[patcheudor]

>What would he pressurize your lines with? An air compressor? He'd have to dig up the lines or disconnect them first and gas from the line would likely escape in quantities large enough to discourage such tricks.

On the gas meter on my house anyway, the underground pipe mates at a valve. It doesn't seem hard or particularly dangerous to shut that valve off, disconnect the meter, connect whatever, then open the valve again.

[jacquesm]

If you leave the valve attached to the mains line then you can access the house lines, usually there is even a special port for this that you could use without disconnecting the mains line that is used for leak inspection (they evacuate the lines and measure the rate of seepage). Once you connect something in the line and you open the valve again all pilot lights will have been extinguished and won't re-light due to safeties.

Anyway, if you want to destroy someone's house there are much quicker, less obvious and easier ways to do so.