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Suggested Citation:"Summary." 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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Page 1
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Suggested Citation:"Summary." 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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Page 2
Page 3
Suggested Citation:"Summary." 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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1 Summary The objective of this research project was to develop guidance for assessing and mitigating electrical fires on transit vehicles. 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 problems of electrical fires on transit vehicles has recently been exacerbated by more crowded bus engine compartment configurations, equipment layout within auxiliary compartments, routing of cables, and multiple changes to vehicles to reduce environmental impacts, weight, and cost. This report 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. The research team collected and categorized more than one hundred forty (140) documents related to the prevention, mitigation, and reporting of transit vehicle fires from both North American and international industry resources. The team created a database to categorize and organize the data collected from these documents according to various functional classifications. This database is found in Appendix A. Our literature review did not turn up much information concerning fires that have occurred on transit buses and rail cars. As a result, the team developed a pair of questionnaires to capture key data requirements on causes of fires and their prevention from North American transit systems, one for transit buses and one for transit rail cars. The team received data from over 50 transit systems. Reports were collected on 164 recent bus fires from 47 different bus operators. The number one root cause identified in these incidents was electrical in nature. Fifty-four percent of the incidents were a result of electrical issues. Fire reports were also collected from nine rail transit systems. Of the 67 thermal events reported on rail cars, 12 occurred in heater units, six occurred in traction motors, and six resulted from shorted high voltage cables. In addition to the fire data collected by our surveys, the research team questioned the properties to reflect each system’s concerns about fire prevention for their fleet. The properties that responded cited a lack of information available in the areas of training and procurement. These systems also responded that their most successful strategies for reducing the incidence of vehicle fires included improved preventive maintenance procedures and additional fire prevention training for their technicians. The properties also indicated there is an industry need for additional research on the use of fire suppression systems on battery electric buses and rail cars. The research team used the fire data collected to develop recommendations for preventing electrical fires on transit vehicles. The team focused on preventive maintenance processes and training programs for maintenance staffs assigned to Preventive Maintenance Inspections (PMIs) to identify and reduce electrical fire risk factors. The goal was to develop recommendations to be used by transit system maintenance staffs that will alert them to potential electrical fire hazards on buses and rail cars. The

2 investigation team recommended that transit systems review their current PMI programs and ensure that they are designed to identify risks that could lead to thermal events and make the proper repairs. As part of the research, the team found that the qualifications of the PM inspectors at different transit systems vary significantly. The project team strongly recommended that all transit systems assign only experienced mechanics to perform preventive maintenance work. Several of the properties surveyed indicated that they had few if any vehicle fires, and they attributed this to their implementation of predictive maintenance procedures. The investigation team recommended that all systems consider adding predictive maintenance functions to their PM programs. The research team is recommending that all transit systems examine the training provided to the mechanics who perform PM inspections to make sure it provides adequate instruction for assessing fire risks. The team suggested that a good training program for mechanics assigned to do PM Inspections should include several days of classroom training coupled with many hours of hands-on training. The team recommended that an experienced inspector periodically review each trainee’s progress with the training staff and supervision, and it should be the supervisor’s decision when the student can become a “Qualified PM Inspector”. The project team identified two subject areas from the survey results that would benefit from additional investigation and research. • A study of the efficacy of current fire suppression systems installed on conventional diesel, CNG and hybrid powered buses. • An evaluation of fire suppression systems on battery powered transit buses and electric rail vehicles. The team recommended that these research activities be undertaken as part of this project. The Project Panel directed the investigation team to conduct these two additional research activities. The research team developed a plan to conduct these two research activities. The team reached out to over 50 operating properties, bus and rail car manufacturers, and fire suppression suppliers to collect the data required to complete this research. For the study on the effectiveness of fire suppression systems, responses were received from 24 transit systems. The data showed that 20 of the respondents have equipped all the buses they purchased in the last three years with fire suppression systems. Most of these systems were supplied by one of two manufacturers. Suppression systems were primarily installed to protect the engine compartments and exhaust systems. Eleven of the transit properties reported they had experienced at least one fire on buses equipped with fire suppression systems, for a total of 65 fires. Of those 65 fires, all but seven were extinguished by the on-board suppression system. That works out to an 89.2% success rate. Based on the data collected by this study, the research team recommended that all transit systems order their new conventional diesel, CNG, and hybrid buses with fire suppression systems. For the second study on fire suppression systems on electric powered vehicles, the team reached out to all fire suppression system suppliers, and Battery Electric Bus (BEB) and electric rail car manufacturers in North America. Responses were received from three suppliers of fire suppression systems. Only two BEB builders responded, and no electric rail car rebuilders filled in the questionnaire. All three fire suppression system suppliers indicated that additional research and testing needs to be performed

3 before fire suppression systems can be provided that will be effective on electric vehicles. The two BEB builders responding indicated they have installed fire suppression systems on about 25% of the buses they built. Neither bus manufacturer has conducted any research in the effectiveness of fire suppression systems for their buses. Because of the lack of experience with fire suppression systems on electric vehicles, the project team is recommending that additional research be conducted to determine whether there are benefits to installing fire suppression systems on electric vehicles. The research team made a series of recommendations to mitigate the number of electrical fires occurring on transit vehicles. Some of these recommendations can be implemented successfully by individual transit systems. Others might be most effectively implemented industry-wide in conjunction with the American Public Transportation Association (APTA) or other rail standards development organizations. APTA committees could potentially take a leadership role in implementing the research findings.

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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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