RSSB Interior Crashworthiness R&D

Jim Lupton, Raymond Ford

Rail Safety and Standards Board, UK

Abstract

Funded by the UK government, the Rail Safety and Standards Board is responsible for the development and delivery of a programme of research and development (R&D) on behalf of Britain's rail industry. The R&D is aimed at improving the safety and efficiency of Britain’s mainline railway network so naturally a good proportion of it is aimed at preventing accidents. A major stream of work though is also aimed at minimising the risk of injury from accidents when they inevitably occur. This paper presents key results from recent R&D aimed at improving interior crashworthiness and specifically covers: • A review of the criteria used to quantify harm to passengers • Development of a new rail oriented anthropometric test device (ATD or crash test dummy) • An investigation into the safety benefits of lap belts for rail vehicles • A review of recent major rail accidents in Britain • Research defining requirements for effective emergency lighting • Research into windows for containment and escape.

Introduction

Following on from the groundbreaking research led by the British Railways Board during the 1980s and 1990s, the Rail Safety and Standards Board (RSSB) and its predecessor, Railway Safety, has managed a multi-million pound programme of R&D funded by the UK government since 2001 on behalf of the UK rail industry. Originally a program directed towards improving safety, RSSB’s remit for R&D is now much more comprehensive and aims to find innovative ways of helping government and industry achieve the key objectives of: • Increasing capacity and availability • Improving performance in terms of health and safety, punctuality, and reliability • Reducing cost • Integrating all of these to compete effectively with other transport modes (or complement them as

appropriate) and deliver a sustainable future for the railway. The portfolio of R&D currently being conducted is very diverse and falls into three broad areas; R&D that improves how the railway is operated, R&D that improves the railway’s management systems and R&D that improves its engineering. Work covers such broad areas as seeking a better understanding of public behaviour and railway crime, improving the way in which safety related decisions are made and how to make real-time communications more effective. Further details can be found at www.rssb.co.uk. Research aimed at improving the engineering of the railway falls into four topics: • Vehicle Track Interaction • Track and Structures • Signalling, Telecoms and Electrification • Traction and Rolling Stock. Naturally, RSSB's crashworthiness R&D falls within the traction and rolling stock topic and represents a good proportion of the work done there (although not exclusively, for instance work is also looking at alternative future fuels and improving the environmental impact of current fuels).

The following diagram illustrates some of the work currently being done to improve crashworthiness (along with reference numbers that can be used to locate the reports on the Internet):

Figure 1: RSSB crashworthiness research

All of this work is underpinned by understanding obtained from previous accidents seen in the UK, for example:

Accident Year Losses Nature of accident Clapham 1988 35 fatalities/ 470 injured Two trains collided then another Southall 1997 7 fatalities/ 139 injured High speed train passes signal at danger and

hits freight train Ladbroke Grove

1999 31 fatalities/ >400 injured Multiple unit passes signal at danger and hits high speed train

Hatfield 2000 4 fatalities/ 70 injured High speed train derails on broken rail Potters Bar 2001 7 fatalities/ 85 injured Multiple unit derails at points Great Heck 2001 10 fatalities/ 82 injured High speed train is derailed by road vehicle

and subsequent points then hits freight train Ufton Nervet 2004 6 fatalities/ 60 injured High speed train is derailed by road vehicle at

level crossing and subsequent points

Table 1: Recent significant rail accidents in the UK Naturally R&D in this area aims to bring about change to the railway that will reduce injury in the event of collisions and derailments. This requires consideration of the four principal mechanisms that cause injury: loss of survival space, intrusion, ejection and fire. RSSB’s strategy, like no doubt many other railways, is to reduce injury by: 1. Eliminating the risk of injury in the first place, ie: by preventing the derailment or collision 2. If an accident does occur, vehicles need to be capable of absorbing the impact energy in a way that

does not put occupants at risk 3. The motion of the vehicle needs to be controlled by keeping it upright and in line so that the forces that

the occupants see can be managed 4. Interiors must be designed in such as way as to protect occupants as far as possible 5. If all else fails, vehicles and operating procedures must be designed to facilitate escape and rescue RSSB's research covers work in each of these areas, however the focus of this paper is to provide a basic understanding of the key findings from work done looking into improving interior crashworthiness.

Injury Criteria – T066 The objective of all crashworthiness requirements for rail vehicles is the protection of passengers against injury in an accident. Investigations into appropriate rail injury criteria commenced in the 1990s and involved a widespread review of rail accidents in the UK, the nature of injuries sustained and the causes of those injuries. Injury criteria were set to prevent loss of passengers’ consciousness and to protect against fractures of the limbs (arms and legs), both of which would prevent unaided evacuation in an emergency. Levels were also set to limit the intrusion of tables into the abdominal region where the impact on vital organs could lead to fatalities. Current research has undertaken a systematic review of the criteria in the light of more recent accidents and developments in related medical knowledge. The recommended, revised criteria are shown below.

