It's a good question, but you're worried overmuch. Liquid Wrench is
flammable, but it's not gasoline, nor anything close to it. Generally a
film of it on metal parts will not support combustion -- you might get a
brief dark-blue flame surrounding the oiled part, for less than a second,
but nothing worth worrying about. Make sure there's good ventillation,
because you will probably get some smoke and/or "hot Liquid Wrench" fumes.

I've had a lot more luck with PB blaster, especially in combination with
heat.

It is not that flammable.  I wouldn't worry about it.  I've started small
fires with it but it won't explode or anything and you can blow out the
flames easily.  Of course, you can avoid starting these fires by spraying
the bolt AFTER torching it instead of immediately before...

I have found that using heat first, then a penatrant, made more sense.

Ken