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MicroFire Atlas

Experiment family · large-scale fires

Real fires inside a spacecraft.

After a Cygnus cargo ship left the space station, empty of crew, NASA lit fires inside it on purpose and watched them spread. NASA calls Saffire the first time a large-scale fire was set on purpose inside a spacecraft in orbit.

20
runs, each from a NASA table
40.6 × 94 cm
largest sample (Saffire 1)
54.1 kPa
lowest pressure (VI-2)
3
NASA documents, every value cited

Background scenery is an illustration. Every number on this page comes from NASA.

607080901001520253035Pressure, kPa (sea level is about 101)Oxygen, %Exploration atmosphere A (34 %, 56.5 kPa)Alternate atmosphere (28.5 %, 66.2 kPa)BASS-II test GMT45-T1: 18.5 % O₂ at 101.325 kPaBASS-II test GMT45-T2: 18.5 % O₂ at 101.325 kPaBASS-II test GMT45-T4: 18.7 % O₂ at 101.325 kPaBASS-II test GMT45-T15: 18.7 % O₂ at 101.325 kPaBASS-II test GMT100-T5: 18.8 % O₂ at 101.325 kPaBASS-II test GMT100-T6: 18.8 % O₂ at 101.325 kPaBASS-II test GMT100-T13: 17.5 % O₂ at 101.325 kPaBASS-II test GMT100-T16: 17.6 % O₂ at 101.325 kPaBASS-II test GMT175-T9: 16.4 % O₂ at 101.325 kPaBASS-II test GMT175-T10: 16.4 % O₂ at 101.325 kPaBASS-II test GMT175-T18: 17.4 % O₂ at 101.325 kPaBASS-II test GMT178-T11: 17.1 % O₂ at 101.325 kPaBASS-II test GMT178-T12: 16.8 % O₂ at 101.325 kPaBASS-II test GMT178-T14: 16.9 % O₂ at 101.325 kPaBASS-II test GMT178-T17: 16.9 % O₂ at 101.325 kPaBASS-II test GMT190-T19: 17.2 % O₂ at 101.325 kPaBASS-II test GMT190-T20: 17.2 % O₂ at 101.325 kPaBASS-II test GMT190-T21: 17.2 % O₂ at 101.325 kPaBASS-II test GMT190-T22: 17.1 % O₂ at 101.325 kPaBASS-II test GMT190-T23: 17.2 % O₂ at 101.325 kPaBASS-II test GMT190-T24: 18.2 % O₂ at 101.325 kPaBASS-II test GMT216-T25: 20.8 % O₂ at 101.325 kPaBASS-II test GMT216-T26: 20.8 % O₂ at 101.325 kPaBASS-II test GMT216-T27: 20.7 % O₂ at 101.325 kPaBASS-II test GMT216-T28a: 20.7 % O₂ at 101.325 kPaBASS-II test GMT216-T28b: 20.7 % O₂ at 101.325 kPaBASS-II test GMT216-T29: 20.7 % O₂ at 101.325 kPaBASS test GMT96-T8: 21 % O₂ at 101.325 kPaBASS test GMT96-T7: 21 % O₂ at 101.325 kPaBASS test GMT131-T10: 21 % O₂ at 101.325 kPaBASS test GMT222-T11: 21 % O₂ at 101.325 kPaBASS-II test B1: 20.6 % O₂ at 99.35 kPaBASS-II test B2: 20.6 % O₂ at 99.35 kPaBASS-II test B3: 20.9 % O₂ at 99.35 kPaBASS-II test B4: 20.6 % O₂ at 99.35 kPaBASS-II test B5: 20.9 % O₂ at 99.35 kPaBASS-II test B6: 20.1 % O₂ at 99.35 kPaBASS-II test B7: 20.6 % O₂ at 99.35 kPaBASS-II test B8: 20.1 % O₂ at 99.35 kPaBASS-II test B9: 20.1 % O₂ at 99.35 kPaBASS-II test B10: 20.1 % O₂ at 99.35 kPaBASS-II test B11: 20.1 % O₂ at 99.35 kPaBASS-II test B12: 20.5 % O₂ at 99.35 kPaBASS-II test B13: 20.1 % O₂ at 99.35 kPaBASS-II test B14: 14.1 % O₂ at 99.35 kPaBASS-II test B15: 20.1 % O₂ at 99.35 kPaBASS-II test B16: 16.5 % O₂ at 99.35 kPaBASS-II test B17: 16.6 % O₂ at 99.35 kPaBASS-II test B18: 16.5 % O₂ at 99.35 kPaBASS-II test B19: 16.4 % O₂ at 99.35 kPaBASS-II test B20: 16.5 % O₂ at 99.35 kPaBASS-II test B21: 19.8 % O₂ at 99.35 kPaBASS-II test B22: 19.8 % O₂ at 99.35 kPaSaffire IV sample IV-1: 22 % O₂ at 100 kPaSaffire IV sample IV-2: 22 % O₂ at 100 kPaSaffire V sample V-2: 26.2 % O₂ at 70.7 kPaSaffire V sample V-3: 25.4 % O₂ at 71.3 kPaSaffire V sample V-4: 25.7 % O₂ at 72.6 kPaSaffire VI sample VI-2: 31 % O₂ at 54.1 kPaSaffire VI sample VI-3: 30.3 % O₂ at 54.6 kPaSaffire VI sample VI-4: 28.8 % O₂ at 55.2 kPaLUCI SIBAL (simulated lunar gravity): 20 % O₂ at 101.3 kPaLUCI PMMA rod (simulated lunar gravity): 20 % O₂ at 101.3 kPa
Saffire runBASS-II testLUCI burn (simulated lunar gravity)Dashed rings: two NASA exploration-atmosphere scenarios (not tests, and not a universal Moon-base specification)

