Introduction
Outdoor workers are exposed to natural UVR emitted by the sun. Since optical radiation is vectored, the irradiance of a worker is individual, even at identical activities at the same site. Depending on various parameters, exposure levels may lead to acute (e.g. erythema) or long term (e.g. skin cancer) hazards. For prevention, protective measures (either technical, organisational or personal) are required to minimise exposure to a level as low as reasonably achievable. In cases of occupational disease, retrospective determination of disease has to be carried out as precise as possible. This article deals with professions at risks supported with EU data and examples of national data, legislation, policies and strategies related to natural UV, risk assessment and prevention.
Natural Ultraviolet radiation
Ultraviolet radiation (UVR) is vectored electromagnetic radiation in the wavelength regime 100 nm to 400 nm. The UV radiation spectrum is divided into three regions UV-A (315 nm to 400 nm), UV-B (280 nm to 315 nm), and UV-C (100 nm to 280 nm). UVR is invisible for the human eye. It belongs to “Optical Radiation", which is a “Physical Agent" in terms of OSH.
The sun is the main source of natural UVR. When the sunlight passes through the atmosphere, all UV-C and most UV-B is absorbed by ozone, water vapour, oxygen and carbon dioxide. UV-A is not filtered as strongly by the atmosphere. The degradation of the ozone layer of the atmosphere due to some gases, especially chlorofluorocarbon (CFC), may result in higher exposure to UV-B on earth and higher incidences of skin cancers[1][2] [3]
Although being known as essential for human health, e.g. production of vitamin D, (over)exposure to UVR can be hazardous.
Hazardous biological effects of UVR
UVR penetrates human tissue only skin deep, human organs are out of reach. Thus, biological effects are limited to the eye and the skin and have to be distinguished this way. It has been subject to science for long years to understand effects of UVR on a molecular level, resulting in biological action spectra to display the wavelength dependence of biological hazards (e.g. reference action spectrum for erythema in human skin from [4], and adopted by CIE[5]).
Effects on the eyes
The eye is designed to receive electromagnetic waves in a certain wavelength regime and to convert this information first into chemical signals and then into electric potentials. This biochemical process highly depends on the selected wavelength and the intensity of the light beam. Given its structure, only a small band of optical radiation (namely the “visible light") propagates through the whole eye to be detected in the retina.
Radiation at shorter wavelength (UVR) is absorbed in the front parts: UV-C is absorbed in the superficial layers of the cornea, while UV-B is absorbed by the cornea and the lens. UV-A passes almost quantitatively through the cornea and is absorbed in the lens.
Acute overexposure of the eye to UVR includes mainly inflammation of the cornea and the conjunctiva, called photokeratitis and photoconjunctivitis, respectively. Severity of the symptoms ranges from mild irritation to severe pain, and the recovery may last a few days. Chronic exposure to UV-A and UV-B can cause cataracts of the eye’s lens. Treatment of this disease is possible in most of the cases by replacing the natural lens with an artificial one. Ultraviolet filters are incorporated into these artificial intraocular lenses to prevent UV-A from entering the eye and damaging the retina.
UVR exposure is particularly hazardous, since the body's protective glare aversion response, the "blink reflex," is activated only by visible light. Therefore, it is important to protect workers from the dangerous effects of UVR if their work puts them at risk of UVR exposure.
Effects on the skin
The penetration of the skin by UVR is wavelength-dependent. Roughly spoken, the longer the wavelength, the deeper UVR penetrates the skin. UV-C is absorbed in the very upper layer of the skin, the Stratum Corneum, while UV-B penetrates through this layer and reaches the epidermis. UV-A penetrates the skin down to the dermis. None of the UVR is supposed to reach the subcutaneous layer.
Excessive short-term exposure to UVR leads to sunburns (erythema), an inflammation of the skin. Delayed tanning as an increase in skin pigmentation may be a subsequent result of overexposure to UV-B. Exposure to UV-A may also lead to immediate pigment darkening.
