MISSISSIPPI STATE -- The task of refilling a propane tank may take more planning than it seems it might at first glance.

In Mississippi, state regulations prohibit carrying propane cylinders in the passenger compartment of vehicles, including anywhere inside a sport utility vehicle or van. Liquified propane tanks can be carried in the trunks of cars, in the beds of pickup trucks or strapped to the outside of a vehicle.

"This allows the driver to avoid several dangers," said Herb Willcutt, safety specialist with Mississippi State University"s Extension Service. "The first is the possibility of a gas leak being ignited by anything within the passenger compartment."

This can include cigarettes, lighters and sparks of any kind. In an auto accident, the tank could rupture and ignite. A second reason to keep LP cylinders out of passenger compartments is because they can roll around and cause damage or become a projectile in a sudden stop or turn.

"Safely transport a cylinder in an upright position in the trunk of a car or the bed of a truck," Willcutt said. "An empty milk crate, cardboard box, wooden crate or similar-sized, flat-bottom box can contain the cylinder snugly for transport. Tie the cylinder in the vehicle to keep it from sliding or rolling around the trunk or bed of the truck."

Since SUVs and vans are completely open inside, there is no place to separate passengers from the tank. Willcutt advised using another vehicle to transport the tank, or tying it to a luggage rack outside the vehicle.

Minimize the time a tank is in a vehicle, which means keep the trip as short as possible and take the cylinder out of the vehicle upon arrival.

"Vehicles parked in direct sun during the summer can reach 140 degrees inside. This could cause the pressure relief valve to open and allow gas to escape into the vehicle, where it could later be ignited," Willcutt said. "Also, the greater the distance and the longer the vehicle is in traffic, the greater the chance that the vehicle will be involved in an accident."

Store propane tanks in a cool, dry location away from sources of fire and occupied homes and buildings. Never store a cylinder in any part of the house or near appliances or gas water heaters. Make sure storage areas are well-ventilated to allow any gas leaks to safely dissipate.

"Cylinders are fairly indestructible, but they do age and rust and the valves may develop leaks," Willcutt said. "They must be certified after a period of years, and dealers visually inspect them before refilling."

Replace cylinders having a noticeable gas odor, and those that leak gas over a period of time. As of April 1, 2001, all tanks being sold or refilled must have an overfill protection device, a valve which limits how full a tank can be filled, leaving room for the gas to safely expand.