Propane characteristics Safety reminders If you smell gas Uncapped lines Safety relief valve Read your tank gauge Appliance safety Lighting pilots Maintenance Gas grilling tips Weather emergencies Download PDF version Disclaimer       What to do if your safety relief valve pops off Propane expands when heated. That increases the pressure in the tank. Above a certain pressure, the relief valve opens to release a small amount of vapor. That release keeps the pressure from building up too much inside the tank. Once excess pressure has been released, the relief valve closes automatically. It’s important to keep your tank painted with a white, aluminum or other reflective color. A rusty, unpainted or dark-colored tank may cause pressure build-up resulting in a safety relief valve discharge. Call your propane marketer whenever your relief valve pops off, so they can determine the cause.