BY DANIEL BAKER, CHRISTOPHER GOULD, AND JERRY KNAPP
IN FEBRUARY 2024, two separate explosions of common flammable and explosive gases, one in Los Angeles, California, and one in Virginia, demonstrated the dangers of responses to releases of explosive gases. Virginia had a familiar type of response: A propane leak and subsequent explosion killed one firefighter and injured nine others, with several Maydays with heavy entrapment and rapid intervention team operations in the basement of a home. In California, several firefighters were seriously burned during a response to a compressed natural gas (CNG)-fueled truck fire and subsequent explosion.
According to the Fire Department of New York (FDNY) publication Watchline, in LA, “A CNG-fueled semi-trailer exploded as members attempted to contain the truck fire, injuring several. The truck was not transporting CNG and had no trailer attached to it at the time but was fueled by two 100-gallon tanks of CNG, one of which had failed. According to the LAFD, ‘There was no warning of an impending explosion.’”1 We are all aware that accurate size-up and identification of alternate fueled vehicles are challenging on the scene of a vehicle fire, especially due to the small placarding of these vehicles. The purpose of this article is to familiarize you with CNG in transportation emergencies with CNG-fueled vehicles and virtual pipelines. We will review strategic and tactical considerations and lessons learned from two responses to virtual CNG pipeline incidents in New York.
NY Case Histories
In early December 2023, a tractor trailer carrying CNG left the roadway and came to rest under an overpass on Interstate 88 in upstate New York. A Quantam 51 upright tube trailer was leaking, and one cylinder had rocketed from the container. Most of the remaining cylinders were full and under pressure. The crash presented numerous challenges, including the extrication and technical rescue of the truck driver, the stabilization of leaking cylinders, and the emergency and deliberate venting of natural gas (NG) to the atmosphere so that the trailer could be safely removed from the ravine beneath the highway. The Duanesburg (NY) Fire Department, with assistance from multiple mutual-aid departments, the Schenectady County Hazardous Materials Team, the Schenectady (NY) Fire Department, and the New York State Office of Fire Prevention and Control, brought the incident to a conclusion after about a day and a half.
Later that month, on December 21, a second incident occurred in Glenville, New York, in another part of Schenectady County. The driver tried to go under a railroad bridge that did not have enough clearance. A Quantam 51 upright tube trailer carrying CNG struck the bridge and caught fire. The Alplaus (NY) Fire Department, assisted again by Schenectady County, the City of Schenectady Office of Fire Prevention and Control, and multiple mutual-aid companies, responded quickly and contained the fire and protected surrounding homes. In this incident, multiple cylinders rocketed from the trailer and traveled long distances, creating a large incident footprint that required hazmat teams to look for potential gas migration and verify that the natural gas had been consumed by the fire. Several homes were evacuated as a precaution and reoccupied the morning after the crash. In addition, the railroad bridge was damaged and required inspection and testing before it was returned to service.
Responses to releases of explosive gases (propane and NG) are common calls for most fire departments in the United States and usually present minor danger. Responses are complicated and often result in firefighter injuries or line-of-duty deaths when personnel lack critical understanding of design details of new CNG fuel tanks, CNG virtual pipelines, their safety devices, product hazards, etc. The use of CNG is increasing in the United States, especially as a vehicle fuel. It is important for us to thoroughly understand these systems so we can effectively and safely respond toemergencies. Unfortunately, the level of training required for these dangerous calls, as well as what we think of as routine gas leaks, is not in any mandated basic training programs but instead left to our varying levels of advanced training.
NG Properties
NG has a flammable range of 4-15% gas in the air but may vary slightly depending on specific concentrations of other gases that may be added. It is not toxic but acts as a simple asphyxiating gas. NG is odorless but in distribution pipelines is odorized with mercaptan; we are all familiar with that sulfur-like smell that healthy humans can detect at less than 1 parts per million (ppm).2
NG asphyxiations of civilians are extremely rare. Healthy humans can detect the odorant at less than 1 ppm due to its low vapor density. At 2-4 ppm of gas or odorant, most people get nauseous or recognize the hazard and self-evacuate.3 It is important to keep in mind that that 4% NG (lower explosive limit) is 40,000 ppm; there are documented cases of utility workers killed by leaking high-pressure gas lines in excavations without proper self-contained breathing apparatus (SCBA) or personal protective equipment (PPE). CNG used in both vehicle fuel and virtual pipelines is odorized. Due to its low odor threshold, it can provide valuable size-up information in emergencies. Releases of large amounts of CNG in enclosed spaces (such as truck maintenance shops) from CNG truck fuelor trailer loads present both fire/explosion and possible asphyxiation hazards.
