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Grzegorz Owczarek, CIOP-PIB

Eye protection

Introduction

The most typical eye protection against external factors (e.g. radiation, dusts and droplets), is a natural protective mechanism of a human eye. The thin layer of slightly oily lachrymal fluid produced by the conjunctiva protects the human eye against pollution and infections. However, this natural protection is often insufficient in both everyday life and work environment. If you are exposed to dust, acids, molten metal’s, grinding wheels, hazardous optical radiation – you need to take the proper precautions and protect your eyes. If you don’t, it’s possible to lose the precious gift of sight, meaning you may never see your loved ones again. Thousands of eye injuries occur in the workplace each year, warranting the need for total eye protection. Wearing the eye protection that your job or location requires is a simple way to keep your eyes safe. There are many statistics related to work-related injuries. Is not possible to include in short study detailed data connected with real statistics. In generally, of the eye injuries approximately 95 % were caused by particles or chemicals.This article provides information to end-users of eye protectors as well as employers and occupational safety and health (OSH) specialists #[Link to main category OSH in general, subcategory "Legislation"]#. This article includes information on types of eye protectors, technical requirements, tests methods, and procedures for selecting of eye protectors for different workplaces.

Legislation applicable to eye protection
Eye protectors are a part of personal protective equipment (PPE). The principles regulating the choice and the application of PPE in the European Union have been laid down in the directive 89/656/EEC [1] of 30 November 1989 on the minimum health and safety requirements for the use by workers of personal protective equipment at the workplace. The 89/686/EEC directive [2] is a “New Approach” directive laying down Basic Health and Safety Requirements (BHSR) and leaving it to standards, primarily European harmonized standards, to give technical expression of the relevant requirements contained in the directive. This Directive lay down the conditions governing placing PPE on the market and free movement within the Community and the basic safety requirements which PPE must satisfy in order to ensure the health protection and safety of users.

Types of eye protectors
Each type of individual protection Personal protective equipment is made to protect our eyes from contact with something that we call a harmful or dangerous factor #Link to OSHwiki article: risk assessment#. Examples of these factors are [3]:


 * Impact (e.g. fragments of solid bodies),
 * Optical radiation (e.g. radiation related to welding processes, sunglare, laser radiation) ERO-12-08-13 UVR at work and Health or ERO-12-08-10 Introduction to UVR at work,
 * Dusts and gases (e.g. coal dust Dust and aerosols – Welding fumes or aerosols of harmful chemical substances ERO-12-07-7 Gases),
 * Droplets and splashes of fluids (e.g. splatters appearing while pouring fluids)
 * Melted metals and hot solid bodies (e.g. chips of melted metals appearing in metallurgical processes),
 * Electric arc (e.g. occurring while conducting high-tension works).

To protect eyes against these harmful or dangerous factors, there are eye protective equipment in four basic categories [3]:


 * 1) Spectacles;
 * 2) Protective goggles;
 * 3) Face shields;
 * 4) Welder’s face shields (this category of eye protection includes hand screens, face screens, goggles and hoods).

The eye protective equipment in these four basic categories are equipped with vision systems, oculars, meshes or filters. Filters include: welding filters, ultraviolet filters, infrared filters, sunglare filters, and filters protecting against laser radiation. The eye protective equipment can also be part of the respiratory protective devices (vision systems in masks) or head protection equipment (face shields mounted in industrial protective helmets). The eye protective equipment in all of these categories are composed of (1) a transparent part (vision systems, oculars, meshes or filters) and a (2) frame (spectacles and goggles) or (3) a housing with a harness (shields). All types of eye protectors have to meet the basic safety and health requirements described in the Directive 89/686/EEC [2].

Requirements
The intended use of the eye protective equipment determines the needed protective properties and how the equipment should be designed and constructed. When the eye protective equipment is mainly used, for example, to protection against solid bodies, splashes of fluids and droplets of molten metals, the basic characteristics needed are:
 * 1) Mechanical resistance (also in low and high temperature),
 * 2) Tightness and resistance to ignition in contact with items of much higher temperature (up to c.a. 1500oC).

