Since it's around gas, seening as how I haven't ever tried to set the stuff on fire :eek: I don't know how flamable it is. What you might want to consider as an alternitive is Borax or Comet powder cleanser.
Of course, what you want to do is try and find the enterence point and, if you have ants, their trail so you can follow it straight to the source.
If it's roaches, use Borax and make balls out of it.
Basically, all you do is make a dough out of the Borax with flour and water, oh, and a bit of sugar, roll it up into little balls, stick it behind the stove, in the back of the cupboards, anywhere where the bugs would hide and where any children and pets can NOT get to it.
If you want to try Comet (or any powder cleanser that has bleach in it, Ajax works well also) just sprinkle a line around the base boards of whatever room(s) you want to treat as well as around the foundation of your house. Don't vacuum it up until either the bugs are gone, the powder is gone or until you are ready to apply a fresh line. Bugs don't like the stuff and they won't cross it; the bleach burns their litlle bug feet.
Cedar oil (or chips, as long as they are *real* cedar) works awesome at killing and keeping unwanted critters outside where they belong. Just don't get cedar near your inverts or reptiles.