In recent years, the transit industry has seen an increased embracement of and investment in fire suppression systems on board vehicles. A bus fire can lead to a handful of serious complications, including passenger security, costs to cities or agencies, loss of capacity and traffic disruptions.

But while significant safety protocol is in place to protect the lives of both the passengers and the driver, the new challenge is social media and the rapid dissemination of information.

In a true thermal event, a video or photo of the scene could quickly find its way onto YouTube or Facebook, making an incident and a brand highly visible to the public eye.

However, new and improved fire suppression systems help detect any signs of a fire, even before flames come into play. Better detection leads to a quicker and more efficient response to out-of-the-ordinary conditions with different modes of suppression, depending on the needs of the vehicle.

The combined value of a fire suppression system garners a great deal of worldwide industry interest — both among agencies and researchers — which will only further expand in the coming years.

What is A Re-flash?

If a fuel leak contacts a hot surface, such as an engine, a fire is ignited once it reaches a flash point. A fire suppression system can knock out a fire; however, if the heat is not successfully lessened as well, a secondary fire can occur as the fuel continues to leak. This is what’s known as a re-flash.

One way to combat this problem is by investing in fire suppression systems that offer a prolonged duration of solution discharge. This will help take the temperature below flash point.

Fogmaker North America’s water mist system discharges for a full 60 seconds on average. The mist continues to blanket the exposed surfaces to help eliminate the possibility of a re-flash.

Detection tech meets new needs
Whether it’s to fulfill environmental legislation or improve fleet efficiency, the movement toward alternatively-fueled vehicles in the transit industry continues to grow.

But as alternative fuels provide major benefits to agencies worldwide, they have also introduced new fire risks. In some cases, this technology has resulted in increased bus engine compartment temperatures as well as gas leaks.

According to Science Partner (SP) Technical Research Institute of Sweden — notable for its fire research — an event that raised a lot of awareness was an explosion on a CNG-fueled bus in Holland. All passengers escaped safely, but footage of the vehicle and its 50-foot flames gained thousands of views after a bystander uploaded it to YouTube.

Fire suppression system manufacturers are combating the facts with improved protective measures. This includes the installation of gas detection devices on board the vehicle, but more importantly, equipment that can provide earlier fire detection overall.

“Traditional diesel buses have known hazards too, but it’s easier to identify a leak if you can see a pool of diesel,” says Scott Starr, director, marketing, for Firetrace, an Arizona-based fire suppression systems manufacturer. “With compressed gas, it’s more of a vapor, which requires different detection.”

As part of its fire suppression system, Firetrace offers a protection system to help monitor the gas levels in critical spaces within the bus to prevent them from reaching an explosive level. Alarms and warnings go off at the driver’s station. An alert is issued on the vehicle as well.

“As buses develop and become more complex, new challenges will inevitably come up,” says Starr. “But, I’m confident there will always be a solution — so far there has been good development of technology.” 

Advanced, early heat detection
Regarding heat detection, the industry is seeing more pressurized tube systems. For Fogmaker North America, an Exton, Pa.-based fire suppression system manufacturer, this technology is called Loss of Pressure (LOP). And Firetrace refers to its proprietor pressure system as Firetrace Detection Tubing (FDT).

Fogmaker’s Loss of Pressure fire suppression system uses high-pressure water mist technology. The discharged solution suppresses the fire by knocking out the oxygen in the environment and provides a cooling element as well.

Fogmaker’s Loss of Pressure fire suppression system uses high-pressure water mist technology. The discharged solution suppresses the fire by knocking out the oxygen in the environment and provides a cooling element as well.

According to Jeff Krueger, director, engineering and quality, at USSC Group, Fogmaker’s parent company, the significant advantage of the pressure tubing system is that it doesn’t require any electrical input to initiate. Electrical sources, battery backups and control panels are not needed, which makes the system fail safe with regard to activation upon thermal event. It activates by sensing heat, and once that heat reaches a certain point, the fluid-filled tubes rupture, opening a valve that releases the suppression agent.

“Since most fires start with smoke or steam, the fire could, in some cases, be detected through heat before there are even any flames,” says Jonas Brandt, vehicle fire safety project manager with SP’s fire research division.

If the system activates, the driver can simply locate the cause of the failure, clean out the burst fluid area and get back on the road.