If we want to know whether the eye protective equipment protects against an electric arc, we should specify the electrical properties of materials that the eye protector is made of. Testing characteristics of spectral transmission of optical radiation through translucent elements (i.e. oculars, vision systems, and filters) allows us to determine against what range of radiation spectrum the equipment tested provides protection to. Requirements for types of eye protectors are specified in the European Standards EN 166:2001 [3]. In general, requirements of eye protective equipment – according to this standard – consists of:
 * General rules during designing and constructing them,
 * Basic, particular, optional range of requirements.

Basic rules in designing and constructing each type of eye protective equipment included:
 * There shall not be any protruding parts or sharp edges which can cause discomfort or skin irritation;
 * all parts of eye protective equipment in contact with its users skin should not be made of any materials that we know causes skin irritation;
 * Headbands, especially when used as an essential holding element, shall be at least 10 mm wide over any portion, which may come into contact with the user’s head. Headbands should be self-adjusting.

Eye protectors are a form of PPE. In the hierarchy of risk control all items of PPE are considered to be the final line of defense. This is mainly because they protect only the user and do not take into account negation of the risk to others in the vicinity. However, because PPE is the “last resort” after other methods of protection have been considered, it is important that users wear it all the time they are exposed to the risk.

Characteristics of eye protectors
Basic requirements [3] must be fulfilled by all eye protective equipment. Furthermore, according to the intended use, types of the eye protective equipment, if necessary, must meet one or more of the particular requirements Occupational safety and health risk assessment methodologies. Optional requirements are related to additional properties of the eye protective equipment. These requirements consist of optional characteristics which can be considered as useful/positive for a wearer during use. To meet the requirements of specified standards, the characteristics of the eye protective equipment must be by strictly determined. According to EN 166:2001 [3] there are 26 characteristics that respond to the requirements of the eye protective equipment. A summary of those characteristics with their short description are shown in Table 1.

Table 1a: General rules for designing and constructing eye protective equipment

Source:

Table 1b: Basic requirements for eye protective equipment

Table 1c: Particular requirements for eye protective equipment

Table 1d: Optional requirements for eye protective equipment

EN standards appropriate for each type of eye protector
Table 2: List of EN standards appropriate for each type of eye protector

Source: Overview by the author

Test methods
Verifying whether the eye protective equipment is characterized by protective features, described in the previous chapter, is realized by conducting laboratory tests. The laboratory tests gives us the chance to determine the limits in which the tested eye protective equipment does or does not comply with the considered feature according to the  requirements stated in the standard. Test results of the eye protective equipment can be expressed as a specific number (e.g. light transmission factor or spherical power) or organoleptic evaluation (e.g. damage or lack of damage after testing resistance to high speed particles). Laboratory tests can be divided into two basic groups: (1) test for evaluating optical parameters and (2) non-optical parameters. Test methods for eye protective equipment are described in detail in the European standards EN 167:2001 (Personal eye protection. Optical test methods) [4] and EN 168:2001 (Personal eye protection. Non-optical test methods.) [5].

Figure 1 shows welding goggles after high speed particle test according to method described in EN 168:2001 [5] (impact of a steel ball (0,86 g) at velocity 120 m/s).

Figure 1: Welding goggles after high speed particle test



Source: Photo by Grzegorz Owczarek (CIOP)

An example of spectral transmission of optical radiation for filter against infrared we can see on figure 2.



Source: Measured by Grzegorz Owczarek (CIOP)

Procedures for selecting eye protectors for different workplaces
Principles for the use of any type of eye protectors to protect against various types of hazards are the same as for any other group of personal protective equipment. This means that when organizational and other technical solutions (e.g. collective protection measures) are not sufficient, the employer must provide employees with eye protectors appropriate to the type and level of risk.

Spectacles are the most widely used eye protection equipment. It is recommended that they also have forehead protection against dangerous splatters of fluids or fragments of solid bodies. An example of a model of such spectacles is presented in figure 3.

Figure 3: Spectacles Source: Photo by Grzegorz Owczarek (CIOP)

If a higher degree of eye protection is required, protective goggles should be used. Their construction ensures tight adhesion to the user’s face, which also provides protection against biological factors. We should remember that the ventilation systems of goggles are often very different one from another, though they are a key feature to be considered when selecting situation appropriate protective goggles. Figure 4 presents goggles with the so-called direct and indirect ventilation systems. Better protection against droplets and splashes of harmful substances is ensured by goggles with indirect ventilation system. The majority of goggles’ allow for their use with corrective glasses; however, before choosing and purchasing the equipment it is recommended to verify if this quality is available for that particular type of goggle. If the expected hazards require protection of the entire face, face shields should be used.

