Recommendations for the Risk Assessment of Buffer Stops and End Impact Walls

Transcription

1 Recommendations for the Risk Assessment of Buffer Stops and End Synopsis This document gives details of a recommended method which, if followed, would meet the requirements of section 11, Buffer Stops and End, of RIS-7016-INS 'Interface between Station Platforms, Track, Trains and Buffer Stops'. Copyright in the Railway Group documents is owned by Rail Safety and Standards Board Limited. All rights are hereby reserved. No Railway Group document (in whole or in part) may be reproduced, stored in a retrieval system, or transmitted, in any form or means, without the prior written permission of Rail Safety and Standards Board Limited, or as expressly permitted by law. members are granted copyright licence in accordance with the Constitution Agreement relating to Rail Safety and Standards Board Limited. In circumstances where Rail Safety and Standards Board Limited has granted a particular person or organisation permission to copy extracts from Railway Group documents, Rail Safety and Standards Board Limited accepts no responsibility for, nor any liability in connection with, the use of such extracts, or any claims arising therefrom. This disclaimer applies to all forms of media in which extracts from Railway Group documents may be reproduced. Published by Copyright 2018 Rail Safety and Standards Board Limited

2 Issue Record Issue Date Comments One 02/06/2018 Original document. Supersedes GCRC5633. Document status changed from Code of Practice to Guidance. The document also merges the two parts of the risk assessment methodology which were previously spread over two documents, GCRC5633 and GIGN7616. This methodology has been reviewed and updated in. Superseded Documents The following Railway Group documents are superseded, either in whole or in part as indicated: Superseded documents Sections superseded Date when sections are superseded GCRC5633 issue two Assessment of Buffer Stops, Arresting Devices and End GIGN7616 issue two Guidance on Interface between Station Platforms, Track and Trains All 02/06/2018 Appendix A 02/06/2018 Supply The authoritative version of this document is available at Enquiries on this document can be submitted through the Customer Self-Service Portal Page 2 of 20

3 Contents Section Description Page Part 1 Introduction 6 G1.1 Purpose 6 G1.2 Structure of this document 6 G1.3 Approval and Authorisation 6 Part 2 Assessment of Buffer Stops and End 7 G2.1 Risk assessment of buffer stops and end impact walls at existing locations 7 G2.2 Risk estimation 8 G2.3 Risk mitigation measures 9 G2.4 Reassessment of risk 9 G2.5 Competencies of people carrying out the risk assessment 10 G2.6 New construction 10 Part 3 Tables A1 - A6 11 G3.1 Tables 11 G3.2 Table A1 - Buffer stop collision risk estimation proforma 11 G3.3 Table A2 - Assessment of potential for collision risk weighting factor 12 G3.4 Table A3 - Assessment of buffer stop risk weighting factor 13 G3.5 Table A4 - Assessment of train risk weighting factor 14 G3.6 Table A5 - Assessment of end impact wall risk weighting factor 14 G3.7 Table A6 - Assessment of overrun risk zone behind buffer stop 15 Definitions 19 References 20 Page 3 of 20

4 List of Figures Figure 1: Assessment of overrun risk zone behind buffer stop 15 Figure 2: The overrun risk zone for an energy absorbing buffer stop with frangible decking (not to scale) 16 Figure 3: The overrun risk zone for an energy absorbing buffer stop (not to scale) 17 Figure 4: The overrun risk zone for a fixed buffer stop (not to scale) 17 Page 4 of 20

5 List of Tables Table 1: Relevant extract from section 11.2 of RIS-7016-INS 7 Page 5 of 20

6 Part 1 Introduction G1.1 Purpose G1.1.1 G1.1.2 This document gives details of a recommended method which, if followed, would meet the requirements of section 11, Requirements for Buffer Stops and End Impact Walls, of RIS-7016-INS, 'Interface between Station Platforms, Track, Trains and Buffer Stops'. Should an infrastructure manager (IM) choose not to follow the recommended method of meeting the requirements of section 11 of RIS-7016-INS set out in this document, it should assure itself that the method it is following is as effective, and no less safe, than the method that is recommended here. G1.2 Structure of this document G1.2.1 G1.2.2 G1.2.3 G1.2.4 Relevant requirements in section 11 of RIS-7016-INS are reproduced in the sections that follow. Specific responsibilities and requirements are set out in the RIS itself. Use of the risk estimation methodology notes that increasing use has been made of the risk estimation methodology, set out in Part 3 of this document, to support proposals to encroach into the overrun risk zone defined in RIS-7016-INS. Whilst the methodology may serve to inform such judgements, it should be noted that it, alone, is not sufficient for this purpose. In addition, the mitigations contained within the risk assessment may introduce or affect other hazards not related to the buffer stop. For example, moving the stopping position further away from the buffer stop may increase platform train interface risk. G1.3 Approval and Authorisation G1.3.1 The content of this document was approved by Infrastructure Standards Committee on 07 March G1.3.2 This document was authorised by on 27 April Page 6 of 20

