Part 11 should contact the manufacturer directly. THIS ABSTRACT PRESENTS THE FULL TEXT OF THE NOTICE.