Contrary to what a lot of people think, plumbers are licensed to work on gas systems, both natural gas and LPG (liquified petroleum gas). A gas leak is a potentially dangerous situation for obvious reasons.
Gas companies make PSAs and send out flyers informing their customers what to do if they smell gas. They recommend getting out of the house immediately and calling the purveyor or local gas company. In most cases the gas company will come out, check to see if there is a leak and locate it. If the leak is on an appliance and the appliance can be shut off with a valve, the gas company will shut it off and red tag it for you with information on what is leaking so it can be fixed. If the leak is not on an appliance or can’t be shut off with an isolation valve, the gas meter will be shut off and locked out. Once that happens, a licensed plumber must be called and all leaks, not just the main offending one, must be fixed along with code upgrades made as they pertain to gas appliances such as furnaces or water heaters.
Usually what we find in these situations is there is more than one leak on the system, oftentimes many leaks, and the system must be made 100% airtight before it can be turned back on. If the property is located within a municipality, a city permit must also be secured and the gas system must be inspected by a city inspector, then released to the gas company to remove the lock and turn the gas back on. This scenario can get very expensive and be very time consuming.
Most leaks we find are small but noticeable because the odorant used in gas is intentionally very potent so that you will notice a leak. Odorant is used in gas because it has no taste or odor in its natural state.
If you smell gas once in a while but never very strong, call a plumber first because we can typically find the leak without the hassle of dealing with the meter being locked out and turned off. If you come home and have a very strong odor of gas, do not turn on any lights, open the refrigerator, or do anything other than leave immediately and call the gas company.