Case study: What fire chiefs must know about CNG trucks

Updated on June 27, 2017

Several organizations have brought the growing issue of alternative fueled vehicles to the attention of the fire service. One such program is the NFPA’s “Alternative Fueled Vehicle Safety Training” funded through the Federal Emergency Management Agency.

While this training centers on electric, hybrid and hydrogen-fueled vehicles, there have also been incidents where both propane- and natural gas-fueled vehicles have initially caught firefighters unaware of their potential dangers.

The Indianapolis Fire Department experienced such an event in 2015, and has gone to great lengths to both research what happened and provide insight gained through their experience by publishing both a Significant Incident Investigation Team report and by producing an extensive PowerPoint covering the incident. I spoke to Capt. James King of the IFD’s training division about the incident.

In the predawn hours of Jan. 27, 2015, IFD received a 911 call from a nearby business for what at first sounded like a routine vehicle fire in a trash truck at the intersection of 86th Street and Westfield Blvd. A single engine company was dispatched and on arrival they discovered a well-involved fire in the hopper body or compacter area of a Republic Services residential garbage truck.

On arrival, the engine company officer requested that the trash truck driver drop the load in the street. But for whatever reason, the driver wouldn’t comply with this request.

Indianapolis SIIT Team Investigation

Near miss with CNG

The engine company crew took a supply line and initially pulled 1¾-inch lines to attack the fire, when the driver of the truck informed the fire crew that the “gas tanks” were located on the top of his truck.

This was the first indication that the vehicle was fueled by something other than diesel fuel. The engine officer requested a ladder truck be dispatched and that unit placed an elevated stream into operations in an attempt to cool the rooftop fuel tanks.

Less than 15 minutes from the engine’s arrival, several of the rooftop tanks filled with compressed natural gas (CNG) BLEVEied, spraying shrapnel in a 360-degree pattern and striking one firefighter in the helmet with a force that knocked him to the ground.

One of the tanks traveled a quarter mile and landed about 40 feet in the front of an elementary school. The garbage truck sustained considerable damage from both the fire and the resulting blast.

Additional units, including a hazmat unit, battalion chief and safety officer, were dispatched following the explosion. The incident was terminated approximately two hours after the initial call, but prompted an extensive follow-up investigation that resulted in the SIIT report.

Detecting natural gas

IFD discovered that Republic Services had 97 such CNG-powered vehicles in their Indianapolis fleet as well as CNG vehicles being used by at least three other major companies in their response area. The information developed during the investigation indicates that there are four types of tanks being used on CNG vehicles.

The type involved in this incident consisted of a plastic gas-tight liner reinforced by a composite wrap to provide additional strength but keeping them lightweight.

The CNG used to fuel vehicles may or may not have mercaptan added to provide the smell we normally associate with natural gas. As many trash companies reclaim and resell the methane naturally produced by a landfill, this may also be the source of the CNG used in their vehicles.

While mercaptan may not be present, each vehicle has a built-in natural gas meters to detect any potential leaks from seals or through damage.

In this incident, the design of the rack holding the tanks to the top of the vehicle may have had a significant part in the subsequent explosion. The rack was designed for maximum protection against tanks puncture during a motor vehicle crash.

However, this design also appears to have prevented water from cooling the tanks from the impinging fire in the compacter. Each tank that ruptured had an external pressure-relief valve at each end of the tank, but the water intended to cool the tanks could not penetrate the tank holder.

Instead, it cooled the pressure-relief valves to a temperature where they did not activate, which allowed the pressure within the tanks to increase to a point where they ruptured close to the center point of each tank.

Avoid a BLEVE injury

Retired Colerain Twp. (Ohio) Battalion Chief Randy Ellert is now the safety manager for the Cincinnati-based Rumpke Waste and Recycling, one of the nation’s largest family-owned solid waste firms. He said the number of CNG trucks on America’s roadways is increasing.

CNG and diesel trucks can pose risks to firefighters when they are impacted by fire. The most important step a driver can take is to safely eject the burning load and pull the truck away. Ellert also encourages fire departments to use the Indianapolis incident as a case study before they encounter a CNG truck fire in their jurisdiction.

The IFD report listed these 12 significant lessons learned from this incident.

1. In an incident of this type with a confirmed CNG-propelled vehicle, insist that the driver dump the load from the hopper.
2. Position apparatus at an angle in the area of the front corners of the garbage truck.
3. If possible, confirm how long the hopper has been on fire.
4. Attempts to extinguish the refuse on fire should only be made if there is access to the hopper through an opening.
5. This attack should be unmanned if possible by a deck gun or unmanned master stream.
6. Secure a 500-yard area in all directions.
7. Positioned personnel behind apparatus as a shield after critical functions have been completed.
8. The cascade cover will prohibit effective tank cooling if the tanks are exposed to direct flame contact.
9. Provide department-wide training concerning recognition of these types of vehicles and the dangers posed by them to responders and the public.
10. Update response protocols involving CNG-propelled vehicles, especially those vehicles with CNG tanks covered by steel. The normal response of cooling fuel tanks for fear of BLEVE will most likely not work in these types of incident and can lead to serious injury or death.
11. If there is a risk of BLEVE, and the fire cannot be extinguished soon after the fire is started, evacuate the area and prepare for exploding tanks and materials to shrapnel.
12. Re-enforce the need for a thorough and complete 360-degree size-up when responding to these types of incidents.

Ironically, on March 23, 2015, Indianapolis’ neighboring Fishers Fire Department had a similar fire involving another CNG-powered Republic Services truck. Upon its discovery, the truck driver immediately dumped the load and pulled the vehicle away from the fire.

Firefighters quickly handled the dumped load and small fire remaining in the vehicle without incident thanks to following these IFD guidelines.