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Thatcham Heads to a Safer Future |
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| To offer adequate protection,
a head restraint should be as high as the top of the head
and as close as possible to the back of the head, touching
is best. |
Thatcham Heads to a Safer Future
Since Thatcham launched their first New Car Whiplash Ratings in
2002, most motor manufacturers have upgraded their head restraints
across their new model ranges; their intention and Thatcham’s
being to bring about a reduction in the risk of suffering a whiplash
injury in a crash. Several high profile manufacturers have been
actively improving head restraint geometry and so, compared with
2003, Thatcham have seen a:
• 26% increase in those seats rated as GOOD
• 18% increase in those seats rated as ACCEPTABLE
• 33% reduction in those seats rated as POOR
• 15% reduction in those seats rated as MARGINAL
Recent insurance research has indicated a significant reduction
in whiplash injuries occurring in vehicles fitted with anti-whiplash
systems. Designs from Volvo and Saab tackle the issue in different
ways. Saab’s system automatically moves the head restraint
to support the head and neck in the crash, whereas Volvo’s
system absorbs much of the energy of a crash by controlled bending
of the seat. The data indicates a 43% reduction in whiplash injuries
occurring in Saab vehicles compared with their previous generation
and a spectacular 49% reduction in injuries for occupants in Volvos
fitted with their WHIPS seat.
Although seat design is a vital component in reducing whiplash,
motorists also need to play their part by adjusting their head restraint
properly and checking its position before driving off. As Thatcham
are keen to point out: ‘Remember it’s a head restraint
and not a head rest. Is Your Head Restraint Correctly Adjusted?’
The Fundamentals
Whilst not uncommon in frontal and side crashes, whiplash most commonly
occurs in low speed, rear crashes. It’s believed that the
cause is the sudden whip-like movement of the head relative to the
torso. Mild symptoms involve stiffness and tenderness in the muscles
of the upper back and neck, headaches and dizziness. More serious,
long term cases can involve permanent impairment, neurological and
musculoskeletal injuries. Disorders associated with a whiplash type
injury are usually short term, resolving within a few days or weeks.
However, a minority of cases may develop longer lasting symptoms,
reduced functionality or disability. Despite the good prognosis
for most people, 10% of occupants are still reporting symptoms a
year after their crash. Current estimates are that 5% of whiplash
cases will continue to have a reduced functional capacity or related
disability at 1 year and that for 1%, this will be permanent.
Those at greatest risk from whiplash are women in the 20 to 50 age
group. Women are more than twice as likely to suffer from whiplash
injuries as men and are also more likely to go on to develop long
term symptoms. Factors influencing this difference may include seating
posture and neck muscle strength.
It is generally accepted that whiplash is an acceleration injury.
That is to say that the injury comes from the differential motion
between the occupant’s torso and head during an impact. As
the occupant’s vehicle is struck from behind, their vehicle
is pushed forward. As their seat is then subsequently also pushed
forward, the occupant’s body begins to accelerate, but, due
to inertia, their head attempts to remain in place. This lag causes
the neck to deform into an ‘S’ shape.
The head will then begin to bend backwards (the extension phase),
as the head begins to catch up with the accelerating torso. If a
poor head restraint is fitted that doesn’t prevent further
differential movement, we see the hyperextension phase. Up until
recently, much research had focused on the possibility that whiplash
was caused by muscular over-extension during this phase. Current
head restraint design, therefore, ims to prevent these hyperextension
injuries by preventing this motion. However, injuries are still
occurring, suggesting that some injuries are happening earlier in
the motion. Recent research is focused on the possibility of internal
nerve damage to the spinal canal caused during this initial ‘S’
shape phase by the rapid acceleration of the body relative to the
head, causing pressure changes in the neck leading to pain and inflammation.
Head Restraint Use
A head restraint that is behind and close to a person’s head
can reduce the risk of a whiplash injury in a rear end crash. Although
most head restraints are adjustable, many are not capable of being
adjusted high enough or close enough to the back of the occupant’s
head to provide protection. In a recent study, Thatcham found that
78% of drivers failed to adjust their head restraints correctly,
or were driving cars with head restraints incapable of correct adjustment.
