For a low-pressure gas leak at a single family dwelling, if there is no fire, firefighters should begin by

• A. Venting the structure from the highest point
• B. Entering to locate the leak
• C. Turning off the main gas valve
• D. Evacuating occupants and closing doors

Answer: (A)

Ventilate the structure from the highest point. The immediate danger with a gas leak is the buildup of potentially flammable or asphyxiating gas inside the building. Opening upper vents or windows lets the gas, which tends to rise, escape quickly to the outdoors and dilutes what remains inside. This rapid reduction of gas concentration lowers the risk of ignition and injury, buying crucial time to conduct further safety steps.

Entering to locate the leak or trying to shut off the main valve from inside can expose responders to a dangerous, pressurized atmosphere before it's safe to do so. Evacuating occupants and closing doors are essential for life safety, but they don’t reduce the gas concentration inside as effectively as starting with top-level ventilation. After the area is vented and conditions are safer, other actions like securing the gas supply can be addressed.