Beyond the Rule of Thumb
Survival Tip 40
Natural gas service is a fact of life in most urban and suburban areas, providing obvious benefits to a community’s quality of life. However, it also presents the potential for serious injury and death to those first responders who fail to understand its unique characteristics during incidents involving uncontrolled releases. Among these is the fact that natural gas is lighter than air and odorless in its natural state. To aid the general public in detecting a leak, a very small amount of mercaptan, an odorant, is added. Mercaptan contains sulfur and gives natural gas an odor similar to that of rotten eggs.
Unfortunately, first responders all too often relegate calls for a “gas odor” to the despised category of “smells and bells,” usually reserved for nuisance calls. As a result, they may let their guard down and on arrival fail to fully appreciate the problem’s magnitude and neglect to take appropriate actions to protect themselves and the public. That is, until the scene lights up around them and the Mayday calls begin.
Listed below are some recommendations first responders should consider when dispatched to a report of an odor or leak of natural gas. Additionally, before such an incident occurs, first responders should meet with local natural gas company representatives. Together, they can discuss appropriate response strategies to such a leak and how the local fire department and gas utility can best work together during these events.
1. Don’t park near a building reported to contain a natural gas odor or to be the source of a known or suspected leak. This means that personnel may need to walk some distance while carrying equipment. However, if an explosion occurs, your apparatus is less likely to be in the direct line of flying debris. This also allows you the opportunity to assess the situation gradually, approaching on foot rather than stopping directly in front of a building. After detecting a strong natural gas odor, you will have to back up, which may not always easy, especially if another unit followed right in behind you.
Also, remember that the complainant’s address may not be that of the source of the leak–that person may have only detected the leak at that location. In some situations, the caller may have only been traveling through the area and used a cell phone to report the odor. Under these circumstances, first responders may have greater difficulty determining the source of the leak and determining a safe means of approaching the scene and parking their apparatus. When this occurs, be alert and approach the scene slowly. At the first moment anyone on the apparatus detects the odor of natural gas, STOP. Don’t continue driving into harm’s way. Look for visual clues, such as vapor clouds, and listen for the sound of escaping gas. If additional apparatus were dispatched on the call, consider having them approach the reported location from a different direction to get another perspective on the incident.
2. Any incident involving a known or suspected leak of natural gas calls for full personal protective clothing, including SCBA. This includes using protective hoods and gloves. Personnel should also carry a spanner wrench to close the control valve on most residential gas meters. Although some larger gas meters may require using a pipe wrench to stop the flow of gas, having a spanner wrench handy will allow you to react quickly during the majority of incidents. Remember that some “pocket” spanner wrenches may not always work for this purpose. If ordered to close the gas meter control valve, the last thing you want to do is to have to go back to the apparatus for a spanner wrench. By the time you return, it could be too late.
3. On confirming a known or suspected leak of natural gas, first responders should request the local gas company to respond for assistance. Such assistance includes operating street-level control valves and providing additional combustible gas indicators for use at the scene. Remember that first responders themselves should never attempt to operate street valves that control the flow of natural gas. Some first responders are reluctant to request operation of a street valve because they do not want to escalate the incident and shut down the gas supply to an entire block or perhaps an even larger area. Yet on any given day, this is preferable to getting blown up.
During one incident, we shut down the gas supply to one unit of an apartment complex on Thanksgiving Day. We were not very popular with all the folks in that building attempting to prepare their festive turkey dinner and we faced their wrath. But we didn’t blow anybody up, and they got over it. Remember: An inconvenience is temporary, while dead is forever.
4. Eliminate ignition sources and evacuate affected areas. Although this sounds like common sense, it is almost always easier said than done. On arrival at any hazardous materials incident, isolating an area and denying entry is sometimes akin to herding cats. When you have a situation involving a rapidly spreading flammable vapor cloud, the need for quick action cannot be overstated. Remember that although the goal of eliminating ignition sources often involves control of electric utilities, this control must be away from any potential ignitable atmosphere. As a general rule, for areas suspected of containing a dangerous level of gas, if an electric appliance is on, leave it on. If it is off, leave it off. The safest means of isolating electric service to an affected building or area is to have a local electric company representative terminate power at a remote source; for example, by opening a pole-mounted fuse.
