Propane tanks are common for gas grills and outdoor heaters, leading to frequent concerns about them exploding from simple sun exposure. A tank will not explode simply from sitting in the sun on a hot day. Propane tanks are engineered with specific safety features to prevent catastrophic failure. The danger lies not in the tank exploding, but in the uncontrolled release of gas that may occur if the tank overheats.
Understanding Tank Design and Pressure Limits
Propane is stored as a liquid. As the tank temperature increases, the liquid converts to gas, causing the internal pressure to rise. Standard propane cylinders are designed to account for this pressure change with a significant safety margin, constructed from robust steel to withstand pressures far greater than those encountered during typical use.
A safety mechanism called the Pressure Relief Valve (PRV) is a primary safeguard built into every tank. This spring-loaded valve automatically opens and vents excess pressure before it reaches a dangerous level. Although normal operating pressure varies widely with ambient temperature, the PRV is typically set to open at approximately 375 pounds per square inch (psi).
The tank’s mechanical strength includes a substantial safety factor, meaning its ultimate burst pressure is many times higher than the pressure at which the relief valve activates. This tiered system ensures the PRV releases pressure long before the structural integrity of the steel tank is compromised. Propane tanks are also only filled to about 80% capacity, leaving a necessary vapor space for the liquid to expand safely as the temperature rises.
What Happens When Tanks Overheat
When a propane tank is exposed to excessive heat, such as direct summer sun, the internal pressure can climb high enough to activate the PRV. This is the tank functioning exactly as intended to prevent rupture. The activation of the relief valve is accompanied by a hissing sound as propane vapor is released into the atmosphere.
The gas released during venting is colorless, but it contains the odorant ethyl mercaptan, which smells like rotten eggs. This odor signals that the tank is venting and immediate action is necessary. The danger shifts to the hazard of a flammable gas cloud forming near an ignition source.
If you detect this hissing or smell the strong odor of propane, the area around the tank is filled with highly flammable gas. The tank itself is not failing, but the vented gas can easily find a spark from an appliance, vehicle, or nearby electrical source. You should immediately move away from the tank and call the fire department or a qualified propane technician. Let the tank cool naturally; avoid spraying it with cold water, which could cause a rapid, uneven temperature change.
Practical Safety Guidelines for Hot Weather
The best defense against PRV activation is preventative storage and handling, especially in hot conditions. A propane tank should never be stored where the temperature could exceed 120°F (49°C). Storing a tank in direct sunlight, particularly on a dark surface, can cause its surface temperature to exceed this limit quickly.
Always store propane tanks outdoors in a shaded, open area to ensure proper ventilation. Never place a tank inside an enclosed structure like a garage, shed, or basement, as this allows any vented gas to accumulate dangerously. For transportation, secure the tank in an upright position and never transport it inside the passenger compartment of a vehicle.
A full tank should never be left inside a vehicle, even briefly, as the interior temperature can rapidly climb past the safe threshold, triggering the relief valve. When a tank is not connected to an appliance, ensure the gas valve is tightly closed, even if the tank seems empty. The tank must be placed on a sturdy, flat surface to prevent tipping, which is necessary for the PRV to work effectively by venting vapor instead of liquid propane.