7 Part 2 Assessment of Buffer Stops and End G2.1 Risk assessment of buffer stops and end impact walls at existing locations RIS-7016-INS issue one Part 11 Requirements for buffer stops and end impact walls 11.2 Requirements for existing buffer stops in stations Buffer stops shall be provided at terminal or bay platforms. Rationale To ensure that the train can be halted in a safe manner that reduces the risk of serious injury to people on the station platform and train. Guidance The current risk assessment will indicate whether the buffer stop is adequate for the location concerned. The risk assessment takes account of: a) Risk of harm to people. b) Risk to critical structures. c) The factors listed in Requirements for end impact walls in stations. d) The type and condition of the buffer stop provided. e) The history of buffer stop collisions. gives a method of risk assessment. Table 1: Relevant extract from section 11.2 of RIS-7016-INS G2.1.1 G2.1.2 G2.1.3 G2.1.4 G2.1.5 RIS-7016-INS requires all terminal or bay platforms to have a current, documented assessment of the risk arising from a train overrun at a terminal or bay platform (see section 11.2 of RIS-7016-INS). The risk assessment considers both the likelihood of overrun and the potential consequences. It includes the range of possible overruns contributing to the risk, from low speed events (which may result in injuries) to higher speed events (which are less likely, but could have more significant consequences). Section 2.2 of this document, together with Tables A1 to A6, describes a model for estimating the risk arising from a train overrun at a terminal or bay platform. The estimates of fatalities and weighted injuries produced by the model in Tables A1 to A6 are based on the estimates and breakdown of buffer stop collision risk in s Safety Risk Model, as documented in issue eight of the Risk Profile Bulletin (see Section 2.3 of this document sets out mitigation measures that may be appropriate, based on the estimated buffer stop collision risk. Page 7 of 20

8 G2.1.6 Models and tools, such as those presented in this document for estimating buffer stop collision risk, are only an aid to the assessment of risk and are not a replacement for professional expertise and judgement. G2.2 Risk estimation G2.2.1 G2.2.2 G2.2.3 G2.2.4 G2.2.5 G2.2.6 G2.2.7 Tables A1 to A6 set out an approach that allows the risk arising from a train overrun at a terminal or bay platform to be estimated. All six tables need to be completed to estimate the buffer stop collision risk. Table A1 sets out instructions for carrying out the overall assessment of risk. It requires the input of the average number of buffer approaches per day, the average number of passengers per train, and five risk weighting factors based on the potential for collision, features of the buffer stop, the trains approaching the buffer stop, the presence of an end impact wall and the area behind the buffer stop. The five risk weighting factors are calculated by completing Tables A2 to A6 and transferring the result to the appropriate section of Table A1. Tables A2 to A6 are completed by identifying the relevant category for each factor affecting the buffer stop risk and assigning the appropriate risk weighting factor. Where none of the categories are applicable, then an appropriate risk weighting factor is estimated by judgement based on comparison with the existing categories. The risk weighting factors included in the model are believed to be generally applicable for the majority of buffer stops. However, for particular buffer stops, there may be additional factors significantly affecting the risk. Where this is the case, these additional factors need to be identified and incorporated appropriately into the estimate of risk. The appropriate risk weighting factors are multiplied on Table A1 to get an overall risk weighting factor. The overall risk weighting factor is multiplied by a risk index for each risk category to get an estimated rate of fatalities and weighted injuries per 100 years. These are then summed across the risk categories to get a total estimated rate of fatalities and weighted injuries for the buffer stop. Normally, the number of people affected in a typical assessment scenario should relate to an off-peak train approaching the buffer stops (for example at midday). However, if it is considered that there is a significant difference between off-peak and peak populations in the overrun risk zone, it may be appropriate to carry out an assessment for the two periods separately, before adding the resulting risk in fatalities and weighted injuries to represent a typical day. The assessor should consider the magnitude of the variation between these two assessments when combining them. This would involve adjusting the platform population values, as well as the average number of train approaches and average passengers per train for the two assessment periods. Where a change is being introduced to the overrun risk zone, for example installing a new kiosk, any increase in risk associated with the change should be considered and appropriate mitigations implemented. Further information and guidance on making safety decisions is provided in 'Taking Safe Decisions' published by, on Page 8 of 20