Figure 4: Protective goggles with direct (a) and indirect (b) ventilation systems



Source: Photo by Grzegorz Owczarek (CIOP)

Face shields (Fig. 5) protect the entire face and their large protective surface minimises the probability of penetration by dangerous fluid splatters. Face shields may be used with spectacles, corrective glasses, goggles and some respiratory protection devices.

Figure 5: Face shield Source: Photo by Grzegorz Owczarek (CIOP)

The last of the basic categories of eye protective equipment are welder’s face shields, i.e. devices protecting the user against harmful optical radiation and other specific hazards arising during weldingDust and aerosols - welding fumes and/or related techniques. Welder’s face shields include: face screens, hand screens, goggles, spectacles and hoods. Figure 6 presents a welder’s face shields.

Figure 6: Welder’s face shields Source: Photo by Grzegorz Owczarek (CIOP)

Field of use of eye protectors
for each given purpose of eye protective equipment a symbol is assigned  (digits: 3, 4, 5, 8 or 9); this symbol should appear as part of the equipment marking. The purpose of the eye protection systems, the relevant symbols and a short description of the field of use are presented in table 2.

Table 2: Purpose, symbols and description of the eye protective equipment field of use

Source:

Independently of the material used for making filters (e.g. polycarbonate, non-organic glass, polymetacrylane, cellulose acetate), its basic function is to protect eyes against dangerous optical radiation. For industrial applications it is welding, ultraviolet and infrared radiation, visible radiation provoking sunglare and laser radiation. The basic parameter classifying the filter protection  -independently of its purpose – is the level of protection. It is a parameter determined based on a light transmittance factor. 23 levels of protection were defined (1,2; 1,4; 1,7; 2; 2,5; 3; 4; 4a; 5; 5a; 6; 6a; 7; 7a; 8; 9; 10; 11; 12; 13; 14; 15; 16). Following their purpose, code numbers are attributed to the filters.

The complete marking of a filter is composed of the code number and the protection level. Welding filters are an exception as they are marked only with one of the aforementioned protection levels. The list of code numbers and markings for different types of filters is presented in the table 3.

Table 3: List of markings (code numbers and protection levels) for different filters 

Source:

Table 3 does not include filters used for protection against laser radiation. Due to the fact that the laser radiation is characterised by a high degree of cohesion, monochromaticity and orientation, and that the angle of beam divergence usually does not exceed several miliradians, eye protection against this type of radiation are tailor-made for a given type of laser. Laser radiation filters have to ensure effective protection against the radiation of a wavelength emitted by a given type of laser. Moreover, the housing and filters have to resist the laser radiation, which, in the event of high power/energy density, may damage the protection itself. For individual eye protection against laser radiation of the wavelength ranging from 180 µm to 1000 µm spectacles, goggles and face shields are used. Laser radiation filters are marked with codes from L1 to L10. These markings are defined at the basis of optical density of the filter for the wavelength for which the protection is to be ensured and based on the laser radiation resistance. If dangerous laser radiation remains in the visible spectrum (from 400 nm to 700 nm), and the eye protective equipment lowers this radiation to values defined for lasers of class 2 (radiation power P ≤ 1 mW for CW lasers – in this case physiological defence reactions, including the blinking reflex, contribute to  eye protection), then such protection equipment is called protective equipment for laser adjusting.

Conclusions
For construction of oculars and optical filters, advanced technological solutions are available and commonly used. The use of technology consisting of modification of optical radiation transmittance spectrum characteristics enables the adjusting of the light transmittance factor to values corresponding to given lighting conditions and thus the user’s requirements in the event of protection against the visible radiation (sunglare).

