Injury Risk Analysis of a Wheelchair User in a Frontal Impact Motor Vehicle Crash

Alex Leary, BS, Gina Bertocci, PhD
University of Pittsburgh

Slide 1
Injury Risk Analysis of a Wheelchair User in a Frontal Impact Motor Vehicle Crash

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Alex Leary, BS, Gina Bertocci, PhD
University of Pittsburgh

Slide 2
Research Question

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What is the injury risk associated with an occupant using a manual wheelchair as a vehicle seat in a 20g/48kph frontal impact?

Slide 3
Background

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1990 ADA – Increased public access for people with disabilities

Census Bureau (1995) 2.3 million long term users of mobility equipment - 600,000 employed

Approximately 60,000 wheelchair users are injured every year (NHSTA 1991-1995)

Many wheelchair users are unable to transfer to a motor vehicle seat

2494 fatalities between 1991-1995 due to improper or no securement

Slide 4
Significance

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Most wheelchairs are not designed to handle motor vehicle impact loads

Frontal impacts account for the majority of fatalities

There is a need to determine the impact injury risk to occupants using wheelchairs as vehicle seats

Slide 5
Standards

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Provide guidance to manufactures

FMVSS – Vehicle Seats, Mandatory Legislation

SAE Standards – Tiedowns and Restraints, Voluntary

ANSI/RESNA WC-19 – Transport Wheelchairs, Voluntary

Slide 6
Standards: FMVSS Seating Systems (207)

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Federal Motor Vehicle Safety Standards

Specifies strength requirements for automotive seats and their attachment assemblies

Assesses structural integrity

Specifically designed for folding front automobile seats

Slide 7
Standards: FMVSS Occupant Crash Protection (208)

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48kph/20g frontal impact on new vehicles

Injury Criteria

  • HIC < 1000
  • Chest Deflection < 3" (H3 Dummy Only)
  • Chest Deceleration < 60g
  • Neck Force -400N < 3300N
  • Neck Moment 190 Nm flexion, 57 Nm extension
  • Femur Load < 2250 lbs.

Slide 8
Standards: SAE

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SAE Recommended Practice J2249

  • Wheelchair Tiedown and Occupant Restraint Systems (WTORS)
  • Four point tiedown system
  • 20g/30 mph frontal impact test

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ANSI/RESNA WC-19

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Voluntary standard addressing wheelchair crashworthiness

Four point tie-down securement system

  • Limits on anchor position

Securement device dynamically tested in 20g/30 mph frontal impact

  • No major structural failure
  • Excursion limits (head, knee, and wheelchair)
  • ATD and Wheelchair must remain upright

Slide 10
Methods: Injury Risk Assessment

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Determine occupant response to 48kph/20g frontal impact sled testing

Use injury criteria to characterize injury risk

  • HIC
  • Tri-axial neck force and moment
  • Frangible Abdomen – Abdominal Crush
  • Chest and pelvis accelerations

Slide 11
Injury Criteria

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Allow measured quantities on an anthropomorphic test dummy (ATD) to be translated to injury risk

Head – Head Injury Criterion (HIC)

Neck – Tension, Compression, and Shear Limits

Chest – Peak Acceleration Limit

Abdomen – Lap Belt Submarining Indication

Slide 12
Head Injury Criteria

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Predicts the probability of life threatening brain injury

Algorithm that evaluates the head acceleration history over a 36 second window

Measured by an accelerometer in the ATD head

Must be less than 1000

Slide 13
Neck Injury Criteria

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Mertz HJ. Injury assessment values used to evaluate Hybrid III response measurements. NHTSA Docket 74-14, Notice 32, Enclosure 2 of Attachment I of Part III of General Motors Submission USG 2284. March 22, 1984

Time dependent force levels measured by a tri-axial load cell in ATD neck

Slide 14
Neck Injury Criteria Graph

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Graphic description: a graph presenting the neck injury criteria to be met: compression, tension and shear of neck.

Slide 15
Chest Injury Criteria

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FMVSS specifies < 60g peak acceleration

Measured by accelerometer in ATD chest

Slide 16
Abdominal Injury Criteria

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Abdominal injury is caused by lap belt submarining – when the belt slips over the anterior iliac crests (ASIS points) of the pelvis

Measured by the frangible abdomen – a biofidelic deformable foam insert that records deformation caused by the lap belt.