According to the U.S. Department of Energy, NG is an odorless, gaseous mixture of hydrocarbons—predominantly made up of methane (CH4). It accounts for about 30%4 of the energy used in the United States. About 40% of the fuel goes to electric power production5 and the remainder is split between residential and commercial uses, such as heating and cooking, and industrial uses. Although natural gas is a proven, reliable alternative fuel that has long been used to power natural gas vehicles,6 only about two-tenths of 1%7 is used for transportation fuel. There are 175,000 vehicles in the United States fueled by CNG; as the number of NG-fueled vehicles increases, we must understand the hazards and the tactics required for safe mitigation of vehicle fires powered by NG.
For example, in Rockland County, New York, a large beer distributor’s Web site states that the 200 delivery trucks in service all use CNG for fuel. As we saw in the California example, these may result in anything but a routine truck fire. As CNG becomes more common as a motor fuel, department responses to truck and car fires involving high-pressure CNG cylinders will also increase, as will the need to be fully prepared. According to a CNG vehicle manufacturer, currently there are more than 11,000 transit buses, 5,500 school buses, and 17,000 refuse trucks in service today in the United States.
CNG Basics
CNG is compressed to less than 1% of its volume at atmospheric pressure and stored at up to 3,600 pounds per square inch (psi). It is 3.5 times less energy dense than gasoline. It takes 3.5 more volume of CNG to equate to the same energy production. This density is why CNG fuel tanks are much larger than gasoline tanks and often cut into available space in the vehicle.
CNG is compressed, not liquefied like liquid propane. Liquefied natural gas (LNG) is also a fuel source but is not as common as CNG. The Department of Energy describes why LNG is not a cost-effective vehicle fuel: LNG’s relatively high production cost and the need to store it in expensive cryogenic tanks limit the fuel’s use in commercial applications. LNG must be kept at cold temperatures and is stored in double-walled, vacuum-insulated pressure vessels. LNG is suitable for trucks that require longer ranges because liquid is denser than gas and, therefore, more energy can be stored by volume. LNG is typically used in medium- and heavy-duty vehicles. Some railroads are experimenting with LNG-fueled locomotives. “Florida East Coast Railway (FECR), in partnership with the Natural Gas for High Horsepower Summit, officially rolled out its 24-unit LNG fleet in November 2017, making it the first North American railway to adopt LNG. The fleet consists of 12 pairs of back-to-back GE ES44C4 locomotives with a purpose-built Chart Industries fuel tender in between. FECR, a Class 2 regional railway, is also the first railway in the United States to haul LNG as a commodity, under a Federal Railroad Administration (FRA) waiver.”8 It is also important to note that LNG has significantly different associated fire hazards and reactions as compared to CNG when released accidentally into both land and water and is beyond the scope of this article. It is crucial to know the characteristics that define each type of tank.9
CNG Vehicle Fuel Hazards
In smaller vehicles, the CNG tank is typically mounted in the trunk or in place of the standard gasoline tank. In pickup trucks, it may be in front of the bed behind the cab. Buses may have CNG tanks under the passenger compartment or above it in an enlarged roof section.
Larger trucks may have the traditional saddle (diesel) tanks replaced with a CNG tank. Long haul tractors may have three to five CNG tanks behind the cab where the sleeper would be in either vertical or horizontal configuration. These trucks may have saddle tanks of CNG as well. Refuse trucks (not rear loaders) may have cylinders above the cab or several large cylinders attached to the rear, under a cosmetic cover.
Four Types of CNG Tanks
A Type 1 CNG tank consists of solid steel, originated in 1900, and has steel walls 0.5 to 1.5 inches thick. Because of its weight, it typically has a diameter of 11 to 16 inches. It is low cost but not suitable for uses where weight is an issue.
A Type 2 tank is hoop-wrapped (wire, fiberglass, or carbon fiber) with composite fiber around a steel liner. It is typically used for personal vehicle fuel tanks or medical-grade oxygen in health care settings. It is vulnerable to corrosion, acids and abrasions, and UV light.
A Type 3 tank is aluminum wrapped with carbon fiber and has a service pressure of 3,600 psi. It weighs less than a Type 1 or a Type 2, is more costly, but is cheaper in the long run due to its ability to hold more gas. It is primarily used for heavy-duty truck fuel and transportation of CNG.
A Type 4 tank is the lightest weight due to the nonmetallic (polymer) liner wrapped with carbon fiber. It is lower cost due to the high-density polyethylene liner but has lower heat resistance and is best suited for slow filling with CNG. It is typically used as a fuel tank for vehicles and for tube trailers for virtual pipelines.
