The other day I was driving down the road when suddenly there was an
extremely loud blast inside my car, and I saw a flash too.  It wasnt a
backfire or anything like that, it was directly inside the drivers
compartment, and sounded like a gun or firecracker.  Luckily I was on
a gravel backroad with no other traffic, because I slammed on the
brakes and stopped the car.  I had no idea what had happened and
looked around for anything burning or gunshot holes in the windows or
something.  The engine was still running and sounded ok, nothing
inside the car was burning, no broken windows or anything else.  I
stopped the car and got out and looked over the exterior of the car,
tires, etc.  Then I looked under the hood.   I finally got back in the
car, started the car and drove off in a very nervous manner.  

I think I finally solved the explosion today.  When I got in the car,
I noticed the bottom half of one of those Bic lighters on the floor
near the gas pedal.  I looked at it, and it was badly cracked and I
could see it exploded.  Apparently that lighter fell down the
defrosters, and got hot enough to explode.  I dont know if the piece
fell out of the floor heater duct, or if the explosion blew a hole in
the defroster ductwork.  I plan to see if I can look up under the dash
and look for a hole, but the main thing is that I think I solved the
mystery explosion.  I think I need to put some screen over those
defroster holes, because something is always falling in there, and
this time is could have been quite dangerous.

Just wanted to let everyone know about this.  The car is a 89 Caprice
and the lighter a Baby Bic.

Mark