109 Improved Evaluation of Hydrogen Sulphide (H2S) Exposure by Use of Index Compared to Time Weighted Average (TWA)

Abstract

Abstract Introduction The acute effects of H2S levels are well known. The effect of low average exposure and short peaks are still debated. In 2018 we hypothesised that the peaks height and frequency are just as important as TWA, and we suggested an exposure index. It considers the number of peaks, peak height and time in different exposure intervals. We have tested how the index corresponds to TWA, and to exceedance of occupational exposure limit (OEL) and ceiling value (CV). Method An algorithm that makes this calculation from measurement data is published. The algorithm was adapted to data export format from logging gas alarm equipment MicroClipX3 from Honeywell Analytics. Data from more than 7000 workdays was collected among four groups with sewage related work: Sewerage network (including cesspools and septic tanks), plant, pumping stations and water distribution network. The index is compared to TWA and exceedance of OEL and CV. Results When the exposure appears to be strongly influenced by peaks, and of exceedance of ceiling value or short term exposure limits, the Index value gives a more differentiated picture of the complexity of the exposure compared to use of TWA. Correspondence between index and TWA decreases as peakiness increases. Conclusions Evaluation by index might be a good tool to evaluate exposure with multiple acute effects and a peaky appearance, such as H2S. This will give a more reliable risk evaluation and protection of water and wastewater workers.