The effect of gas exposure on welders at a large engineering plant in Bloemfontein, South Africa

Abstract

Not much data are available on low-level chronic exposure to gases present in the ambient air of welding workshops. This is especially true with regard to South African welding conditions. A study was conducted to determine the ambient gas exposure of welders in a large engineering plant in Bloemfontein, South Africa. The aim of the study was the characterisation of gas exposure during the summer and winter months for the determination of possible health risks after chronic exposure to air inside a welding shop. Gases were sampled by means of a direct reading instrument called the Processes Monitoring System (PMS-64). The system was installed at a stationary sample base in the centre of the workshop. Data were collected during one week of each month, extending from February 1997 to July 1997, so as to include both summer and winter months in the experiment. The data were retrieved from the system by means of a computer printer. It was then processed and divided into eight-hour TWA concentrations and weekly TWA concentrations. The PMS-64 was equipped to sample the following gases: NH3, CO, Cb, C102, C2H40 , H2, HCI, HCN, H2S, NO, N02, O2, 0 3, PH3 and S02. The concentrations found in the welding shop were compared to the environmental Threshold Limit Values (TLV) or occupational TLV recommended by global authoritative organisations. In the absence of such specific TLV's, a calculated environmental TLV, consisting of one fortieth of the occupational TLV, was used. High C2H40 concentrations were found in the welding shop as a result of the oxy-ethylene welding process. Hydrogen chloride emissions continuously showed low-level concentrations. It is expected that welders could experience chronic irritation as a result of this exposure. The gases, PH3, CO, 0 3, and 502. were sporadically present in low concentrations, but this occurred only during the winter months. The H2 concentrations measured were high, but the indicator O2 concentrations never dropped to hazardous low levels. It is concluded that the welders exposed to the ambient air in the workshop will experience health problems after chronic exposure as found during the study. The results emphasise the importance of exposure characterisation studies in order to provide for the identification of pollutants and to implement engineering control of emission sources.