Application of mixed models to assess exposures monitored by construction workers during hot processes

Particulate exposures were assessed among construction workers engaged in h ot processes in four jobs (boilermakers, ironworkers, pipefitters and welde r-fitters) at nine sites in the U.S. After being trained by occupational hy gienists, the workers obtained shift-long personal samples at each site for total particulates (TP), Selected samples mere also assayed for manganese (Mn), nickel (Ni), and chromium (Cr), Workers provided information about pr ocess- and task-related covariates that were present on the days of monitor ing. Data were investigated with mixed-model regression analyses that desig nated the jobs and covariates as fixed effects and the worker and error ter ms as random effects. Results indicated that the within-worker variance com ponents, but not the between-worker variance components, could be pooled am ong jobs. Mean air levels for a given agent varied by roughly six to 100 fo ld among the jobs, with boilermakers and ironworkers experiencing much high er levels of TP and Mn than pipefitters and welder-fitters. Limited data al so suggested that welder-fitters were exposed to greater Levels of Ni and C r than pipefitters, Sufficient sample sizes were available to evaluate the effects of covariates upon exposures to TP and Mn, As expected, processes i nvolving more than 50% hot work led to substantially higher levels of TP an d Mn than those involving shorter durations of hot work, Local-exhaust or m echanical ventilation reduced exposure to TP (but not Mn) by as much as 44% , and shielded or manual arc welding increased exposure to Mn (but not TP) by about 80%, Parameters estimated with these mixed models were used to cal culate probabilities that workers were exposed at levels above U.S. occupat ional exposure limits (OELs). Regarding TP and Mn, these calculations sugge sted that 26-95% of exposures to boilermakers and pipefitters and 2-13% of exposures to pipefitters and welder-fitters exceeded the current Threshold Limit Values. Among welder-fitters, limited data also pointed to probabilit ies of 2-50% for exceeding particular OELs for Ni and Cr, Using the signifi cance of the estimated random-worker effects as a gauge for the uniformity of exposure within a job, administrative or engineering changes appear appr opriate for reducing exposures to boilermakers and ironworkers, while indiv idual personal environments should be in investigated for pipefitters and w elder-fitters, (C) 1999 British Occupational Hygiene Society, Published by Elsevier science Ltd. All rights reserved.