EN 397: 2012
Impact / Shock Absorption
Where helmets are of the type intended to protect a static user from predominantly falling hazards, a series of impact tests are carried out using a fixed headform, with a falling mass striker. The helmet under test is placed onto a suitably-sized (and dimensioned) headform, mounted on top of a load cell, which in turn is mounted to a rigid (and monolithic) base. A striker, in this case with a hemispherical surface, of a suitable mass (5 kg) is dropped onto the helmet from a specific height (1 metre). The force transmitted through the helmet is measured using the load cell beneath the headform, and recorded onto a graph. For a helmet to meet the requirements of EN 397, the maximum transmitted force, after suitable signal conditioning, cannot exceed 5 kN. This test is carried out on several helmet samples, following pre-conditioning to high temperature, low temperature, water immersion and UV ageing. There is also the option to expand the temperature range for the pre-conditioning if claimed by the manufacturer.
Industrial helmets are tested to ensure they offer sufficient protection against sharp or pointed objects. The test is based on a method similar to the shock absorption test, in that a striker is dropped from a set height onto the helmet fitted to a fixed headform. However, in this case, the striker is a pointed cone (of mass 3 kg, dropped from a height of 1 metre), and rather than measure the transmitted force, the assessment is based on whether the striker makes contact with the headform underneath the helmet. This can be carried out using indicator material (e.g. plasticine or soft metal) on the headform itself, or by establishing electrical contact between the striker and headform (where if the striker contacts the headform, a circuit is complete which sounds an alarm). As with the impact testing, this is carried out on helmets pre-conditioned to high temperature, low temperature, water immersion and UV ageing.
Most specifications for protective helmets include a number of requirements for the design of a helmet in addition to the specific performance requirements. These typically encompass the area of coverage provided by the helmet, as well as the field of vision afforded to the user when worn. They can also cover a number of ergonomics and safety-based requirements, such as clearance between the head and the shell of the helmet (particularly in the case of industrial helmets).
Chin strap anchorage
Helmets can only protect when retained on the head, therefore, a chin strap may be supplied to ensure retention in typical workplace conditions. EN 397 requires that either the helmet shell or the headband is fitted with a chinstrap or with the means of attaching one, i.e. anchorage points. Any chinstrap supplied must have a minimum width of 10 mm when un-tensioned and be attached either to the shell or to the headband.
The strength of the strap anchorage(s) should be sufficient to enable any attached chin strap to hold the helmet on the head but not so great that the strap would become a strangulation hazard. In the method for measuring chin strap anchorage strength specified in EN 397 the helmet is mounted onto a suitably sized headform and the chin strap passed around an artificial jaw. A tensile force is then applied to the artificial jaw at a rate of 20N/min until the artificial jaw is released, due to failure only of the anchorage(s). The standard requires that the force at which this occurs shall be no less than 150 N and no more than 250 N.
EN 397 includes a number of optional test on helmets where additional protection is claimed. Helmets can claim protection against very high or very low temperatures, splashes of molten metal, electrical voltages up to 440 V, and lateral deformation. Each of these categories include tests to prove the helmet’s suitability for protection against these hazards.