Protecting Workers from Ultraviolet Radiation - icnirp

8.3.4 Personal dosimeters
Protecting Workers from Ultraviolet Radiation
In recent years, broad-band safety meters became available which are small enough to be used as
personal dosimeters, i.e. fixed to a person’s clothing or hat and worn during the workday. These
personal safety meters either add up the dose continuously or record the time varying irradiance
to be read out after the working day. They may even provide audible warning or flashing lights
to cease exposure. Some are designed specifically for protecting against overexposure to solar
UVR (often in the shape of wrist bands or lapels) mimicking the CIE erythemal effectiveness
curve and some may require the input of skin sensitivity. The accuracy and the price vary widely
for broad-band safety meters, mainly depending on the quality of the spectral responsivity of the
detector.
Besides electronic instruments, a number of film dosimeters have been developed. These are
based on photo-induced changes of chemical or biological materials. The magnitude of the
change is related to the effective UVR dose. They accumulate the effect over a certain time and
are subsequently analyzed in a laboratory. Since the level of exposure is determined with some
delay, they can not be used as a direct warning device against overexposure. These dosimeters
may be used for occupational safety assessments where the exposure level is assessed for a
specific source and task to decide on the need for protective measures or more accurate
assessment. The advantage when compared to electronic instruments is that they are very light
and can be worn without impeding the worker. However, the spectral response only roughly
follows erythemal effectiveness curve or the ICNIRP hazard action spectrum. Film dosimeters
have been most extensively optimized for solar UVR measurements weighted with the erythemal
effectiveness curve. For the measurement of UVR emitted by other sources, dosimeters would
need to be calibrated specifically according to the spectral distribution of the source to be
measured and the action spectrum to be used.
The most commonly used, reliable material for personal UV dosimetry has been the
thermoplastic polysulphone. The basis of the method is that when the film is exposed to UVR at
wavelengths principally in the UVB waveband, its UV absorption increases. In practice, the film
(around 40 m thick) is mounted in cardboard or plastic photographic holders. Other film
dosimeters, referred to as biosensors, are based on the effect of UVR on the germination of
spores. Basically, any type of measurement system can be used to evaluate personal exposure.
Ideally, personal dosimeters would have the following characteristics:
• Be easy to handle and not impose restrictions on the activities of the wearers.
• Have a linear UV dose response and be independent of dose rate.
• Have a photoadditive response, where each wavelength acts independently and the effect
of polychromatic radiation is the sum of the effects of all wavelengths involved.
• Match the action spectrum of the photobiological effect being monitored S(λ) or
alternatively CIE erythemal curve.
• Have a response independent of temperature and humidity.
• Exhibit no 'dark effect' (continuing response when radiation exposure terminated) and be
stable in long-term storage.
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