Paul Jackson Discusses UV Light Exposure Limits

Paul Jackson, managing director of UV Light Technology, discusses the occupational ultraviolet (UV) light exposure limits specified by the EU Optical Radiation Directive 2006/25/EC. UV lamps are routinely used for non-destructive-testing (NDT) crack detection, particularly within the aerospace and automotive industries. Many workers exposed to artificial UV light sources are increasingly concerned about risks to their health and safety.

This is often a result of media coverage concerning the potential detrimental effects of UV light from natural sunlight and sunbeds, which has led to widespread misinformation and misunderstanding regarding UV light exposure in the workplace. Occupational UV light exposure in the UK will be subject to the new Control of Artificial Optical Radiation at Work Regulations 2010, which will bring into law the European Physical Agents (Artificial Optical Radiation 2006/25/EC) Directive. This incorporates statutory UV light exposure limit values (ELVs), which are due to become law on 27 April 2010.

It specifies the minimum health-and-safety requirements for the protection of workers from risks arising from exposure to UV light and provides clarity on precisely what is required for the safe use of UV light in the workplace. It states that employers must determine personal UV light exposure levels and compare with the ELVs as a means of assessing risk and necessary controls. Workers must not be exposed above the ELVs and must be provided with specific information and training. Ensuring compliance with the UV light exposure limits by appropriate control measures and providing appropriate information and training will not only mean that employers meet their obligations, but will build confidence and the acceptance of safe working practices by the workforce.

UV light is non-ionising electromagnetic radiation, transmitted in the form of waves, which are described by their wavelength and measured in nanometres. It is located between the blue end of visible light and x-rays (400nm to 100nm) and split into the following spectral-range classification bands: UV-A 400nm to 315nm; UV-B 315nm to 280nm; and UV-C 280nm to 100nm. It should be noted that 1nm equals one millionth of a millimetre. The term 'optical radiation' defines the region of the electromagnetic spectrum that includes UV, visible and infrared light. UV light energy - and its potential to cause adverse health effects - is inversely proportional to wavelength across the bands.

The dividing lines between the bands are convenient distinctions and not boundaries where sudden, large changes occur in detrimental health effects. The potential to cause damage to unprotected skin and eyes varies across the bands and classification is, therefore, only a broad indication of the effectiveness for producing adverse health effects. UV-A has the lowest energy and the least potential to cause acute adverse health effects. UV-B has significantly higher energy and more potential to cause acute adverse health effects than UV-A. UV-C has highest energy and generally the most potential to cause acute adverse health effects.

The ELVs take the lower limit of the UV-C region to be 180nm. This is because UV light below 180nm (vacuum UV) is readily attenuated in air and is, therefore, of little practical biological significance. It is well established and generally agreed that low-level exposure to certain wavelengths of UV light provides some health benefits, such as the synthesis of vitamin D3. On the other hand, over-exposure to UV light can cause adverse health effects, such as erythema (sunburn), photoconjunctivitis and photokeratitis (arc eye) in the short term (acute effects) and can be attributed to premature skin ageing, skin cancer and cataracts as a result of repeated exposure in the long term (chronic effects).

The levels of risk for acute adverse health effects are determined by the UV light wavelengths present, the UV light irradiance values and personal exposure time. The key is to avoid over-exposure and this necessitates the strict implementation of exposure limits in order to protect against over-exposure to UV light in the workplace. There are different UV light ELVs depending on the wavelength range of the UV lamp. It is, therefore, necessary to understand the definition and classification of UV light and know the wavelength range of the UV lamp in order to identify the applicable ELV. It should be noted that more than one ELV may apply for a specific wavelength range.

The Control of Artificial Optical Radiation at Work Regulations 2010 and the Optical Radiation Directive are based on ELVs defined by the International Commission on Non-Ionising Radiation Protection (ICNIRP). In cases of persons subjected to UV light exposure from artificial sources, it is necessary to assess the level of risk for adverse health effects by determining personal UV light exposure levels and comparing with the ELVs. Where personal exposure complies with the ELVs, the risk can be considered low for the majority of the population and adequately controlled so far as is reasonably practicable. However, workers must be provided with specific information and training.

