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Helmet Testing
Philosophy and Concepts of Helmet Testing
It is important to realize that a lot of product type testing like helmet testing does not seek to precisely reproduce real life situations, rather it attempts to define a set of requirements that is analogous to the types of situations that might be encountered while engaged in a prescribed activity. Helmet tests are designed to be repeatable, measurable and include a fixed range of situations a helmet might reasonably encounter. At this point the concerns of helmet testing does not include responses of the neck or body as they react with the head during a crash. It is strictly a measurement of how a helmet reacts during an event to protect the wearer's brain. At Snell we believe that as technology continues to evolve, so should helmet design and manufacturing techniques.
The Snell Memorial Foundation has one of the most advanced and busiest helmet testing facilities in the world. Snell's California helmet testing laboratory is the one of the few in the United States accredited to ISO 17025 by the American Association for Laboratory Accreditation (A2LA).
Watch video "How Helmets are Tested in Snell Labs"
WMV, 1.9MB
Before a helmet can be Snell-certified, it is tested in Snell's state-of-the-art test facility. Snell technicians conduct a variety of tests to determine the helmet's performance and ability to stay on the head in different environmental conditions - ambient, wet, heat, cold. Depending on the application and the standard, each helmet must pass all or some of the following tests.
Test types
Impact Test
This
test involves a series of controlled impacts where a helmet
is positioned on a metal head form and then dropped in a guided
fall onto various steel test anvils (Flat, Hemisphere, Kurbstone,
Roll bar, Edge or a Horseshoe type) which simulate different
impact surfaces. The head forms are instrumented with an accelerometer
to measure peak G force or acceleration which is measured
in "G"ravitational units. The impact energy (drop height and
mass), or how hard the helmets are impacted is unique to each
standard. However, in any valid test, if the peak acceleration
imparted to the head form exceeds certain threshold value (around
300 G's, depending on standard and test type), the helmet is
rejected.
Positional Stability (Roll-Off) Test
A
head form is mounted on a stand so that it points face downward
at an angle of 135 degrees. The helmet is placed on the head
form and the straps and buckles adjusted to obtain a "best fit".
A wire rope is hooked to the rear edge of the helmet and brought
forward so that its free end runs across the helmet and downward
towards the floor. The free end of the rope has a mechanical
stop with a 4 kg weight resting on the stop. The weight is raised
to a prescribed height and dropped onto the stop. The resulting
shock places a rotational load on the helmet. The helmet may
be shifted, but must not roll off the head form. Next, the head
form is rotated 180 degrees, the helmet adjusted, and tested
with the wire rope hooked to the front edge of the helmet and
the test is repeated. As in the first case, the helmet may be
shifted but must not roll off the head form.
Dynamic Retention Test
The
helmet is placed on a head form and the chin strap fastened
under a device approximating the contour of the jaw. The jaw
piece is loaded with a 23 kg weight for approximately one minute.
The retention system is tested by simultaneously removing the
23 kg weight and applying a 38 kg mass in an abrupt guided fall.
The retention system fails if it cannot support the mechanical
loads or if the maximum instantaneous deflection (stretch) of
the retention system exceeds 30 mm. Drop heights for the fonts 38
kg mass are different for each standard, however the mechanism
and failure criteria are similar for other types of headgear.
Chin Bar Test
The
chin bar test applies to full face motorcycle, special application
racing and kart racing helmets. The helmet is affixed to a rigid
base with the chin bar facing upward. A 5 kg weight is dropped
through a guided fall to strike the central portion of the chin
bar. Maximum downward deflection of the chin bar must not exceed
the stated distance.
Shell Penetration Test
The
shell penetration test applies to motorcycle, special application
racing, kart racing, skiing and equestrian helmets. The helmet
is affixed to a rigid base. A 3 kg sharply pointed free 3d models striker is
dropped in a guided fall onto the helmet from a prescribed height.
The test striker must not penetrate the helmet or even achieve
momentary contact with the head form.
Faceshield Penetration Test
The
face shield penetration test applies to full face motorcycle,
special application racing and kart racing helmets. The face
shield is affixed to the helmet and shot along the center line
in three separate places with an air rifle using a sharp icons soft
lead pellet. Pellet speed will be approximately 500 kph. For
both types of shield the pellet must not penetrate, and
for the racing helmet any resulting "bump" on the inside of
the shield must not exceed 2.5 mm.
Flame Resistance Test
The
flame resistance test applies to special application racing
helmets only. The test is conducted using a propane flame of
approximately 790 degrees centigrade. The flame is applied to
the shell, trim, chin strap and face shield for a specified
number of seconds, and any resulting fire must self extinguish
within a specified time after flame removal. During the whole
process the temperature of the interior lining of the helmet
must not exceed 70 degrees centigrade.
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