National Academies Press: OpenBook

Assessing and Mitigating Electrical Fires on Transit Vehicles (2021)

Chapter: Chapter 4 Fire Suppression System Studies

« Previous: Chapter 3 Recommendations for Reducing the Incidence of Electrical Fires
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Suggested Citation:"Chapter 4 Fire Suppression System Studies." National Academies of Sciences, Engineering, and Medicine. 2021. Assessing and Mitigating Electrical Fires on Transit Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/26288.
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Suggested Citation:"Chapter 4 Fire Suppression System Studies." National Academies of Sciences, Engineering, and Medicine. 2021. Assessing and Mitigating Electrical Fires on Transit Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/26288.
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Suggested Citation:"Chapter 4 Fire Suppression System Studies." National Academies of Sciences, Engineering, and Medicine. 2021. Assessing and Mitigating Electrical Fires on Transit Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/26288.
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Suggested Citation:"Chapter 4 Fire Suppression System Studies." National Academies of Sciences, Engineering, and Medicine. 2021. Assessing and Mitigating Electrical Fires on Transit Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/26288.
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Suggested Citation:"Chapter 4 Fire Suppression System Studies." National Academies of Sciences, Engineering, and Medicine. 2021. Assessing and Mitigating Electrical Fires on Transit Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/26288.
×
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Suggested Citation:"Chapter 4 Fire Suppression System Studies." National Academies of Sciences, Engineering, and Medicine. 2021. Assessing and Mitigating Electrical Fires on Transit Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/26288.
×
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Suggested Citation:"Chapter 4 Fire Suppression System Studies." National Academies of Sciences, Engineering, and Medicine. 2021. Assessing and Mitigating Electrical Fires on Transit Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/26288.
×
Page 21
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Suggested Citation:"Chapter 4 Fire Suppression System Studies." National Academies of Sciences, Engineering, and Medicine. 2021. Assessing and Mitigating Electrical Fires on Transit Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/26288.
×
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Suggested Citation:"Chapter 4 Fire Suppression System Studies." National Academies of Sciences, Engineering, and Medicine. 2021. Assessing and Mitigating Electrical Fires on Transit Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/26288.
×
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15 Chapter 4 – Fire Suppression System Studies Additional Research Activities As a result of the data collected from the transit systems surveyed, the project team identified two subject areas that would benefit from additional investigation and research. The investigators found that both bus and rail operators were looking for additional data and information on the design and performance of fire suppression systems on buses and rail cars. Because of this the investigation team recommended to the project panel that the following research activities be added to the project. • A study of the effectiveness of current fire suppression systems; and • An evaluation of fire suppression systems on battery powered transit buses and electric rail vehicles. The panel instructed the research team to proceed with these additional studies. Study of the Effectiveness of Current Fire Suppression Systems The data reviewed in Chapter 2 revealed that most transit buses are being equipped with fire suppression systems. Despite having fire suppression systems installed, there were several thermal incidents reported in the survey that resulted in significant fire damage. There is little reliable data available to transit systems regarding the effectiveness of fire suppression systems. Currently, transit agencies are unable to determine if the suppression systems in use are installed in optimal locations, or if the chemical agents being used are effective for the types of fires being experienced. There is no consensus among bus operators about the cost to maintain suppression systems. The project team initiated this study by gathering information on the use and efficacy of fire suppression systems on transit buses with conventional diesel, CNG, and hybrid propulsion systems. Questionnaires were sent out to over 50 transit agencies from North America and information was received from 24 of them. The systems that responded were willing to share their information, provided the source of the information was kept anonymous. From this sample size it was possible to come to some broad conclusions about the usage and efficacy of fire suppression systems in buses. This study focused on some of the basic characteristics of fire suppression systems in use today, their efficacy, and maintenance considerations. One of the main aims of this study was to determine how widely bus fire suppression systems are utilized in North American transit systems. A graph showing what percentage of new buses ordered with fire suppression systems by each transit system is shown in Figure 10. It shows that the specification of fire suppression systems is standard within transit systems, with 20 out of the 24 transit systems surveyed outfitting 100% of their new buses with fire suppression systems. Of the remaining four properties, one had suppression systems installed on 95% of its buses while the three others had installation percentages of 5%, 2%, and 0%. By taking the data presented here as representative of the entire population of transit buses, it is reasonable to say that the use of fire suppression systems is widespread throughout most transit systems in North America.