Firetrace’s system can be routed throughout the vehicle, especially at known failure and heat-bearing points — places where there’s a perceived risk. SP reports that as of July 2014, it is required in Europe to install fire detectors in the engine compartment of buses, which is a known problem area. According to Fogmaker’s Krueger, North American agencies are beginning to incorporate SP protocol when specifying systems for its buses.

Both Fogmaker and Firetrace regard LOP and FDT systems as less of a maintenance challenge as well. Agencies can schedule maintenance to check for pressure on its fire suppression systems alongside a bus’ regular service interval. Over a longer span of time, about five years, technicians can actually take out the suppression agent to ensure it’s still active and possibly exchange fluids.

“There’s no real significant impact on the time it takes to service,” says Firetrace’s Starr. “You get quicker detection and reaction, and it’s easy to verify if things are working. Is there pressure? Then it’s ready to go regardless of a bus’ electrical functionality.”

Versus an electrical system, a pressure tubing system has fewer components that could fail; therefore, agencies are saving on cost as well. Replacement fluid and/or powder are not expensive and there are no other ongoing costs other than the verification that the system’s retaining pressure.

The installation is professionally done, but typically the services and maintenance can be completed in-house with training.

“If your maintenance yard can do an oil change, they’ll be comfortable using our equipment,” says Starr.

Back-end Development
With the amount of electronic systems monitoring on board vehicles — from GPS to tracking technology — there’s great potential for fire suppression data to be collected and analyzed. Certain agencies are looking to increase the use of electronics from an acquisition standpoint to learn more about its own thermal event trends.

“After an event occurs, transit companies would certainly like to have the ability to study some of the information on the area where the fire had occurred,” says Fogmaker North America’s Jeff Krueger. “They’d like the ability, at the point of occurrence, for a signal to be sent out to different key stakeholders, like a maintenance director for instance.”

Though still in development stages, many manufacturers are building electronic tracking systems to integrate into future systems. They would be offered either as part of the total fire suppression package or as a peripheral add-on.

The goal is to help agencies with data lobbying and issues of protection, providing real-time updates.

“Bus technology changes dramatically, so does the amount of systems monitoring on board vehicles, and fires suppression can be yet another part of that plug-in if designed properly,” says Firetrace’s Scott Starr. “It would give agencies the opportunity to monitor these events not only at the scene but remotely as well.”

Liquid or powder?
There are two major methods for putting out fire: liquid and powder solutions. According to SP, an agency can’t go wrong since both are proven methods. The system, as a whole, just needs to knock out all three elements of the fire triangle — oxygen, heat and fuel — effectively.

Firetrace’s Detection Tubing is a proprietary pressurized tube system that can be routed throughout the vehicle, especially at failure points.

Firetrace’s Detection Tubing is a proprietary pressurized tube system that can be routed throughout the vehicle, especially at failure points.

Starr says the most popular fire suppression agent in the U.S. right now is ABC Dry Chemical. It is usually a mix of monoammonium phosphate and ammonium sulfate. Used frequently in fire extinguishers, this chemical is very flexible and a capable fit for the conditions found in a motorcoach or bus.

Liquid solutions such as water mist, on the other hand, are newer to the market. While it’s prevalent in Europe, water mist systems have only began to increase in the U.S. in recent years.

“If you go back five years, there were minimal water mist systems in the transit industry,” says Krueger. “Now, we have several thousand units installed in North America with a continued strong growth curve as agencies become more aware of this proven technology and its advantages.”

Mercedes and Volvo are two of Fogmaker’s biggest clients using its fire suppression system with high-pressure water mist on most of their vehicles. In Fogmaker’s European branch, 85% of its clients use water mist.

“It’s a pretty telling story on the focus of trends,” says Krueger. “We have about 150,000 water mist units currently in production.”

The system displaces the oxygen in the fire triangle with the water mist turning to steam and pushing the oxygen out of the environment, thus choking the fire.

One of its most notable benefits is that it not only suppresses the fire by knocking out the oxygen, but provides a cooling element as well. This takes the heat out of the fire, which helps eliminate re-flash scenarios.

Another advantage appealing to agencies recently is that the water mist system is environmentally friendly, whereas some powders and chemicals can be harsh. From a post-activation standpoint, the system also features easy clean up.

After activation, the fuel is blanketed by AFFF — a commonly used low-expansion foam. The fuel then cannot contact the hot surface again as the foam acts as a barrier between the surface and any continued fuel leaks. Once the fire is successfully suppressed, no powder needs to be swept or collected — agencies can simply power wash the covered area.