At the risk of being a dick.....Fuch it I can live with being a dick...look at this.

http://www.914world.com/bbs2/index.php?showtopic=157207

I work with CNG and LNG fuel trucks coast to coast 3,600lb working pressure. A fuel tank will not explode, only in the movies and in the news, the fire triangle. Fuel, Heat, Oxygen, remove ANY one you will not have fire. In the past 15 years there have been only two tank failure deaths and guess what human error was the cause.

Transfering truck to truck

I've seen the aftermath of a lay down propane tank exploding due to a building fire.

then someone removed the pop off valve, aka human error

A house here in WA. just blew up about the same result as the Toyota,
From a natural gas leak.

Acetylene is bottle at a much higher pressure. Same thing could happen in your shop if the valve is left open.

I have done everything to make safe as possible.
large lower vents in trunk (heavy gas)
A hose from the PRV to outside.

Your right though, WorstCaseSenario = shit happens.

Your not a Dick , Just not a believer

No, but IIRC they figured it must of failed. All the firefighters said it wouldn't explode, after they picked themselves off the ground they saw it up in the air. The tank had flattened right out (ends popped off), came down went though my buddies brand new shop roof and right through a customers boat transom. I saw it the day after, the tank was still stuck in the ground though the transom.
This happened in the early 90's so I can't find a news link to it.

All tanks that size here are rentals (by law I believe), so if the valve was tampered with it was done by the gas company and I'm sure I would have heard about it.

Why I said "Transferring truck to truck" is we had a major happening in Toronto, the Canadian guys should know this one. Huge fire, many tanks failed. Happened only a few years ago so it should come up in a search but I have to go out....

bottom line have respect for any pressurized gas, liquids, springs, be safe.
Think about what your going to do. We need some to kick around, and your family will miss you.

Its a fire tetrahedron now: Fuel - heat - oxygen - uninhibited chemical response

LPG is not the same as acetylene.

Mark ,Propane tanks have evolved greatly since the 90's




Check out this site , I like the lawn mower;
http://www.ferrellautogas.com/Vehicles