5. Use a combustible gas indicator to detect the presence of natural gas. This is preferable to attempting to detect the leak using the odorant added to natural gas. Of course, first responders using the device need to be properly trained in its use and know the calibration gas used. If the calibration gas is not methane, then you must know how to correct the instrument reading for methane. This usually requires using a correction factor. Although some instruments will do this automatically, many more require the user to manually convert the reading by multiplying it by a numerical value predetermined by the instrument’s manufacturer.
Remember that since natural gas is lighter than air, you must look at upper areas where the gas could rise and collect. If you are using an extension probe for the device, consider that these longer probes require additional response time to obtain an accurate reading. If you don’t know what this additional time is, now is the time to find out. If you make a bad decision based upon an erroneous reading (either because you don’t know how to use the device or it was not properly maintained), you and your department face the potential for grave legal and civil liability issues. This is in addition to any injuries and loss of property that occur, not to mention the bad news coverage you’ll get when something blows up and you get the blame. If you’re not sure how to use the combustible gas indicator assigned to your apparatus, now is the time to learn.
6. The source of any leak of natural gas is generally from one or more of four locations and each presents its own particular set of hazards. These are:
- Inside: Accessible living area
- Inside: Limited access area
- Outside: Aboveground
- Outside: Belowground
Inside: Accessible living area. These incidents usually involve a leak of natural gas at an appliance (e.g., a hot water heater, a stove, or a furnace) or from the supply line to that device. The danger here is that first responders may be inclined to approach the appliance to attempt to control the leak by closing the appliance’s supply valve, thereby placing them in an area subject to an explosion. A usually safer method is to close the control valve on the gas meter. Although this will shut down all gas-fed appliances, it will usually place first responders farther from the source of the leak. However, in older homes where gas meters may be located inside, perhaps in a basement, any attempt to shut down the gas supply, whether at the gas meter or at the appliance, may once again place first responders in danger. In a situation such as this, it may be safer to evacuate the structure and have a gas company representative close a street valve.
Inside: Limited access area. Incidents involving limited access areas usually involve crawl spaces underneath single or multifamily occupancies. Examples include a leak from a supply lines or a leak at an appliance such as a floor furnace. It is usually advisable for first responders to NOT enter a crawl space or other limited access area to attempt to close a control valve in the supply line or at the appliance.
Outside: Aboveground. Incidents involving a leak of natural gas that occur outside may involve a gas meter or supply lines coming into or out of the meter. Leaks involving a supply line could originate from a fitting or from a complete rupture of the line.
As an example of the latter, a homeowner who had been locked out of his residence located an open window on the first floor. At first glance, the window was too high, yet he was able to reach it by standing on a small pipe that ran along the outside of the house a few feet off the ground. Unfortunately for him, the “pipe” was a natural gas supply line that fed the home’s gas meter. Once he placed his entire body weight on the pipe, it pulled completely away from the meter nearby. The result was an ongoing release of natural gas that the fire department could not control, because it was on the inlet side of the meter. Had the break in the line occurred on the outlet side, first responders might have been able to control the release by closing the control valve located at the meter. Remember, any attempt to control a flow of gas at a meter when the meter is near a leak is extremely dangerous. This incident required a gas company representative to operate the street valve. Furthermore, this incident required immediate evacuation of the surrounding area since gas leaking from the damaged line entered the open window, thereby quickly filling the entire structure and subjecting first responders to a potential for a significant explosion.
In addition to entering windows, natural gas, since it is lighter than air, can enter buildings through other exterior openings such as soffit vents, HVAC air intakes, and cracks in exterior walls.
Outside: Belowground. A leak of natural gas belowground can sometimes be one of the most dangerous situations first responders can face. Locating the leak, identifying and protecting any potential exposures, and controlling the flow of gas may all be elusive. The two most probable causes of a belowground leak include lines damaged during excavation and leaks resulting from defects in the underground supply line, the valves, or the fittings. A leak at an excavation is usually easy to detect by sight and sound; just look for the backhoe or auger nearby and listen for the roar of the escaping gas. However, some first responders downplay the severity of these incidents because they believe the natural gas will dissipate harmlessly into the atmosphere because of its low vapor density. However, as was discussed earlier, the unfortunate reality is that the escaping gas has the potential to enter nearby structures though exterior openings. In one situation, natural gas escaping from an excavation accident entered soffit vents of a nearby home only to be ignited by an attic fan. Imagine the surprise of first responders when the home’s roof blew off during what they considered to be a relatively minor outside gas release.
