‘Safety First with UV Light’ for industrial, medical and scientific applications

When ultraviolet light is mentioned many people immediately think of either sunbeds, counterfeit money detectors, insect traps or fish pond disinfection units. However UV light is all around us, not just occurring naturally from sunlight, but supplied by companies such as UV Light Technology Limited, which through high-tech industrial, medical and scientific applications make our daily lives more comfortable, healthier and secure. Some examples include:

  • UV blacklight fluorescent inspection processes make working life easier for quality control engineers, forensic scientists, police officers and auction houses to name but a few. In NDT magnetic particle and dye penetrant UV fluorescent inspection processes highlight cracks in aircraft undercarriages, automotive steering systems and many other safety-critical components upon which our lives may depend. In the field of forensic science, UV blacklight helps unearth vital evidence at crime scenes. The inspection of works of art under UV blacklight is a means of revealing imperfections and evidence of restoration, an important aspect of authentication for valuation and sale.
  • UV light curing of materials has emerged in recent years as perhaps the most exciting and versatile material technology. These single component, solvent-free material systems cure almost instantaneously on exposure to UV light with efficient use of energy. They offer unrivalled and unique process advantages in times of stringent legislation changes restricting the use of many solvents. UVA, UVB and UVC light sources are employed depending upon the type of material to be processed i.e. adhesives, resins, coatings or inks.
  • UVC germicidal lamps are used within engineering control measures to reduce infection caused by airborne transmission of bacterial pathogens within built environments. Furthermore, some of the water we drink has been disinfected using UV-C light, as has a wide variety of food, drink and medical supplies packaging.
    Ultraviolet light sources which closely correlate to natural sunlight are used in a vast range of applications to establish the ageing effects of the sun on materials for safety and aesthetic reasons, such as, testing aircraft windscreens or examining the effects of degradation on building materials.
  • UV light is used in many medical applications, from treating Vitamin D deficiencies and relieving the unsightly effects of Psoriasis to fluorescent dyes used in conjunction with UV blacklight to identify cancerous cells in the internal organs of patients.
  • UV light is used as an integral part of so many processes across a wide range of industries and applications. However, there is widespread misinformation and misunderstanding regarding personal UV light exposure. This is certainly the case regarding regulatory compliance, where four years after the introduction of EU Regulations on exposure to UV light, many companies and organizations are still not aware of their statutory obligations under the legislation.

This article is intended to provide an insight into regulatory compliance creating awareness and assisting those responsible for the health and safety of persons exposed to UV light in the workplace, to identify their duties and possible obligations to revise existing risk assessments under the Management of Health and Safety at Work Regulations 1999.

The Control of Artificial Optical Radiation at Work Regulations 2010, brought into law in Great Britain on 27th April 2010, the European Physical Agents (Artificial Optical Radiation 2006/25/EC) Directive. This provides clarity on precisely what is required for safe use of UV light in the workplace. It imposes a legal duty on employers to protect workers who may be at risk from artificial UV light exposure.

The regulations define:

  • Statutory UV light exposure limit values (ELVs) for unprotected skin and eyes
  • Minimum health and safety requirements for the protection of employees from the risks arising from UV light exposure

The regulations require:

  • Employers to determine personal UV light exposure levels and compare them with ELVs as a means of assessing risk and necessary controls.
  • That employees must not be exposed above the statutory ELVs and must be provided with protection, specific process information and training.

Ensuring compliance with the UV light exposure limit values and providing specific hazard awareness training will provide employers with peace of mind that their legal obligations are satisfied. The result is risk assessment and control is covered and this builds confidence and acceptance of the process by the workforce. This is an important point because 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 potentially detrimental effects of UV light from natural sunlight and sunbeds, which has to lead to widespread misinformation and misunderstanding regarding UV light exposure in the workplace. There are different UV light exposure limit values depending on the wavelength range of the UV lamp and in some cases, more than one exposure limit value may apply for a specific wavelength range. It is, therefore, necessary to understand the definition and classification of UV light and know the wavelength range of the UV light source in order to identify the applicable exposure limit value.

What is UV light?

UV light is non-ionising electromagnetic radiation, transmitted in the form of waves, which are described by their wavelength and measured in nanometres (nm). 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:

  • UVA (315 nm – 400 nm)
  • UVB (280 nm – 315 nm)
  • UVC (100 nm – 280 nm)

UV light energy and therefore 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. Classification is therefore only a broad indication of the effectiveness for producing adverse health effects.

