Indoor leaks. Evacuate the building immediately. Shut off the gas at the appliance’s supply line – or, if you cannot identify the leaking appliance, shut off gas at the meter or service valve only. When you are certain the gas is off and all ignition hazards are eliminated, coordinate ventilation procedures with National Grid. Ventilate the building from the top down, using natural air currents. Never ventilate while personnel are inside.
Outdoor leaks. Evacuate the area immediately. Contact National Grid immediately to shut off the gas. Never try to operate underground pipeline valves or relief vents.
Eliminate ignition hazards. Do not use doorbells, garage door openers, light switches, matches or lighters. Use only intrinsically safe radios and flashlights in the vicinity of a gas leak.
Recognizing gas leaks
Utility companies like National Grid add an odorant to natural gas called mercaptan, which smells like sulfur or rotten eggs. Although mercaptan often aids in detection of natural gas leaks, you may not be able to smell this odorant if you have been exposed to it for too long, or if the mercaptan odor is masked by other odors. Mercaptan may also be stripped from the gas due to chemical and physical processes. This effect is known as “odor fade.”
You should never rely on your nose alone to detect a natural gas leak! In any gas leak incident, use a combustible gas indicator to be certain a flammable atmosphere does not exist. In addition, stay alert for any of these gas leak warning signs:
A distinctive, sulfur-like odor
A hissing, whistling or roaring sound
Dirt blowing into the air from a hole in the ground
Continuous bubbling in water
Dead or dying vegetation (in an otherwise moist area) over or near a pipeline
An exposed pipeline after a fire, flood or other disaster
A damaged connection to a gas appliance
If National Grid does not distribute natural gas in your department’s response area, please coordinate your incident response with the appropriate local gas utility.