16 Figure 10 – Installation of Fire Suppression Systems The project team also collected data on how many manufacturers are providing fire suppression systems as well as where critical components were placed. This data was collected to see what areas transit systems considered the most fire prone and to build a base of knowledge for further study. Table 2 shows the relative popularity of different fire suppression system suppliers. The manufacturer’s names were kept anonymous. From the data shown here it is possible to say that Supplier A is by far the most popular supplier of fire suppression systems, with 20 of the properties surveyed saying that they use Supplier A’s systems in their buses. Supplier B is the second most popular with five of the surveyed properties saying that they have used their fire suppression systems. Finally, Supplier C’s and Supplier D’s systems were only installed on two transit systems each. There were several properties that used more than one manufacturer. This occurred because there were some instances where the bus builder sells a bus with a fire suppression system already installed, without any input from the transit system. Therefore, if the property bought buses from several different bus builders, it would also likely have several different fire suppression systems in use. While this table may provide a picture of the size or popularity of certain manufacturers, it does not necessarily portray the efficacy of any of these systems. A transit system may decide to rely on one manufacturer because it is simpler to maintain a single system, or because it is more convenient for the bus builder. In any case, this data provides a glance into the popularity of different fire suppression system manufacturers among bus transit systems. 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Pe rc en ta ge Property Percent of buses with Fire Suppression Systems

17 Table 2 - Supplier Popularity The data in Figure 11 shows that the main reasons for installing a fire suppression system was either because of a regulatory requirement or a request from the property itself. Over half of the transit systems surveyed had fire suppression systems installed for one of these two reasons. Four properties surveyed bought buses that already had fire suppression systems installed on them. The rest of the properties installed the systems because of a variety of safety concerns. These included concerns over the age of the buses or simply a desire to minimize losses in the event of an unfortunate incident. Reasons for including fire suppression systems appear to differ significantly between regions of the US. Property Supplier A Supplier B Supplier C Supplier D Property 1 X Property 2 X Property 3 Property 4 X Property 5 X Property 6 X X Property 7 X Property 8 X Property 9 X Property 10 X X Property 11 X Property 12 X Property 13 X Property 14 X X Property 15 X X Property 16 X X Property 17 X Property 18 Property 19 X X X Property 20 X Property 21 X Property 22 X Property 23 X Property 24 X

18 Data was also collected that shows the most common locations of critical fire suppression system components. Graphs for this data are shown in Figure 12. Figure 12 - Component Locations 0 2 4 6 8 System Request Manufacturer inclusion Regulatory Requirement Safety OtherN um be r o f p ro pe rt ie s Figure 11 - Reasons for System Installation

19 These graphs show the areas that the transit properties believe are in the greatest danger of catching fire. All of the properties surveyed had both sensors and nozzles in the engine compartment of their buses, which seems prudent, given that a large percentage of fires are caused by either electrical shorts or fluid leaks, both of which occur in the engine compartment of a bus. The next most common area to place critical equipment was near the exhaust pipe. This also fits well as exhaust leaks are responsible for a considerable number of reported fires. Similar attention is paid to the fuel tanks and electrical boxes with several transit systems saying that they include sensors and nozzles in this area. Lastly, some systems also had sensors and nozzles placed in other areas such as the wheel wells and battery/electrical boxes because of the fires experienced in those areas by those properties. The research team also collected information on the efficacy of fire suppression systems on transit buses. Each property was also asked to list the number of fires they experienced on their buses equipped with fire suppression systems, as well as the number of times their fire suppression system failed. This data is shown in the graph in Figure 13. From this graph, it appears that the fire suppression systems employed by most transit agencies are extremely effective. Of the 24 properties that responded to the survey, just under half reported having a fire on one of their buses equipped with fire suppression systems. Figure 13 – Efficacy of Fire Suppression Systems Of the transit systems that experienced fires, two properties that reported one of their fire suppression systems failing. Figure 14 compares the number of fires to the number of system failures. This diagram shows that out of 65 total fires reported, there were seven cases where the fire suppression system failed to stop the fire. That is an equivalent success rate of 89.2%, which signifies that these fire suppression systems were effective. Based on this data the research team is recommending that all transit systems order their new conventional diesel, CNG, and hybrid buses with fire suppression systems. 0 5 10 15 20 25 30 Pr op er ty 1 Pr op er ty 2 Pr op er ty 3 Pr op er ty 4 Pr op er ty 5 Pr op er ty 6 Pr op er ty 7 Pr op er ty 8 Pr op er ty 9 Pr op er ty 1 0 Pr op er ty 1 1 Pr op er ty 1 2 Pr op er ty 1 3 Pr op er ty 1 5 Pr op er ty 1 6 Pr op er ty 1 8 Pr op er ty 1 9 Pr op er ty 2 0 Pr op er ty 2 1 Pr op er ty 2 2 Pr op er ty 2 3 Pr op er ty 2 4 Nu m be r o f Fi re s/ F ai lu re s Transit system Fires and System Failures Number of Fires System Failures

