Expert: Mike Fulcher - 6/16/2008

Question
I have a butane lighter that I'd like to store in my souvenirs box and I'm trying to decide whether there are any realistic safety risks to storing it indefinitely as it is (without emptying it beforehand, which takes a very long time to do by hand). I'm hoping you may be kind enough to follow my reasoning so far and offer your take on this...

Now as far as I've figured this out, for the butane in the lighter to spontaneously ignite, two things need to happen:

1) butane vapor must leak, over time, and accumulate in the box in a proportion favorable to ignition
2) a spark or an open flame of some sort must occur

Now regarding 1): the lighter is currently physically intact and I can guarantee that it will not suffer any shock while in storage (in fact, it will most likely remain inert for years). Therefore, if the butane does leak, it will be either because:

a) some very slow but constant chemical/physical reaction in the butane tank gradually increases pressure over the years until the tank breaks
b) due to imperfect design or implementation of the fuel tank (very likely in mass-produced items), butane is constantly leaking, albeit at a very slow rate

I don't know enough about butane or the environment in the butane tank to know whether scenario a) is at all possible. Now I'm going to assume the worst and consider that scenario b) is in effect.

For the butane to form a potentially combustible mixture, it also has to accumulate in the box over time, i.e. it must escape the box even more slowly than it escapes the lighter's tank. I have no idea whether this is possible. The box is made out of cardboard and has a solid lid that covers the sides, but it's not hermetically sealed in any way. Can butane escape through pores in the cardboard? I don't know. If it can't, it would have to travel several centimeters against the force of gravity (it's heavier than air, right?)

Regarding 2), I can guarantee that open flames and electrical devices inside the box are completely out of the question, therefore the only culprit could be static electricity. Again, I don't know whether it is possible for a static charge to accumulate indefinitely in an inert box.

So...what do you think? Is there anything I've overlooked?

Thank you for your answer!

Answer
You seem to have thought this through very well.  You are correct in assuming the butane will eventually leak out over time.  It will, but unless the box is completely sealed it will diffuse from the box much faster than it will accumulate.  Unless something is moving inside the box, no static electricity will build-up either.  I think the only potential risk would be if the box were engulfed in flame, but if you're at that point I'm sure you won't have much concern for a lighter.