Leaks caused by defects in underground supply lines, valves, or fittings are sometimes indicated by natural gas rising to the surface through cracks in streets or sidewalks, and the gas may even create bubbles if the crack or other street-level opening is covered with water. During one incident, the pressure of natural gas escaping from a defective underground supply line pushed up the soil from underneath, causing a noticeable bulge in the front yard of a residence. Aside from the potential for this bulge to rupture, the natural gas escaping underground can travel numerous paths, including migrating through soil and following the path of underground conduits for electrical wires. By these paths, the gas can enter nearby structures through crawl spaces, or at the point where the conduits enter a building, or through an underground electrical equipment vault.
The potential for explosion involving the latter is obvious. What may not be obvious, however, is how during one incident, explosive natural gas readings were found in the aboveground conduit for a buried electric service cable that ran to the base of a residential electric meter. At another underground leak, a local gas company representative discovered the presence of natural gas behind an electrical outlet cover plate on the first floor of a nearby residence, and determined that the building’s walls were filling with natural gas; the potential for a disastrous explosion was imminent. Fortunately, local electric utility company personnel were able to use a remote switch to terminate power to the residence and eliminate ignition sources in the immediate area.
In a situation such as this, first responders could believe that they have nothing more than a minor release of natural gas through a crack in the street, while all around them the buildings nearby could be filling with natural gas. The incident could appear to be under control until the first of several nearby houses explode off their foundations. One way such situations develop is that natural gas traveling through soil can be stripped of the mercaptan odorant. As a result, occupants of buildings near the underground release may be unable to detect the presence of any gas; first responders who conduct a check on these buildings as a precaution may also fail to detect it. This is one more time when the correct use of a combustible gas indicator is a matter of life and death. Never depend on the “lack of an odor” when declaring an area safe from a suspected leak of natural gas, especially during situations described here.
7. Use caution during ventilation operations to remove natural gas from a building. Too many first responders believe that once they have controlled a leak that has allowed natural gas to enter a structure, all they have to do is ventilate the building to remove the gas. Unfortunately, this activity sometimes receives the same low level of attention paid to smoke removal following a fire, but there are considerable differences. First and foremost, the gas being removed is still flammable and the only reason it may have not yet exploded is that the concentration of gas is above its upper explosive limit. For example, the generally reported flammable range for methane is between five and 15 percent. Although the goal of ventilation is to reduce that concentration to zero, in situations in which the concentration is above the 15-percent upper explosive limit, in attempting to reach that zero concentration, the gas will enter the flammable range. If there is an uncontrolled ignition source present that first responders were unaware of when they started ventilating, the environment could be ripe for an explosion as the concentration approaches 15 percent. Of course, this is probably also the same time that first responders are taking up equipment and preparing to leave because, in their minds, the leak has been stopped and the incident is over.
A good rule of thumb to follow when operating electric fans is to make the final power cord connection away from the fan and back at the source of power (e.g., a remote generator or apparatus). The last thing you want is to have an energized power cord produce a spark as you attempt to plug in a fan near the source of a gas leak.
There is a big difference between ventilating after a fire and ventilating after a natural gas leak. How big a difference? That will depend upon the size of the ensuing explosion if it’s not done correctly.
Questions or comments on this or any other monthly Hazardous Materials Survival Tip can be directed to Steven De Lisi at HazMatSurvivalTip@comcast.net.
Click here for more info on Steven De Lisi’s book, Hazardous Materials Incidents: Surviving the Initial Response.
Steven M. De Lisi is employed by Tetra Tech EM Inc. as a program manager responsible for planning, training, and exercise activities related to hazardous materials response. He recently retired from the fire service following a 27-year career that included serving as the deputy chief for the Virginia Air Guard Fire Rescue and a division chief for the Virginia Department of Fire Programs (VDFP). De Lisi is a hazardous materials specialist and as an adjunct instructor for VDFP, he continues to conduct hazardous materials Awareness and Operations-level training for fire suppression and EMS personnel. De Lisi began his career in hazardous materials response in 1982 as a member of the hazmat team with the Newport News (VA) Fire Department. Since then he has also served as a hazardous materials officer for the Virginia Department of Emergency Management; in that capacity, he provided on-scene assistance to first responders dealing with hazardous materials incidents in a region that included more than 20 local jurisdictions. De Lisi holds a master’s degree in public safety leadership and is the author of the textbook entitled Hazardous Material Incidents: Surviving the Initial Response, published by PennWell.
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Subjects: Natural gas incidents, gas explosions, firefighter hazmat training