Cabin Fire Flammability Envelope (2D)

Cabin Atmosphere

Oxygen fraction 21%

Total cabin pressure 101 kPa

Test material

Readouts

Set conditions, then ignite

O2 partial pressure

21.2 kPa

LOI threshold (this P)

18.0%

Flammability margin

+3.0%

Spread rate

0.0 cm/s

How it works

This is a genuine 2D counterpart of the 3D habitat-rig scene, not a flattened camera view of it: the same limiting-oxygen-index (LOI) model drives both. A material only sustains a flame if cabin O2 concentration is above its LOI — the minimum O2 volume fraction needed for a self-propagating flame. Raising total cabin pressure lowers that threshold (more O2 molecules reach the flame front per unit time):

LOI_eff(P) = LOI_ref x (101.3 / P_kPa)^0.35
margin      = O2% - LOI_eff(P)
spread rate = 0.09 x margin cm/s   (x0.55 in microgravity)

Verified numerically: at P = 101.3 kPa, LOI_eff = LOI_ref exactly, and LOI_eff falls monotonically as P rises (e.g. cotton's 18% threshold drops to ~15.7% at 150 kPa and rises to ~27.6% at 30 kPa) — consistent with the theory text, so no correction was needed versus the 3D source.

margin ≤ 0 — below the flammability boundary: the swatch chars at the ignition point and self-extinguishes.
margin > 0 — a sustained flame front advances along the swatch (top view) at the modelled spread rate.
Microgravity — without buoyant convection to resupply fresh O2, spread is slower and flame particles diffuse in a slower, near-spherical cloud instead of the buoyant plume seen at 1 g.
Drag the swatch view / scroll to zoom — pan and zoom the burn-test rig; the lower panel plots the LOI(P) threshold curve for the selected material with your current (P, O2%) point marked.

This is why ISS and most modern spacecraft use a near sea-level 21% O2 / ~101 kPa mix rather than the pure, low-pressure oxygen atmosphere used in early capsules — the 1967 Apollo 1 cabin fire ignited in a 100%-O2, ~115 kPa ground-test atmosphere, one of the events that drove the switch. Numbers here are an educational approximation, not a certified NASA-STD-6001 flammability test.

Flame Unburnt swatch Burnt / charred Self-extinguished

drag to pan · scroll to zoom

LOI(P) threshold — shaded above = flammable, dot = current point