How Snell test helmets

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 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).

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.

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 260-300 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 Rigidity 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.

Frontal Head Restraint Test

Some special application racing helmets are configured with Helmet-M6-Terminals to allow the attachment of the flexible tethers connecting to Frontal Head Restraint devices. These are devices designed to limit the forward motion of the head in frontal impacts. The tethers may bear much of the inertial load of the head and helmet potentially reducing the stresses to the wearer's cervical spine and the base of the skull. The apparatus shall provide a means for measuring the combined load applied to the shoulder straps and the load in each tether.

Chin Bar Impact Test

The chin bar impact test applies to some special application racing helmets. The helmet is placed in a special cradle which can move downward freely along guide wires or one or more rigid rails delivering its contents to impact against a flat anvil. The cradle with the helmet and head form shall be dropped along the guides such that the chin bar will strike the flat anvil. The shock acceleration at the design center of gravity of the head form shall be measured by means of a tri-axial accelerometer and data recording system. If the impact velocity measurement is 5.5 m/s or more and the peak magnitude of the recorded acceleration of the head form is 275 G or less, the sample shall be deemed to meet the test requirement.