Speaker - Mark Hoover, National Institute for Occupational Safety and Health

Sampling by filtration is an important method for collecting and evaluating any type of airborne material, including nanoparticles and other ultrafine aerosols such as radon decay products. Given the considerable current interest in characterizing and controlling risks to worker health from potential exposures to engineered nanoparticles, this course will present fundamentals of inertia (efficient collection for large particles) and diffusion (efficient collection for very small particles) that affect the efficiency and most penetrating particle size (MPPS) of filters; efficiency and MPPS for the various filter types that can be used for collection of nanoparticles; and issues for selection of filters with appropriate collection efficiency, MPPS, durability, pressure drop, and surface characteristics. A series of practical problems will also be presented on how to avoid common errors in flow calibration and control when rotameters are used to monitor and control the sampling flow rate. Because rotameters are typically located downstream of a filter or other sampling device, the internal rotameter pressure is lower than the ambient atmosphere from which the sample is being drawn. Depending on the pressure drop conditions (perhaps 1 psi for a filter and perhaps several psi for other sampling instruments such as a cascade impactor) the errors can exceed the 5% level recommended for making a correction. It will be emphasized that both the rotameter equation and the ideal gas law must be used to determine the actual flow rate associated with a given scale reading in relation to the calibrated flow rate for that scale reading. Course problems will demonstrate how confusion can be eliminated by defining and using a multiple-frame-of-reference scheme involving the following conditions of temperature and pressure: (1) calibration, (2) operation (inside the rotameter), and (3) ambient (typically the actual conditions where the worker is located and the sample is being taken), as well as two types of reference conditions (4) normal or standard ambient (760 mm Hg and either 20 degrees Celsius or 25 Celsius), and (5) standard (760 mm Hg and either 0 degrees Celsius for chemists or 25 degrees Celsius for ventilation specialists).This system clarifies that the rotameter equation is only to be used for the correction between calibration and the operation, and that the ideal gas law is to be used for corrections among all other combinations of the frames of reference. An Excel spreadsheet with detailed examples and calculations will be demonstrated and provided to course participants.