12 charts

The data, visualised

Every bar and dot carries a source tag. Hollow or faded marks are estimates; warnings flag values that exist only inside a paper's plots.

Timeline VI-3 events CO / CO₂ Heat release Spread vs airflow O₂ limits Pressure Opposed vs concurrent Duct size Conditions map Saffire I–VI Pressure rise

Three decades of experiments

Each dot is a source on the platform it used. 1993 (Skylab review) → 2025 (ISS Combustion Integrated Rack).

ISSMirCygnusDrop towerParabolicGroundSkylabModel

The challenge brief mentions 1993–2024; the newest source (R10, ISS CIR poster) is from 2025. Faded dots have an inferred year.

Source

Saffire VI-3: smoke came late

Two-sided PMMA in a Cygnus at 54.6 kPa, 30.3 % O₂.

Burning · 780 s

Most hazardous gas released

637 s

Ignition

981 s

Smoke detected

1120 s

Flow 20 → 5 cm/s

1420 s

Flow off

0s300s600s900s1200s1500s

The paper gives no gas time-series; the red band shows only that most hazardous gas was released before smoke was detected at 981 s. The burning band uses the reported 780 s burn duration.

Source

CO₂ and CO against crew exposure limits

Rise at the Far-Field Diagnostics inlet, Saffire IV–VI.

CO₂ partial-pressure rise (mmHg)

CO rise (ppm)

Both PMMA tests (VI-3, VI-4) pushed CO₂ over the 1-hour limit and CO over the 24-hour limit.

Source

Heat release per Saffire test

Average and peak heat release as reported. Missing bars = '—' in the paper.

VI-2's average (3650 W) exceeds its peak (3217 W) in the same table row — listed under Conflicts. The headline uses the peak value.

Source

Flame spread rate vs airflow

Coloured by platform. Microgravity spread rises with airflow.

The Mir low-flow point is the mid-point of reported ranges (0.05–0.10 mm/s at 0.3–0.5 cm/s). Ground points are diamonds.

Source

Oxygen limit: Earth vs low gravity

Below each bar the material cannot burn. Shorter blue bar = more dangerous in space.

PMMA: 13.6 % in orbit vs 16 % on Earth — a −2.4 % oxygen margin of safety. A ground method extrapolates 13.4 % .

Getinax: Earth vs Mars gravity (no µg data). Nomex: no µg limit known — it did not ignite at 22.1 %.

Source

Lower pressure, slower flame — a ground proxy

Dotted lines: pressures that reproduce µg, Moon and Mars spread (thin cotton, R11).

R12 rates are derived from the reported 140 mm over 150 s / 450 s. R18 values below 60 kPa exist only in a plot.

In µg the pressure limit is far higher: flames died at 78 % of initial pressure vs 13 % in 1g .

Source

Opposed vs concurrent spread

SIBAL cotton-fiberglass fabric in real microgravity.

Concurrent flames also grew longer: ~40 mm vs 24 mm opposed in Saffire I .

Source

Duct and sample size change spread rate

Concurrent spread of the same fabric in different tunnels.

Saffire IV (30 cm duct vs 46 cm for I–III) values appear only in a plot and are not drawn. Wide samples in the big duct spread more slowly.

Source

Test conditions map

One dot per test or condition reported in the briefs. Faded = pressure not stated (drawn at 1 atm).

Source

Saffire I → VI

Six orbital fire experiments inside empty Cygnus cargo vehicles.

	Flew	Samples	Flow	Pressure	O₂	Spread	Heat	What we learned
I	2016–17	SIBAL 40.6 × 94 cm	20 cm/s	not stated	21.7 %	1.8 conc / 1.3 opp mm/s	≈ 1200 W	First large fire in orbit; flame stopped the moment airflow was cut
II	2016–17	9 samples 5 × 29 cm	20–25 cm/s	not stated	22.1 %	2.1 – 2.6 mm/s	460 W (PMMA)	Silicone did not burn; Nomex not ignited by pilot flame
III	2016–17	SIBAL 40.6 cm wide	25 cm/s	not stated	not stated	2.3 conc / 0.98 opp mm/s	—	Spread speed scales with airflow; duct size matters
IV	2020–21	SIBAL 50 cm, 2-sided PMMA 18 cm	20 cm/s	100 kPa	22 %	plot only	3150 W avg (IV-1)	Thick fuels: flames pinned at the leading edge
V	2020–21	Cotton jersey, PMMA	20 cm/s	70.7–72.6 kPa	25.4–26.2 %	plot only	2800 W avg (V-2)	Flame jumped a 4.5 cm gap; quiescent extinction not guaranteed
VI	Dec 2023	SIBAL, 2- & 1-sided PMMA	20 cm/s	54.1–55.2 kPa	28.8–31 %	not reported	3217 W peak (VI-2)	CO/CO₂ beyond crew limits; smoke seen late (981 s)

Saffire I

P n/a · 21.7%

Saffire II

P n/a · 22.1%

Saffire III

P n/a · O₂ n/a

Saffire IV

100 kPa · 22%

Saffire V

70.7 kPa · 25.4%

Saffire VI

54.1 kPa · 28.8%

■ pressure · ■ oxygen — the series moves toward the low-pressure, oxygen-rich exploration atmosphere.

Source

Pressure rise in a sealed chamber (sizing the relief valve)

1g tests in a 6.35 m³ chamber. Green = mitigation (heat exchanger, quench bars, slower burns).

The 3.527 psi SIBAL run popped the chamber relief after the L2 heat exchanger's coating ignited — a reminder that mitigation hardware is itself fuel. Starting at lower pressure also cut ΔP linearly (0.921 → 0.541 psi from 11.7 → 5 psia).

Source