Use your CGI to monitor the air around the building.

If gas concentrations are well below 5% volume in air (100% LEL) and you can enter the building without risk, check for natural gas in the following locations:

• The areas where any underground water, sewer, electric or drain lines enter the building.
• The regulator, meter bar and all piping that supplies natural gas, as well as the piping around all gas-fired appliances, such as water heaters and clothes dryers.
• The spot where the gas service enters the building.
• Any cracks in the wall.
• All high points in the ceiling where natural gas could collect.