Reliability assurance standards for certifying self contained rescue (SCSRs) and filter self rescue respirators (FSRs) for use by miners were discussed. The rationale for establishing reliability standards for SCSRs and FSRs was presented. A need for incorporating reliability engineering concepts into the respirator certification process arose as a result of several reports of performance failure of SCSRs and FSRs that were received from the mining industry in the 1980s. The performance failures were determined to be related to reliability issues associated with product design and performance, conditions of use and storage, and duration of use or product age in spite of the fact that the respirators met the quality standards of the manufacturers. Reliability assurance was discussed in terms of the performance of SCSRs and FSRs and other respiratory protective equipment. NIOSH has emphasized four elements in establishing guidelines for assuring the reliability of SCSRs and FSRs: probability, failure free performance of intended function, conditions of use, and duration of use. It was noted that reliability assurance goes a step beyond quality control because it provides engineering proof of the performance capability of the products. This proof has become an important fifth element in defining the NIOSH reliability requirements. The basic need for establishing reliability engineering standards for FSRs and SCSRs was illustrated using summaries of anecdotal reports of performance failures associated with conditions of use, product age, design, or a combination of these. A common factor identified from the reports was the need for more reliable respirators. Guidelines for certifying the reliability of FSRs and SCSRs developed by NIOSH, the Mine Safety and Health Administration, and the Bureau of Mines were discussed. Future changes anticipated in Part II of Title 30 of the Code of Federal Regulations, which dealt with respirator certification standards, were considered.