20 Because data was received from only 24 of the over 50 transit systems contacted, and less than half of the properties that responded indicated that they had experienced at least one fire on a bus equipped with a fire suppression system, the results of this survey were limited. The research team feels that to expand the research on fire suppression systems, it would be helpful to have an industry data base to document all fires that occur on transit buses and the effectiveness of the fire suppression systems during those events. Figure 14 – Ratio of Fire Suppression System Successes to Failures The research team tried to determine how much each property spent maintaining their fire suppression systems each year. This data set was the hardest to produce as many transit agencies do not track the money that they spend maintaining the fire suppression systems on their vehicles. Eleven properties were able to provide their maintenance costs (Figure 15). The data varied between properties. Property 1 spent $47 per bus/year, while Property 6 spent close to $2000 per bus. There appears to be no correlation between the total amount spent on maintenance and the overall efficacy of the system. Property 24 spent close to $1500/bus maintaining their fire suppression systems but reported five system failures for the six fires reported. Meanwhile, Property 21 spent about $200 on the maintenance of their suppression systems and experienced no system failures. There was not enough data collected to come to any conclusions about fire suppression system maintenance. The research team is recommending all transit systems follow the suggested maintenance practices supplied by the fire suppression system manufacturers. 89% 11% Fires and System Failures Suppressed Fires System Failures

21 Figure 15 – Maintenance Costs per Bus per Year Evaluation of Fire Suppression Systems for Use on Battery Powered Transit Buses and Electric Rail Cars This study focused on the analysis of information pertaining to the use of fire suppression systems on battery powered transit buses and electric rail cars. The research team contacted the known vendors of vehicle fire suppression systems in North America to collect any test data they might have on electric vehicles equipped with their systems. The team also attempted to contact electric bus and rail car builders in North America to get data on their use of fire suppression systems on electric vehicles. The team received responses from two electric bus builders, none of which were North American rail car builders. Therefore this report does not attempt to make definitive recommendations that transit systems can use when specifying fire suppression systems for their new all-electric buses and electric rail cars. Rather it identifies a need to perform additional development and testing of fire suppression systems for electric vehicles. The research team reached out to four North American vehicle fire suppression system manufacturers with a questionnaire. Three of the manufacturers returned the surveys. These suppliers reported that they have sold approximately 13,000 fire suppression systems for diesel/CNG/hybrid buses in North America, and another 600 systems for battery powered buses in the last 3 years. These manufacturers have not yet sold any fire suppression systems for electric rail cars. Each of these manufacturers use completely different suppression technologies. Supplier A uses a dry chemical extinguishing agent, Supplier B uses a water based fogging system and Supplier C’s system uses an aerosol system containing a solid oxidizing chemical. Fire suppression systems are designed to remove at least one of the three components that make up a fire: oxygen, heat, and fuel. The three systems described above remove both the oxygen and heat from a fire. On a vehicle the suppression system is only effective for the period of time the system is dispensing the suppression agent. After the suppression agent is completely expelled, oxygen is re- 0 500 1000 1500 2000 2500 Co st s (U SD /b us /y ea r) Property Maintainance costs