The International Agency for Cancer Research (IARC) has classified solar UVR as a carcinogenic for humans (Group 1) in 1992[6] and this assessment was confirmed in the IARC monograph 100 D on radiation published in 2012[7]. For melanoma skin cancer, the incidence of being UVR induced is rather small. Squamous cell carcinomas (SCC), actinic keratosis (AK, pre-stage cancer) and basal cell carcinoma (BCC) are called non-melanoma skin cancers (NMSCs) and most possibly related to UVR exposure. The correlation for SCC and AK is mostly clear[8] [9] while there is a smaller incidence for BCC[10]. There is a correlation between the incidence of NMSC and skin type according to the Fitzpatrick scale[11]: skin type I is at the highest risk to develop NMSC, skin type VI the lowest. The Fitzpatrick scale identifies six different skin types, based on skin pigmentation, ability to tan, and the rapidity of receiving a sunburn. Skin type I, representing very fair skin, is the most sensitive to UV damage[12]. According to a European multicenter case–control study (2016)[13] nearly all individuals with fair skin who work outdoors are at a high risk of developing skin cancer at some point in their lives, as compared to the general population, which has a one-in-three chance of developing non-melanoma skin cancer. This risk is particularly pronounced for those who have spent many years working outdoors for long hours each day.
The exposure level is a determinant factor for the development of skin cancer[14]. The International Commission on Non-Ionizing Radiation Protection (ICNIRP) describes the acceptable daily exposure at each UV wavelength as being equivalent to approximately 1.0 to 1.33 Standard Erythema Dose (SED). This standardised dose assumes that 1 SED equals 100 J/m−2 of erythemal effective UVR exposure. The radiant exposure (J/m−2) is the accumulated radiant energy per unit area in joules per square meter. Outdoor workers are often exposed to higher doses than the exposure level of 1 to 1.33 SED/day.
Chronic exposure to UVR may also result in photoageing of the skin, which means an accelerated loss of elasticity. Additionally, UVR radiation potentially influences immune functionality, leading to a decrease or increase in immune responses.
More detailed information can be found in the article UV radiation at work and health.
Factors influencing UV irradiance
The irradiance of solar UV on earth depends on various direct and indirect factors. Direct factors include:
- Daytime: from sunrise until sunset, the solar spectral irradiance and the intensity change due to the varying angle between the light beam and the horizon. This is directly connected to air mass and thus absorbance.
- Season: due to the obliquity of the ecliptic, we experience seasons. In wintertime, angle between the light beam and the horizon is smaller as in summertime, resulting in lower irradiance.
- Altitude: The higher above ground, the less air mass is above us. Therefore, absorption is lower and thus irradiance higher.
- Solar activity: The sun does not emit constantly. Within a cycle of years, the sun's emissions resemble a sine wave.
On a local level, other factors (mainly on a timescale) have an impact:
- Weather: Cloudiness influences irradiance due to refraction and diffusion of the beam. These factors are correlated mainly to the water concentration in the atmosphere. In the case of complete cloud cover, UVR from the sun is reduced by about half. Incomplete cloud cover is unable to adequately shield UVR and typically only 10% is blocked by clouds. In some cases, diffusion, refraction and reflection phenomena can even increase the amount of UVR[12].
- Ozone layer: Local variations in the ozone layer of the atmosphere directly influence absorption of UV. The less ozone is present, the more UVR is transmitted.
The irradiance does not necessarily reflect the exposure. As people move, their position and orientation changes with respect to the sun, and therefore also the exposure changes. To gain insights into exposure patterns of workers, long-term measurements using personal dosimeters are necessary.
Comparison of UVR from natural and artificial sources
UVR emerges from natural as well as artificial sources. Technically, there is no evident difference on photons from natural and artificial sources. The continuous power spectrum of the sun can be described with a Black-body radiator following Planck’s law with an effective temperature of 5900 K. Technical applications on earth rarely need such high temperatures. To emit a substantial amount of UVR, a Black-body radiator should have an effective temperature above 2000 K. Artificial sources working at those temperatures are steel smelters and mainly molten fused quartz.
