While the utility company should always be notified, firefighters must be familiar with how gas detection meters work and realize that any reading, or the distinctive odor of gas, indicates the potential for a hazard to exist. Photo Craig Jackson
Firefighters and other emergency personnel routinely respond to emergencies involving natural gas. Such emergencies can include residential fires, odors or leaks in buildings, damaged gas lines or, worst case scenario, an explosion with ensuing fire. Often, emergency responders arrive on scene before the utility company and begin efforts to secure the area. A basic knowledge of natural gas and how to eliminate or control hazards can streamline emergency operations and, more importantly, ensure the safety of all personnel on scene and the community they serve.
About Natural Gas
Predominately methane, natural gas is colorless, tasteless and, in its natural state, odorless. Transmission pipeline and utility companies add a distinctive odorant, butyl mercaptan, to natural gas so leaks can be quickly and easily identified. Natural gas is lighter than air and tends to rise, while most other flammable gases have higher vapor densities and tend to move downward.
Natural gas is non-toxic and considered a simple asphyxiant. Utility companies indicate that the natural gas mixture from the pipeline will typically have a lower explosive/flammable limit (LEL/LFL) of 5% and an upper explosive/flammable limit (UEL/UFL) of 15%, or a flammable range of 5–15%.
Natural gas typically originates in underground deposits and is extracted in a number of ways. Energy companies have developed alternative processing methods to create natural gas, and currently there is a boom in natural gas in North America that has reduced gas prices and encouraged its use. Transmission pipelines transport the natural gas at pressures of up to 1,500 psi throughout the country to local natural gas distributors.
Gas distribution systems operate at pressures ranging from 0.25–99 psi and consist of mains, services, valves and meters that are constructed of steel, cast iron, ductile iron, wrought iron or plastic, depending on the system age and type of service.
Natural gas transmission and distribution piping system installations must conform to rigid construction requirements set forth in ANSI B31.8, Gas Transmission and Distribution Piping System Standard. NFPA 54, the National Fuel Gas Code, contains requirements for the installation of natural gas piping and appliances inside of buildings. The U.S. Department of Transportation (DOT) maintains jurisdiction over the safety of transmission pipelines, and distribution systems must comply with DOT regulations, along with any public utility commission requirements.
Utility companies must ensure the integrity of their natural gas distribution systems through a comprehensive safety program that involves surveying, monitoring, maintenance and testing. Most utility companies are responsible for the entire distribution system, including the natural gas meter. Property owners are responsible for all natural gas piping inside buildings downstream of the meter. Many rural and suburban areas don’t have piped natural gas service. In these areas, the gas service may be bottled gas, such as liquid propane gas (LPG). The information contained in this article doesn’t apply to LPG. Fire departments should be aware of where there is natural gas service in their coverage areas.
Here are some tips for handling incidents involving natural gas:
After determining an incident involves natural gas, immediately notify the utility company. Once they arrive on scene, instruct utility company personnel to report to the incident commander (IC) or the liaison officer. Many utility workers receive incident command system (ICS) training to work within the emergency response operation and can assist in evaluating the problem, recommend actions to take and request additional resources as needed.
When dispatched to investigate a gas odor, notify the utility company immediately. Utility company employees are well trained and equipped with gas detecting instruments. Odors can come from many causes, including petroleum products such as gasoline, propane, marsh gas, sewer gas and industrial gases.
Responding crews must attempt to identify the type of gas causing the odor and the source of the leak. Gas meters that are setup to read LEL should be used to determine where the hot zone is. Firefighters must be familiar with how these meters work and realize that any LEL reading on a meter (or the distinctive odor of gas) indicates the presence of gas and the potential for a hazard to exist. Meters must be calibrated regularly to be effective, and at a gas incident, if the fire department doesn’t have a meter, they need to know where to get one and have it brought to the scene. To verify readings, try to use two meters instead of one.
Escaping Natural Gas Outside a Building
Notify the utility company immediately if un-ignited natural gas is escaping from the ground from an excavation or from an open pipe outside a building. Establish a hot zone around the location of the leak. This hot zone should include any area where gas detection equipment indicates a reading of 1% or more.
Extinguish all flame and other ignition sources within this hot zone. Be aware that any electrical equipment—including that which is brought to the scene by the fire department—presents a possible ignition source if not rated for flammable atmospheres. Turning electrical equipment on or off can create a spark and ignite leaking gas. Check surrounding buildings for any presence of natural gas odors. Reroute and restrict vehicular and pedestrian traffic from entering the area until utility company personnel bring the natural gas flow under control. If the leak continues, the hot zone must be continuously monitored and may need to expand.
