From Unofficial Stationeers Wiki
Different ratios of Volatiles and Oxygen will produce different temperatures and pressures during combustion. Combustion will create a large amount of Heat, pressure, and Carbon Dioxide. This reaction is useful inside a Furnace for smelting ores and creating alloys, but can be catastrophic when inside a Canister or a room. Currently as of version v0.1.1089.5513, it is labeled in the atmospheric analyzer as H2, but it is not Hydrogen.. When burned, it produces heat, Pollutants, and Carbon Dioxide in the following reaction:
2 [Volatiles] + 1 O2 → 3 X + 6 CO2 + Heat
This reaction is inconsistent with volatiles being simple hydrocarbons (too much CO2 is produced), but it may be consistent with more complex organic molecules. The reaction appears to only take place with specific quantities of gas, so Oxygen is often left over even when there is an excess of volatiles.
Volatiles have a specific heat of 20.4 Joule / mol.