Passenger injury recommended levels for 50th percentile male passengers in rail vehicles (to be used in conjunction with the acceleration pulse detailed in AV/ST9001) Head and Skull injuries HIC 500 over a duration of 18 ms for injury

Recommendation of HIC 150 over a duration of 18 ms to prevent temporary confusion.

Neck injuries Neck injury criterion (Nij) = less than 1.0 using: Fzc Tension 6806 N Fzc Compression 6160 N Myc Flexion 310 Nm Myc Extension 135 Nm.

Peak Tension 4170 N Peak Compression 4000 N

Chest injuries Upper chest (Thorax) Lower chest (abdomen)

Combined Thoracic Index (CTI) less than 1.0 Viscous Criterion (V*C) less than 1.0 Chest acceleration 60g (3ms cum exceedance) Chest deflection 63mm CTI intercept :chest acceleration 57g :chest deflection 103mm

Abdominal injuries Peak force not to exceed 6.73 kN Viscous Criterion (V*C) 1.98 m/s

Pelvic injury No criterion recommended Femoral (and acetabular) injuries Axial force (max) 7.56 kN

(potential measure of bending moment, max to be between 250 and 320 Nm)

Knee displacement 15.2mm maximal displacement Tibial index: Tibial index level not to exceed 1.3

Table 2: Revised injury criteria for rail applications

A new rail oriented anthropometric test device (ATD) – T201 Having identified the injury criteria to be applied for rail applications, it was necessary to have the tools for measuring the performance of vehicle interior components against those criteria. A vital tool in the evaluation of such developments is the “crash test dummy” – the “Anthropomorphic Test Device” or ATD. The ATD must be capable of assessing those injury mechanisms applicable to rail vehicles. Table impacts on the abdominal region are a unique feature in rail accidents (when compared with other modes of transport) and no available ATD was capable of evaluating injuries caused by such impacts. A standard HYBRID III ATD was modified to incorporate an instrumented abdomen for evaluation of table edge impacts and the instrumentation was enhanced to give valid data. The modifications to the ATD

also included modification of the spine, giving greater flexibility of the spine base and hips. The resulting ATD was designated the HYBRID 3RS.

Figure 2: The Hybrid 3RS ATD with instrumented abdomen It was further recognised that the increased flexibility was extremely relevant to a thorough evaluation of 2-point lap belts. An investigation into the safety benefits of seatbelts for rail vehicles – T201 A review of accidents over the last 30 years revealed a changing pattern in the causes of injury. Between 1973 and 1983 the most significant factor was the overriding of vehicles, in which one vehicle would climb over an adjacent vehicle and crush the survival space of that vehicle. In the latter part of the second period, passenger ejection emerged as a significant cause of injury.

Figure 3: Accident casualty data 1973 - 2004 Ejection of passengers occurs through windows, inter-vehicle connections and ruptures of the vehicle bodyshell. Evaluation of accident data confirmed that ejection through vehicle bodyside windows occurred almost exclusively when vehicles were derailed and subsequently jack-knifed or rolled over. Statistically, approximately 50% of passengers ejected were fatally injured. Accidents to date in the UK have all involved vehicles with toughened glass.

