Immediately put out all smoking materials and any other open flames. Do not operate lights, appliances, cell phones or telephones. Flames or sparks can trigger a fire or explosion.
Insure that everyone leaves the building or area where you suspect gas is leaking.
If it is safe to do so, then turn off the main supply valve on your tank. To close the valve, turn it to the right (clockwise).
Once you have left the area, call your gas retailer and report the leak. If you are unable to reach your retailer, then call 911.
Stay away from the endangered area until your gas retailer has determined that it is safe for you to return.
Do not attempt to use your gas appliances until you have your system checked. You can have your retailer or a qualified professional check your entire system to ensure that it is leak free.