Hydrogen Sulphide (H2S) Exposure Hazard Assessment: An Algorithm for Generating Exposure Index Based on Direct Instrument Readings

Abstract

Objectives Increased use of small affordable alarm sensors with logging or network capabilities has improved the ability to monitor exposure. The large datasets generated from these monitors calls for development of a computer algorithm to assess these data. Methods We examined 88 time series of hydrogen sulphide (H2S) from wastewater works previously used for developing the exposure index. The time series covered 331 h, where 16 h had readings different from zero. Results The developed algorithm reproduced the manual assessed index almost perfectly (linear regression β = 1.02, R2 = 0.97, P < 0.001). Time-weighted average (TWA) values of the 88 time series showed a mean value of 0.04 ppm (range 0.0–0.9). The mean index value was 18 (range 0–337), with a good linear fit (β = 0.002, R2 = 0.93, and P < 0.001). The index gave us a better resolution and basis for risk assessment than the TWA, and managed to combine evaluation of TWA and exceedance of ceiling value in one number. Conclusions As long as peaks above ceiling value occur, we find alarm tools with an H2S sensor to be an essential personal protective equipment against H2S. The proposed method has been verified, and it removes some common human errors in graph evaluation. Use of the index is a possible way of quantifying risk level in exposure to H2S in one single number and provides better understanding of the risk of exposure, as it eases the analysis and evaluation of large numbers of time series.

A cross-sectional study of sensory-motor neuropsychological function among sewage plant and sewage net workers exposed to hydrogen sulphide when handling wastewater

“…However, both level and pattern of exposure may be different in the community studies compared to our occupational study; Exposure levels above 1 ppm are very uncommon in community settings ( Guidotti 2010 ), while the general low exposure level in the work environment, with 8-h time-weighted average (TWA) measurements below 5 ppm, is accompanied by occasional more frequent and higher situational or task-related exposure peaks above 10 ppm, and all groups with active sewage work may even have incidents of exposure above 100 ppm ( Austigard et al 2018 , 2023 ; Austigard and Smedbold 2022 ).…”

“…A thorough presentation of exposure sampling and the development of the hydrogen sulphide index ( Austigard et al 2018 ), and a detailed description of work tasks and exposure conditions for the study group, besides results from lung-function examinations, and respiratory and gastro-intestinal symptoms, with the corrected index equation, can be found in previously published studies from the project ( Heldal et al 2019 ; Austigard and Smedbold 2022 ).…”

Risk Characteristics of Hydrogen Sulphide Exposure in Wastewater Collection and Treatment Related Occupations

“…Most days where H 2 S was detected have only 1 peak, as detected by the algorithm ( Austigard and Smedbold, 2021 ). Table 3 summarizes the number of peaks observed of different sizes by SEG and in total.…”

“…Assuming all exposed time for the 7083 days are measured, this corresponds to 0.15% of the total work time. In the previously presented expert collection among wastewater workers ( Austigard, 2018 ; Austigard and Smedbold, 2021 ), 4.8% of the time were above the LOD (16 h out of 331 h), with LOD 0.1 ppm. By re-assessment of the 2018/2021 dataset we found it to contain 0.8% above 1.6 ppm (17% of all data points above 0.1 ppm).…”

“…Descriptive information in the raw data was used to categorize and aggregate data for each detected workday per person. We used a previously published algorithm ( Austigard and Smedbold, 2021 ) adapted to the format of the exported data files, to calculate daily exposure measures of H 2 S, such as number of peaks, peak height, TWA, and duration, for each person. Multiple runs (on and off multiple times a day) are combined for the same person on the same day.…”