Fatalities Serious

73/83 84/04 73/83 84/04 100%

50%Ejection

Crush

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Fatalities Serious

73/83 84/04 73/83 84/04 100%

50%Ejection

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Two options are available to reduce the number of ejections through windows: a) the fitting of seat belts and b) the installation of laminated glass windows. Both options have been explored in depth, although the initial consideration of seatbelts was limited to the two-point (lap) type, mainly as a consequence of the nature of the accident at Ufton Nervet in 2004. A review of three-point (lap and diagonal) belts is currently in hand. The research investigation concentrated on answering the question: “Are passengers likely to be more seriously, or less seriously, injured by wearing two-point (lap) belts?” The political, commercial and emotional issues were therefore set aside. In assessing the benefits of seat belts account had to be taken of the possible consequences in relation to the current design philosophy. Modern seats are designed to restrain the passenger in a collision, absorbing the passenger’s energy in a less injurious manner and constraining them in the seat location. This is particularly relevant since, in the vast majority of instances, vehicles involved in collisions receive a longitudinal (end-on) impact. Such seats had been evaluated using crash-test dummies (ATDs) and their performance assessed against injury criteria determined through the previous research undertaken in the early 1990s. The fitting of seat belts would necessitate increasing the strength and stiffness of the seats to carry the seatbelt loads, thereby inflicting greater injuries on passengers choosing not to wear belts and who impact the seat in front. The research therefore included a comparison with unrestrained occupants of such crash-worthy seats. Preliminary computer simulations of restrained passenger impacts indicated that the flexibility of the lower spine and pelvic regions was crucial to a realistic evaluation of the seat belts. It was also recognized that effective measurement of the impact on the abdominal region was appropriate for a rigorous evaluation of potential injuries. The HYBRID 3RS ATD, by its very construction, had greater flexibility in both respects and an instrumented abdominal region. Initial testing confirmed the greater realism of the representation. Test programme variables included three sizes of ATD (5th percentile female, 50th percentile male and 95th percentile male), a range of seat pitches representative of UK vehicles, and restrained and unrestrained seat occupants. The standardized UK rail crash pulse was used. Whilst many channels of data were collected, it was recognized that the two most significant injury criteria were those indicative of head injury (HIC) and neck injury (Nij).

Figure 4: Unbelted and belted impacts (5th percentile) High-speed film gave an early indication of the potentially serious neck injuries that would be sustained by restrained occupants, and the analysis confirmed that the neck injury criterion was the most significant factor. Smaller occupants, as represented by the 5th percentile female ATD, and larger occupants in seating with the longer inter-seat pitch, were extremely vulnerable to excessive levels of neck injury. By comparison, the unrestrained ATDs were constrained in a less injurious manner by the energy absorbing crash-worthy seat in front. The head injuries were less serious and less significant than the neck injuries in both the restrained and unrestrained cases. A sample comparison is given in Figure 5 below, taken from the tests with a 50th percentile male ATD.

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Figure 5: Neck injury relative to seat pitch (50th percentile) (NIJ = 1 is the limit in AV/ST9001)

A serious risk of entrapment of persons restrained by seatbelts was identified in the tests. The knees of an unrestrained person impacting the back of the restrained passenger’s seat caused deformation of the seat back and tightening of the restrained occupant’s belt. This tightening of the belt had the potential to inflict serious injury. Further investigation also revealed that two-point restraints were not suitable for restraining children below the age of 12 years unless accompanied by a booster seat or other suitable device. The misalignment of the belt across the abdominal region of the smaller wearer had the potential to inflict serious injury on the vital organs within the abdominal region. A review of detailed accident data collected for the six most recent accidents (all of which were high speed) revealed that in areas of vehicles subjected to loss of survival space there had been very few injuries. Evidence indicated that passengers in these areas had been thrown clear of the crush by the impact. Had such passengers been restrained by a seatbelt, it was unlikely that they would have survived the intrusion. Thus, it was likely that two-point restraints would increase the number of fatalities where structural intrusion prejudiced passenger survival space. From the accident data it was concluded that the number of fatalities likely to have resulted from intrusion, if restrained, could have been significantly more than the number of fatalities from ejection that could have been saved by seatbelts. On the other hand ejection could be largely eliminated by less hazardous measures such as strengthening windows. A review of recent major rail accidents in the Britain – T310 Every train accident is unique and every rail vehicle within that train has its own accident – usually with the vehicles on either side of it. In order to reduce passenger injuries it is therefore necessary to provide mitigation for a wide range of accident scenarios. Effective measures can only be identified by investigating accidents and establishing trends in the causation of injuries. Seven major recent accidents were reviewed in depth in order to establish: § The causal link between passenger injury and train furniture. § The injury severity and body region affected, for sustained injuries. § The cause of fatalities. § Basic Human Factors Information such as actions of survivors. § The mechanism of passenger injury.

The accident at Ufton Nervet, having happened at the time of the research, provided the opportunity to carry out an unprecedented review.

Figure 6: The Ufton Nervet accident investigated The vehicles were examined in detail in order to assess the condition at every seat position or other significant location. Signs of human impact or injury were recorded. Approximately 200 anonymous passenger witness statements were scrutinized in order to locate the passengers within the vehicles and to identify the injuries sustained at those locations. This was matched with the vehicle data collected. The vehicles were then mapped, photographic evidence was linked to each vehicle map and the injury mechanisms were investigated. Additionally, a number of post-accident witness interviews were undertaken to give a view of what happened in each vehicle. The interviews and statements provided invaluable information regarding passenger injuries and their causation. They also provided invaluable information regarding the reactions of people during the accident, what actions they took in the immediate aftermath of the accident and why they took those actions. Information obtained from the passenger witness statements included: § Passenger to coach attribution § Passenger direction of travel § Passenger seating position in aisle or window seat § Passenger location in table-bay, open-bay or uni-directional seating § Passenger injury severity and anatomical area affected § Type of passenger injury sustained § Cause of passenger fatalities The internationally recognised Abbreviated Injury Scale (AIS) was used to grade the severity of passenger injury. This is a non-linear scale ranging from 1-6, where level 6 is currently un-survivable. Whilst the scale is used by the rescue services for prioritising urgent medical attention on the basis of immediate threat to life, rather than the long-term consequences of the injuries, the scale provides a vastly improved method of classifying the severity of injuries for analysis. Following the successful investigation of the Ufton Nervet accident, a further six accidents were analysed. Altogether 650 anonymous passenger witness statements, provided by British Transport Police (BTP), were examined. The confidentiality of the statements was retained throughout this process and any attributable information removed.

