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Eyewear testing

Protective eyewear sold in the European Union must be CE-marked, in accordance with the PPE Directive 89/686.

The process to achieve certification of protective eyewear involves testing against the requirements of harmonised European standard EN 166:2001 for industrial eyewear. Other standards may also apply depending on the application (see table 1). Note that the PPE Directive applies also to prescription eyewear if that eyewear also includes protective features – irrespective of whether they are for industrial or leisure use.

Table 1: European standards applicable to industrial eyewear
Standard Description
EN 1836:2005 Requirements and test method for sunglasses
EN 166:2001 Requirements for protective eyewear
EN 167:2001 Optical test methods for protective eyewear
EN 168:2001 Non-optical test methods for protective eyewear – for example, requirements related to strength, durability, resistance to ignition, resistance to chemicals and resistance to impact
EN 169:2002 Requirements for welding filters
EN 170:2002 Requirements for ultraviolet filters
EN 171:2002 Requirements for infrared filters
EN 172:1995 Requirements for sun glare filters for industrial use
EN 174:2001 Requirements for downhill ski goggles
EN 175:1997 Requirements for eye and face protection during welding

For eyewear intended to be used as PPE in the workplace, the key standard generally is EN 166. This article describes some of the requirements and associated tests which EN 166 applies to protective eyewear. As table 1 indicates, optical test methods for protective eyewear are specified in EN 167, and non-optical test methods are specified in EN 168.

EN 166 specifies the minimum requirements for a range of performance tests, and these will be described in detail. This standard contains a set of requirements referred to as ‘basic requirements’, which may be regarded as mandatory. These cover all types of protective eyewear (including spectacles, goggles and face shields), as well as a further set of tests referred to as ‘particular requirements’, which must be applied if certain end-uses are envisaged for the eyewear or if the manufacturer wishes to make additional claims regarding protection. These include requirements covering resistance to high-speed particles, molten metal or chemical splash. Finally, there is a range of tests referred to as ‘optional tests’, which include, for example, resistance to fogging and resistance to surface damage by fine particles.

Basic requirements

The basic requirements include assessments for field of vision, transmission and diffusion, refractive properties and robustness, as well as resistance to ageing (stability to heat and resistance to UV), corrosion and ignition.

The main purpose of the field of vision, transmission and diffusion tests, refractive properties and resistance to UV tests is to ensure that the eyewear does not impede or distort the vision of the wearer, and allows sufficient light through to the wearer’s eyes. In particular, the field of vision test is intended to ensure that nothing in the frame or the periphery of the oculars (the lenses) impedes vision. The refractive tests include three test procedures: spherical, astigmatic and refractive powers.

 

Figure 1: A target is used during the assessment of spherical and astigmatic refractive powers – EN 166:2001 Clause 7.1.2.1

Spherical and astigmatic refractive powers are measured by viewing a target through a telescope (figure 1), with the test ocular placed between the object lens of the telescope and the target. The test operative sets up the focusing of the telescope so that he or she can view the target clearly with no test ocular in place. With the test ocular in place (and assuming the vertical and horizontal bars of the target go out of focus), the adjustments made to the telescope to bring first the horizontal and next the vertical bars successively into focus are noted. The change in the focusing power of the telescope to make these adjustments is directly related to the refractive and astigmatic power of the test ocular.

The prismatic power of the eyewear is determined using a different method. Two beams of light are set up to converge on a target, and the test eyewear is placed in these beams so that the beams pass through the centre of the oculars. Any horizontal and vertical deflection of the two beams from the original convergent point on the target is recorded. The horizontal and vertical prismatic differences are calculated from these measures of deflection. The optical powers should be as neutral as possible, in order that the eyewear does not create any unintended hazard.

Any tendency for eyewear to create a diffusing effect should also be minimised. The diffusion test measures this property. A laser beam is directed towards a light detector, firstly through a circular mask and then through an annular mask. The level of light detected is recorded for both masks. The measurements are taken once again with the test ocular in the path of the beam, at a point before the beam passes through the masks.

Transmission tests measure the percentage of incident light which the oculars transmit to the wearer’s eyes. Where the oculars are not required to have any filtering action, the percentage level of transmitted light (referred to as ‘luminous transmittance’) must be greater than 74.4 per cent.

On the other hand, some circumstances might require that the oculars limit or filter the light passing through – by reducing the overall amount of light, while reducing the transmittance of a specific wavelength band (such as the ultraviolet band or the infrared band). For non-filtering oculars, any test device which produces an overall percentage transmission value across the complete visible spectrum is satisfactory.

