In case of a disaster, you should understand the dangers posed by your propane tanks and how to turn them off. Now this article is written primarily about the large tanks, 250 gallons and above. These tanks are normally placed in a stationary location with permanent piping to your gas appliances.
In case of the loss of electricity, these propane tanks should not be affected, although depending on the type of appliances you own, they may not work without power. In case of an earthquake, mudslide or similar disaster, the tank or piping may be damaged. In this case, you need to turn the tank off.
The first thing you need to understand about propane is that it is heavier than air and will flow along the ground like water. So it there is a serious leak, stay uphill from the tank or leak if possible.
The propane tanks are easy to shut off. There is a valve at the top of the tank that is like the one on your barbeque, just turn the valve until the gas shuts off. This propane shut off valve is normally covered by a hinged dome. Go and take a look at your tank and find out where this valve is located prior to a problem.
If the propane tank itself is damaged, stay away from it and evacuate the area. Remember propane will flow downhill and spread out so you may have to warn neighbors. Do not come back until the gas has completely dissipated.
If you smell gas in the house from a leak caused by damaged or loose pipes, evacuate the house, shut the gas off and wait for the gas inside the house to dissipate. After the gas is turned off make sure that any damage or leaks are repaired and all of your pilot lights are relit. Get a representative of the propane company or a plumber to repair your system and relight the pilot lights. Just remember that propane is highly flammable and under the right conditions explosive and can kill you.