Figure 7: Injuries summarized by body region (Note: One passenger may have several injuries)

Whilst seats and tables were the causes of a large proportion of injuries sustained, this was indicative of the vital role they play in constraining passengers. These injuries were seldom of a life-threatening nature and were usually in a minor category. Injuries caused by seats were mainly to the head, face, neck and legs, whilst injuries caused by tables were mainly to the abdomen, chest and head. Requirements for effective emergency lighting – T314 A common feature of most major accidents was the failure of the lighting throughout the train. Many passengers expressed very strong views that “any light would have been better than no light”. Whilst emergency lighting was specified for all vehicles, the requirement related mainly to conservation of the vehicle batteries for operation of safety systems during times of power failure. Earlier work had indicated it is reasonable to expect that, in the immediate aftermath of an accident, any passenger in a relatively undamaged vehicle and having no more than minor injuries is likely to make a conscious decision whether to evacuate or not. Other work indicated that, based on approximately 100 different scenarios, the risks of evacuating the vehicle were almost always greater than the risks of staying on board the train. That being the case it was concluded that the objectives of the emergency lighting should be: • To survive the accident and continue to provide interior lighting in the aftermath • To provide sufficient light to make staying in the vehicle a perceived option • To provide sufficient light to highlight passengers requiring medical attention and to allow it to be

administered • To provide sufficient light to permit safe evacuation of the vehicle to an adjacent vehicle or, when

necessary, to the outside • To provide sufficient light adjacent to emergency notices or facilities to render them usable. • Not to provide lighting that would encourage non-preferred action (such as floor level lighting or

excessively lit exit signs that would imply that escape was the most appropriate action). Tests were carried out to establish the minimum lighting levels and uniformity that would meet the above objectives, and an analysis of accident data was used to establish the minimum durations for which the emergency lighting should remain available. An assessment was also made of the time taken by the rescue services to reach the scene and arrange on-site lighting, including the difficulties of access to

Injuries by Body Region

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some parts of the rail network. The opportunity was taken to establish the lowest level and uniformity that could be tolerated for retrospective installation where the cost of a full system could not be justified.

Figure 8: Emergency lighting trials Windows for containment and escape – T424 Investigations into a number of recent accidents in the UK emphasised the roles windows had played. On the one hand a number of fatalities had resulted from people being ejected from trains via windows that had broken. On the other hand large numbers of people had broken windows in order to escape. Ejection through train bodyside windows had occurred where the windows had failed due to being internally impacted by passengers, luggage or other objects; or due to being externally impacted by ballast, crash debris, or other objects; or due to structural deformation of the vehicle structure.

Figure 9: Passenger impact simulation The objective of the research was to identify appropriate window performance requirements for reducing the risk of ejection in an accident. Tests were developed for assessment of a window’s ability to contain passengers being thrown against it in an overturning vehicle and to resist impacts from external objects.

8 Lights Saloon

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These tests were successfully applied to a newly developed double glazed window, with laminated glass on the inner pane, which had been developed for retrospective installation. Fitting of such a window to all locations within a vehicle, though effective in resisting ejection, would make escape via the window considerably more difficult. An investigation of all recent accidents was undertaken to identify all individual vehicles involved where lives would have been placed at risk by an inability to escape via a window. Whilst the Ladbroke Grove accident was the most significant in this respect (because of the presence of fire), it was concluded that laminated glass would not have placed lives at risk in that accident. In the recent accidents, although many people had escaped through windows, there was no case where escape via windows was essential. More detailed accounts of this research can be found at www.rssb.co.uk using the specified reference number.

Acknowledgements

RSSB would like to acknowledge the involvement of AEA Technology Rail and Transport Research Laboratory who delivered much of the aforementioned research on its behalf. RSSB would like to thank the stakeholders who give their time willingly to help steer and peer review the research and continue to do so.