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Diesel fuel carriage in locomotives, while safe in normal operational conditions, presents a potential hazard in the event of serious accident or derailment. Development of an effective mitigation method against this hazard requires an understanding of operational conditions that lead to fuel spill and fire. This paper describes a study of fire hazard stemming from rail accidents and potential approaches to mitigation. Data for the study was obtained from a large sample of National Transportation Safety Board (NTSB) investigation reports for accidents involving both freight and passenger locomotive accidents over a 10-year period. Approximately 25% of the events reviewed resulted in fuel release. In addition, of the events that resulted in fuel loss, a large majority (almost 70%) resulted in fire. Most cases with major fires led to loss of life and/or property, including destruction of multiple locomotives. Typical road locomotives carry 3,000–4,500 gallons of diesel fuel during normal operation. As the locomotive consumes fuel, large volumes are available for vapor generation within the tank. In a post-collision scenario, the vapor that vents to the atmosphere at temperatures close to flash point of the fuel presents a significant fire hazard. Further, flammable mists can be generated by the sprays that develop due to fuel leaks from the post-impact movement of a train. Previous laboratory tests on a scaled tank demonstrated that fire in a fuel-rich vapor can flash back inside the tank causing an explosion or a large fire. This paper also assesses potential technologies to prevent or mitigate fire hazards in locomotive fuel tanks. These include fuel tank leak prevention or reduction of outflow from breached fuel tanks, monitoring vapor concentration within fuel tanks, and limiting vapor concentrations inside tank to maintain levels below the Lower Explosive Limit (LEL). Potential benefits of the latter method include minimization of pollution from escaping vapor as well as partial recovery of reusable fuel from vapor.

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It is estimated that up to 9.3 million persons may be impacted by locomotive horn noise and up to 4.6 million of those may be severely impacted.1 In 2009, there were over 1,900 incidents, over 700 injuries and over 240 fatalities at highway-rail grade crossings.2 The National Academy of Engineering Committee on Technology for a Quieter America has indicated that the public would benefit if train warning horns were more directional and has recommended that research and development be undertaken to better understand the effects on safety and benefits to the public.3 A directive train horn has the potential to focus audible warning signals to desired locations including pedestrians and motorists at highway-rail grade crossings while minimizing noise to the surrounding community and employees in the locomotive cab. As a part of an ongoing Federal Railroad Administration (FRA)-sponsored research and development effort, the authors have examined the feasibility of and recommended an acoustical specification for an optimized train horn that would improve the detectability of the warning signal for motorists at critical positions along the crossing road while reducing the area of environmental noise impact. The detectability, noise impact area and occupational noise exposure have been compared for the optimized horn and several typical standard horns. Near the beginning of most sounding events (1/4-mile from the grade crossing) the optimized horn reduces noise exposure because a narrow beam of sound can be generated and focused at the grade-crossing. As the train approaches the crossing, the beam width must become wider. It is found that detectability could be improved and noise impact area reduced by up to 57%, but the optimized horn must have a directivity pattern and amplitude that dynamically changes as a function of train position relative to the crossing. Current acoustic source technologies which generate directive sound were examined including “acoustic hailing devices” (AHDs) which are recent technological advancements typically used for naval communications. Capable of focusing high amplitudes of sound within a narrow beam and dynamically changing the directivity pattern through electronic beam steering, AHDs have been identified as a feasible means of meeting the required specifications. A critical design issue for the optimized horn is controlling the directivity pattern at low frequencies. Development and testing of a prototype is in progress and actual improvements to detectability and reductions in noise impact will be analyzed. The paper briefly discusses the feasibility of the optimized horn and general information on cost and implementation.