Anyway, most sources of artificial optical radiation emit line spectra without any continuous content. For example, mercury-vapor lamps, welding arcs, or gas burner flames emit prominent line spectra especially in the UV wavelength regime.
In summary, any UVR is equal. The only difference is the composition of the spectra.
“Outdoor" - Occupational activities
Since time immemorial, human beings are working outside in the sun. The human body has evolved into its present form by combining several advantages. We walk upright (erect, since homo erectus) to descry enemies and preys, but also to minimise the surface of the skin exposed to the sun and thus to prevent body overheating. As a result, we only have few so-called sun spots like nose, bald head, ear, and instep. Undoubtedly, nature did not provide sufficient prevention of skin cancer as humans did not get old enough to suffer from the disease.
Nevertheless, working activity often requires non-upright body positions for many hours (kneeling, crawling, and stooping). Nowadays, especially in the European climatic zone, body overheating is of secondary importance. As man gets older, solar influence dominates the risk factors that promote skin diseases.
Occupations at risk of exposure to natural UVR
Outdoor workers are constantly exposed to natural UVR and are therefore at higher risk of skin cancers. An outdoor worker is anyone who spends more than 22% of their working time outdoors[15]. The intensity and frequency of such exposure varies greatly between sectors and even within one same occupation – this would depend on local circumstances (UV Index) and an individual’s activities and skin pigmentation. Posture is also an important factor. For example, many tasks in traditional agricultural jobs require the worker to bend over. The back and back of the neck are therefore more exposed than the face. The exposures by fishermen will have similar postural aspects, but the reflection from the water and the time of day may result in higher exposure doses to the eye and skin. Maritime jobs belong to the occupations with the highest UVR exposure, both in terms of intensity and frequency of exposure.
In the framework of the Genesis-UV project (Germany), data on solar UV exposure have been collected since 2014 based on measurements taken from 1000 test persons wearing electronic data logger dosimeters during their working time for 7 months each. The measurements produced over 3 billion valid data records covering more than 250 occupations and 650 activities[16]. The results reveal that of the ten occupations with the highest radiation exposure, many are found in the construction sector, but some also in the raw materials extraction and agricultural sectors[17]. However, the Genesis-UV study also showed a large variability in exposure within an occupation, and even found that job descriptions are often not sufficient to make an estimate for exposure. Therefore, a risk assessment of all working activities remains necessary[16] [18].
It is important to keep in mind that exposure of workers against UVR from the sun is affected by many factors:
- Position against source (sun);
- Shadow provided by trees, buildings, vehicles, temporarily installed machines (e.g. cement silo at construction sites);
- Work organisation (hours of the day);
- Clothing as result of outside temperature
Workers at construction sites and roads
On construction sites, many different activities have to be carried out directly in the sun. While indoor-construction workers (electrician, heating installer etc.) are only minor exposed, e. g. brick layer, plasterer, concrete workers, steel builders, and road construction workers are exposed at a very high level. Their work has often to be carried out in the bright summer sun, and no shadow is or can be provided. Figure 1 lists the occupations in the construction sector with the highest exposure to solar UVR based on the Genesis-UV project. The exposure is shown as yearly standard erythema dose (SED). One SED is equivalent to an exposure of 100J/m2 and is independent of skin type. Therefore, the same exposure dose in SED that causes erythema in fair skin may have no effect on darker skin. Not only individual factors such as skin type but also individual behaviour may aggravate the risk, e.g. working without proper protection, in shorts, etc.
Figure 1: UV Radiation exposure in construction – Genesis-UV
Source: [17]
Workers in agriculture
Farmers often work seven days a week, especially when cattle is involved. During summertime, most work has to be done outside on the field. Questioning of farmers revealed interesting lifetime work pattern: Mostly they work from childhood days on, many hours per day and do not go for holiday. Especially in agriculture, seasonal workers are employed. Seeding or harvesting has to be done in very short time period with a high number of workers. Figure 2 shows that seasonal workers are most exposed to UVR.