Specific requirements for transmission for any eyewear which has a filtering action will be found in one of the specific standards listed in table 1. For Instance, EN 170 is intended for wearers who are exposed to ultraviolet light during their work, while EN 172 is intended for protection against sun glare. The requirements in standards such as EN 170 and 172 are more detailed than EN 166. The maximum transmittance is specified for certain parts of the visible and ultraviolet spectrum.

As an example, in EN 170 the maximum percentage transmission of light permitted in the part of the ultraviolet spectrum from 313-365nm varies between 10 per cent and 0.3 per cent, depending on the basic transmittance. So, for an ocular which has a luminous transmittance of 75 per cent, the maximum transmission in this range is 10 per cent. However, the maximum transmittance in the ultraviolet range (below 313nm) is 0.0003 per cent for all eyewear covered by EN 170.

Exposure to UV light can affect the transmission properties of oculars. Therefore, these properties are measured again after the eyewear has been exposed to UV light. To meet the EN 166 requirements, there are limits on how much the transmission results can change. The diffusion results must meet the same requirements as the unexposed results. A further requirement of filtering eyewear is that the variation in transmittance is minimised across the viewing area of the ocular.

Box 1: Explanation of some terms
  • Nanometre (nm): equivalent to 10-9m or a millionth of a millimetre and used to express the wavelength of light
  • Visible light: light with wavelengths between 400nm and 780nm
  • UV: Ultra-violet light – in the range of 100-400nm
  • IR: Infrared radiation, wavelength from 780nm to >2,000nm.

The final test procedure in EN 167 is the test for assessing the quality of the materials and surface. SATRA utilises a light box fitted with polarising filters through which to view the illuminated sample (figure 2). Defects likely to impair vision can be easily spotted using such equipment. Defects are permitted within 5mm of the frame, but not elsewhere across the ocular.

 

Figure 2: An assessment of the quality of eyewear materials using a polariscope – EN 166:2001 Clause 7.1.3

Apart from exposure to UV, other non-optical tests within the basic requirements include robustness tests and resistance to heat, ignition and corrosion. There are two robustness tests – ‘minimum robustness’ and ‘increased robustness’.

The minimum robustness test involves placing a static load of 10kg, acting through a hemispherical contact surface of 22mm diameter, on the centre of an ocular resting on a support plate. The ocular must not sustain any damage which results in cracking through the entire thickness into two or more pieces. Nor must fragments of 5mg or more become detached from the inside face of the ocular. Substantial deformation of the ocular is also not permitted. A witness paper system consisting of a disc of carbon paper on top of a disc of white paper is placed on the support plate beneath the ocular. If the static mass causes sufficient deformation of the ocular, it will compress the carbon paper/white paper system against the base plate, and mark the white paper. The minimum robustness test is only applicable to cover plates or to filtering oculars, and is not carried out where there is a requirement that increased robustness or resistance to high-speed particles is required.

The carbon paper witness marking system is also used with the increased robustness test. This test can be used on complete eye protectors, and involves dropping a steel ball onto the eyewear. For complete eyewear, the test is carried out with the eyewear mounted on a head form marked with the centres of the pupils and the lateral protection points. As with the minimum robustness test, the ocular must resist substantial deformation, cracking into two of more pieces, or the loss of fragments of 5mg or greater. The frame must also resist breaking into two or more pieces or breaking such that the oculars are no longer contained. The test is carried out both on the oculars and on the lateral protection area of the eyewear.

The lateral protection area of eyewear protects against impacts from the side. In testing, the lateral protection area must remain intact, be totally attached to the eyewear and prevent penetration by the steel ball.

Stability to elevated temperatures is tested by exposing the eyewear to a raised temperature (55°C for 60 minutes). After the test, the eyewear is allowed to cool for 60 minutes before it is examined for deformation. Corrosion testing involves placing the eyewear for 15 minutes in a boiling salt solution (10 per cent by mass of sodium chloride in water), followed by immersion in a room temperature salt solution of the same concentration – also for 15 minutes. The eyewear is wiped and allowed to dry before assessing any metal parts for corrosion.

The ignition test involves heating the end of a steel rod to a temperature of 650°C, after which the end of the heated rod is then lowered onto the test eyewear (figure 3). The contact is maintained for ten seconds, and the tester observes whether any part of the eyewear ignites or whether it continues to glow after the heated rod is withdrawn. All external surfaces of the eyewear should be tested – including oculars, frames and arms.

