My NFPA 58 books are packed away, and I forget whether they say portable propane tanks "should" not or "shall" not be stored indoors; and it really doesn't matter.
The situation is thus: LP gas is stored inside a cylinder under pressure. It is highly sensitive to temperature changes. If a full 20# cylinder is stored in at a temperature above 104 degrees (such as in a hot garage or in a closed car) for more than 2 hours, there's an excellent chance that the heat will build up the pressure to the point that the pressure relief valve will open, and the excess pressure will be exhausted to the local atmosphere. Of course, what will be expelled to lower the pressure is a flammable gas. In a closed environment, if the air/gas mixture achieves flash point (between 2% and 10% LPG, approx), and there is a source of ignition, you will have a floomph.
Further, any cylinder has the possibility of a leak. If vapor leaks out and reaches the above conditions, again, you will have a floomph.
Now, depending on the amount of gas that has leaked and the size of the closed area, the floomph may be minor or major, but most would agree a floomph is to be avoided. The easiest way is to never bring the cylinder inside (or put one in any closed area, such as a car trunk or a closed grill cabinet) in the first place.
Now, most of us will look at it realistically instead of legally; fork lifts run inside with propane tanks all the time, for example. But, they are changed out fairly frequently, people are around them during use and would smell a leak, etc. The full tanks are stored outside. The same is true for occasional use of propane heaters. A little common sense can be applied.
But, in Harv's case, he's going to advise a public, commercial enterprise, so he's got to be prepared to put his foot down and tell them: You just can't roll a grill indoors and use it the same way you would outdoors. It just doesn't work that way. Now, I suspect the chef or whoever serves as the country club's restaurant manager knows that, but the brass who think the grill is a keen idea don't. And Harv doesn't want to appear smarter than them, so I tried to remind him of a couple of things that the management might not know.
