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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
Alex Leary, BS, Gina Bertocci, PhD
University of Pittsburgh
Slide 2
Research Question
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
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
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
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)
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)
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
SAE Recommended Practice J2249
- Wheelchair Tiedown and Occupant Restraint Systems (WTORS)
- Four point tiedown system
- 20g/30 mph frontal impact test
Slide 9
ANSI/RESNA WC-19
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
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
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
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
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
Graphic description: a graph presenting the neck injury criteria to be met: compression, tension and shear of neck.
Slide 15
Chest Injury Criteria
FMVSS specifies < 60g peak acceleration
Measured by accelerometer in ATD chest
Slide 16
Abdominal Injury Criteria
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
Graphic description: three photographs showing the frangile abdoment and how it is inserted into the ATD.
Slide 18
Methods: Sled Testing
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.
Measured
- Head, Chest, Pelvis Accelerations
- Neck Moments
- Neck Forces
- Belt Forces
- Tiedown Forces
- Crash Pulse
Slide 20
Methods: Sled Testing
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
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
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
Graphic description: photo of fractures in the frame of a wheelchair with a sling seat.
Slide 24
Results: HIC (max 1000)
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)
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
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
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)
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
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
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
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?
The End
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Updated: March 12, 2002
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