I need a situation that I'm not sure how to research. CW fire, and burns. Info needed about gasses and fire/burns in the following parameters….

(I have someone in an advanced alien tech space ship survive a 'fall' into a planet. It will probably be in a questionably old and somewhat damaged space ship, during low-zero gravity on the way to the planet, and some level of gravity while entering into a planet's atmosphere. The atmosphere and planet itself are at least temporarily habitable for humans.)

Is there a gas/combination of gases that are less flammable than our atmosphere, that humans can breathe?

The mixture COULD

1. Slowly suppress breathing

2. Cause unconsciousness after at least 5-15 minutes?

3. Potentially combust/explode after some time

The air situation could be our atmosphere/oxygen mix being slowly mixed with some other gas(es). It doesn't matter if the gasses would be somewhat explosive at the end of the change/mixture.

Possible burn scenarios include

1. A fire ball pushes through

2. I go star trek and explode some interfaces

3. Something that burns on contact with skin spills through the area to partially cover someone.

It needs to theoretically be able to survive with limbs intact, but still be possible for fire/burns.