On November 2, 2003, Baltimore County fire officials reported two firefighters trapped beneath the rubble of an exploded duplex after a natural gas leak explosion. The firefighters were transported to the shock trauma unit where they were treated for non-life threatening injuries. The explosion also forced firefighters to work for more than an hour to free the trapped firefighters. Companies were initially dispatched for a “smell of gas inside of the residential structure” and then an explosion occurred while they were on the scene.
Article updated September 20, 2018
One of the least respected but potentially deadly call types responded to by fire departments are indoor natural gas leaks. We run these with a frequency that causes us to become complacent and forget that natural gas leak calls and gas explosions can kill.
How many of the natural gas leak calls do we run without even detecting small amounts of gas? But we need to recall the inherent dangerous properties of natural gas, and why it can kill us if we fail to respect it.
Natural gas is lighter than air and will usually dissipate rapidly in the outside environment. Inside buildings, however, it tends to collect, particularly in attics and dead air spaces. The flammable (explosive) limits are approximately 4-15 percent in air.
Natural gas itself is nontoxic; however, it displaces oxygen and can result in asphyxiation if in a confined space. Flammable gas ranges can only be determined by a combustible gas instrument.
Natural gas leak incidents
In incidents where crews are called to respond to natural gas leaks, or some version of that from dispatch, we need to remember to take caution when responding, and this begins from the time we leave the station. Dispatch should collect as much information as possible as well as ensuring the occupant is directed to perform the following:
- If the caller can detect a strong odor of gas, they should be instructed to leave the building immediately.
- They should also be instructed not to hang up the telephone and not to operate any electrical switches, television sets, appliances or other electrical devices.
- They should be told to not pull any circuit breakers and to not re-enter the building
While responding, get all possible information from dispatch and initiate a response from your local gas company to assist. Take a few seconds to plan your route into the address based on best access to the closest hydrant as well as weather conditions. If necessary, air requirements to incoming crews regarding access streets, directions and staging areas.
First units on scene should stage 300-400 feet from the reported address. If possible, stage at the closest hydrant or maybe even stretch a dry supply line to the hydrant. Take a quick minute to see if the occupants have evacuated. This is generally a good first clue that the occupants felt the leak was significant enough to leave.
Contact the occupant and get all pertinent information:
- What types of appliances utilize natural gas?
- Was any work done on them lately?
- Is this an ongoing problem?
Natural Gas Incident size-up and Mitigation
1. Scan for gas with a gas monitor.
Ensure all personnel are wearing full PPE and SCBA. Utilizing a gas monitor, bring your crew to the house, paying attention to the smell of the methyl mercaptan odorizer present in natural gas. This will generally be noticed before your monitor picks up any reading.
Don’t depend only on the smell of mercaptan; this odorant will quickly desensitize your sense of smell and you won’t notice this smell after a while.
Approach the entrance and begin utilizing your gas monitor to scan for gas. If scanning for natural gas, I generally start by scanning high, as natural gas is lighter than air. I also scan middle and low levels in case the source of the gas leak is not natural gas but from propane sources such as gas grills, propane soldering torches, propane firepits or propane heaters. Remember that propane may be the primary source of fuel in more rural areas.
2. Know your gas monitor’s sensing capabilities.
Many gas monitors take time to move environmental air into the sensing chamber and analyze the mix. If you are in a hurry and your device takes more than a few seconds to analyze your sample, you may end up walking into a higher area of gas concentration before you are aware of it.
3. Limit access and consider evacuating non-firefighters.
A minimum number of personnel should be allowed to enter the area to size-up the situation while any additional responding units stage in a location out of the potentially dangerous zone. Consider immediate evacuation of the structure and other exposures. Request traffic control by the police department if needed.
4. Shut off natural gas supply.
Attempt to locate the source of the gas and location of any shut-off devices. If unable to rapidly assess the location of the gas leak, or the levels detected on your monitor are more than 10 percent of the monitor’s LEL (lower explosive limit), shut off the external gas supply at the meter. Any readings on your gas monitor should cause the IC to call for ventilation.
5. Control all sources of ignition.
Just be aware that if the gas meter readings are above the HEL (high explosive limit), ventilating will take the air/fuel mixture through the explosive limits before it gets better. Control all sources of ignition. If it is necessary to secure electrical power to a structure, utilize outside breakers. Ensure that one of your engine companies is connected to a hydrant and a protection line has been pulled for suppression prior to any further intervention.
6. Begin ventilation to clear out the natural gas.
Utilize explosion-proof fans to exchange the inside air. If your department does not possess explosion-proof fans, positive pressure with gas fans is an option — just ensure that they are not running in an area where the levels of natural gas are present and ensure your “pressure cone” has a good seal around the door being used for ingress of ventilation air.
7. Continuous gas monitoring
Once the structure has been ventilated sufficiently to allow for personnel to enter safely without SCBA, start coordinating diagnosis/isolation tactics with your gas company representatives. The gas company service representative should only do restoration of gas service. Only allow building occupants back into the structure if the gas monitor levels have been reduced to 0 percent, and the gas company service representative concurs.
