Read this story in the '60s, although I think it dated from the '50s. I am certain it appeared in either Amazing or Fantastic (these magazines were half reprint 1965-69), or one of the reprint digests put out by the same publisher, Ultimate. American author, written in English.
Two spacemen have crash-landed on a planet that seems to be one giant swamp; the air is filled with nasty little midge-like creatures that are so oppressive the men are forced to wear space suits even though the atmosphere is breathable.
There is some explosive element (hydrogen?) in the planet's atmosphere that will explode if it is exposed to an open flame, so they can't repair their ship, meaning they are stranded forever. Humanoid creatures inhabit this planet, but the same atmospheric element somehow oppresses their minds, preventing them from making full use of their intelligence.
Knowing they are doomed, the two Earthmen decide (without consulting the natives!) to commit suicide by blowing up the whole planet! One opens his helmet and lights a cigarette, but the result is not as expected - the flame spreads out slowly, burning off his eyebrows but otherwise not harming him.
The upshot: the element is burned away, the midges are gone, the natives can make use of their full intelligence and the astronauts can repair their ship. Happy ending.