Mission scenarios
ISS, Moon or Mars?
Gravity changes how a fire gets its oxygen. Pick a destination to see the equivalent Earth test pressure, which materials the sources say stay safe, and what we know about the low-pressure, high-oxygen atmospheres planned for exploration.
Destination
ISS
- Gravity
- ≈ 0 g (microgravity)
- Equivalent Earth test pressure
- ≈ 33 kPa
- ≈ 33 kPa on Earth gives similar concurrent spread (thin cotton)
- Cabin atmosphere
- ≈ 101 kPa, ≈ 21 % O₂, ventilation ~10–20 cm/s
Thin fabric · 10 cm/s · 21 % O₂, 101 kPa
Burning — Blue with a yellow tip, hemispherical
Illustrative flame from the Flame Lab modelOpen in Lab
Which materials stay safe on the ISS?
Only what the sources state. 'No data' means the briefs do not cover it.
PMMA
BurnsSteady at 13.6 % O₂ — below its 16 % 1g limit.
SIBAL / cotton
BurnsSpreads in both opposed and concurrent flow.
Nomex HT90-40
Did not burnNot ignited by a 460 W pilot flame in Saffire II; did not burn at 21–22 % on ISS.
Silicone
Did not burnNone of the Saffire II silicone samples burned.
Ultem
Did not burnDid not burn at 21–22 % O₂, ~15 cm/s.
Why gravity matters here
“Spacecraft environments generally present low velocity air currents produced by ventilation and heating systems (of the order of 0.1 m/s), and fluctuating oxygen concentrations around that of air due to CO2 removal systems.”
“A reduction in ambient pressure to 33 kPa results in similar flame spread rates as those observed in microgravity.”
Getinax: a material that becomes safer with less gravity
Flammable on Earth above 19 % O₂, yet rated safe on the Moon and non-flammable up to 23 % O₂ on Mars — partial gravity can reduce flammability for some materials.
“For example, Getinax, which is flammable on Earth (eli m- 19%), will be a safe material for Moon application (g=162 cm/sec2).”
“On Mars, where g=376 cm/sec 2, Getinax will not be flammable up to 23% of oxygen concentration.”
Exploration atmospheres: low pressure, high oxygen
Saffire V and VI burned materials at 54–73 kPa and 25–31 % O₂ — close to planned Moon/Mars habitat air.
| Test | Pressure | O₂ | |
|---|---|---|---|
| V-2 | 70.7 kPa | 26.2 % | |
| V-3 | 71.3 kPa | 25.4 % | |
| V-4 | 72.6 kPa | 25.7 % | |
| VI-2 | 54.1 kPa | 31 % | |
| VI-3 | 54.6 kPa | 30.3 % | |
| VI-4 | 55.2 kPa | 28.8 % | |
| Planned SEA | ~60 kPa | ~34 % |
What happened
“They include microgravity, low velocity flows, and potentially low pressure (~60 kPa) and elevated oxygen concentration (~34%).”
“This is an important fire safety issue for space exploration vehicles and space habitats which will very likely have different environments than those currently used on the International Space Station, such as reduced pressure and enriched oxygen concentration (SEA).”
“Extinguishment [7]. Extinguishment of thin charring fuels at increased oxygen cannot be assumed to occur rapidly in quiescent conditions. Saffire V-2 (cotton jersey): low flow for 35 s; flow was off for 70 seconds. Plot axes: Flow Speed (cm/s), Sample Temperature (deg C), Relative Time (s), Sample Thermocouple #8. Media: 10 X speed video, top view.”
“For the PMMA tests, ambient concentrations of carbon dioxide exceeded the 1-hour carbon dioxide limit.”
Highest peak heat release (3217 W, VI-2) and the CO/CO₂ limit exceedances all came from the low-pressure, oxygen-rich Saffire VI runs.