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Vision Lab

Published: 01st Feb 2011

The influence of the European Union PPE Directive has spread beyond the European market. Increasingly, suppliers of PPE products to other markets look for CE marked goods and certification that indicate compliance with the EU Directive.

This is also influenced by construction companies, mineral and oil enterprises, and shipping and airline businesses, that operate on a global scale, many having their bases within Europe.

Other factors such as worker expectations, litigation, and the introduction of ethical working practices mean that worker safety is now a high priority.

Many global companies operating in the Middle East look to procure CE marked products.

In this article we look at two of the most common areas of PPE supply - eyewear and visibility garments - and explain some aspects of how these products are tested and certified.

SATRA Technology Centre recently invested in a new photometer and spectrophotometer as part of a purpose-built optics laboratory to offer comprehensive in-house testing of reflective clothing.

The photometer measures the performance of retro-reflective materials, and the spectrophotometer measures the colour of background material. Combined with its existing protective eyewear facility, SATRA calls this ‘Vision Lab’. SATRA’s head of protective clothing, Peter Doughty, explains the services available for suppliers, manufacturers and distributors.

Protective eyewear

Eyes are particularly vulnerable to permanent damage and across the world, more than a thousand work-related eye injuries occur daily, many of which could be prevented by using protective eyewear.

Eyewear can offer protection against lasers or intense light sources (known as optical hazards) as well as physical threats, such as airborne dust particles or fragments of material. For this reason, safety glasses need to provide an adequate level of protection and are subject to tests for optical properties as well as for the mechanical protection that they provide.

In Europe, protective eyewear, which includes safety glasses and goggles for personal use, must comply with the requirements of the Personal Protective Equipment (PPE) Directive. Relevant European standards for these products include EN 166:2002 Personal Eye Protection - specifications which detail 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 are 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 percent, and lightly tinted reading glasses can reduce light by 40 percent.

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 percent 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 22mm diameter hemispherical probe, without breakage or excessive deflection.

Where increased robustness is needed, a 22mm diameter (43g) steel ball is dropped from a height of 1.3 metres (5.1m/s) 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.

High-speed particle testing of eyewear

There are many environments where it is important to protect the eyes and face against high speed flying fragments. In these cases, it is important to provide employees with protection against high energy impacts.

Eyewear claiming to provide protection against high speed particles needs to conform to all of the mandatory requirements of EN 166, as well as the high speed particle tests described. EN 168:2002 clause 9 also specifies a test method for testing the resistance of eyewear to high-speed particles. This test is simple in principle - the eyewear is placed on an appropriate head form, and a 6mm diameter steel ball is propelled at a controlled speed, at a specified point on the eyewear.

SATRA uses a compressed air propulsion system to achieve this, accelerating the ball along a horizontal barrel toward the head form. The speed of the ball is measured using a sensor mounted just before the exit point of the barrel, based on the assumption that frictional/air resistance losses between the end section of the barrel and the point of impact with the eyewear are negligible (the release point from the barrel being in close proximity to the eyewear). The acceleration of the ball, and therefore the speed of impact, can be varied by adjusting the pressure of the air in the chamber before release.

Typical speeds required for eyewear are:

• 45m/s (101 mph) for low energy impact

• 120m/s (268 mph) for medium energy impact

• 190m/s (425 mph) for high energy impact

At a minimum projectile mass of 0.86g, this equates to kinetic energies of 0.87, 6.2 and 15.5 joules respectively. These energies may not appear to be high, but with a maximum contact area of only a few square millimetres and a typical deceleration time of less than ten microseconds, the pressure exerted can be huge (more than 1,000 bar) - certainly enough to penetrate eyes or flesh. It should be noted that spectacles are only tested at low energies and only full face shields can claim protection against the higher energy impacts.

To ensure that protective eyewear will not fracture or deform and make contact with the eyes or flesh, it is impacted at four points during testing - frontal points and side points of both eyes. It is then inspected for damage or contact with the head form. Contact is checked using carbon paper placed behind the eyewear, which will show a mark if impacted.

Eyewear claiming protection against high speed particle impacts must also meet the mandatory optical requirements for all protective eyewear, including field of vision, transmittance of light, diffusion of light (although there is a reduced requirement for this type of eyewear), and spherical, astigmatic and prismatic refractive powers.

The eyewear must also meet the requirements for lateral protection. Here a probe is used to check that the eyewear prevents ingress of matter from the sides of the face.

