Airborne Concentrations of Methylene Diphenyl Diisocyanate (MDI) in North American Wood Mills During the Manufacturing of Oriented Strand Board (OSB)

Abstract

Air monitoring data were collected from industrial hygiene surveys over an 8-year period in oriented strand board (OSB) mills. Personal samples were taken to evaluate potential employee exposures to MDI. Area samples were taken to determine the effectiveness of control measures used in the mills to prevent fugitive emissions of wood dust, MDI, and MDI-coated wood dust from the OSB manufacturing process. Personal sampling results (578 samples covering 11 different job categories) ranged from 0.0002-0.524 mg/m3, with a GM = 0.001 and GSD = 3.71. Area sampling results (1657 samples covering 14 stationary locations in the mills) ranged from 0.0002-2.5 mg/m3, with a GM = 0.004 and GSD = 5.52. The statistical range of the data suggests high variability. While exposures to MDI above the established limits (0.051 mg/m3, 8-hour time-weighted average, 0.2 mg/m3, ceiling) can and do occur when engineering controls are not maintained and/or proper work practices and personal protective equipment are not followed/used for certain high exposure potential tasks, the data indicate that over 97% of the personal and 92% of the area sampling results are less than 0.051 mg/m3. Wipe testing was performed to determine the presence of removable, unreacted diisocyanates (NCO functional groups)from various surfaces. Positive results were found in about 13% of the wipe tests on surfaces confined to the blender, forming line, and hopper deck process areas.

Variable precision in visual perception

“…After BADS returned a parameter combination, we recomputed the log 16 likelihood 10 times with that combination and took the mean, to reduce sampling noise. 17 We performed this process for 10 different initializations and took the maximum of the 18 log likelihoods as the maximum log likelihood for the model, LL max (M). 19 20 Model comparison metrics 21 We use the Akaike Information Criterion (AIC, (Akaike, 1974)) and the Bayesian 22…”

“…To the best of our ability, we examined the effects of these factors, to 14 ensure that our conclusions are robust. 15 16 Apparatus and stimuli 17 Subjects were seated at a viewing distance of approximately 60 cm. All stimuli were 18…”

“…consider two kinds of variability in the precision of the measurement noise: the 16 oblique effect (O) and "residual" variable precision (V). 17 2. The observer's decision model.…”

Measurements of Airborne Methylene Diphenyl Diisocyanate (MDI) Concentration in the U.S. Workplace

“…Under these conditions, there is a greater likelihood of the release of airborne MDI if local exhaust ventilation is unavailable, marginal or if enclosures have been compromised. (7) All of the OSB and many of the Binder applications involve spraying. Some CASE and Rigid Foam applications are also spray applied.…”

Mass spectrometry-based analysis of murine bronchoalveolar lavage fluid following respiratory exposure to 4,4'-methylene diphenyl diisocyanate aerosol

“…Furthermore, many hot applications and thermal processes such as fires can release free MDI fumes from products. However, after heating, MDI tends to recondense in the air at ambient temperatures (Karoly et al, 2004). Because MDI hydrolyzes slowly in the atmosphere (the half-life of MDI in the air is 0.92 d), exposures to aerosolized MDI in the workplace are likely to be to small particulates containing free isocyanate.…”