National Academies Press: OpenBook

Assessing and Mitigating Electrical Fires on Transit Vehicles (2021)

Chapter: Chapter 3 Recommendations for Reducing the Incidence of Electrical Fires

« Previous: Chapter 2 Review of Data
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Suggested Citation:"Chapter 3 Recommendations for Reducing the Incidence of Electrical Fires." 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 12
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Suggested Citation:"Chapter 3 Recommendations for Reducing the Incidence of Electrical Fires." 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 13
Page 14
Suggested Citation:"Chapter 3 Recommendations for Reducing the Incidence of Electrical Fires." 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 14

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12 Chapter 3 – Recommendations for Reducing the Incidence of Electrical Fires Data Analysis The investigation team studied the electrical fires listed in the Bus and Rail Databases created for the work described in Chapter 2. The primary cause for most of these incidents was classified by the transit agencies supplying the information as either “maintenance issues” or maintenance related. This implies that a maintenance process was either missed or completed in a way that contributed to the origin or spreading of the fire. The team noted that most of the incidents occurred many years after the vehicles were manufactured, which is an indication that the original vehicle designs were not a significant cause of or contributor to the fires. Many transit properties that responded to the team’s questionnaire concerning fires on vehicles indicated that training and maintenance were the primary areas where they needed assistance. As a result, the research team investigated the types of training and maintenance guidelines that would help prevent future fire occurrences. The team focused on preventive maintenance processes and training programs for maintenance personnel assigned to Preventive Maintenance Inspections (PMIs). Some of the transit systems responding to the team’s questionnaire indicated that their approach to preventing electrical fires included the development of PMI programs that emphasized fire prevention. The team approached these properties for additional information that could be used to develop best practices and recommended guidelines for bus and rail PM inspections. One such best practice was the creation of a training program that teaches technicians how to identify and reduce electrical fire risk factors. To reduce the hazards of electrical fires on transit vehicles, the investigation team is recommending that transit systems review their current PMI programs and ensure that they are designed to identify potential thermal events before they occur and make the proper repairs. A robust Preventive Maintenance Inspection (PMI) program is the foundation for a successful fleet maintenance operation. Keys to an effective PMI program are the design of the inspection process, the staffing of the program, and the inclusion of predictive maintenance elements in the program. Design of the Inspection Process All bus and rail car manufacturers’ maintenance manuals contain recommendations for items that need to be checked during inspections. The research team is suggesting that transit maintenance departments review the electrical sections of the manuals for all their fleet to make sure all procedures for the clamping and securement of power cables, cable routing, and inspection of insulation condition are included in their PMI procedures and inspection checklists. Inspections should include the testing of connections for proper securement. All bolted cable connections need to be periodically retorqued to the manufacturer’s recommendations. There are no known detailed American standards for the inspection of electrical cabling on buses and rail cars. The Australian government publishes a standard for fire protection of mobile equipment: Standard AS 5062. Section 3.3.1.4 of the Australian Standard provides guidelines for inspection of vehicles to reduce the potential for fire risk. These guidelines include checks for: • Clamps not being tightened;

13 • Missing cable clamps; • Incomplete maintenance activities that may have created additional fire risks; and • Damage or deterioration of cables and mechanical components. The research team is recommending that these Australian inspection guidelines be incorporated into all transit system PMI procedures. When vehicle manufacturers’ engineers design buses and rail cars they route and secure cables and electrical wiring to minimize the risk of shorting. When maintenance crews change out components, they may not replace clamping devices properly or route cables the way the manufacturer designed. This results in an increased chance of electrical fires. The research team is advising transit systems to photograph the engine compartments of new buses and power cable routing on new buses and rail cars. This will create a graphic record of the original cable routing, which will serve as a valuable tool for crews inspecting and making repairs to the vehicles. Cable routing diagrams should be included in repair manuals or repair instructions when appropriate. Inspection Staff Just as important as the inspection process is the need to have qualified, experienced mechanics performing PMIs and making the proper repairs. It is critical that the mechanics doing PMIs be able to identify potential electrical fire hazards and make the necessary repairs to prevent the fires from occurring. The investigation team found that the qualifications of the PM inspectors at different transit systems vary significantly. Some properties schedule their inspections for the night shift, which results in mechanics with little experience performing inspections. Other locations use their more experienced mechanics to do troubleshooting, leaving the PMIs for the less experienced members of the staff. The project team is recommending that transit systems assign experienced mechanics to perform preventive maintenance inspections and repairs. If it is not possible to assign experienced mechanics to perform PMIs, it is recommended that systems implement a program where an experienced mechanic and/or first line maintenance supervisor makes spot checks of the work performed on PMIs. Recommendations for the Training of PM Inspectors The research team suggests that all transit systems examine the training provided to the mechanics who perform PM inspections to make sure it is adequate for identifying fire risks. Several of the properties interviewed advised the research team that they feel it takes 5 to 6 months to train an experienced mechanic to become a qualified PM inspector. As a minimum, 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 classroom portion should emphasize the vehicle manufacturer’s guidelines for preventive maintenance inspections. It should also include thorough physical reviews of each type of vehicle in the system’s fleet, emphasizing proper hose and cable routings for each one. Photographs of improper routing, chaffing conditions, and improper clamping should be presented to the students. This will help the student understand why PM inspections are such a critical part of the vehicle maintenance program. Each student should be given an instruction manual describing how to complete each item on the inspection checklist for each type of vehicle in the fleet. The manual needs to contain all important vehicle specifications and a series of illustrations showing the original routing of all hoses and cables. At the end of the class each student should be required to pass a test identifying actual defects planted on a vehicle by the training staff.

14 After completing the classroom portion of the training, it is a best practice to assign each student to an experienced PM inspector for several months of mentoring. Once the training inspector and the shift supervisor feel the student is capable of performing inspections independently, the student should begin to perform scheduled PMIs on a solo basis. The supervisor needs to monitor the student’s performance. It will be up to the supervisor to determine when the student becomes a “Qualified PM Inspector.” Predictive Maintenance Functions A number of the properties that responded to the team’s questionnaire advised that they did not have many issues with electrical fires on their vehicles because they had incorporated predictive maintenance work into their PMI programs. The theory behind effective predictive maintenance is to replace critical components as they approach the end of their useful life and before they fail in service. Bus maintenance staffs reported that they change starters, alternators, and fan motors on a mileage basis. Rail staffs talked about changing traction motors, current collection equipment, and main power cables with support brackets on a time and/or mileage basis. Sometimes these component changes are included in planned mid-life or quarter-life overhaul programs. These types of programs are eligible for FTA funding which minimizes the effect on the property’s operating budget. The research data indicates that adding predictive maintenance to the PM inspections is a good way to reduce the risk of electrical fires on buses and rail cars. The investigation team is recommending that all systems add predictive maintenance to their PM programs.

Next: Chapter 4 Fire Suppression System Studies »
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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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