  • UVA has the lowest energy and the least potential to cause acute adverse health effects.
  • UVB has significantly higher energy and greater potential to cause acute adverse health effects than UV-A.
  • UVC has the highest energy and generally the most potential to cause acute adverse health effects.

The exposure limit values 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.

UV light-induced health effects

It is well established and generally agreed that low-level exposure to certain wavelengths of UV light provides some health benefits, for example, synthesis of vitamin D3. On the other hand, overexposure to UV light can cause adverse health effects, such as erythema (sunburn), photo conjunctivitis 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 is determined by UV light wavelengths present, UV light irradiance values and personal exposure time.

The key is to avoid overexposure to UV light in the workplace and this necessitates the strict implementation of exposure limit values.

UV Light Exposure Limit Values (ELV’s)

The Control of Artificial Optical Radiation at Work Regulations 2010 and the Optical Radiation Directive is based on exposure limit values defined by the International Commission on Non-Ionising Radiation Protection (ICNIRP)(4).

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 exposure limit values.

Where personal exposure is below the exposure limit values, the risk can be considered low for the majority of the population and adequately controlled so far as is reasonably practicable. In addition, workers must be provided with specific information and training.

Where personal exposure exceeds the exposure limit values, then additional control measures must be implemented which decrease exposure to below the exposure limit value.

Almost all UV light sources in the workplace are broadband and therefore this article only refers to this type. Also, lasers are not considered.

The exposure limit values 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 30 J/m2eff takes into account variations of different UV light wavelengths in causing biological hazardous effects such as erythema, photo conjunctivitis and photokeratitis. This is necessary because some UV light wavelengths have a very significant effect, others a proportionally less effect and some almost none at all, depending on the effect in question. It provides a measurement which is weighted by wavelength according to a spectral weighting function (Sλ) which is directly proportional to the biological hazardous effect.

The maximum permissible UV-A light radiant exposure value (HUV-A max) of 10,000 J/m2 is an unweighted value and is in addition to the above.

It is necessary that compliance is achieved with both exposure limit values detailed above. This is achieved by adopting the most restrictive exposure limit for the eyes, which will depend on the UV light wavelengths and irradiance values emitted by a particular UV light source. This is explained in more detail in the UV light measurement section.

Paths to Compliance with The Control of Artificial Optical Radiation at Work Regulations 2010

When assessing a personal UV light exposure scenario in the workplace the crucial question is, can a clear and unambiguous statement be made that the UV light ELVs are observed or exceeded?

Employers must assess the level of risk for adverse health effects by determining UV light personal exposure levels and comparing with the UV light ELVs. This can be done by referring to UV light source manufacturers’ data or conducting a UV light measurements and assessment survey. Workers must not be exposed above the ELVs and must be provided with specific information and training.

Referring to UV light Source manufacturers’ data

Where the operating instructions for a UV light source provide the type of data illustrated below in Figure 1, then this will allow determination of personal exposure for assessing compliance with the exposure limit values. This is the most user-friendly way of presenting data for ease of operator understanding and risk assessment.

It is necessary for duty holders to limit personal UV light exposure time at the specified positions, to ensure that the maximum permissible exposure times for the unprotected skin and eyes are NOT EXCEEDED within an 8 hour period per day. If the maximum permissible exposure times are exceeded then 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 provision of personal protective equipment (PPE).

All persons must be aware of maximum permissible exposure times (hazard value) for the unprotected skin and eyes, at specified distances from a UV light source where less than 8 hours per day.

Where persons are exposed to UV light from multiple sources the cumulative effects must be assessed and controlled.

The distance at which the maximum permissible UV light exposure time is equal to 8 hours is known as the Hazard Distance (HD), beyond which the applicable exposure limit value cannot be exceeded.

UV light measurements and assessment

In the case where a UV light source manufacturers’ data is not available or inadequate, a clear and unambiguous statement cannot be made that the exposure limit values 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 the UV light source would cause a person, located in a specific position, to exceed either of the exposure limit values. This requires specialist measurement equipment, knowledge and expertise.

Generally, two separate UV light irradiance values, Eeff (W/m2) and EUV-A (W/m2), must be measured at appropriate distances from the UV light source.

Maximum permissible exposure times (teff max and tUV-A max) at the measurement positions can then be calculated as follows:

where teff max > tUV-A max

i.e. the maximum permissible exposure time for the unprotected skin and eyes is longer than the maximum permissible exposure time for the unprotected eyes.

In this case, to comply with both ELV’s the shortest maximum permissible exposure time for the eyes at each measurement position is adopted and therefore, in this case, there are separate maximum permissible exposure times for the skin and eyes. This is the case with the UV 250W hand lamp example provided in Figure 1.

where tUV-A max > teff max

i.e. the maximum permissible exposure time for the unprotected eyes is longer than the maximum permissible exposure time for the unprotected skin and eyes.