High visibility clothing and European test methodology

Being highly visible under both day and night time conditions is an essential requirement in many hazardous situations. While the hazards may be common to many professions, the working environments where high visibility garments are worn are extremely varied. This is represented in the different designs of high visibility clothing currently available, ranging from vests used by warehouse operatives to water resistant jackets and trousers worn by highway maintenance workers or railway engineers.

Most high visibility product standards define fabrics that have high daytime visibility as ‘background material’ and other material - generally in the form of tape with night time reflective properties - as ‘retro-reflective material’ that functions under illumination.

Some standards (non-European) allow for the manufacture of products for daytime use or night time use only but, in practice, most garments are designed for both.

There are also ‘combined performance’ materials. Rather than using two different materials to provide night time and daytime high visibility, a single material is used that is highly visible during the day and also highly reflective when illuminated in the dark.

Personal Protective Equipment (PPE) is a device or appliance designed to be worn or held for protection against hazards. Among the most commonly used items of PPE are high visibility garments. These are now in widespread general use by construction and maintenance workers on the road and rail networks, airports, docks and harbours, and also by emergency services and security personnel. High visibility garments are also worn by those who are not engaged in professional or work activities, such as school children, cyclists and motorcyclists, and those engaged in sporting activities such as road running and horse riding.

The European Union (EU) Directive 89/686/EEC covers different types of PPE, and places them into one of three categories:

• Items that are of simple design which protect from minor (gradual) injury

• Intermediate design products, which afford protection in circumstances where injury could be severe

• Complex design items, which protect against death or irreversible injury

High-visibility PPE falls into the middle or intermediate category.

It is a prerequisite for all categories of PPE that the design of an article should be recorded in a technical file. For intermediate and complex category products the technical file must be subject to examination and approval by a European Notified Body, such as SATRA.

The examination of a technical file and the products it covers by a Notified Body supposes that the product under assessment is an example model. If the sample assessed is type-approved, then an EC type-examination certificate is issued by the Notified Body. The EC type-examination certificate thereafter allows an article to be CE marked.

Whatever the category of PPE that is supplied, it must meet the basic health and safety requirements (BHSR) of the PPE Directive. For all items of PPE there are two established means by which it can be determined whether an article meets the provisions of the EU Directive 89/686/EEC. One is to assess the product directly against the BHSR using a technical specification developed and agreed by the Notified Body and manufacturer. The other is to use harmonised European standards known as ‘ENs’ that carry a presumption of conformity.

The European standards that have been produced for visibility garments are:

• EN 471:2003 + A1:2007 - ‘High-visibility warning clothing for professional use’

• EN 1150:1999 - ‘Visibility clothing for non-professional use’

Each of the harmonised standards contains an annex ZA that describes how the standard covers basic heath and safety requirements in the PPE Directive, which helps a manufacturer to produce an article to meet the essential requirements of the EU Directive 89/686/EEC.

The design requirements for high-visibility garments for professional use are set out in Clause 4 EN 471:2003 + A1:2007. The standard requires that garments meet the requirements of one of three classes, which are defined according to the visible areas of fluorescent background fabric and bands of retro-reflective tapes that are present on a garment.

Importantly, there are defined areas and proportions in which the fluorescent materials used in the garment must be used. This is to ensure that the design of a garment maintains the enhanced visibility of a wearer in daytime conditions as they move about or undertake different actions. This is also why there is a primary requirement to ensure that the body of a garment and, where present, sleeves and trouser legs, are encircled with fluorescent material.

Similarly, to help maintain the visibility of a garment user when illuminated by vehicle headlights in darkness, the standard requires that reflective tapes applied to garments have to be a minimum of 50mm wide, and that they are positioned according to the requirements of the standard.

The standard sets out design requirements - one of these designs must be met if compliance with the standard is to be claimed. The standard covers requirements for a range of garment types, including coveralls, trousers, jackets, waistcoats, shirts and tabards.

It is imperative that manufacturers and suppliers of high-visibility clothing devise designs that incorporate the requirements of the standard and utilise materials that are specified for use within the standard. Suppliers of products must, of course, also consider the market that they intend to supply.

As EN 471:2003 + A1:2007 permits different colours of background material to be used and different classifications of garments, it is not unusual for some organisations, such as railway and maritime authorities, to specify particular classifications of garments for their own use.

One other important factor in the design of garments to meet EN 471:2003 + A1:2007 is that the size range has to be considered. The design assessment of a garment is based on the smallest sized garment in a range. It can therefore be misleading to compare the classification of two similar style garments, without knowing the size ranges in which they have been made available.