Natural Gas Burning Outside
When natural gas is burning, notify the utility company immediately. Only utility company personnel should operate valves on mains. However, emergency responders trained in the use of curb keys may close curb valves on natural gas services, but they should never turn on valves or curb valves. Restoration of gas service requires re-ignition of pilot lights, checking safety equipment associated with burners and other tasks that require specialized training. Once something is shut off, leave it off. Turning the wrong valve or opening a closed valve could further endanger life or property. Leave these actions to utility company personnel.
The best method to control an outdoor natural gas fire is to shut off the natural gas flow. In most cases, emergency responders should not attempt to extinguish the fire while gas continues to escape, as an explosion could result. Establish and maintain a hot zone. If the natural gas fire has spread to exposed combustibles, a hose stream or extinguisher can be used to extinguish the exposed fires, using care not to extinguish the gas fire itself.
Do not fill an excavation where gas is leaking with water, as water could enter the gas main system. If it proves necessary to extinguish a natural gas fire before gas flow can be stopped, then use dry chemical. Do this only as a last resort because escaping unburned gas creates the potential for explosion.
For an uncontrolled gas leak with no ignition, evacuate everyone—including firefighters—from the immediate area.
Escaping Natural Gas in a Building
When escaping natural gas is found in buildings, notify the utility company immediately. Clear the building of occupants. The IC should determine if the natural gas can easily be shut off inside the building without risk to personnel, or if it must be shut off at the outdoor meter, which should be equipped with a valve that can be shut off with a wrench.
It may prove hazardous for firefighters to enter a building to shut off the gas inside. Ventilate the building by opening the doors and windows. Do not operate any electrical switches, phones or other equipment that could create sparks (including non-intrinsically safe radios and ventilation fans) in the hot zone. When ventilating a building above the flammable range, firefighters may bring the atmosphere down into the flammable range, which could result in an ignition. Do not be complacent if gas readings are high.
Natural Gas Burning In Buildings
When escaping natural gas is burning in buildings, the IC should notify the utility company immediately and determine if the gas can be shut off inside the building or must be shut off at the outdoor meter.
In certain industrial or commercial buildings, turning off the natural gas might seriously interrupt important and costly processes, or create further hazards. The utility company and facility management can help determine the proper action. If the natural gas supply can’t be safely shut off, prevent fire extension by wetting surrounding combustibles with a fog stream until utility company emergency crews can control the burning flow of natural gas.
Indoor Natural Gas Piping or Meters
Notify the utility company immediately when a fire endangers indoor natural gas piping or a meter. The utility company is best equipped to shut off the supply of natural gas. The on-scene IC may elect to shut off the supply at an inside valve, if it can be done safely.
In some rare cases, natural gas may burn out of control from an appliance. Notify the utility company when a natural gas fueled appliance is involved in fire. You can typically control the fire by shutting off the gas flow at the appliance shut-off valve, if it can be safely accessed, or at the meter valve. Prepare to check for exposure fires behind and above the burning appliance. Do not turn on the appliance or meter valve once turned off.
Gas in Manholes, Vaults, Sewers
Various types of gas from a variety of sources can be found in sewers: natural gas, propane, gasoline, sewage and electrical cable burnout. The utility company can help identify the type of gas involved and trace its source.
Do not attempt to extinguish any of these flames if gas becomes ignited. Establish a hot zone around the opening and keep vehicles and bystanders away from nearby manhole covers. Prohibit smoking and other potential sources of ignition.
Before anyone enters, always test the atmosphere of a manhole, vault or sewer, first for oxygen levels and then for flammable gases, carbon monoxide and hydrogen sulfide. Firefighters should not enter manholes, vaults or sewers—leave that to utility personnel. No one should enter a manhole if dangerous concentrations of gases or vapors are known or suspected, and if personnel enter, they must follow specific confined-space entry procedures.
Temporarily vent a manhole by removing its cover and the covers on either side until you reach manholes free of gas. Perform actions to prevent sparks, such as wetting the manhole cover and rim before removing the cover and avoid working directly over the cover.
Check the basements of adjoining buildings for any evidence of gas intrusion. If found, ventilate by opening windows and doors. Shut off open flame devices, and don’t operate any electrical switches. If natural gas is involved, handle as suggested in the section on escaping gas in buildings.
When under control, natural gas, like many other hazardous materials, is as harmless as it is widespread. In addition to many residential and commercial purposes such as heating and air-conditioning, water heating, cooking, drying and power generation, natural gas is widely used in industrial settings every day. But how we respond to natural gas emergencies can mean the difference between life and death for civilians as well as emergency responders. It’s critical that meters are properly maintained and calibrated, personnel are properly trained in their use and standard operating guidelines for response to gas emergencies exist.
Sidebar - Quick Guide for Natural Gas Emergencies
- Immediately notify the utility company
- Isolate and eliminate potential ignition sources
- Evacuate the area
- Meter the immediate area & gas migration areas
- Establish a hot zone (explosion and collapse)
- Ventilate the building if appropriate
- Establish rapid intervention crews