9 G2.3 Risk mitigation measures G2.3.1 G2.3.2 G2.3.3 G2.3.4 The estimated risk calculated using Tables A1 to A6 may indicate that risk mitigation measures are required. If so, the existing arrangements at the location may need to be reviewed and work planned to implement risk mitigation measures. The duty of co-operation requires any appropriate train and station operators to be informed of the output of the risk assessment and their views considered in the review of existing arrangements. Mitigation measures that may be appropriate based on the estimated buffer stop collision risk are set out below. These measures are not necessarily exhaustive and other buffer stop collision risk mitigation measures specific to the location may also need to be identified and considered: a) Implement effective changes to address issues identified by investigation of buffer stop collisions (Table A2). b) Reduce permissible speed on approach to buffer stop to 25 mph or below (Table A2). c) Improve illumination if assessed as poor (Table A2). d) Screen any identified driver distractions (Table A2). e) Implement measures to improve adhesion (Table A2). f) Increase distance of normal stopping position from buffer stop (Table A2). g) Improve the type of buffer stop (Table A3). h) For buffers fitted to the track, improve the condition of the track and rail joints if assessed as poor (Table A3). i) Move buffer stop to reduce risk in the overrun area (Table A6). j) Provide end impact walls (Tables A5 and A6). k) Relocate items within the overrun risk zone that increase risk (retail units, offices etc) (Table A6). Where a more detailed risk assessment and cost benefit analysis may be required to consider more costly measures, such as providing end impact walls or relocating structures, additional considerations may include: a) Assessment of a probability distribution of buffer stop collision with speed. b) More accurate consequence models to consider the effects of a buffer stop collision across the range of potential impact speeds. G2.4 Reassessment of risk G2.4.1 G2.4.2 Where there is reason to believe that the previous risk assessment has become invalid, for example, after any significant change in the circumstances at a location, it may be necessary to reassess the risks. Significant changes that can typically require reassessment include: a) Remodelling of track layouts. b) Introduction of different rolling stock. c) Any increase in approach speed. d) Increase in the number of trains using the line. Page 9 of 20

10 G2.4.3 G2.4.4 G2.4.5 e) Changes to signalling arrangements. f) Change in use of the area behind buffer stops. g) Construction of structures or other critical supports behind buffer stops. Where a risk assessment has been based on the approach presented in this document, a change affecting terminal tracks can be considered significant if it is likely to change any of the identified risk weighting factors in Tables A2 to A6. This may include the occurrence of buffer stop collision incidents. As the accumulation of small changes can sum up to a large change over a period of time, it is good practice for the continued validity of the risk assessment at a location to be periodically reviewed. A suggested maximum interval between reviews is two years. When action has been taken to reduce the risk at a buffer stop, the risk assessment may be updated to take account of the change. G2.5 Competencies of people carrying out the risk assessment G2.5.1 People carrying out risk assessments based on the approach presented in this document should: a) Have been briefed on and understand the risk assessment process presented in this document. b) Have the professional expertise and judgement necessary to understand the required technical aspects of the infrastructure, operations and buffer stop equipment. c) Have the ability to gain and make use of local knowledge regarding the surroundings of the buffer stop. G2.6 New construction G2.6.1 For new construction, the risk estimation model set out in this document may be of assistance when considering: a) The type of buffer stop to be provided and its design. b) The provision of end impact walls. c) The need for additional safety measures. (See section 11 of RIS-7016-INS.) Page 10 of 20