In contrast to former times, agricultural work has become more and more mechanised. Tractors, harvesters, and related machines have closed driver’s cabins, where exposure to natural UVR is reduced by the window glass. However, the driver has to get out of the vehicle more often than one would expect, and thus exposure is present. Additionally, a farmer working outside without machinery often wears broad-brimmed hats, while a driver in the cabin does not (due to heat inside). He gets out bareheaded.
Figure 2 UV Radiation exposure in agriculture – Genesis-UV
Source: [17]
Seamen and fishermen
Mainly during the second half of the last century, European seamen were hired on European-flagged ships to travel the world. Beside short-routes in Europe, trips in the vicinity and across the equator were done. Under good weather conditions, work on-deck hat been carried out with short-legged and short-sleeved clothing as mandatory uniform. As we know today, the exposure may be a factor of 3.5 higher in the vicinity of the equator, and additionally, wavy water reflects UVR to an amount of 25 to 30%, raising exposure of the seamen[6]. One may reflect also that working times per day exceed eight hours regularly due to lack in personnel and free-time activities. But also local fishermen are exposed to high levels of natural UVR. A study carried out in North Italy[19] monitored a total of 7 fishermen, working on three different fishing boats for their occupational solar UV exposure with personal UV dosimeters. The study found high individual UV exposure levels, even if the measurement campaign was conducted during partially clouded spring days, with 43% of the daily personal UV measurements potentially exceeding the limits of 1 - 1.3 SED (Standard Erythemal Dose per day, Workers’ UV exposure was mainly influenced by the characteristics of the work activity, the postures adopted, and the type of boats, e.g. insufficient shading structures on the boat.
Further examples
The online Genesis-UV database[20] contains data on UVR for almost 100 different occupations, suboccupations and tasks. The available data provide information on the daily distribution of radiation based on half-hour values, daily mean values for each month, and extrapolated data for the entire year.
European legislation on natural UVR sources
Directive 2006/25/EC on the minimum health and safety requirements regarding the exposure of workers to risks arising from artificial optical radiation[21] does not address the risk of natural UVR. The evaluation report of Directive 2006/25/EC[22] stated in its conclusions that several stakeholders indicated that the Directive is insufficient since it does not cover outdoor work and the associated increased risk of skin cancer. Even though there is no EU Directive specifically addressing natural UV sources, the Occupational Safety and Health (OSH) framework Directive 89/391/EEC[23] lays down general principles concerning the prevention of occupational risks, and this implicitly include risks to workers arising from natural UVR sources. According to the OSH framework Directive, employers have the responsibility to avoid the risks to workers from natural UVR sources, need to assess the risks from natural UVR sources that cannot be avoided, and must implement appropriate protection measures following the hierarchy of control measures established in the Directive.
The EU Member States must have a national legislation in place enforcing the OSH framework Directive 89/391/EEC and protecting workers from all occupational risks, which includes those originating from natural UVR sources.
Risk assessment and measurement of exposure
The occupational risk related solar radiation changes from day to day and between hours of day together with changes of UV-Index. UV-Index reflects the degree of hazard from solar radiation and its values can be the base of risk assessment for a particular workday[24] . The results of risk assessment must be used to provide an adequate protection plan for a particular workday[25].
The UVI is a measure of the intensity of UV radiation on the Earth’s surface that is relevant to effects on the human skin. UVI values are grouped into five exposure categories (figure 3)[24]. Worldwide, meteorological institutes use the UVI to provide information on solar UVR and the appropriate prevention measures. WHO has developed the SunSmart Global UV App. The application for mobile devices describes the level of solar UV radiation at a specific location and indicates when to take sun protection measures[26]. For the European region, a four-day forecast of UV Index is provided by the Copernicus Atmosphere Monitoring Service and presented in an interactive online map[27].
It has to be taken into account that the UVI is determined solely for a horizontal plane. The personal exposure for people moving and/or working in the sun may not be calculated appropriately, as the angle between the surface of the skin and the horizontal plane always varies. Such variations range from 90° irradiation (maximum) to pointing away from the source (no exposure). Nevertheless, the UVI is a useful measure to appraise solar UVR and thus to prevent hazardous influence.
