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  • ATSB RESEARCH AND ANALYSIS REPORT ROAD SAFETY

    RESEARCH GRANT REPORT 2007-03

    Helmet protection against basilar skull fracture

    Dr. T. J. Gibson K. Thai

    Human Impact Engineering

    June 2007

  • Published by: Australian Transport Safety Bureau Postal address: PO Box 967, Civic Square ACT 2608 Office location: 15 Mort Street, Canberra City, Australian Capital Territory Telephone: 1800 621 372; from overseas + 61 2 6274 6130 Facsimile: 02 6274 3117; from overseas + 61 2 6274 3117 E-mail: atsbinfo@atsb.gov.au Internet: www.atsb.gov.au

    Human Impact Engineering 2007

    To encourage the dissemination of this publication, it may be copied, downloaded, displayed, printed, reproduced, and distributed in unaltered form (retaining this notice). Subject to the provisions of the Copyright Act 1968, no other use of the material in this publication may be made without the authorisation of Human Impact Engineering.

  • DOCUMENT RETRIEVAL INFORMATION Report No. RSRG 2007-03

    Publication date June 2006

    No. of pages 50

    ISBN 978-0-642-25581-5

    Publication title Helmet protection against basilar skull fracture

    Author(s) Gibson, T. J.; Thai, K.

    Organisation that prepared this document Human Impact Engineering 3/ 36 Albert Street, St. Peters NSW 2044 Australia

    Centre for Automotive Safety Research University of Adelaide SA 5005

    Sponsor [Available from] Australian Transport Safety Bureau PO Box 967, Civic Square ACT 2608 Australia www.atsb.gov.au

    Reference No. May2007/DOTARS 50261

    Project Officer John Collis

    Abstract In Australia, it is compulsory for all motorcyclists, pillion passengers and side-car passengers to wear helmets certified to AS/NZS 1698. Most riders prefer to wear full-face helmets, which appear to offer better facial protection during a crash. Some researchers have noted a greater prevalence of fractures to the base of the skull in full-face helmeted riders. The aim of this study was to improve the understanding of basilar skull fracture (BSF) causation in motorcycle crashes, to assess the capability of current helmets in reducing the risk of this injury and to assist in future standards setting.

    A review of available field data on the incidence and causation of BSF to motorcyclists was completed and the findings compared with crashes collected in the CASR Head Injury Database. This database contains in-depth investigations of 174 mainly fatal motorcycle accident cases collected in South Australia between 1983 and 1994. It includes autopsy data, including an investigation of neck injury, the helmet and a detailed crash report. The CASR data was found to be representative of fatal crash studies in the literature and to consist of high severity crashes. In 70% of the cases full face helmets were worn. BSF was seen in 59% of these cases. Almost 50% of the severe impacts to the head were in the facial region and 42% of these impacts were to the chin bar. The prevalence of BSF was found to be mainly due to the migration of the skull fracture to the base of the skull due to the severity of the impact to the face (and other regions of the head).

    Only two motorcycle helmet standards currently include chin bar tests: Snell M2005 and UN ECE 22.05. The tests have significant differences in their requirements and do not specifically address the issue of basilar skull fracture. The test requirements were assessed using a typical current Australian full face helmet. The results are discussed in terms of the protective requirements demonstrated in the field accident data and an understanding of current biomechanical injury tolerance. The study shows that the protection offered by the Australian motorcycle helmet needs to be extended to cover the facial area, with the aim of reducing facial fractures. The conflicting criteria required of a test method, to protect from facial fracture and brain injury, whilst not causing neck injury are also discussed, and the needs for further work are outlined.

    Notes

    (1) ATSB reports are disseminated in the interest of information exchange. (2) The views expressed are those of the author(s) and do not necessarily represent those of the

    Australian Government or the ATSB.

    ii Helmet protection against basilar skull fracture

  • CONTENTS

    Executive summary .......................................................................................................................... 1

    Acknowledgements........................................................................................................................... 6

    Abbreviations.................................................................................................................................... 7

    1 Introduction ............................................................................................................................ 10 1.1 Background.................................................................................................................. 10 1.2 SCOPE AND AIMS OF THE STUDY ....................................................................... 12

    2 Method..................................................................................................................................... 13 2.1 HEAD AND NECK INJURY IN MOTORCYCLE CRASHES................................. 13 2.2 BSF IN MOTORCYCLE CRASHES.......................................................................... 15 2.3 SUMMARY................................................................................................................. 17

    3 Biomechanics of Basilar Skull Fracture ............................................................................... 19 3.1 Anatomy of BSF .......................................................................................................... 19 3.2 The Mechanisms of BSF ............................................................................................. 20 3.3 Fracture Tolerances of the Neck, Face and Skull ........................................................ 21 3.4 Summary...................................................................................................................... 23

    4 ANALYSIS OF THE CASR DATABASE ........................................................................... 24 4.1 Aim of the Analysis ..................................................................................................... 24 4.2 Results ......................................................................................................................... 24 4.3 Discussion.................................................................................................................... 36

    5 Current Helmet Chin bar Test Methods .............................................................................. 38 5.1 Overview...................................................................................................................... 38 5.2 Results of Comparative Testing................................................................................... 40 5.3 Discussion.................................................................................................................... 41

    6 DISCUSSION.......................................................................................................................... 43

    7 CONCLUSIONS..................................................................................................................... 46

    REFERENCES............................................................................................................................... 47

    Appendix I - Motorcycle Accident Case Studies ......................................................................... 50

    Helmet protection against basilar skull fracture iii

  • EXECUTIVE SUMMARY

    Background Since the 1960s, it has been compulsory for all motorcyclists, pillion passengers and side-car passengers in Australia to wear helmets certified to the Australian Standard AS/NZS 1698. In a 2001 survey of over 1200 motorcyclists in NSW (de Rome, Stanford & Wood, 2002), all riders indicated that they usually wore helmets. The majority (87%) of riders preferred full-face helmets.

    In a 1988 review of crash performance of Australian market motorcycle helmets, Dowdell et al. (1988) examined 200 crash-involved helmets and found that the chin bar of the full-face helmet was the region with the highest average number of impacts. Almost 50% of the severe impacts were to the front of the helmet and 40% of these impacts resulted in basilar skull fractures (BSF). A recommendation was made that specifications be developed for a test aimed at reducing the effect of frontal impacts to the face by improving the energy absorption of helmets in this area.

    Two current motorcycle helmet standards include chin bar tests: Snell M2005 and UN ECE 22.05. For the Snell test, a mass is dropped onto the chin bar of the helmet and a limit is set on the deformation allowed of 60 mm. For the ECE 22.05 test, the helmet mounted on a rigid headform with a chin is dropped onto a flat steel anvil. The acceleration measured at the centre of gravity of the headform is limited to 275 G.

    These two chin bar tests have significant differences in their impact on helmet design and do not specifically address the issue of basilar skull fracture. The focus of the Snell test appears to be on movement of the chin bar towards the face and facial injury, while the ECE test focuses on the extension of the protective area of the head to the chin bar, based on prevention of brain injury rather than skull fracture.

    Aims of the study The aim of this study is to improve the understand