Posted By Ken Taylor Depends upon what is burning, Ciaran, but we need to consider both toxic effects and asphyxiation. Typical contents may be: CO (unconscious after 2/3 breaths at c1.28% with death in 1-3 mins) CO2 (may lose consciousness in a few mins at c9%) Low O2 (12-16% loss of muscular coordination; 6-10% nausea vomitting, cannot move freely; <6% convulsions followed by cessation of heart function and breathing). Other toxic gases present may be: Acetic acid, Acrolein, Ammonia, Hydrogen chloride, Hydrogen cyanide, Hydrogen sulphide, Nitrogen dioxide, Sulphur dioxide, etc, etc. You can look up individual toxicities, but this will not take account of the synergistic effects. Needless to say, on top of all this we have to also consider the heat effects including damage to the brain and lung linings!