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Hazardous emissions and health risk during laser cleaning of natural stones

: Kusch, H.-G.; Heinze, T.; Wiedemann, G.


Journal of cultural heritage 4 (2003), Supp.1, pp.38s-44s
ISSN: 1296-2074
Journal Article
Fraunhofer IWS ()

The laser removal of unwanted surface layers on artworks and artifacts made from natural stones is connected with the emission of airborne dust and volatile components containing hazardous substances. The health risk depends on the hazardous substances, the threshold limit values, the emitted amount and the size of the emitted particles. Emission and workplace concentrations were determined during optimal cleaning of encrusted sandstone and limestone as well as painted sandstone with pulsed Nd:YAG lasers NL 102 and NL 201 manufactured by BMI. The emission rate increases with layer thickness from 0.1 to 3.5 mg s-1. The rate will rise considerably for lasers with higher average power. The operator works directly in front of the emission source and usually in a separated laser area. Hence workplace concentrations of inhalable dust can reach 50 mg m-3. The main hazardous substances concerning sandstone are respirable dust as a whole and respirable quartz dust. Concerning limestone, the mai n substances are totally respirable dust, inhalable calcium oxide dust, and sulfur dioxide, if gypsum is removed and dissociated. Further hazardous substances such as iron-, aluminum-, magnesium-, and phosphor oxide are, as far as the health risk is concerned, of minor relevance. Without protection, the concentrations would exceed the threshold values. The concentration can be reduced essentially by an exhaust system with a nozzle placed close to the source. In this way the workplace concentration falls clearly below the threshold value for lead of only 0.1 mg m-3 during the removal of white lead paint.