In this case, to comply with both ELV’s, the shortest maximum permissible exposure time for the eyes at each measurement position is adopted and therefore, in this case, tUV-A max is disregarded and there is only one maximum permissible exposure time for both skin and eyes.

Specific information and training

All persons who have the potential to be exposed to UV light which could cause adverse health effects to the unprotected skin or eyes must be provided with suitable and sufficient information and training. Subjects covered must include:

  • The exposure limit values and potential adverse health effects of overexposure to UV light on their unprotected skin or eyes.
  • Results of determination and assessment of personal UV light exposure levels with an explanation of the significance and potential risk. It is important that the risks are put into perspective.
  • Control measures and safe working practices to minimise the risk.
  • Heightened photosensitivity.
  • Detection of adverse health effects, reporting procedures and entitlement to a medical examination where necessary.
  • Entitlement to appropriate health surveillance where necessary.
  • 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.
  • UV light cannot be seen or felt, therefore it is important that workers are regularly reminded.

Heightened Photosensitivity

The UV light exposure limit values 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 which may be required before any exposure to UV light.

Heightened Individual Susceptibility

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 persons.

Individuals who are intrinsically photosensitive are normally aware of their heightened photosensitivity.
Individuals who are exposed to photosensitising agents, either ingested, injected or externally applied, may not be aware of their heightened photosensitivity.
Some examples of chemical compounds which enhance photosensitivity are:

These may enter the body by ingestion, injection or absorption through the skin. The speed of effect and severity of symptoms depends on the route of entry.

Heightened Collective Susceptibility

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.

Control measures for protection against over-exposure to UV light

The decision on which control measures are most appropriate should be based on the general principles of prevention set out in The Management of Health and Safety at Work Regulations 1999, which implements Article 6 (2) of Council Directive 89/391/EEC. This dictates that priority, as far as is reasonably practicable, should always be placed on engineering and administrative control measures. Personal protective equipment should be seen as a last resort, where there is some residual unacceptable risk which cannot be controlled using engineering and/or administrative control measures. A combination of preventive and protective control measures should be selected from those listed below, which are appropriate to the particular UV light source and application.

Engineering Control Measures

  • Containment – guards, screens or curtains
  • Interlocks
  • Limiting operation
  • UV optical filters
  • Design and layout of workplaces and workstations
  • The positioning of the UV light source
  • Reflected UV light
  • Timed UV light exposure
  • Emergency stops

Administrative Control Measures

  • Information and training
  • Limitation of personal UV light exposure
  • Distance from UV light source
  • Controlled areas
  • Warning labels, signs and lights
  • Routine servicing and maintenance

Personal Protective Equipment

  • Protection of the skin
  • Protection of the eyes

Conclusion

The use of UV light within the workplace is essential, often representing cutting edge technology and providing innovative new product and process developments. There is hardly an aspect of daily life where UV light technology has not contributed in some way to make our lives more comfortable, secure, healthier and even fun. Depending upon the application, typical benefits can include, improved productivity; enhanced quality; reduced costs, energy-saving; less solvent emission.

Whilst we must accept that there are risks associated with all human activity, personal UV light exposure levels which comply with The Control of Artificial Optical Radiation at Work Regulations 2010 will mean that risks are low for the majority of the population and adequately controlled. In addition, providing the necessary information and training for workers will not only satisfy regulatory requirements but also build their confidence and acceptance of the process.

References

  • Control of Artificial Optical Radiation at Work Regulations 2010 – Health and Safety Executive.
  • Artificial Optical Radiation Directive 2006/25/EC of the European Parliament and of the Council (of 5 April 2006). On the minimum health and safety requirements regarding the exposure of workers to risks arising from physical agents (artificial optical radiation) (19th individual Directive within the meaning of Article 16(1) of Directive 89/391/EEC).
  • The Management of Health & Safety at Work Regulations 1999.
  • Guidelines on limits of exposure to ultraviolet radiation of wavelengths between 180 nm and 400 nm (incoherent optical radiation). The International Commission on Non-Ionizing Radiation Protection, Health Physics, August 2004, Volume 87, Number 2.ICNIRP Statement – Protection of Workers against Ultraviolet Radiation – Health Physics, July 2010, Volume 99, Number 1.
  • ‘Safety First with UV Light’ – Risk Management in the Workplace – Paul Jackson.
  • Paul Jackson – unpublished work.