The National Institute for Occupational Safety and Health (NIOSH) tests and approves self-contained self-rescuer respirators (SCSRs) used when escaping from mining accidents. All SCSRs use a mouthbit-noseclip interface which prevents verbal communication between escaping miners. A nosecup has been commercially developed to allow verbal communication and may be manually applied to NIOSH-approved SCSRs. PURPOSE: To determine the metabolic effects of an experimental nosecup on the performance test criteria applied to three different modified SCSRs. METHODS: The NIOSH Automated Breathing and Metabolic Simulator, a computerized system which simulates human oxygen consumption (VO2), carbon dioxide production (VCO2), minute ventilation (VE), and breathing waveforms, was used to test SCSRs with and without the nosecup. The protocol was a SCSR performance test with three periods of duration, VO2, VCO2, VE, and breathing frequency, respectively, repeated in sequence until the SCSR reached termination criteria per federal regulations (42CFR84): 5 minutes, 3 L/min, 3.2 L/min, 65 L/min, 25 breaths/min; 15 minutes, 2 L/min, 1.8 L/min, 44 L/min, 20 breaths/min; and, 10 minutes, 0.5 L/min, 0.4 L/min, 20 L/min, 12 breaths/min (all STPD). RESULTS: To characterize effects of the nosecup, results by each SCSR at each VO2 were averaged then subtracted from the averaged SCSR+nosecup data. Positive results indicate increases and negative results indicate decreases caused by the nosecup. The following results at each level of energy expenditure (VO2, L/min) are average-inhaled CO2 concentration (%); average-inhaled O2 concentration (%); peak inhalation pressure (mmH2O); peak exhalation pressure (mmH2O); peak inhaled dry-bulb temperature (degrees C); and, peak inhaled wet-bulb temperature (degrees C), respectively: 3 L/min, 0.53%, -33.7%, 49 mmH2O, 40 mmH2O, -5 degrees C, -3 degrees C; 2 L/min, 0.89%, -30.87%, 20 mmH2O, 13 mmH2O, -7 degrees C, -4 degrees C; and, 0.5 L/min, 0.56%, -36.7%, -6 mmH2O, -31 mmH2O, -5 degrees C, -2 degrees C. Using criteria in 42CFR84, the nosecup increased the duration of one SCSR by 6 minutes, decreased the duration of another SCSR by 13 minutes, and caused a hypoxic condition (FIO2 < 19.5%) early in the evaluation of the third SCSR at 6 minutes. CONCLUSION: An experimental nosecup may have adverse effects on the performance by 2 of 3 NIOSH-approved SCSRs.