 

Figure 3: A resistance to ignition test – EN 166:2001 Clause 7.1.7

Particular requirements

There are a number of requirements for protection against specific hazards, such as protection against high-speed particle and resistance to fogging. These are required only if the eyewear is intended for protection against particular dangers. If the eyewear meets the specific requirements, either the ocular or the frame (or both, depending on the requirement), will need to carry a specific code. Table 2 shows the marking codes for frames and oculars, depending on the hazard.

Table 2: EN 166 markings for protective eyewear
Requirement Symbol for ocular Symbol for frame
Marking associated with the basic requirements only – for all protective eyewear
Scale number or shade number Required for filters only  
Manufacturer's identification Required Required
Number of the standard   EN 166
Optical class 1, 2 or 3  
Mechanical strength:
minimum robustness
enhanced robustness

If high-speed particle testing requirements are met, the S symbol is replaced by one of the symbols below:
Low energy impact
Medium energy impact
High energy impact

Impacts at extreme temperatures – code is followed by a T – for example, FT, BT or AT

No symbol
S



F
B
A

No symbol
S



F
B
A
Particular/optional requirements and associated marking
Droplets or splashes of liquids   3
Large dust particle   4
Gas and fine dust particle   5
Short circuit electric arc 8 8
Molten metals and hot solids 9 9
Resistance to surface damage by fine particles K  
Resistance to fogging N  
Enhanced infrared reflectance R  
Replacement oculars o
(above inverted triangle)
 

Note should be taken that there are some tests in the above table which are not suitable for all eyewear types. For instance, under the particular and optional requirements in the above table, the only valid tests for spectacles are those where the marking symbol is a letter (such as K-resistance to surface damage by fine particles test, N-fogging, R-enhanced infrared reflectance, S-enhanced robustness and F-low energy impact). Categories A and B (high and medium energy impact) are not permitted for spectacles. Spectacles cannot be tested against liquid splashes, or large dust particles, because they are inherently unable to protect against certain hazards.

Like enhanced robustness, the resistance to high-speed particle test is carried out on complete eyewear, and tests both the oculars and the frame. The particle used for these tests is a 6mm diameter steel ball bearing weighing 0.86g. Low energy impact (at a speed of 45m/s) is applicable to all types of protective eyewear, but the medium energy impact (at 120m/s) is only applicable to goggles and face shields. The high energy impact test (at a speed of 190m/s) is only applicable to face shields. This test is usually carried out with the samples at ambient temperatures, but as an option can be carried out on samples exposed to extreme temperatures. In this version of the test, the eyewear is impact tested after conditioning at 55°C and -5°C. The criteria for passing or failing in the high-speed impact test is the same as for Increased robustness.

Ignition testing is part of the basic requirements. However, for more extreme environments, two tests are provided. One of these assesses the resistance of protective eyewear to an electric arc hazard. The other tests resistance of protective eyewear to penetration by hot solids. This latter assessment involves dropping a 6mm diameter steel ball, heated to 900°C, onto the eyewear and noting the time from dropping the ball to the time penetration through the ocular occurs.

Optional requirements

As the name suggests, the resistance to surface damage test assesses the ability of the oculars or lens to resist damage by fine abradant particles – in this case sand with a specific grain size. After exposure to the abradant, the diffusion test is repeated on the ocular. An increase in the measured diffusion would indicate that the surface of the ocular has been damaged.

In the fogging test, the surface of the ocular is exposed to a very humid atmosphere above a water bath heated to 50°C. If oculars are without an anti-fog (or anti-mist) coating, condensation usually occurs within one or two seconds of the exposure starting. Any ocular which resists the formation of condensation for greater than eight seconds is regarded as being anti-fog. Prior to this test, the eyewear is immersed in fresh water, which has the effect or removing water-soluble anti-fogging treatments.

All protective eyewear sold within Europe must be CE-marked, according to the European PPE Directive. The majority of protective eyewear spectacles intended for use in an industrial or occupational situation will be within the Intermediate Category of PPE. This requires both testing and also inspection of the manufacturer’s technical file by a Notified Body, before a type-examination certificate can be issued.

Eyewear protecting against certain hazards (such as chemical splash), would be regarded as Complex Category PPE. In addition to testing and the type-examination, the production of such eyewear must be subjected to regular audits by a Notified Body according to one of the two procedures in article 11 of the PPE Directive.

Further information on SATRA's PPE certification and testing services is available at www.satra.com/ppe

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