The scientific report that was commissioned at the beginning of the research project contains a justification as well as a specification of research questions regarding pulsed incoherent optical radiation at workplaces. On the basis of a presentation of the findings concerning the photothermal and photochemical effects of optical radiation on biological tissue, a description of the corresponding risks to the eyes and skin is provided. The domestic and international exposure limit values are compared and their historical development is explained in terms of pulsed radiation sources. On this basis, radiation-relevant parameter limits are defined from the perspective of the impulse and pulse behaviour as well as in terms of the examined spectral ranges for the experimental investigations carried out in the second part of the project. Finally, proposals are made regarding the biological tissues and structures on which these experiments can take place.
The continuous (cw) and pulsed UV radiation exposures of spore films carried out in a pilot study in advance served to validate the experimental setup, and were able to demonstrate an approximately 30 % increase in the harmful biological effect (disinfection rate) of pulsed compared to cw UV radiation. Research into the Bunsen-Roscoe law demonstrated its limited scope of validity as per both very high and very low levels of irradiance. A variation of the pulse duration and pulse repetition frequency resulted in a linear and exponential dependence of the disinfection rate. Some evidence pointed to an influence of the experiment duration and the number of applied pulses on the disinfection rate.
On the basis of the scientific report and the pilot study, experiments conducted at an external research facility exposed human skin to cw and pulsed UV radiation in vitro. Dose-effect curves for the induction and repair of cyclobutane pyrimidine dimers (CPDs) subsequent to cw irradiation demonstrated linear behaviour, while with increasing doses, a (fluorescence) saturation is thought to have set in. Basal cells demonstrated a capacity for repair that was 20 % higher than that of suprabasal cells.
In terms of the Bunsen-Roscoe law, no or only minor differences between pulsed and cw irradiation were discovered for CPD induction, CPD repair and apoptosis. The principle of accumulation is applicable. The reciprocity rule did not apply, however, if the biological endpoint under consideration was based on cellular processes as a radiation response. When varying both the pulse repetition frequency and the pulse duration, no effects were discovered in terms of the CPD induction, although effects were found regarding the DNA repair and apoptosis induction. The experiment duration was another factor to take into account.
The results from F 2377 lead to the initial conclusion that in comparison with cw UV irradiation, the use of pulsed UV radiation sources at workplaces does not lead to a higher damage induction or an impairment of the processing of damage in human skin cells. The current exposure limit value concept therefore remains valid.
Unit 2.2 "Physical Agents"