If you keep a spare tank of propane for your grill, most sources advise not storing it in your garage. Amerigas is slightly less conservative, endorsing enclosed storage only in structures not attached to your home’s living space.
There are a significant number of road-going vehicles that are fueled with liquified propane gas (LPG) or compressed natural gas (CNG), and a smaller number fueled with hydrogen (H2). Are there legal restrictions on parking such vehicles in enclosed spaces (workshops, residential garages, etc.) due to the risk of a leak?
I know that NFPA codes/standards cover gaseous fuel systems, fueling, repair facilities, and parking facilities not in single family buildings. I recall nothing of the details though, sorry. That might be a good place to start if no one comes by with more knowledge.
I have a van that runs on propane and I’ve put 175,000 miles on it since 1999 so I’ve a bit of experience with an alternative fuel vehicle. The DOT certified tanks approved for vehicles are light years tougher than any static tank made, with valves inside that shut off the flow of propane if the filler valve were to be sheared off in an accident. People always ask if I’m scared to drive it but seriously, the only thing I worry about would be getting into an accident with another vehicle carrying 20-30 gallons of very flammable liquid contained in a tank that can be breached by a strong person with a screwdriver. If their tank ruptures and catches fire around my propane tanks then my chances of becoming air pollution go up dramatically and I’d be running as fast as I could to get the hell away from the whole shitshow.
And so far the only places I’ve had even a question about my fuel source is when travelling aboard one of the Puget Sound ferries, when I was required to wire a red tag to one of my tanks to let firefighters know which vehicle to drop over the side in case shit goes pear shaped. Oh, and Arizona, which had laws banning LPG and CNG fuelled vehicles, no idea if that’s still a thing.
This gets into state laws, but they often specifically allow AFVs that meet certain requirements and are under some fuel capacity, e.g. https://afdc.energy.gov/laws/11979
Hydrogen is lighter than air while propane is heavier than air. Propane will sink into your basement or the bottom of a tunnel, or a swale & stay there. Hydrogen isn’t as dangerous because it vents up/out.
Grill tanks are 4+ gallon tanks & are not filled to the top; usually between 3½-4 gallons, or about 80% full. Under normal usage, including being outside in the summer, because they’re not filled to the top, even when the propane expands as it gets warm, it doesn’t expand that much because of the relatively small quantity in that tank & has to stay in the tank.
The tanks we use are larger, anywhere from 10 gallons up to 25 gallons per tank. If we’re using 10 gallon tanks, we’re carrying three or four of them. Because of the larger size, they have PRV (pressure relief)/ spitter valves on them. If they get too warm / too much expansion, the spitter valve will open & vent propane until it drops below the max pressure & the valve closes again. If you park it in your attached-but-uninsulated garage, it could heat, release propane via the PRV, which could then find it’s way into your house & down to the basement where you house’s HVAC/water heater are typically located. If you happen to have natural gas, having propane down there when you heater/hot water heater kicks on could be problematic. Even a match, whether for smoking or b-day candles could be explosive in the right (wrong?) conditions. That being said, I don’t think I’ve ever seen a privately owned LPG vehicle. I believe I’ve seen passenger cars, but they’re always part of a fleet, a utility or transit company, mainly because the infrastructure isn’t there to recharge on the road if you take a trip, which wouldn’t be an issue for a fleet vehicle only driving around town.
While I don’t know of specific laws against it, it’s not a good idea, just like how I wore a seat belt long before they passed a law making it mandatory & no one that I know of parks in an attached garage; in many cases, it’s not only a safety issue, it’s not fitting into a standard garage issue so the safety issue becomes a secondary point.
Dad had his pick-up truck switched over to propane and had a big tank fitted across the bed of his truck. He said it saved money on fuel and that it kept the engine cleaner. I don’t recall there ever being any parking issues, but I do remember that we had to plan long trips carefully because of the fueling issues.
He bragged that when he traded that truck in, they gave him extra money because the engine was so clean and moved the propane tank and stuff to the new truck for free. (I suspect that Dad might have stretched the truth at times.)