Safety glasses and goggles are subject to tests for optical properties as well as for the mechanical protection they provide.
Eyes are particularly vulnerable to permanent damage. Therefore, personal protective equipment (PPE) in the form of safety glasses needs to satisfy a number of important criteria to provide an adequate level of protection.
Protective eyewear, which includes safety glasses and goggles for personal use, must currently comply with the requirements of the Personal Protective Equipment (PPE) Directive and the PPE Regulation from 21st April 2018 if supplied into Europe. Relevant European standards for these products include EN 166:2002 Personal eye protection – specifications which details functional requirements for various types of eye protectors, used against typical hazards found in industry, laboratories and educational establishments, which are likely to impair vision or damage the eye. Related standards EN 167:2002 personal eye protection – optical tests and EN 168:2002 personal eye protection – non-optical test methods provide test methods for optical and non-optical properties.
The optical tests detailed in EN 167 ensure that no form of protective eyewear will unacceptably distort or restrict the wearer’s vision, and include checking for spherical, astigmatic and prismatic refractive powers. Other test methods include assessment of light diffusion and variations in luminance transmittance.
Transmittance of light is an important parameter. Measurements have shown that ordinary reading glasses with no protective properties may reduce the light reaching the eye by around 10 per cent and lightly tinted reading glasses can reduce light by 40 per cent. Protective eyewear can similarly reduce vision in low light conditions. The measuring equipment used provides a highly controlled beam of light that is collected by a detector. The detector is calibrated for 100 per cent transmittance with no ocular (the transparent glass or plastic component) in position. The ocular is then placed in front of the detector to interrupt the light beam and the reduced light collected is measured.
Non-optical tests covered in EN 168 include field of vision to ensure that frames do not unacceptably impede peripheral vision.
Physical property tests ensure that the eyewear provides the mechanical protection claimed and remains fit for use after normal wear and tear.
Safety eyewear is tested for resistance to ignition using a heated probe at 650ºC. A steel rod is heated to the required temperature and the heated end face is pressed onto all parts of the test sample except elastic headbands and textile edgings.
As an absolute minimum for robustness, oculars must withstand a force of 100N (approximately 10kg) applied via a 122mm diameter steel ball, without breakage or excessive deflection. Where increased robustness is needed, the steel ball is projected to impact the defined points on the frame and oculars under high and low temperature conditions (55ºC +/- 2ºC and -5ºC +/- 2ºC).
Corrosion resistance tests involve immersing the sample in a solution of sodium chloride (salt) at both boiling point and room temperature. The sample is then dried off and checked visually 24 hours later for any corrosion. Other tests include assessing the usability of the eye protector after exposure to ultraviolet light originating from strong sunlight or welding arcs.
Further information on SATRA's PPE certification and testing services is available at www.satra.com/ppe
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