Where personal exposure exceeds the ELVs, additional control measures must be implemented that decrease exposure to below the ELV. The UV light ELVs for a broadband source are defined below. Both exposure limits are applicable to all types of UV lamps used for NDT applications. The ELVs define a level of UV light exposure, below which nearly all individuals may be repeatedly exposed without adverse acute health effects and incorporate significant safety margins. The maximum permissible effective radiant exposure value (Heff max) of 30J/m2 takes into account variations of different UV light wavelengths in causing biological hazardous effects, such as erythema, photoconjunctivitis and photokeratitis.

This is necessary because some UV light wavelengths have a very significant effect, others proportionally less effect and some almost none at all, depending on the effect in question. It provides a measurement that is weighted by wavelength according to a spectral weighting function, which is directly proportional to the biological hazardous effect. The maximum permissible UV-A light radiant exposure value (HUV-A max) of 10,000J/m2 is an unweighted value and is in addition to the above. It is necessary that compliance is achieved with both ELVs detailed above. What this means is that, for UV-A blacklights used for NDT applications, there will be separate maximum permissible UV light exposure times for the unprotected skin and eye.

The user should ask if a clear and unambiguous statement can be made that the UV light ELVs are either observed or exceeded. Where the operating instructions for a UV lamp provide the type of data illustrated below, this will allow the determination of personal exposure scenarios for assessing compliance with the ELVs. This is the most user-friendly way of presenting data for ease of operator understanding and risk assessment. It allows a clear and unambiguous statement to be made that the UV light ELVs are either observed or exceeded. It is necessary for duty holders to limit personal UV light exposure time at the specified positions above to ensure that the maximum permissible exposure values for the unprotected skin and eye are not exceeded within any continuous eight-hour period.

If the maximum permissible exposure values are exceeded, the UV light irradiance must be reduced by appropriate control measures. These could include containment, moving further away from the UV light source, reducing exposure time, or, as a last resort, the provision of personal protective equipment (PPE). However, if this information is not available, a clear and unambiguous statement cannot be made that the ELVs are either observed or exceeded. In this case, UV light irradiance measurements will most likely need to be made to assess whether or not exposure to a particular UV lamp would cause a person, located in a specific position, to exceed either of the ELVs. This requires specialist measurement equipment, knowledge and expertise.

If either one or both are less than eight hours, control measures are necessary to ensure that personal UV light exposure is below the ELVs. Persons at the measurement position should be advised to either limit their exposure time, so as not to exceed the maximum permissible exposure time within any continuous eight-hour period, or reduce the UV light irradiance to which they are subjected, by using containment, moving further away from the UV light source - or, as a last resort, PPE. All persons who could be exposed to UV light, which could cause adverse health effects to the eye or skin, must be provided with suitable and sufficient information and training.

This must include: the potential adverse health effects of over-exposure to UV light on the eyes or skin; control measures and safe working practices to minimise the risk; heightened photosensitivity; the entitlement to appropriate health surveillance where necessary; the detection of adverse health effects, reporting procedures and entitlement to medical examination where necessary; and the necessary pre-operational checks to UV light equipment. For example, where a filter glass is fitted in front of a UV bulb, always ensure it is intact and securely mounted in the correct position. The UV light exposure limits may not be adequate protection for photosensitive individuals and special precautions may be necessary.

These individuals should seek medical advice with respect to additional protective measures that may be required before any exposure to UV light. Check that all persons who could be exposed to significant levels of UV light are not unusually photosensitive, exposed to photosensitising agents or, less commonly, aphakic or pseudophakic. This can be done by using questionnaires.

Individuals who are intrinsically photosensitive are normally aware of their heightened sensitivity, while individuals who are exposed to photosensitising agents, either ingested, injected or externally applied, may not be aware of their heightened sensitivity. Check for any possible effects on the health and safety of employees, which could result from the interaction between UV light exposure and photosensitising chemical substances. NDT magnetic particle or dye penetrant fluorescent inspection techniques offer the potential of greater sensitivity and the probability of the detection of hairline cracks in many safety-critical components upon which our lives may depend, such as aircraft landing gear and automotive steering systems. It is, therefore, essential that UV light continues to be used within the NDT industry to ensure the quality and safety of these types of components.

While we must accept that there are risks associated with all human activity, UV light exposure at levels that comply with the new Control of Artificial Optical Radiation at Work Regulations 2010 will help to ensure that risks are low and adequately controlled. Jackson is a metallurgy and materials technology graduate from Aston University in Birmingham. He has published a book and runs training courses entitled 'Safety First with UV Light'.


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