The level of foam compression corresponds to abdominal injury levels (Rouhana 1989)

Slide 17
The Frangible Abdomen

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Graphic description: three photographs showing the frangile abdoment and how it is inserted into the ATD.

Slide 18
Methods: Sled Testing

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University of Michigan Testing and Research Institute

Six total tests

  • Four sling seat configurations
  • Two rigid seat configurations

20g/30 mph frontal impact

SAE J2249, ANSI/RESNA WC-19 Compliant Crash Pulse

Slide 19
Methods: Sled Testing cont
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Measured

  • Head, Chest, Pelvis Accelerations
  • Neck Moments
  • Neck Forces
  • Belt Forces
  • Tiedown Forces
  • Crash Pulse

Slide 20
Methods: Sled Testing

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UMTRI testing facility summer 2000

Six manual wheelchairs tested to WC-19 standards (48 kph frontal impact)

  • Two rigid seat configurations
  • Four sling seat configurations

Graphic description: a photograph of the sled test set up with ATD sitting in a manual wheelchair.

Slide 21
Seat Configurations

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Graphic description: two photographs, one of manual wheelchair with a rigid seating system and the other of a manual wheelchair with a sling seating system.

Slide 22
Results: Wheelchair Damage

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Major frame fractures in two wheelchairs configured with sling seats

Not WC-19 compliant

Graphic description: photo of a fracture in the frame of a wheelchair with a sling seat.

Slide 23
Results: Wheelchair Damage

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Graphic description: photo of fractures in the frame of a wheelchair with a sling seat.

Slide 24
Results: HIC (max 1000)

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Graphic description: a table showing Head Injury Criteria (HIC) results. HIC 32 millisecond time interval for rigid seat 1 (534) and rigid seat 2 (934), sling seat 1 (340), sling seat 2 (620), sling seat 3 (596), sling seat 4 (866). HIC unlimited time interval for rigid seat 1 (890) and rigid seat 2 (1269), sling seat 1 (644), sling seat 2 (1089), sling seat 3 (965), sling seat 4 (1204).

Slide 25
Results: Chest Injury Risk (max 60g)

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Graphic description: a table showing peak chest accelerations, (g), of the ATD in the rigid seating systems 1 (46.5) and 2 (55.0), and sling seating systems 1 (44.9), 2 (45.4), 3 (46.6) and 4 (55.3).

Slide 26
Results: Neck Injury Risk

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Graphic description: this table shows the results of Neck Injury Risk, represented as compression, tension and shear time dependent forces, of the ATD in the rigid seating systems 1 and 2 and sling seating systems 1 through 4. Both wheelchair tests with rigid seats exceeded the neck force injury criteria in shear and tension. Two of the four wheelchairs with sling seats exceeded the neck injury criteria; one in tension and one in shear.

Slide 27
Results: Abdominal Injury Risk

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No indication of lap belt submarining

Abdominal compression indicates less than 5% chance on AIS>3 injury in all tests

Slide 28
WC-19 Excursion Limits (mm)

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Graphic description: this table shows the ATD head and knee and wheelchair excursions. WC-19 excursion limits are 650 mm for head, 375 mm for knee, and 200 mm for wheelchair. The excursions of all tests were within the allowable ranges.

Rigid seat 1 head (515), knee (209), wheelchair (61); rigid seat 2 head (641), knee (287), wheelchair (142); sling seat 1 head (476), knee (236), wheelchair (N/A);(340), sling seat 2 head (565), knee (265), wheelchair (31); sling seat 3 head (494), knee (265), wheelchair (22); sling seat 4 head (591), knee (292), wheelchair (31). All tests complied with excursion limits.

Slide 29
Discussion: Injury Risk

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Neck forces in tension and shear posed the greatest injury risk

Choice of HIC time interval affects injury prediction

Chest injury risk was low

Abdominal injury risk was low

Slide 30
Discussion: WC-19

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Two tests failed due to structural failure

All tests remained within excursion limits

Some tests passed WC-19 standards which showed positive injury risks

Possible need for injury risk assessment in WC-19

Slide 31
Discussion: Rigid vs. Sling

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Both wheelchairs with rigid seat configurations showed neck injury risk

Averaged HIC36 and HICunlimited values were over 100 points higher for wheelchairs with rigid seats

Seat configuration type may affect occupant injury risk

Slide 32
Questions?

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The End

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Updated: March 12, 2002

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Please note: This information is provided a archival information from the Rehabilitation Engineering Research Center on Wheeled Mobility from 1993 to 2002.

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