How long will an SCBA last?
Self-contained breathing apparatus duration depends on usable free air in the cylinder and the wearer’s consumption rate (work rate, fitness, stress).
Duration (minutes) = Usable free air (litres) ÷ Consumption (L/min)
Free air ≈ water capacity (L) × filling pressure (bar) for ideal gas estimate; subtract a reserve pressure (often ~55 bar) so you do not plan to breathe the cylinder empty.
SCBA Duration Calculator
SCBA · breathing air time
Estimate usable duration from free-air volume and consumption rate. Exit IDLH atmospheres with reserve remaining.
Formula: Duration (min) = Usable free air (L) ÷ Consumption (L/min)
- Heat, stress, and leaks raise real consumption above planning rates.
- Leave the hazard with low-air warning and reserve still available.
- Cylinder “30-minute” ratings assume a standard work rate.
Typical planning consumption rates often fall around 40 L/min moderate work to 100+ L/min heavy work — use your brigade or manufacturer figures.
Frequently asked questions
Why is rated duration shorter in real fires?
High work rate, heat, stress, and leaks raise consumption. Always leave the IDLH atmosphere with reserve air remaining.
Is free air exactly V × P?
It is a common estimate. Follow cylinder markings and manufacturer tables for the exact set.
Cylinder “30-minute” rating?
Manufacturer ratings assume a standard consumption (often 40 L/min). Heavy work shortens that dramatically — recalculate.
Can I use this for escape sets?
Escape sets are sized for egress only. Do not treat them as working SCBA duration.
