Just spotting this topic, and reading the 90 minute fuel aspect, and thinking... Well that's 90 minutes of fuel, minimum! Then thinking Natural Gas, it won't go out. Now, I'm remembering a job we did last year, where the gas did go out, and all the time! It was on a busy road, and had a new gas siezemic shut off valve.
Every time a large truck would go by, the gas would shut off! It was required by and provided by the utility. Meant to operate in an earthquake. It had a little ball that would fall off a holder, and into a valve that would shut off the gas. So, I guess natural gas might not be such a wise idea after all.