I don't know much about sparks and bullets, but I do know a fair amount about gas and structures. Being on a fire department will do that for you.
A municipal restaurant will use natural gas, while more rural restaurants will use propane. You can tell the difference externally as propane will have a tank and natural gas is piped in. With natural gas, there's a little (about six inch) cover located outside the building to shut off the gas.
I don't remember how large the supply line is for either system, but it isn't that big. This matters because a building has X cubic feet of space. Normally the amount of either gas in the air is extremely minimal. Propane is heavier than air and I believe natural gas is also. When the value is open (for example, turning on a burner), the gas leaks outs, relatively slowly filling the room to explosive levels.
However, it doesn't fill the room evenly. The concentration will be heaviest nearest the source, and slowly expand throughout the room. And people use this principal safely every day of the week. I used it for dinner last night, and didn't blow up a thing. I turned on the burner, releasing propane. A second or so later, the igniter on the stove, creating sparks, caused the small gas bubble to explode and my burner was lit.
Now the implications of this to your problem. Let's say that your guy opens all of the burners, without hitting the igniters. (By the way, most ovens now have a safety device to prevent this happening.) Or he's more advanced and saws the gas line in half. Gas starts being released, creating a bigger and bigger bubble. But this isn't a quick process. And it's going to be a while before it builds up enough to blow up an entire room (like measure in hours, not minutes).
Meanwhile, as this bubble is expanding, if it hits an ignition source, you get a boom, although a lot smaller than you want. Fire departments get little booms all the time. Big booms are the exception.
Your idea could work, but it's going to take a while and most likely will misfire. On the flip side, how many people know this?
Best of luck,
Jim Clark-Dawe