Propane tanks are refillable, but if you have more than one tank and need to store it someplace when it is not in use, the last place you want to put it is under the grill; instead, choose some place that is flat, dry and away from any source of ignition.
Propane Tank Fires
In 1995, the San Francisco Chronicle reported that 2,000 gas grills erupt in flames each year. The cause of these fires was, more often than not, overfilled tanks that sat beneath the grill, leaking propane in high heat, and exploding. Fortunately, the National Fire Protection Agency reports that since 2002, all propane tanks between 4 and 40 pounds must be equipped with overfill prevention devices, or OPDs, which prevent the tanks from being more than 80 percent full.
Where and How to Store Spare Tanks
Extra propane tanks should be kept as far from a heat source as possible. Propane101.com advises consumers to store propane tanks upright vertically in a dry, well-ventilated area on a flat surface. Storing extra tanks on flat concrete is a good choice, but never store them indoors, not even in the winter. The National Fire Protection Association recommends leaving extra tanks outdoors in the winter, even if that means they might rust. Should the tank rust, buy one the following summer.
Propane101.com also recommends that tanks be stored upright because it keeps the relief valve in contact with the air in the tank. If you store a propane tank horizontally, you risk positioning the relief valve below the propane level (even if the tank is only half full). If the valve opens, you will create an instant fire hazard when propane leaks out instead of air. Always store tanks vertically with the relief valve above the liquid propane level of the tank.