SCBA Cylinder Work Time
Time to low-air alarm and to empty from rated scf, current pressure, alarm pressure, and consumption rate.
Example
You enter
- Cylinder rated volume (scf) 88
- Rated pressure (psi) 4500
- Starting pressure (psi) 4500
- Low-air alarm pressure (psi; typically ~33% of rated) 1485
- Consumption rate (L/min; ~40 light, ~100 heavy) 40
You get
- Available scf to alarm 59.0
- Time to low-air alarm 41.74
- Time to empty (math aid only) 62.3
Checked against published worked examples from: NFPA / NIOSH.
Details, formula, and sources
ScopeNFPA 1981 governs cylinder ratings; exit at the alarm, not at empty.
Formula or tableavailable_scf_to_alarm = (P_start - P_alarm) / P_rated * V_rated. time_to_alarm_min = available_scf / consumption_scfm. Time-to-empty is a math aid only; exit at the low-air alarm.
Source and editionNFPA 1981-2019; NIOSH 42 CFR 84.
Free accessnfpa.org/freeaccess for NFPA 1981 TOC; ecfr.gov for 42 CFR 84.
What governsEstimate. AHJ and licensed fire protection engineer govern.
API field namesV_rated_scf, P_rated_psi, P_start_psi, P_alarm_psi, consumption_lpm, available_scf_to_alarm, time_to_alarm_min, time_to_empty_min
- Rated scf manufacturer-published per cylinder rating (e.g., 88 scf for 60-min 4500 psi)manufacturer technical bulletin
- Low-air alarm typically ~33% of rated pressureNFPA 1981 §6.2 alarm threshold
- Exit policy NFPA 1500 / incident-command practice trains members to exit at the alarm, not at emptyNFPA 1500