Get to Know Your Gas Leak Size Up Tools

By Jerry Knapp, Rockland County Fire Training Center

Natural gas and propane leaks are a common call for most fire departments in New York. Strategic and tactical size up of releases of these explosive gases is the real challenge for us on-scene and the focus of this article.

Natural gas and propane have no odor. Civilians call us when they detect the odorant at levels below one part per million. This is the reason we get called to so many minor leaks, which is both a blessing and a curse for us. The blessing is we respond to and resolve the leak when it is far below dangerous levels. The curse is we get complacent because nothing ever happens, there is not near enough gas to turn this call into a life threat at most gas calls. But when we are complacent and it is a major leak it can have devastating consequences.

The hidden curse of these calls is the tree links of the failure chain that leads to disaster: most fire departments have limited training in natural gas/propane response procedures. It is not in any of our required training programs, so we have limited training on our gas meters (have you ever used them in a tabletop explosion chamber?) and our SOPs are generally weak and do not contain procedures for the seven types of natural gas leaks we routinely respond to. Paramedics have procedures for different types of heart attacks, we should have procedures for different types of gas leaks.

Lower and Upper Explosive Limits

For natural gas, we need 5% gas or 50,000 ppm to reach the lower explosive limit (enough gas to ignite/explode). It is when the leak is sufficient to enter the flammable range is when things can get exciting for us. In the case of propane, the flammable range is about 2-9% gas in the air. Response procedures are similar with three important exceptions: natural gas is lighter than air, propane is heavier than air, the flammable ranges are a bit different and your meter has a correction factor depending on what calibration you use. Read the directions for your meter!

Current Meters

It is likely you have a four-gas meter with the following sensors: LEL (lower explosive limit), oxygen, carbon monoxide and probably hydrogen sulfide. These are the required sensors for confined-space entry gas detection and are not specifically designed for explosive gas detection.

Let’s look at your LEL sensor. It likely is a catalytic bead-based unit. Gas enters the sensor (pumped in or passive entry) and it is exposed to two heated coils. One has a catalyst (chemical) on it that allows it to burn below its explosive level (LEL). The other heated coil is a reference. When the gas burns, it further heats the coil which in turn increases the electrical resistance over the reference coil and then the software provides us with a numerical reading in percent of the LEL.

The catalytic bead sensor has serious limitations. It is blind to low levels (1-3% LEL) of gas, which is why you can respond to a gas call and smell gas, but your four-gas meter reads zero! It will shut off to protect itself from burning out at 100% LEL (a very dangerous place to be). In our explosion chamber, you can see your instrument react to natural gas and propane, see its alarm limits and cross sensitivities to other gases. For example, your CO sensor will detect propane, hydrogen and acetylene. Just because it is showing you a CO reading, it may be detecting another gas it is sensitive to. Read the directions.

Four important points … First, read the directions that came with your meter. You may have noticed that I think it is important! Second, your SOP must contain an action level. An action level is what you want your firefighters to do when the meter reads a certain level. For example, your meter will alarm at 10% LEL. This is a good mandatory evacuation level for both civilians and firefighters. There is no national standard (your fire department must set it for its own operations) for action level, but your SOP must contain this important direction for your officers and members. Third, you can poison (kill) the sensor by exposing it to things like vinyl cleaners, petroleum products, hand cleaners and lotions. Fourth, you should pair up your four-gas monitor with an explosive gas detector with a metal oxide-based sensor.

Size Up: Major or Minor?

The strategic goal of our size up is to find out if this is a major (aka life-threatening) release of explosive gas or a minor leak (another annoying minor gas leak). The tactical goal of our size up is to find where the gas is going (nearby rooms, void spaces or buildings) and is it in major (dangerous) concentrations. Strategy and tactical procedures at gas leaks, just like when we are operating at a house fire support our mission of life safety. Life safety of both civilians and firefighters is our mission at gas leaks, not find and fix – that is the gas tech or plumber’s job. Our mission is life safety.

New Tools

Laser-based gas detectors make our size up faster and safer for both us and civilians. In basic terms, the instrument sends out a laser that is tuned to natural gas. The laser passes through the gas cloud and some of the laser energy is absorbed by the gas. The remaining laser beam bounces off the wall, floor, fence or ground and is reflected back to the instrument. The detector calculates the difference in energy sent versus energy it saw reflected and provides us with a number of how much gas is between you and the laser’s target.

It has a 100-foot range, which means you do not have to enter the dangerous area – a huge benefit. It reads instantly. Your currently four-gas meter may take as much as 30 seconds to provide a reliable reading and you or your members are in the kill box during this time. The laser will work through most glass and can reliably detect gas inside buildings without a dangerous entry for your members.

Laser-based gas detectors have been in use by the gas industry for the past 15 years, but are new to the fire service. As a size up tool, they provide instant and reliable detection to tell first in officers and units where there is no gas, where there is some and where there is a lot of gas. Obviously this allows us to make quick decisions on where to deploy our manpower/equipment to meet our mission of life safety. Laser gas detectors can be used both inside and outside for rapid size up. I have used our laser gas detector at gas emergencies and found the leak source before the gas technician. It is that good and that fast from a safe distance. It is also the best tool for locked buildings which I call IEBs (Improvised Explosive Buildings).

MOS

Another tool you must have if you respond to natural gas or propane emergencies is the metal oxide-based detector. These are inexpensive and have multiple uses. The reason you need a MOS-based explosive gas detector is that it will detect very low levels of gas, the levels your four-gas will not see. Additionally, MOS will detect these and other airborne contaminates: acetone, alcohol, ammonia, butane, ethylene oxide, gasoline, halon, hydrogen, industrial solvents, jet fuel, lacquer thinner, methane, propane and some refrigerants. This is similar to an instrument hazmat teams use to detect unknowns. A high-end unit sells for less than $400.

Response to natural gas and propane emergencies should be guided by your procedures for each of the seven types of emergencies. We have covered a couple of the latest innovations and critical aspects in this article. Successful tactical response to natural gas and propane emergencies is based on fully understanding your gas detectors strengths and limitations (read the directions), your ability to use state-of-the-art instruments to rapidly size up the release of explosive gas and your fire department’s SOPs that should be based on gas industry best practices. It is not easy, it takes good instruments and good training. It is a matter of life and death: yours.

Jerry Knapp is a 40-year veteran Firefighter/EMT with the West Haverstraw, New York, Fire Department and is a training officer at the Rockland County Fire Training Center in Pomona, New York. He is the Chief of the Rockland County Hazmat Team, a former nationally-certified paramedic and author of the Fire Attack chapter in the FF1-2 manual published by Fire Engineer and author of numerous articles on house fires. Battalion Chief Knapp is the author of the tactical and scenario-based reference book titled, House Fires. He is on the technical panel for the latest UL Study on Fire Attack at House Fires. He recently retired from the U.S. Military Academy, West Point, as the Plans Officer, Directorate of Emergency Services