Figure 3 – UV index
Source: [24]
To be more precise, a risk assessment according to EN 14255-3:2008 Measurement and Assessment of Personal Exposures to Incoherent Optical Radiation – Part 3: UV-Radiation emitted by sun[28] should be carried out.
Beside the procedure of risk assessment using the solar UV-Index, this standard describes methods of calculation and assessment of skin and ocular exposure factors, methods of erythemal effective radiant exposure and non-melanoma skin cancer radiant exposure and sun protection measures.
Occupational disease
An occupational disease is defined as any disease contracted as a result of an exposure to risk factors arising from work activity[29]. Further on, it is required that the disease is more prevalent among the group of exposed persons than in the rest of the population, or in other worker populations.
Compensation schemes of occupational diseases vary between the European Member States and are mostly based on lists of recognised occupational diseases. Since 1990, a Commission Recommendation concerning the European schedule of occupational diseases is in effect, which has been last updated in 2022[30]. It is divided into two parts: Part I lists ailments which should be adapted as occupational diseases in the national states of the EU; while listings in part II denote ailments with possible relation to occupational activity, and thus can be adopted to part I in future times.
Regarding UVR, only entry 502.01 “Conjunctival ailments following exposure to ultraviolet radiation" in part I relates to an occupational disease[30]. Neither non-melanoma skin cancer, nor other diseases are listed in part I or proposed in part II. Therefore in most EU countries, no diseases related to UVR exposure fall under the compensation system on occupational diseases. An exception is Germany where UV-induced skin cancer is included in the list of occupational diseases since 2015. With 9905 cases reported in 2018, work-related skin cancer is already the third most reported and the second most recognised occupational disease, and by far the most common work-related cancer in Germany[31]. Most of these cases are diagnosed for workers from the agricultural sector followed by the construction sector[16].
Prevention and protective measures
Prevention is achieved best by raising the awareness of the people regarding the hazardous potential of UVR. Handouts and advertising in media ("social media"), nationwide or pan-European campaigns for protection against solar UVR help to find a better understanding for what has to be done to protect the skin during working time or private time. However, protective measures may be taken for prevention.
Natural protective measures
Up to a certain level, the eyes are protected against too much irradiance from the sun due to the geometry of the eye socket. Mostly the eye view is horizontal or downwards, preventing from staring in the sun. Involuntary closing of the eye also reduces irradiance while looking into bright light sources.
The skin is able to tan upon exposure against UVR. Biologically, this is achieved by pigmentation and thickening of the horny layer. The “ultraviolet protection factor" of the skin has been subject to research. Data showed that the protection factor is maximal about 2.5 for Caucasian people[32] , yielding only small protection in comparison to the risk. For example, if the un-tanned skin suffers from erythema after 10 min, the tanned skin develops erythema after 25 min. For outdoor workers in the summertime, this is far too less.
Additional protective measures
Natural protection of the eyes and the skin is often not sufficient to protect from harm arising from solar UVR. Other methods, including technical, organisational and personal measures, can help to minimize the exposure:
- Avoiding high exposure against solar radiation: If possible, work plans should be such that no work in the bright sun has to be done at noon.
- Shadow should be provided, e.g. with cloth around a working place (“housing").
- Planning outdoor activities in such a way that people move along with the shadow.
- Wearing of suitable sun glasses, especially in regions with high albedo (reflection of sunlight e.g. snow, sand, water, large concrete areas).
- Wearing of suitable, skin covering clothing (e.g. long sleeves). It should be taken care that the clothing is non-transparent. UV standard 801 [33] or EN 13758 [34] provide information on the protective properties of clothing against UVR.
- Wearing of suitable headwear, e.g. broad-brimmed hat. Some headwear includes the protection of the neck while working bent over.
- Usage of sunscreen: Skin areas that cannot be covered by clothing should be treated with sunscreen with a high protection factor. One should be aware that application of sunscreen has to be very precise and also to be repeated after 2 hours, roughly. The light protection factor denoted only resembles an estimate and is solely reached if 2 mg/cm² are applied. Sweating for example washes off sunscreen and decreases the protection.