How close does the evidence get to the exploration atmospheres NASA has studied?

Every BASS-II test ran near sea-level pressure. Saffire IV to VI lowered the pressure and raised the oxygen. Saffire VI reached about 55 kPa with 29 to 31 % oxygen: close to NASA's proposed 34 % at 56.5 kPa, but still not there, and still in microgravity, not lunar gravity.

That is why the Evidence Ladder calls Saffire VI the closest analogous evidence, never direct evidence.

Why Saffire is kept separate from BASS-II

  • Scale. Samples up to 94 cm long, against 10 cm or less in BASS-II.
  • Place. A flow unit inside a cargo ship, not a glovebox duct on the station.
  • Air. Pressure and oxygen were changed for later flights; BASS-II stayed near 1 atm.

The atlas compares the two families on shared dimensions, but never merges their rows into one table.

Saffire 1 and 2 (Saffire I to III flew in 2016 and 2017)

One wide cotton-fiberglass sheet burned for seven minutes, then nine small samples, including silicone, which NASA found appeared less flammable in microgravity at the flow speeds tested.

Saffire IV and V (2020 to 2021)

Thick fuels and longer burns, and the first runs at lower pressure with more oxygen.

Saffire VI

Pressure near 55 kPa and oxygen near 30 %, the closest any test in this atlas gets to the exploration atmospheres NASA has studied.

What NASA concluded

  • “For the first time, a large-scale fire was intentionally set inside a spacecraft while in orbit.”
    Reported observationSaffire I-III results, PDF p. 26
  • “Unlike 1-g, the results revealed that a steady flame could be achieved even for a wide sample burning in concurrent-flow.”
    Reported observationSaffire I-III results, PDF p. 26
  • “The flames spread more slowly than prior tests in smaller ducts. This behavior of the flame demonstrated the importance of confined spaces for potential spacecraft fires.”
    Authors' interpretationSaffire I-III results, PDF p. 26
  • “Flammability of silicone in microgravity appears to be reduced compared to normal gravity, at least for the flow speeds tested.”
    Authors' interpretationSaffire I-III results, PDF p. 26
  • “Despite this significant heating load, the fabric was not ignited.”
    Reported observationSaffire I-III results, PDF p. 25
  • “Extinguishment of thin charring fuels at increased oxygen cannot be assumed to occur rapidly in quiescent conditions.”
    Authors' interpretationSaffire IV and V results, PDF p. 7
  • “Flames on thick fuels in concurrent flow did not spread and were instead pinned to the leading edge of the sample”
    Reported observationSaffire IV and V results, PDF p. 13
  • “In one case, a flame was seen to jump a 4.5 cm gap to ignite a previously warmed PMMA surface.”
    Reported observationSaffire IV and V results, PDF p. 13
  • “Collectively these results demonstrate that the human hazard from a fire in a spacecraft is very similar to terrestrial fires where the heat from the fire is not the principal hazard and rather the smoke and gaseous products are a much greater concern.”
    Authors' interpretationSaffire VI results, PDF p. 6
  • “The smoke from the fire event was readily detected by an ionization detector and a light scattering system but a typical alarm threshold was only achieved at 981 seconds.”
    Reported observationSaffire VI results, PDF p. 6
  • “However, the ambient concentrations of carbon monoxide and carbon dioxide rose significantly with the PMMA tests exceeding the 1-hour carbon dioxide limit and the 24-hour carbon monoxide limit.”
    Reported observationSaffire VI results, PDF p. 6
  • “Further work will be needed to extend these results to the partial gravity environment expected on future mission to the moon and Mars.”
    Authors' interpretationSaffire VI results, PDF p. 6
  • “Practical scale fires ranging from 1.5 to 3.2 kW were tested in unmanned spacecraft with free air volumes of 17 to 19 cubic meters.”
    Reported observationSaffire VI results, PDF p. 6