The design requirements for non-professional use high visibility garments differ in a number of ways and are set out in EN 1150:1999. Unlike professional use garments, the main design criterion is based on the area of visible or exposed material in each garment size that is to be supplied, which in turn is based on the height of the intended wearer.

The standard also permits eight different fluorescent colours to be used in combination, which enables a wide range of designs to be approved. Most garments that are approved by SATRA are single colour garments.

The design of EN 1150 garments also permits the more imaginative use of retro-reflective materials. Material can be provided in tape form, but also in other shapes such as a logo, providing that the material is evenly distributed around the body.

Effective high visibility PPE works by combining different materials that produce a high level of contrast between the user of a product and the background against which they are set. The specifications for these products take account of the nature of the hazard that is posed to a person and the risk of injury that may be encountered. For example, working on a motorway entails more risk than walking on a pavement in an urban area.

The standards for high visibility garments, and those for accessories, set out the minimum performance requirements for retro-reflectivity. These include retro-reflectivity testing after potentially destructive pre-treatments have been applied. To maintain an effective level of retro-reflectivity, materials must retain their performance after any treatment which is prescribed for them. For example, if a retro-reflective tape is claimed to be effective after ten dry cleaning cycles, then evidence that the minimum specified level of retro-reflectivity can be maintained after cleaning must be provided by testing.

The retro-reflectivity of tape is achieved by different means. The most commonly used type is one that uses bead technology. Microscopic glass beads of different diameters are distributed over the surface of a substrate layer, which is usually, but not exclusively, a textile material. These beads are stuck to the substrate by a silvered adhesive layer which forms a mirror around that part of the bead that is embedded.

The performance of the tape is determined by several factors, including bead sizes, how spherical they are, their distribution over the surface of the substrate layer and the depth to which they are embedded in the adhesive layer.

The durability of a tape depends not only upon how well individual beads are held in position on the tape, but also the flexibility of the adhesive layer and the inherent strength of the substrate material. Any loss of beads will, of course, lead to a reduction in the retro-reflective performance of the tape.

Another type of retro-reflective tape often used on high-visibility PPE incorporates micro-prismatic structures. This type of material is embossed with many reflectors that are shaped liked the corners of a cube. These may be arranged in different orientations to provide different paths of retro-reflection. Each micro-prismatic shape functions by reflecting light from the three sides of its structure. The geometry of these micro-prisms is such that light is reflected back towards its source. The collective effect of the many micro-prisms embossed on a tape provides the required level of retro-reflection. A retro-reflector does not return light shone onto it exactly to the point of origin. Rather, it returns a cone of retro-reflective light towards the source of illumination. Retro-reflected light can therefore only be seen if a viewer is within the cone of retro-reflection. For example, a car driver can see a pedestrian wearing a retro-reflective garment because the driver sits more or less behind the headlights of the vehicle. The laboratory measurement of retro-reflective materials is undertaken to define the effective cone of retro-reflection of a material.

EN 471 permits two performance levels of tape. In many instances, buying authorities will only purchase garments that are manufactured using the highest performing ‘level 2’ tape which provides greater visibility, particularly at a distance (see Table 1).

Therefore, manufacturers should always make sure that the retro-reflective material they intend to use meets their market’s demands. Buyers of high visibility garments may also specify that retro-reflective tapes are able to withstand specific cleaning treatments, usually appropriate to the type of contamination that their clothing may experience. For example, clothing that becomes contaminated with oil may require dry cleaning. It is, therefore, important to determine whether a retro-reflective material has the ability to withstand repeated solvent immersion.

Both EN 471 and EN 1150 also refer to the harmonised standard EN 340:2003, which specifies the general requirements for protective clothing. It is within this standard that wider considerations for garment safety are specified. These requirements, which set out testing to be undertaken to meet innocuousness, ergonomic and comfort requirements, also define design criteria for a range of PPE types, which of course includes high visibility garments.

Author

Peter Doughty

SATRA is one of the world’s leading test facilities for PPE (personal protective equipment) and safety product certification. Mike Cooper,

Chris Ohren-Bird and other SATRA experts will be attending the Intersec Trade Fair and Conference in Dubai, and will be happy to meet with any company with an interest in the testing and certification of protective eyewear, reflective clothing and other forms of PPE. Please contact SATRA on +44 (0) 1536 410 000 or email ppe@satra.co.uk

For general information on safety products, please visit the SATRA website at www.satra.co.uk/visionlab

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Published: 01st Feb 2011 in Health and Safety Middle East

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Peter Doughty, SATRA