11 Part 3 Tables A1 - A6 G3.1 Tables G3.1.1 Risk estimation The tables below are for information only, the risk assessment can be downloaded here: a) Table A1 Buffer stop collision risk estimation proforma. b) Table A2 Assessment of combined potential for collision risk weighting factor. c) Table A3 Assessment of buffer stop risk weighting factor. d) Table A4 Assessment of train risk weighting factor. e) Table A5 Assessment of end impact wall risk weighting factor. f) Table A6 Assessment of area behind buffer stop risk weighting factor. G3.2 Table A1 - Buffer stop collision risk estimation proforma G3.2.1 G3.2.2 G3.2.3 s to Table A1 The overall risk weighting factor is calculated by multiplying together the number of approaches per day, the average number of passengers per train and the risk weighting factors, as appropriate, along each row. The shaded boxes with N/A represent factors not applicable to that risk category. The risk index is a value derived from s Safety Risk Model to convert risk weighting factors into an estimate of the fatalities and weighted injuries per 100 years. The final column is calculated by multiplying the risk index by the overall risk weighting factor. The total risk for the buffer stop is then the sum of the risk across all risk categories. Page 11 of 20

12 G3.3 Table A2 - Assessment of potential for collision risk weighting factor G3.3.1 G3.3.2 G3.3.3 s to Table A2 History of buffer stop collisions - the safety management intelligence system (SMIS) holds records of the following types of incidents involving buffer stops: a) Any case of a train striking a buffer stop, other than in a siding, where damage is caused to the train. b) Any other case of a passenger train striking a buffer stop (irrespective of any damage to train or buffers). c) Any train striking buffer stops in a siding where there is damage to the train. d) Changes introduced following a collision may include: measures to amend driver training programmes or instructions; changes to infrastructure; and changes to inspection and maintenance procedures. Permissible speed can be determined from the Sectional Appendices. Driver distractions include items such as an advertising hoarding that may catch the driver s attention on the approach to the buffer stop. Page 12 of 20

13 G3.3.4 Evidence of potential adhesion problems on the approach to the buffer stop should include consideration of any history of poor adhesion, whether the approach is covered by a structure, and the potential for leaf contamination. G3.4 Table A3 - Assessment of buffer stop risk weighting factor G3.4.1 G3.4.2 s to Table A3 The type of track is only relevant if the buffer is fitted to the track and the forces required to stop the train are transmitted through the track. The condition of the track relates to the ability of the track joints and rail fastenings to withstand the lateral and vertical forces associated with a buffer stop collision. Page 13 of 20

14 G3.5 Table A4 - Assessment of train risk weighting factor G3.5.1 G3.5.2 G3.5.3 s to Table A4 Rolling stock is considered to be not interface compatible with the buffer stop if the height of the buffer beam does not substantially overlap the buffers or anticlimbers on the train. It is partially compatible if the buffer beam overlaps, but the rolling stock has a centre coupler and the buffer stop is not suitably adapted. Rolling stock is considered to be energy compatible with the buffer stop if the design of the buffer stop meets the requirements set out in RIS-7016-INS. The combined risk weighting factor is obtained by multiplying together the values assigned to each of the individual factors. G3.6 Table A5 - Assessment of end impact wall risk weighting factor Page 14 of 20

15 Uncontrolled when printed G3.7 Table A6 - Assessment of overrun risk zone behind buffer stop Figure 1: Assessment of overrun risk zone behind buffer stop Page 15 of 20

16 G3.7.1 G3.7.2 G3.7.3 Table A6 is structured as follows: a) Part 1 assesses the risk to people in the overrun risk zone. b) Part 2 assesses the risk to people inside, or in the immediate vicinity of, a small structure (such as a kiosk) located within the overrun risk zone. c) Part 3 assesses the risk to people who may be affected by the collapse of a significant structural support (such as a footbridge or roof column) located within the overrun risk zone. d) Part 4 assesses the risk to people who may be on frangible decking and who would be affected by a buffer stop collision. The 20 m overrun risk zone is divided into risk areas A, B, C and the frangible decking area D as shown in Figures 2, 3 and 4 below. The areas are based on the assumption that, in most cases, a train overrun at a buffer stop will travel in a straight line (frangible decking and area A); in some cases, the train may deviate from a straight line (area B) and, in a few cases, the train may jackknife (area C). If the area under analysis concerns more than one track and buffer stop, each buffer stop should be analysed separately. It should be noted that it is not possible to accurately predict the path of a train overrun, and therefore a conservative approach should be taken when assigning structures to risk areas A, B and / or C. If a structure is overlapping two of the areas, or very close to the edge of an area, it should be assigned to the higher risk area. Figure 2: The overrun risk zone for an energy absorbing buffer stop with frangible decking (not to scale) Page 16 of 20