Tank Locations
CNG tanks can be in various places on vehicles. On trash trucks, they can be on top over the main compartment, over the cab, or in an extra blister compartment in the rear. Tactically, this location is important, because a fire in the trash can expose the tanks to enough heat to cause them to fail explosively. Dump the load of burning trash to stop the exposure on the tanks if it is early enough in the incident. It is more challenging to avoid putting water on a fully involved truck to allow the thermally activated relief valve to operate and prevent an explosion and rocketing of the tank parts. The critical factor is identifying a CNG-powered vehicle.
Buses typically have tanks over the roof in an enclosed compartment but can be custom mounted almost anywhere. Tractor trailers can have them mounted in place of saddle tanks, vertically behind the cab, or in the trailer portion. Package delivery vans (aka step vans) may have the Type 4 tank mounted along the frame behind the driver.
Relief Value
The relief valve on a CNG tank is thermally activated as opposed to a spring- loaded pressure valve on a liquid propane (LP) tank. Captain Bill Gustin, Mi- ami-Dade (FL) Fire Rescue, provides this advice as reported in his recent training bulletin: “To prevent a boiling-liquid, expanding-vapor explosion (BLEVE), firefighters are trained to apply water to the upper vapor space of tanks. Applying water to tanks reduces internal pressure, which, if allowed to increase, can rupture a tank or send it flying. Tanks containing LP gas are equipped with a pressure relief valve that will open and vent product to reduce internal pressure. Firefighters applying cooling streams on an LP tank will see results if they can cool the tanks to a point where the relief valve closes.”
The most important takeaway from this training module is that CNG pressure relief devices (PRDs) are actuated by heat—at 212°F to 220°F—not pressure. Efforts to cool CNG tanks may cool the PRDs and keep them from venting to relieve pressure. It goes against everything we have been trained on to keep tanks from rupturing.
If fire is impinging on CNG tanks, we must isolate the area 300 feet in all directions and avoid applying cooling streams of water; let the fire burn and allow the PRDs to reach their actuation temperature so they can function as designed to vent internal pressure. Allowing fire to impinge on CNG tanks without cooling them with water seems counterintuitive, but this is the recommendation of every manufacturer of CNG-powered vehicles and fuel systems. To be clear, only withhold water when CNG tanks are burning or fire is directly impinging on them.10
The training division of the Los Angeles (CA) Fire Department describes these types of PRDs as temperature pressure relief devices. A flame length of 50 feet for 10 to15 minutes (depending on the volume of gas in the tank) can be expected if the valve opens. This valve can be a serious hazard to members operating handlines if the vehicle is involved in a rollover or is not upright.
Thermally activated relief valves may be located on each end of the cylinder for saddle tank applications or remotely around the tank. These are on a live gas line at places at one-third and two-thirds the length of the cylinder. The goal is to detect flame or heat impingement on the composite tank and prevent the cylinder from exploding and creating a ground flash and rocketing tank parts.
On some fuel management systems on CNG-fueled trucks, there is a true pressure relief valve on the pressure regulator that will vent to the atmosphere. The pressure regulator steps down pressure from the tanks (3,600 psi) to around 125 psi.
Virtual Pipelines
NG transportation has been commonplace in New York for many years. However, recent developments in the industry have opened new opportunities for producers and consumers alike, increasing the frequency of shipments and the number of miles traveled.
In the past, to use methane, a customer had to be connected to pipeline distribution networks that were part of the permanent infrastructure. Businesses could only beadded to the system if they were in an area already serviced by the industry because the cost of extending service outside of existing service areas was prohibitive.
With the advent of new compressors that can quickly load cargo tanks and advances in lightweight tube trailer construction, the natural gas industry is able to provide customers not on the distribution network with plentiful and reliable energy that is more environmentally friendly than other fossil fuels.
The backbone of the industry is the upright tube trailer (Type 3 tanks) consisting of multiple upright cylinders made of lightweight composites designed to minimize trailer weight and maximize cargo capacity. Another manufacturer has 45-foot trailers that use four large cylinders containing a total of 507,000 cubic feet of gas.
The most common of these in New York is the Quantam 51, with 51 individual cylinders manifolded together. (Think of a traditional SCBA cascade-style system designed for natural gas.)
Housed in intermodal containers or soft-sided van-style trailers, virtual pipeline tankers may not readily indicate the presence of hazardous materials. In transit, the cylinders are at 3,600 psi and a full trailer will hold 500,000 cubic feet of gas and weighs 66,000 pounds. Labeling required by the Department of Transportation (DOT) will indicate “UNID 1971 Methane, Compressed.” The trailers will also have the words “Natural Gas, Compressed” written on the rear doors.
