SATRA hearing specialist John-Mark Edmundson explains the different standards that apply for each aspect of protection for the eyes, ears and head.

People in the workplace often face multiple hazards at the same time. A tree surgeon using a chainsaw, for example, needs to be protected from impacts to the head from falling debris; the effect of sawdust and small particles flying towards the eye; and from the noise of the chainsaw.

Protection can be provided by multiple components, each satisfying their own standard, or it can be delivered by a single product. There are different European standards that apply for each aspect of protection.

This article will look at three standards that could be combined to provide appropriate protection to the head. One option is for a worker to wear a combined system; that is, helmet, eye protection, and hearing protection. The helmet should satisfy EN 397:2012 + A1:2012 and will be fitted with eye protection that meets EN 166:2001, while the earmuffs should meet EN 352-3:2002. A second option is for the worker to wear a separate helmet, eyewear and earmuffs (EN 352-1:2002) or earplugs (EN 352-2:2002). Then of course there are other aspects to consider – such as chemical innocuousness and certification – which will generally also apply.

EN 397 – resistance to impacts

The main helmet shell, together with its harness, provides protection to the top of the head. The typical industrial hard hat is a familiar sight on all building sites and is covered by EN 397:2012 + A1:2012. An impact test is a mandatory and central requirement for such helmets. Other protection may be provided by the shell, and EN 397 includes additional tests covering the design and other safety-based requirements.

The impact test assesses the ability of the helmet to provide basic protection against moderate impacts that might occur on an industrial site, such as from a falling brick. This test is conducted by mounting the helmet onto a fixed head form and then impacting it with a vertical falling mass. The force experienced by the head form beneath is recorded with a maximum transmitted force of 5kN being permitted. An impact energy of approximately 50J is used, which is achieved by dropping a 5kg hemispherical striker onto the helmet from a height of one metre. These impacts are carried out on the crown of the head after conditioning the helmets to high and low temperatures, water immersion and artificial ageing (by exposing the helmets to an intense ultraviolet light). This helps to ensure that helmets remain protective during ‘reasonable’ use.

“this article will look at three standards that could be combined to provide appropriate protection to the head”

In addition to this protection from blunt objects, some protection must be provided against sharp objects. The test used to assess this characteristic uses a falling striker with a 3kg conical point. The shell must prevent the point of the striker making any contact with the head form.

EN 397 also includes a number of tests on helmets where optional protection is claimed. Helmets may be claimed to protect against extremes of temperatures, splashes of molten metal, electrical voltages up to 440V and deformation from lateral forces.

Ergonomic requirements

Helmets can only protect when they are retained on the head and if they fit properly.

For this reason, most specifications for protective helmets include a number of requirements for the design of a helmet, in addition to the specific performance requirements – such as those already mentioned.

There are a number of ergonomic and safety-based requirements, such as the clearance between the head and the shell of the helmet, and the width of the cradle. These ensure the helmet can be worn without causing inconvenience to the wearer.

The rear adjustment must permit adequate fit for any head in the stated size range. In addition, a chin-strap may be supplied. EN 397 requires that either the helmet shell or the headband is fitted with a chinstrap or the means of attaching one. The chinstrap should have a minimum width of 10mm, and the strength of the strap attachment should be sufficient to enable the chinstrap to hold the helmet on the head, but not so great that the strap could become a strangulation hazard. To test this, the helmet is mounted onto a suitablysized head form and the chinstrap is passed around an artificial jaw. A tensile force is applied to the jaw at a rate of 20N/min until the jaw is released due to failure of the anchorages. The force at which this occurs should be no less than 150N and no more than 250N.

“the relevant standards for hearing protection can be found in the EN 352 series”

EN 352 – attenuation of noise

Prolonged exposure to high levels of noise can damage a person’s hearing. In the EU, for example, the level at which hearing protection must be made available is 80dB, and the employer must assess the risk to health. At 85dB, the wearing of hearing protection is mandatory. However, suitable protection – such as earmuffs – can attenuate louder noises to safer levels.

The relevant standards for hearing protection can be found in the EN 352 series. EN 352-3:2002 covers helmet-mounted earmuffs. If ear protection comprises separate ear muffs or earplugs, these would be covered by parts 1 and 2. These standards assess the passive protection – that is, the protection intrinsically provided by the protector’s construction. Parts 4 to 7 contain requirements and tests for active devices, and these take into account the behaviour of electronic circuitry. Such assessments are valuable for conditions where a combination of a high level of protection, situational awareness and ease of communication is needed (for instance, when working near railway tracks).

A range of physical and mechanical tests are carried out to assess the ear protector’s basic performance. Initial testing begins with assessing if the product can fit on the claimed head size range, and whether or not it has appropriate adjustment. The headband force is measured, following which the hearing protectors are subjected to a drop test (or optionally, a ‘low temperature drop’ test), a flexing test, water immersion or an optional water immersion with the headband under stress. After this, the headband force is re-measured and the change in headband force is calculated.

Acoustic assessment of passive hearing protectors includes two basic tests – sound attenuation and insertion loss. These establish whether harmful levels of noise are reduced to acceptable levels at the ear.

The ‘insertion loss’ acoustic test is conducted by an electro-acoustic method. The test evaluates the levels of noise received by microphones placed in a fixture representing the head. This compares the levels of noise received, both with and without the hearing protector in place. The insertion loss test is carried out to ensure that the hearing protection proved by the set of samples assessed is at a consistent level.