17 G3.7.4 Figure 3: The overrun risk zone for an energy absorbing buffer stop (not to scale) G3.7.5 G3.7.6 G3.7.7 G3.7.8 Figure 4: The overrun risk zone for a fixed buffer stop (not to scale) Part 1 considers the people in the open plan area of the overrun risk zone that could be affected by a train overrun. These people will generally have an unobstructed view of the approaching train and freedom to move away from the area quickly if a train overran the buffer stop. The number of people affected within each of the risk areas A, B and C, on average, when an off-peak train (for example midday) is approaching the buffer stops, should be considered. Alternatively, if there are large differences between peak and off-peak numbers, then two assessments should be completed and the results added together. If people in risk areas A, B or C do not have an unobstructed view of an approaching train or are unable to move away from the area quickly, for example in crowded situations, then an obstruction factor should be applied in Part 1 of Table A6. Part 2 considers the people associated with small structures, such as kiosks and shops, where the structure is standalone (that is, independently constructed from the main station structure). The number of people affected if the structure collapsed as a result of a train collision after a buffer stop overrun (that is, the people inside the structure as well as people waiting outside the structure, for example customers waiting to purchase items) should be considered. Page 17 of 20

18 G3.7.9 G G G G The weightings in Part 2 only apply to a maximum of 30 people being affected. If more than 30 people will be affected, then Part 3 should be used to consider more serious consequences. Up to five small structures can be considered in the risk assessment by ticking the box marked 'Include?' Part 3 considers significant structural supports, such as roof columns, multi-storey structures or footbridge supports. Advice from a competent structural engineer should be sought to consider how likely it is for the support to collapse if it were struck by a train overrun. A risk weighting factor of 1 should be used if the collapse of the support will cause the structure to collapse. A risk weighting factor of 0 should be used if the support is redundant and the removal of the support will not cause the structure to collapse. The number of people affected should be considered if the structure did collapse, for example if the removal of the support will cause a section of roof to collapse, people throughout the station might be affected. Up to five small structures can be considered in the risk assessment by ticking the box marked 'Include?' Part 4 considers the risk if frangible decking has been installed in the area directly behind the buffer stop. If no decking has been installed behind the buffer stop, this section will calculate a risk weighting factor of 0 and the length of decking should be entered as 0. Figure 2 shows the layout of the measurement for the frangible decking, the distance between the buffer stop and the frangible decking, D and the length of the decking, L. Page 18 of 20

19 Definitions Buffer stop End impact wall Energy absorbing buffer stop Estimated equivalent fatalities per 100 years Freight line New construction Overrun Risk category Risk index Risk weighting factors Safety management information system (SMIS) Terminal track An assembly provided at the end of a terminal track which is designed to arrest a rail vehicle. This will be designed to accommodate the impact of a train at buffer or coupling height and up to a set speed. A structure or other arrangement located behind a buffer stop, designed to contain a train that has run through the buffer stop, so preventing harm to people or damage to critical structures that would otherwise have been in the path of the train. A buffer stop designed to bring a train to a controlled halt from a pre-determined maximum design speed by providing a means of progressively absorbing the kinetic energy of the train. The estimated equivalent fatalities per 100 years is a measure of the risk arising from harm to people. The derivation of equivalent fatalities is explained in s Risk Profile Bulletin. A line normally only used by non-passenger carrying trains or empty passenger stock. The provision of a buffer stop or arresting device on a new terminal track or the complete replacement of a buffer stop or arresting device on a remodelled track or station layout. The movement of a train or vehicle beyond the designed end limit of a track. The factors associated with buffer stop collisions have been split into a number of risk categories for which different risk weighting factors are appropriate. A value derived from s Safety Risk Model to convert risk weighting factors into an estimate of the equivalent fatalities per 100 years. Estimates of the impact on risk of factors affecting buffer stop risk. The safety management information system (SMIS) is a computer database containing details of events reported by or on behalf of Railway Group members. A dead end or terminating track in a station or at the end of a freight line or siding. Page 19 of 20

20 References The Catalogue of Railway Group Standards gives the current issue number and status of documents published by. This information is also available from railway-group-standards.co.uk. RGSC 01 RGSC 02 Railway Group Standards Code Standards Manual Documents referenced in the text Documents RIS-7016-INS Taking Safe Decisions Interface between Station Platforms, Track, Trains and Buffer Stops Taking Safe Decisions - How Britain's railways take decisions that affect safety, 2014 (available on the website) Other References Risk Profile Bulletin Profile of safety risk on the UK mainline railway Page 20 of 20