As the business relies on an uninterrupted supply of gas with frequent and regular deliveries to customer locations, the number of miles traveled in a particular area can vary but can be quite substantial. When taking into consideration the total number of deliveries, the fact that New York has experienced only five major incidents in the past decade is remarkable.
Although rare, when incidents do occur, they can quickly tax local resources and create hazards to the public and first responders for an extended period. In these cases, a planned and coordinated hazardous materials response is key to bringing the emergency to a safe and expedient conclusion.
Training and preplanning are key to the success of any hazardous materials response, and this is especially true when working with industries where transportation technology is rapidly evolving. The CNG space is no different, as companies seek to expand their markets and take advantage of the latest materials and methods available to maximize the benefits to their customers and their bottom line.
To keep abreast of these changes, first responders must have knowledge of virtual pipeline transportation in their response area. This could be as simple as watching normal traffic patterns and making a note of CNG transportation vehicles that you see on a regular basis. Then you should reach out to the companies. Often, virtual pipeline companies welcome inquiries from fire departments and hazardous materials teams and are eager to provide information and training to support preparedness for highway emergencies involving their equipment.
It is also important to note that travel lanes for these deliveries can change rapidly based on market conditions, the time of year, and available supplies of natural gas from transmission pipelines. The presence of transport trailers in a given area or on a particular highway may only last a short time or may be cyclical based on the needs of a specific customer. Regardless, fire and hazmat officials should reach out regularly to gauge the exposure to risk in their jurisdictions.
Training is vital to the success of these incidents and can take many forms. In New York State, the Office of Fire Prevention and Control offers customized training and consulting services to fire departments by request.
Virtual pipelines and response considerations are also discussed at length during a program at the New York State Academy of Fire Science titled Cargo Tank Truck Specialist. This class covers all DOT specification cargo tanks including those carrying specialty gases, with hands-on instruction using actual tank trailers including a Quantam 51 CNG tube trailer that is on site at the facility.
As previously mentioned, carriers and marketing companies have specialized training for fire and emergency services organizations that are tailored to their equipment and lanes of travel. In most cases, these programs may be offered annually or at the request of local first responders and are free of charge.
Preplanning and exercising of local response plans and interagency cooperation can contribute greatly to the success of an incident. Accidents with virtual pipeline trailers generally require resources at the local, county, and state level from all disciplines, including fire, EMS, law enforcement, environmental conservation, DOT, emergency management, and state and local governments. Each entity brings unique perspective, goals, and objectives to an incident, all of which must be met through a calculated and coordinated unified effort. Without previous consideration, these multiagency efforts can be difficult and can lead to unnecessary delays and potential impacts to the safety of responders and the public.
Look, Listen, Smell, Detect
There are several considerations when encountering a highway or industrial emergency involving virtual pipelines. Foremost of these is the ability of first responders to recognize and correctly identify CNG transportation equipment and then ensure that appropriate resources are called. The Office of Fire Prevention and Control has offered guidance to the fire service in four categories.
Look refers to visual clues that an overturned tractor trailer may involve virtual pipelines. Placards on these trailers will be Red Class 2 and have UNID 1971 prominently displayed on all four sides. The words “Natural Gas, Compressed” will also be stenciled on the container. There will also be markings from the DOT-DOT SP- 16524, which indicate a special DOT permit for compressed gas tube trailers like the Quantam 51.
Another visual cue is white clouds coming from the trailer. The condensed water vapor made visible by the low temperature of the escaping gas indicates an active natural gas leak. Vents in the top of these trailers may also show a release of vapor, but remember:
If the trailer is on its side, these relief devices are pointed directly at responders on the ground; avoid them.
Listen is a very helpful category during the initial size-up of a CNG virtual pipeline incident because leaks from containers and product coming from lifted relief valves will be extremely loud. Storage pressures in Quantam-style trailers average 3,500 psi, meaning leaks will be very noisy and hard to overlook. Uncontrolled releases will last 60 minutes or more, with faint hissing sounds coming from damaged or vented containers long after the initial release has subsided.
Another helpful hint for first responders is to listen to the truck driver if available for valuable information that can aid in your response.
Smell is a sense that is seldom useful or safe during hazardous materials incidents. However, when dealing with natural gas in virtual pipeline applications, an odorant is nearly always added to help with detecting leaks. In these cases, bystanders or first-arriving responders may report a rotten egg odor that is indicative of a release.
Detect means use air monitoring to confirm or rule out the presence of natural gas at an emergency. Standard four-gas fire service meters will detect methane, but remember that photo ionization detectors will not. Four-gas monitors that use catalytic bead sensors are blind to low levels of explosive gases.
