This report describes a National Institute for Occupational Safety and Health (NIOSH) and Mine Safety and Health Administration (MSHA) investigation assessing the prevalence of a lack of sufficient start-up oxygen in CSE SR-100 self-contained self-rescuer (SCSR) devices. The availability of sufficient start-up oxygen is critical to the performance of the SR-100. As part of a routine field testing program of SCSRs used in coal mines, NIOSH and MSHA detected two SR-100s that lacked sufficient start-up oxygen. CSE Corporation subsequently discovered one SCSR that lacked sufficient start-up oxygen in that company's internal quality control program and voluntarily stopped further production and sales of SR-100s. NIOSH developed a protocol to test for the presence of start-up oxygen in field-deployed SR100s. The purpose of the test was to determine if the failure rate of the start-up oxygen in the population of 70,000 field-deployed units exceeded 1%. NIOSH and MSHA used American Society for Quality (ASQ), Sampling Procedures and Tables for Inspection of Isolated Lots by Attributes (ASQC Q3-1988). In assessing the SR-100s, if no more than 3 failures of start-up oxygen occurred in the 500-unit random sample, the SR-100 could be accepted as meeting the Limiting Quality (LQ) rate of 1.25% for start-up oxygen performance.