Predicting occupational exposure to trace metals from welding by non-air monitoring based models
Résumé
Mathematical models for estimating occupational exposure to chemicals were developed as a promising alternative to air monitoring that is pricey and sometimes unavailable. Still, models parameters are derived from former air monitoring. Contrarily, our study aims to calculate all parameters independently of monitoring data. We implemented this approach to assess exposure in welding plants. Then, prediction abilities are evaluated by comparison with air measurements.The Near Field-Far Field (NF-FF) model seeks to give accurate exposure estimation near an emission source. One workplace includes Shielded Metal Arc Welding (SMAW) worker T1 who is in the NF. The other contains induction welding (IW) T2 and packaging workers T3 who are in NF and FF, respectively. The emitted metals are identified from materials compositions. Ventilation rates are calculated by the anemometer technique. Emission rates are calculated using the emission factor method for SMAW and mass balance method for IW, solely based on literature, materials quantities and their compositions. To evaluate the match between measured (6 replicates) and predicted levels, we checked their correlations and tested the mean differences of paired values.T1 is exposed to Al, Cu, Ni, Cr and Pb, while T2 and T3 are exposed to Al, Cu, Ni, Cr and Zn. A strong correlation was found (r = 0.78, p = 0.008) for NF predictions and air measurements. The T-test was significant, confirming that NF predictions and measured levels are quite close.In contrast, our approach did not succeed to predict the FF exposure (insignificant correlation), which is probably due to the mobility of T3.Non-air monitoring based models showed good effectiveness to predict the exposure levels close to emission sources for SMAW and IW processes. Thus, to assess health risks or to evaluate compliance with workplace air standards, our modeling approach that is time and cost saving, can be adopted as a support tool or even an alternative to air monitoring.