Laser-based methane detectors are extremely useful for size-up and pinpointing leaks and releases. Due to the 100-foot instrument range and its immediate reaction time, laser-based detection provides a huge advantage during size-up of any natural gas emergency. Many suburban New Jersey and New York fire departments use these as excellent size-up tools for both inside and outside natural gas emergencies.
Actions to Take
Once you have determined that an incident involves a virtual pipeline tube trailer, take the following immediate actions:
- Consult the North American Emergency Response Guidebook, Guide 115 Gases-Flammable.
- Wear firefighter turnout gear with SCBA when approaching damaged trailers.
- Control traffic that may cause ignition of leaking gas.
- If a leak is suspected, deploy water handlines to protect personnel downrange.
- Beware of fire and explosion hazards: Isolate damaged trailers 330 feet in all directions; ruptured cylinders may rocket and move at high speed over long distances.
- Allow fires to burn and protect exposures; cooling vented cylinders will NOT reseat lifted thermally activated relief valves, which will continue to vent until all product is released.
- Request hazardous materials team support.
- Notify and request assistance from the gas marketer or carrier.
Tactics for virtual pipeline accidents should consider the two major hazards involved, namely flammability of the product and the risk of injuries caused by high storage pressures in the containers.
A thorough damage assessment by first responders and industry experts is key to the safe mitigation of these emergencies. Heavily damaged trailers will require removal of product to eliminate the risk of fire or the unexpected movement of gas cylinders. In these cases, product flaring or transfers are often ineffective, and you must vent gas to the atmosphere after you consult local environmental officials.
The emergency venting process is complex and requires a thorough risk assessment and significant planning and resources. It should not be attempted by inexperienced teams or without consultation and collaboration with industry experts. Due to the volume of gas, venting will take a considerable amount of time.
CNG-fueled vehicles and virtual pipelines will become more common as we seek alternative fuel sources. It is critical that the American fire service has a thorough understanding of these emerging threats to provide good service to those we are sworn to protect and for our members’ safety.
Authors’ note: Thanks to Quantum Energy Regional Field Service Representative Max Moore for his help with this article.
ENDNOTES
- Fire Department of New York (FDNY). Watchline, 2024.
- Agency for Toxic Substances and Disease Registry (ATSDR). Managing Hazardous Material Incidents, Vol. 3. United States Department of Health and Human Services, 2001.
- Agency for Toxic Substances and Disease Registry (ATSDR). Managing Hazardous Material Incidents, Vol. 3. United States Department of Health and Human Services, 2001.
- “Primary Energy Consumption by Source.” U.S. Energy Information Administration, 2020, bit.ly/3TvkgLt.
- “Natural Gas Consumption by End Use.” U.S. Energy Information Administration, 2024, bit.ly/3zjW87N.
- Alternative Fuels Data Center. “Natural Gas Vehicles.” U.S. Department of Energy, bit.ly/3ZnYnSi.
- “Natural Gas Consumption by End Use.” U.S. Energy Information Administration, 2024, bit.ly/3zjW87N.
- Vantuono, William. “Turning on the Gas: Florida East Coast Railway Embraces LNG Locomotives.” International Railway Journal, 21 Mar 2018, bit.ly/4d8lrr8
- Vantuono, William. “FEC Goes LNG.” Railway Age, 10 Nov. 2017, pp. 1-4.
- Gustin, Bill. “Compressed Natural Gas (CNG) Powered Vehicles.” Miami Dade Fire Rescue Training Division.
DANIEL BAKER is the chief of hazardous materials for the New York State Office of Fire Prevention and Control. He has been in the fire service for 29 years and was a small business owner prior to entering state service in 2005. He oversees all state-level hazmat training and the operations of the state hazmat team.
CHRISTOPHER GOULD is a fire protection specialist for New York State. With 30 years of public service, he provides hazardous materials training, supports response operations, and creates digital media for educational and memorial events.
JERRY KNAPP is the chief of the Rockland County (NY) Hazmat Team, has a degree in fire protection, is a 48-year veteran firefighter/emergency medical technician (EMT) with the West Haverstraw (NY) Fire Department, and is a former paramedic. He served on the technical panel for the UL residential fire attack study. Knapp is the coauthor of two Fire Engineering books: House Fires and Tactical Response to Explosive Gas Emergencies. He is the author of numerous articles in Fire Engineering and state, national, and international fire service trade journals. He is also the author of the Fire Attack chapter in Fire Engineering’s Handbook for Firefighter I and II. He retired from the U.S. Military Academy, West Point, where he served as the plans and operations specialist at the Directorate of Emergency Services.
