Significance and Use
4.1 This guide is intended for use by those undertaking the development of fire hazard assessments for rail transportation vehicles and products contained within rail transportation vehicles.
4.2 This guide provides information on an approach to develop a fire hazard assessment, but fixed procedures are not established. Any limitations in the availability of data, of appropriate test procedures, of adequate fire models, or in the advancement of scientific knowledge, will place significant constraints upon the procedure for the assessment of fire hazard.
4.3 A fire hazard assessment developed following this guide must specify all steps required to determine fire hazard measures for which safety thresholds or pass/fail criteria can be meaningfully set by responsible authorities. It is preferred that such exercises have input from various sources.
4.4 Outcomes: Use and Application.A fire hazard assessment developed as a result of using this guide should be able to assess a new product being considered for use in a certain rail transportation vehicle and reach one of the conclusions listed in 4.4.1 – 4.4.4.
4.4.1 New Product Safer than Product Currently in Use.The new product is safer, in terms of predicted fire performance, than the one in established use. In this case, the new product is desirable, from the point of view of fire safety.
4.4.2 New Product Equivalent in Safety to Product Currently in Use.There is no difference between the predicted fire safety of the new product and of the one in established use. In this case, use of the new product provides neither advantage nor disadvantage, from the point of view of fire safety.
4.4.3 New Product Less Safe than Product Currently in Use.The new product is less safe, in terms of predicted fire performance, than the one in established use. In this case, a direct substitution of products would provide a lower level of safety and the new product would be undesirable, and should not be used, from the point of view of fire safety, without other compensatory changes being made.
4.4.3.1 New Product Different in Safety to Product Currently in Use.A new product that is less safe, in terms of predicted fire performance, can nevertheless be made acceptable if, and only if, it is part of a complete, comprehensive, fire safety design for the rail transportation vehicle. Such redesign of the vehicle should include other features such as use of an alternative layout or increased use of automatic fire protection systems, that demonstrably produce the same or better safety for the complete design. In such cases, a more in-depth fire hazard assessment would have to be conducted to ensure that the entire design achieves the safety goals, and the new product would be acceptable only as part of the larger, approved design.
4.4.4 The new product could offer some safety advantages and some safety disadvantages over the item in established use. An example of such an outcome could be increased smoke obscuration with decreased heat release. In such cases, a more in-depth fire hazard assessment would have to be conducted to ensure that the advantages outweigh the disadvantages, and the resulting overall level of safety is no less than that provided by the traditional approach (see Table X1.1 and Appendix X1).
4.5 Following the analysis described in 4.4, a fire hazard assessment developed following this guide would reach a conclusion regarding the desirability of the new product studied. It is essential for the results of the assessment to lead to a design that is at least as safe as the one being replaced.
Scope
1.1 This is a guide to developing fire hazard assessments for rail transportation vehicles. It has been written to assist professionals, including fire safety engineers, who wish to assess the fire safety of rail transportation vehicles, during or after their design (see also 1.6). This guide is not in itself a fire hazard assessment nor does it provide acceptance criteria; thus, it cannot be used for regulation.
1.2 Hazard assessment is a process that results in an estimate of the potential severity of the fires that can develop under defined scenarios, once defined incidents have occurred. Hazard assessment does not address the likelihood of a fire occurring. Hazard assessment is based on the premise that an ignition has occurred, consistent with a specified scenario, and that potential outcomes of the scenario can be reliably estimated.
1.3 Consistent with 1.2, this guide provides methods to evaluate whether particular rail passenger designs provide an equal or greater level of fire safety when compared to designs developed based on the traditional applicable fire-test-response characteristic approaches currently widely used in this industry. Such approaches have typically been based on prescriptive test methodologies. The following are examples of such lists of prescriptive tests: the requirements by the Federal Railroad Administration (FRA) (Table X1.1), the former guidelines of the FRA, the requirements of NFPA 130 (Table X3.1), and the recommended practices of the Federal Transit Administration (FTA). Selective use of parts of the methodology in this guide and of individual fire-test-response characteristics from Table X1.1 (or any other set of tests) does not satisfy the fire safety objectives of this guide or of the table. This guide shall be used in its entirety to develop a fire hazard assessment for rail transportation vehicles or to aid in the design of such vehicles.
1.4 This guide includes and applies accepted and clearly defined fire safety engineering techniques and methods consistent with both existing, traditional prescriptive codes and standards and performance based fire codes and standards under development throughout the world.
1.5 This guide provides recommended methods to mitigate potential damage from fires in rail transportation vehicles, by assessing the comparative fire hazard of particular products, assemblies, systems or overall designs intended for use in rail transportation vehicles. Such methods could include changes to the materials, components, products, assemblies, or systems involved in the construction of the rail transportation vehicle or changes in the design features of the vehicle, including the number and location of automatically activated fire safety devices present (see 4.4.4 for further details).
1.6 This guide is intended, among other things, to be of assistance to personnel addressing issues associated with the following areas.
1.6.1 Design and specification of rail transportation vehicles.
1.6.2 Fabrication of rail transportation vehicles.
1.6.3 Supply of assemblies, subassemblies, and component materials, for use in rail transportation vehicles.
1.6.4 Operation of rail transportation vehicles.
1.6.5 Provision of a safe environment for all occupants of a rail transportation vehicle.
1.7 The techniques provided in this guide are based on specific assumptions in terms of rail transportation vehicle designs, construction and fire scenarios. These techniques can be used to provide a quantitative measure of the fire hazards from a specified set of fire conditions, involving specific materials, products, or assemblies. Such an assessment cannot be relied upon to predict the hazard of actual fires, which involve conditions, or vehicle designs, other than those assumed in the analysis. In particular, the fire hazard may be affected by the anticipated use pattern of the vehicle.
1.8 This guide can be used to analyze the estimated fire performance of the vehicle specified under defined specific fire scenarios. Under such scenarios, incidents will begin either inside or outside a vehicle, and ignition sources can involve vehicle equipment as well as other sources. The fire scenarios to be used are described in detail in Section 5.3.
1.8.1 Fires with more severe initiating conditions than those assumed in an analysis may pose more severe fire hazard than that calculated using the techniques provided in this guide. For this reason severe fire conditions must be considered as part of an array of fire scenarios.
1.9 This fire standard cannot be used to provide quantitative measures.
