Variation in the ratio of respirable particulates over inhalable particulates by type of dust workplace

Risk Assessment of the Carbon Nanotube Group

This study assessed the health risks via inhalation and derived the occupational exposure limit (OEL) for the carbon nanotube (CNT) group rather than individual CNT material. We devised two methods: the integration of the intratracheal instillation (IT) data with the inhalation (IH) data, and the "biaxial approach." A four-week IH test and IT test were performed in rats exposed to representative materials to obtain the no observed adverse effect level, based on which the OEL was derived. We used the biaxial approach to conduct a relative toxicity assessment of six types of CNTs. An OEL of 0.03 mg/m(3) was selected as the criterion for the CNT group. We proposed that the OEL be limited to 15 years. We adopted adaptive management, in which the values are reviewed whenever new data are obtained. The toxicity level was found to be correlated with the Brunauer-Emmett-Teller (BET)-specific surface area (BET-SSA) of CNT, suggesting the BET-SSA to have potential for use in toxicity estimation. We used the published exposure data and measurement results of dustiness tests to compute the risk in relation to particle size at the workplace and showed that controlling micron-sized respirable particles was of utmost importance. Our genotoxicity studies indicated that CNT did not directly interact with genetic materials. They supported the concept that, even if CNT is genotoxic, it is secondary genotoxicity mediated via a pathway of genotoxic damage resulting from oxidative DNA attack by free radicals generated during CNT-elicited inflammation. Secondary genotoxicity appears to involve a threshold.

Personal exposure to metal fume, NO2, and O3 among production welders and non-welders

The objective of this study was to characterize personal exposures to welding-related metals and gases for production welders and non-welders in a large manufacturing facility. Welding fume metals and irritant gases nitrogen dioxide (NO(2)) and ozone (O(3)) were sampled for thirty-eight workers. Personal exposure air samples for welding fume metals were collected on 37 mm open face cassettes and nitrogen dioxide and ozone exposure samples were collected with diffusive passive samplers. Samples were analyzed for metals using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and welding fume metal exposure concentrations were defined as the sum of welding-related metals mass per volume of air sampled. Welding fume metal exposures were highly variable among similar types of welding while NO(2) and O(3) exposure were less variable. Welding fume metal exposures were significantly higher 474 μg/m(3) for welders than non-welders 60 μg/m(3) (p=0.001). Welders were exposed to higher concentrations of NO(2) and O(3) than non-welders but the differences were not statistically significant. Welding fume metal exposure concentrations for welders performing gas metal arc welding (GMAW) and shielded metal arc welding (SMAW) were higher than welders performing gas tungsten arc welding (GTAW). Non-welders experienced exposures similar to GTAW welders despite a curtain wall barrier separating welding and non-welding work areas.

Simulations of airflow and substance concentration around a human body

In order to predict airflow and suspended substance concentration around a human body, we developed a geometric model of the human form and generated grids around it for Computational Fluid Dynamics (CFD). According to a CFSV model proposed by us we made a domain that included a geometric human model and generated the grids within this domain. By using this model with the grids and the developed CFD program, it is possible to simulate the airflow and the transfer of a suspended substance around the body. The simulated airflow provided a different velocity profile for each region of the body due to the characteristics of the body shape. The simulated distribution of the suspended substance concentration demonstrates how usable the present model is for quantifying a substance in any exposed region of the body.