Technologies of light transmittance characteristics modification offer wide possibilities for designing optical filters for radiation ranges that, in work conditions, may constitute a real hazard (ultraviolet, infrared, laser radiation). The modification of the spectrum characteristics is realised by the in-mass tinting of the material, by superficial tinting or by coating the material with reflective or special interference layers. The in-mass tinting (pigments are added in the process of production of the material the filter is made of) is used mainly to produce ultraviolet, visible and infrared radiation filters [12]. The superficial tinting (tinting by immersing the material constituting the substrate for the filter) is used mainly in case of lenses that, after having fulfilled the requirements specified in the standard EN 166: 2001 [3], may be treated as oculars or filters. Coating the filter with an additional reflective layer (e.g. reflecting infrared radiation) results in relatively high amounts of dangerous radiation being reflected from its surface. The protective effect may then also be achieved by reflecting the radiation, not only by its absorption.

The radiation absorbed by the filter naturally causes it to heat. In the event of exposure to intensive infrared radiation the filters only absorbing the radiation (without reflective coating) may heat to relatively high temperatures. Thus the filter itself becomes a source of temperature radiation affecting eyes. Nowadays, it is the more and more popular to cover the surfaces of lenses and interference filters with anti-reflection coating. Such coatings effectively eliminate the reflection of light, e.g. emitted by headlights of a car approaching from the opposite direction (application in driver’s glasses) or subdue the laser radiation of a given wavelength (laser radiation filters).

In order to change the transmission of optical radiation passing through the filter, welding filter constructors also use the effect of the director orientation modification in the liquid crystal layer occurring under the influence of electrical field, which may be generated by light impulses or the photochrome effect. The use of the photochrome effect gives the possibility to change the light transmittance factor depending on the external radiation lighting intensity, usually accompanied by the ultraviolet radiation provoking the photochrome effect. Moreover, back surfaces of oculars and filters may be covered with anti-fog coating. The ageing resistance and the material absolute weight are as important as the fogging resistance, mechanical resistance and filtration properties adapted to given applications.

The parameters, presented in this article, dictate the quality and durability of the product, therefore defining the requirements set for the contemporary eye protective equipment. The use of new materials and technologies is also applicable for the construction of frames, housings and harnesses of the eye protective equipment. Those elements are made mainly of high quality plastics, which do not cause any allergic Irritants and allergens reaction in direct contact with the user’s skin. While constructing elements mounted on the user’s head, a particular importance should be attributed to the comfort of use, with regard to adjusting and regulation as well as the appropriate ventilation and sweat absorption by materials directly adhering to the forehead, etc.

Links for further reading

 * HSE – Health and Safety Executive, Guidance on Regulations “Personal protective equipment   at work (Second edition)”, HSE Books, 2005. Retrieved on 30 January, 2013: http://www.hse.gov.uk/pubns/books/l25.htm
 * CCOHS – Canadian Centre for Occupational Health and Safety, ‘Designing an Effective PPE Program’   retrieved on 30 January, 2013: http://www.ccohs.ca/oshanswers/prevention/ppe/designin.html
 * UE –OSHA – European Agency for Safety and Health at Work, Report – Gender issues in safety and health at work, 2003, Retrieved on 22 June, 2012:     http://osha.europa.eu/en/publications/reports/209/view?searchterm=None
 * UE –OSHA – European Agency for Safety and Health at Work, Summary – New risks and trends in the safety and health of women at work, 2011, Retrieved on 22 June, 2012: http://osha.europa.eu/en/publications/reports/new-risks-trends-osh-women/view
 * COSHH Risk assessment procedure, Retrieved on 22 June, 2012: at:http://www.stfc.ac.uk/she/resources/pdf/sc37chemicalriskassessment.pdf
 * NIOSH – National Institute of Occupational Safety and Health, Retrieved on 22 June, 2012: http://www.cdc.gov/niosh/topics/emres/ppe.html
 * UE –OSHA – European Agency for Safety and Health at Work, European legal requirements relating to work-related MSDs, Retrieved on 22 June, 2012: http://osha.europa.eu/en/topics/msds/legislation_html
 * European Agency for Safety and Health at Work Safe maintenance in practice 24.11.2010, Retrieved on 22 June, 2012: http://osha.europa.eu/en/publications/reports/safe-maintenance-TEWE10003ENC/view?searchterm=PPE%20regulations
 * OSHA Occupational Safety and Health Administration 2003, Retrieved on 22 June, 2012:http://www.osha.gov/Publications/osha3151.pdf