13 October 2013
Year: 2013Price: 10.00
UV sources are used for all kind of applications like gluing, curing and fluorescence detection. On some systems the employee is not completely protected against UV radiation. In this case the workspace must be evaluated by the employer. One way is to use sources rated class 0 according DIN EN 62471:2009. These sources are risk-free. Unfortunately for most systems this rating is not available or reachable.
This means that a risk assessment must be done to determine the total dose during eight hour working day. Methods, measurements and requirements are described in DIN EN 14255-1:2005 while the exposure limits are regulated in 2006/25/EG:
This means that a risk assessment must be done to determine the total dose during eight hour working day. Methods, measurements and requirements are described in DIN EN 14255-1:2005 while the exposure limits are regulated in 2006/25/EG:
In the risk assessment account shall be taken to:
- exposure conditions in normal operation, maintenance and repair work
- duration of exposure to artificial optical radiation
- the wavelength range
- exposure limit values
- impacts on the health and safety of workers, especially for vulnerable groups and photosensitizing chemical substances.
Note, that this list is not a complete excerpt from 2006/25/EG. While 2006/25/EG lists 15 different exposure limit values this paper will concentrate on only tree values
Measurement devices are necessary that are sufficient sensitive to the UV radiation while being not sensitive to other spectral ranges. In most cases the measurement device should be mobile and cost effective too, while being traceable calibrated.
Therefore three groups of measurement devices can be differed. Passive dosimeter based on polysulfone [CIE 98, 1992] or other films, active broadband radiometers and spectroradiometers.
The effective irradiances using the spectral weighting functions Sλ and Bλ, given in 2006/25/EG and depicted in figure 1, can be calculated according equation (1) to (3) for spectroradiometric measurements.
Note that DIN EN 5031:10-2013 lists 28 different actinic spectra. All spectra are tabulated and the effective irradiance can be calculated. One problem is the internal stray light in combination with actinic functions, because those functions can change in magnitudes over only a few nanometers. Then stray light produces and significant measurement error if it is not corrected or known. The second problem is the sensitivity range of the spectroradiometers. Assuming a UVA-Dose of 104 J/m² per eight hour working day the measurement device must be sensitive enough to measure 0.035 mW/cm² in the UVA spectral range. A measurement device for Es must be sensitive enough to measure 0.01 mW/cm².
To reach this sensitivity filtered broadband radiometers may be used if the filter and calibration is adapted to the requirements of 2006/25/EG and DIN EN 14255-1:2005. In addition the mandatory uncertainty must be less that 30%.
Usually broadband radiometers consist of a photodiode (Si, SiC, GaP) with optical filters placed in front. Through the careful selection of the filters, the measuring range can be adjusted. However, differences between Sλ and Bλ and the sensor sensitivity in the range of >80 % or partly non-sensitivity may occur for some wavelength ranges.
In addition to effective sensors standardized versions for UVA, UVB and UVC may be used for a first measurement or to assist spectroradiometric measurements. These standardized sensors are calibrated by their manufacturers for one type of lamp and are therefore only able to reproduce correct measurement results for this type of lamp.
As soon as the lamp’s spectrum changes or other lamps or UV LEDs are used, the measured values differ. This is called spectral mismatch. While characteristics and classification for actinic / effective radiometers are given in DIN EN 5031-11:2011 sensitivity functions may be manufacturer-specific for standardized versions.
