Simulation of respirable mass sampling criteria using single round-nozzle virtual impactor technology.

摘要

Dusts and other particulate matter are generated in many occupational environments. Respirable particles are those particles that are small enough to enter into the alveolar regions to the lungs. Standard-setting organizations have developed respirable mass sampling criteria based upon lung deposition data. Each criterion specifies a particle mass penetration curve, as a function of aerodynamic particle diameter (size-selective), and acceptability requirements for samplers that mimic the curve.; The purpose of this research is to develop respirable mass size-selective samplers using single round-nozzle virtual impactor technology. Virtual impactors have distinct advantages in that: (1) area samplers, as well as compactly designed personal samplers, can be designed; (2) they can be operated in any orientation; and (3) the size-fractionated particles remain airborne and, therefore, can be collected on filters for long-term sampling or passed into real-time instruments.; A theoretical numerical parametric study was performed to look at the parameters that affect the shape of the penetration curve and particle losses. The results are compared to experiments. The numerical parametric study showed that the small particle penetration increases with (1) increasing minor-to-total flow ratio, (2) decreasing angle, (3) increasing throat length, and (4) increasing the nozzle-to-collection probe distance.; Virtual impactor penetration characteristics were compared to the BMRC, ACGIH and ACGIH-ISO-CEN respirable criteria. Each criterion has acceptability requirements. Respirable-classifying virtual impactors are found to be acceptable for ACGIH and ACGIH-ISO-CEN respirable criteria within the scope of this research. A virtual impactor having penetration characteristics similar to the BMRC curve was identified but further work is required for it to be considered acceptable.; A field study was performed in conjunction with the National Institute for Occupational Safety and Health. A machine-mounted continuous respirable dust monitor (MMCRDM) was developed and tested in the laboratory and in an underground coal mine. It utilized an ACGIH respirable classifying virtual impactor followed by a tapered-element oscillating microbalance to provide real-time respirable mass data. Results showed that the MMCRDM operated satisfactory over a 30 day period in a coal mine and the virtual impactor had very low losses.