22 introduced to the immediate area. A key to completely extinguishing the fire is removal of the heat. If exhaust heat ignites a fire, the engine must be shut down to remove the source of heat. If an electrical short ignites a fire the heat will return if the electrical short still exists. Power must be removed from the circuit to stop the short circuit from creating heat. An effective fire suppression system must be able to isolate power when an electrical fire occurs. Battery powered vehicles create a whole new set of challenges for fire suppression systems. These buses are crammed full of high voltage electrical components and interconnecting cables and wiring. Electrical components are spread throughout the whole bus making fire detection and suppression a complicated issue. There are high powered electrical units on the roof, under the bus and in the rear compartment. It would be prohibitively expensive to install fire detectors and suppression delivery systems in all locations where high voltage equipment is installed. Besides the electrical equipment, these buses have large banks of batteries that are used for energy storage. Depending on the chemistry of the batteries conventional fire suppression agents may have issues when used for combatting fires in high powered battery packs. If the suppression agent is conductive, additional electrical shorts can be created. Water can react with the some of the chemicals used in the construction of the batteries and cause an explosive reaction. All three manufacturers indicated that additional research and testing needs to be performed before fire suppression systems can be provided that will be effective on electric vehicles. In the meantime, some transit systems continue to buy fire suppression systems designed for conventional diesel buses and install them in the rear compartments of battery electric buses with questionable benefits. The research team reached out to all North American battery electric bus (BEB) and electric rail car manufacturers with a questionnaire. Responses were received from two BEB manufacturers. Responses were not received from any electric rail car manufacturers, which may be attributed to the minimal interest of North American transit systems for installing fire suppression systems on electric rail cars. The two responding BEB manufacturers indicated that they have supplied fire suppression systems on about 25% of the BEB buses they have built over the last 3 years. The primary reason for the installation of fire suppression systems is customer request. Both manufacturers have installed fire suppression systems from all three of the major American system suppliers. Neither BEB manufacturer has done testing of fire suppression systems on their buses. The location of fire sensors and suppression nozzles is based on customer request. Neither bus manufacturer had any knowledge of fires on any of their buses (Note: While few BEBs are currently in service in the US [about 1200 or 2% of the US transit fleet] the number of BEBs in the US is expected to grow rapidly over the next decade). Neither company has conducted any research programs into the efficacy of fire suppression systems. Battery buses are equipped with sophisticated fault monitoring systems that detect short circuits and other electrical malfunctions. When a fault occurs the bus electrical systems normally are automatically shut down removing the sources of heat that can create a fire. BEB buses also have heat sensing systems that create a fault if excessive heat is detected in the main electrical components or the batteries. If a heat sensor causes a fault, it automatically shuts down the bus electrical systems. Fault detection is used as the first line of defense against electrical fires on BEB buses. The research team’s investigations did not uncover evidence that fire suppression systems are an effective means of controlling fires on electric vehicles. North American electric rail car manufacturers have not been requested to supply fire suppression systems on their current products. The BEB manufacturers have been requested to supply fire suppression systems on a portion of their buses by

23 some customers. In these cases, they install systems similar to what is installed on conventional diesel buses. These traditional fire suppression systems may not be appropriate for BEB buses. There may not be a need for fire suppression systems on BEBs because of the advanced electrical fault detection systems that are standard equipment on these buses. The design of appropriate fire suppression systems for BEBs is not currently known by the BEB manufacturers or fire suppression system manufacturers. The project team is recommending that research be conducted to understand whether there are potential benefits for installing fire suppression systems on battery electric buses. It is also recommended that if there are such benefits identified, fire suppression system manufacturers communicate to all transit systems the specific design elements for systems that are appropriate for use on battery-electric buses.

Next: Chapter 5 Implementation of Research Team Recommendations »
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Transit vehicle fires have safety implications for passengers and employees as well as liability implications for manufacturers, suppliers, and operators. Many of the electrical/arcing fire events experienced in the transit industry have led to a total loss of the vehicle and/or serious smoke incidents.

The TRB Transit Cooperative Research Program's pre-publication draft of TCRP Research Report 229: Assessing and Mitigating Electrical Fires on Transit Vehicles provides transit systems with information and techniques to avoid the interruption of revenue service, passenger injuries, and expenditures of operating and capital funds that occur as the result of fires on transit buses and rail vehicles.

Supplemental to the report is a Presentation describing details of the project.

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