Safety first with UV light

11 May 2010

UV lamp
UV lamp

New regulations have been introduced that affect users of the UV lamps typically used for curing processes in the electronics industry. Paul Jackson looks at the new legislation and the exposure limits it stipulates.

New Control of Artificial Optical Radiation at Work Regulations 2010, brought into law in the UK in April 2010, defines the occupational UV light exposure limits specified by the EU Optical Radiation Directive 2006/25/EC. This article is intended to provide an insight into the new regulations, 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.

011UV lamps are widely used within the electronics manufacturing and testing industry for UV light curing, exposure and fluorescent inspection processes. 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 lead to widespread misinformation and misunderstanding regarding UV light exposure in the workplace.

Occupational UV light exposure in Great Britain is now subject to the new Control of Artificial Optical Radiation at Work Regulations 2010, which brought into law the European Physical Agents (Artificial Optical Radiation 2006/25/EC) Directive. This incorporates statutory UV light exposure limit values (ELV’s) which became law on 27th April 2010. It specifies the minimum health and safety requirements for protection of workers from risks arising from exposure to UV light and provides clarity on precisely what is required for safe use of UV light in the workplace.

It states that employers must determine personal UV light exposure levels and compare with the exposure limit values as a means of assessing risk and necessary controls. Workers must not be exposed above the exposure limit values 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 acceptance of safe working practices by the workforce.

There are different UV light exposure limit values depending on the wavelength range of the UV lamp. It should also be noted that 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 lamp 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:

UV-A 400nm to 315nm - UV-B 315nm to 280nm - UV-C 280nm to 100nm

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. 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 least potential to cause acute adverse health effects.

UV-B has significantly higher energy and greater 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 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.

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, 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 is determined by UV light wavelengths present, UV light irradiance values and personal exposure time.

The key is to avoid over exposure 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).

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 complies with 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.

The UV light exposure limit values (ELV’s) for a broadband source are defined below.

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/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 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 eye.

[x-head] Determination and Assessment of Personal UV Light Exposure Levels

The crucial question is - can a clear and unambiguous statement be made that the UV light exposure limit values are either observed or exceeded?

[x-head] Use of Manufacturers Data
Where the operating instructions for a UV lamp provide the type of data illustrated below in Figure 1, then this will allow determination of personal exposure scenarios 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 allows a clear and unambiguous statement to be made that the UV light exposure limit values 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 8 hour continuous period. If the maximum permissible exposure values 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).

UV Light Measurements

However, if this information is not available, 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 a particular UV lamp 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 lamp.

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


                Heff max 30 J/m2
teff max = _____________
                Eeff (W/m2)

                     HUV-A max 10,000 J/m2
tUV-A max =  __________________
                     EUV-A (W/m2)

Where:
Eeff (W/m2) - measured value of UV light effective irradiance – this is UV light irradiance within the wavelength range 180nm - 400nm (UV-A, UV-B, UV-C) spectrally weighted by Sλ

Sλ - biological spectral effectiveness – this is the relative spectral effectiveness of UV light wavelengths present for producing adverse health effects on the unprotected eye and skin

EUV-A (W/m2) - measured value of UV-A light irradiance within the wavelength range 315nm - 400nm

teff max (s) - maximum permissible exposure time to UV light within the wavelength range 180nm - 400nm (UV-A, UV-B and UV-C) spectrally weighted by Sλ incident upon the unprotected skin or eye

tUV-A max (s) - maximum permissible exposure time to UV light within the wavelength range 315nm - 400nm incident upon the unprotected eye

Heff max (J/m2) - maximum permissible UV light effective radiant exposure incident upon the unprotected skin or eye

HUV-A max (J/m2) - maximum permissible UV light radiant exposure incident upon the unprotected eye

where teff max > tUV-A max
Maximum permissible exposure time for the skin and eye is longer than the maximum permissible exposure time for the eye.

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

where tUV-A max > teff max
Maximum permissible exposure time for the eye is longer than the maximum permissible exposure time for the skin and eye.

In order to comply with both ELV’s, the shortest maximum permissible exposure time for the eye 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 eye. This is the case with the UV 250W hand lamp example provided below in Figure 2.

Specific Information and Training
All persons who have the potential to 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. Subjects covered must include:

 The exposure limit values and potential adverse health effects of over exposure to UV light on their eyes or skin.
 Results of determination and assessment of personal UV light exposure levels with an explanation of significance and potential risk. It is important that the risks are put in perspective.
 Control measures and safe working practices to minimise the risk.
 Heightened photosensitivity.
 Entitlement to appropriate health surveillance where necessary.
 Detection of adverse health effects, reporting procedures and entitlement to medical examination 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.

Enhanced Photosensitivity

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 which 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 persons. This can be done by using questionnaires.

- Individuals who are intrinsically photosensitive are normally aware of their heightened sensitivity.
- Individuals who are exposed to photosensitising agents, either ingested, injected or externally applied, may not be aware of their heightened sensitivity.

Examples of chemical compounds which enhance photosensitivity are:
Antibiotics (e.g. tetracyclines)
Tranquillisers (e.g. phenothiazines, especially chlorpromazine)
Diuretics (e.g. thiazides)
Sulphonamides (e.g. sulphamethoxazole with trimethoprim)
Hypnotics (e.g. phenobarbitone)
Antibacterials (e.g. nalidixic acid)
Coal tar and creosote
Some cosmetics, due to presence of eosin or psoralens
Various plants such as carrot, celery, dill, fig, lemon and some types of weeds

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.

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.

Conclusion
The case for using UV lamps for electronics manufacturing and testing applications is compelling. This is because UV light applications can represent cutting edge technology, providing innovative new product and process developments, often providing improved productivity, reduced costs, lower solvent emissions, better quality and in some cases exciting new business opportunities.

It is essential therefore that UV light is continued to be used for electronic processing and quality control. Whilst we must accept that there are risks associated with all human activity, UV light exposure at levels which comply with the new Control of Artificial Optical Radiation at Work Regulations 2010 will help ensure that risks are low and adequately controlled.

Maximum permissible UV light exposure times for the unprotected skin and eye in any continuous 8 hour period, at various distances within the beam of the UV 250W hand lamp
Maximum permissible UV light exposure times for the unprotected skin and eye in any continuous 8 hour period, at various distances within the beam of the UV 250W hand lamp

Paul Jackson is Managing Director of UV Light Technology Limited

Maximum permissible UV light exposure times for the unprotected skin and eye in any continuous 8 hour period, at various distances within the beam of the UV 250W hand lamp.
Maximum permissible UV light exposure times for the unprotected skin and eye in any continuous 8 hour period, at various distances within the beam of the UV 250W hand lamp.


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