Only 22% had ‘Good’ geometry (were high enough and close
enough to occupants’ heads) and, of those, 11% were fixed
one piece designs with ‘Good’ geometry, such as those
from later Volvo cars.
Head restraint locking is another important element in a good design,
because head restraints that lock are less likely to be pushed out
of adjustment. A locking head restraint will tend to remain in place
during a rear crash, whereas a non-locking head restraint can often
be pushed down by the occupant’s head, negating any protection
that it may have offered. Furthermore, rear seated passengers often
use the front seat head restraint as a hand hold to ease getting
out of the back of the car, so if the restraint fails to lock, again
it may be pushed down, limiting its effectiveness.
To offer adequate protection, a head restraint should be as high
as the top of the head and as close as possible to the back of the
head, touching is best. Although many drivers report initial discomfort
with a head restraint so close, especially those with ponytails,
it is vitally important that head restraints are positioned sufficiently
close to prevent the ‘S’ shape phenomenon. A properly
positioned head restraint is the necessary first step in reducing
the relative motion between head and neck, thus reducing injury.
Effective whiplash protection begins with good geometry The basis
of Thatcham’s Static Head Restraint Measurements is that restraints
must be capable of being positioned as high as the top of the occupant’s
head and as close as possible. Adherence to these criteria is an
important first step in lessening injury risk in a rear end crash.
Thatcham undertakes head restraint measurements in brand new vehicles.
The procedure involves putting a special mannequin in the seat,
set at a 25 degrees recline angle (a typical real world seating
angle). This mannequin represents an average size male and has a
special head known as an HRMD (Head Restraint Measuring Device)
placed on top. Measurements are taken with the head restraint down,
up and also tilted forward, if applicable. Notes are taken of any
locking device and also of seat adjustment controls such as lumbar
and base tilt.
Head restraint evaluations are based on two important measurements.
The first is the distance from the top of the head of an average
size male to the top of the head restraint. A head restraint should
be no more than 6 cm below the top of the HRMD’s head, which
ensures that the restraint is high enough to protect tall occupants.
The second measurement is the backset, the distance from the back
of the HRMD’s head to the front of the restraint. Each head
restraint is classified into one of four geometric zones –
‘Good’, ‘Acceptable’, ‘Marginal’
or ‘Poor’ – according to its height and backset.
‘Acceptable’ and ‘Good’ restraints are high
enough to protect tall occupants and those of average height. ‘Acceptable’
and ‘Good’ restraints also have smaller backsets, which
benefit occupants of all heights.
The Future
Dynamic testing is now being conducted at Thatcham and the results
of this will be published in 2004. Good head restraint geometry
does not necessarily guarantee good occupant protection in real
world crashes. Seat characteristics such as frame and foam stiffness,
and seat back shape can also all have an influence. However, head
restraint geometry is an important first step towards whiplash injury
reduction.
2004 will also see the first, pan-European dynamic whiplash assessment
test. Working with international partners within the International
Insurance Whiplash revention Group (IIWPG) and utilising Thatcham’s
£1 million HyperG sled, the test will go beyond basic geometry
and enable Thatcham to test car seats even more realistically. The
tests will also feature the Centre’s BioRID crash test dummy,
the first “whiplash” dummy whose lifelike spine interacts
more realistically with the car seat, giving a more accurate indication
of a seat’s ability to protect its occupant.
Seats and this new BioRID dummy will be placed on the HyperG sled
and will be subjected to the sort of accelerations that are believed
to result in typical whiplash injuries. The seats will then be rated
according to their ability to reduce these forces and accelerations.
Thatcham sees its job as persuading car manufacturers everywhere
to put increased emphasis on SAFER SEATS.
Further information and up-to-date test results can be found on
the Thatcham website www.thatcham.org.
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