War stories, horror stories, real life drama. Yep, the stage is always set.
Ed mentioned that it only takes an errant spark plug miss to ignite the cloud. That is a real possibility, but that is just one source of ignition. A more constant and always present source of "ignition" on a running engine is the alternator. When the engine is running there is always some arcing occurring where the brushes touch the slip rings of the rotor.
And in the case of a forklift that has been sitting in a calm spot overnight inside a building with an LPG leak, the spark that sends the building into orbit will likely come from the arc that occurs in either the key switch, a starter relay, the starter solenoid, or the brushes of the starter against the commutator. Ignition systems that have a distributor cap also produce a veritable "ring of fire" inside the cap on the secondary circuit, older points style distributors of course have the breaker points arcing.
I am not mentioning these things to try and "one up" Ed or anybody else, I am listing them to show other sources of ignition that are "there" so when you try to drive home the dangers of having repairs to LPG fuel systems done by unqualified people.............the risk of fire and/or explosion is very real, almost to the point of being a sure thing....considering all the things that make sparks or arcs on a perfectly normal, good condition (except for that fuel leak) truck.
I stress all these sources of ignition whenever I have to introduce a newbie mechanic to forklift/LPG training and I try to make it sound as though there is a catastrophe just waiting for somebody to light the fuse every time you put your hands on the fuel system.
I also tell them to never ever release LPG from a fitting without first ventilating the work area and if they are using an incandescent work light when releasing LPG, get it out of the work space. Just one drop of liquid LPG striking the glass bulb will shatter it and a fire ball will be the result.