If you're in the UK this may be useful a Gas Leak can be very dangerous - houses blow up!
From a UK council web site...
* Open the doors and windows to get rid of the gas.
* Check to see if the gas has been left on unlit or if a pilot light has gone out. If so, please turn the appliance off.
* If this is not the case, there is probably a gas escape. Turn the gas supply off at the meter and phone the TRANSCO Gas Emergency Service immediately on 0800 111 999
* Don't turn any electrical switches on or off (this includes doorbells). You can however use the telephone to call the gas emergency service - TRANSCO on the above number.
* Don't smoke, use matches or naked flames.
Peccavi
December 2008