文档介绍：CyclonesA CENTRIFUGAL FORCE IN AIR SAMPLINGA Presentation bySKC Inc.-SELECTIVE SAMPLINGTRADITIONAL CRITERIAFOR PARTICULATE MATTER?Total ?Respirable SIZE-SELECTIVE SAMPLINGNEW INTERNATIONAL CRITERIA?Inhalable?Thoracic?RespirableRELATIVE SIZE OF PARTICLES 1 4 7 10 30 100??RespirableRespirable::4 micron4 micron??Thoracic:Thoracic:10 micron10 micron??InhalableInhalable::100 micron100 micronRESPIRABLERESPIRABLETHORACICTHORACICINHALABLEINHALABLECYCLONES?Traditional workplace samplers for respirable particulate matter?Named for the rotation of air within the chamber?Function on the same principle as a centrifuge?Use rapid circulation of air to separate particles according to their aerodynamic diameterWHY USE A CYCLONE??Some sampling methods require collection of the respirable fraction of particulates. Respirable particulates are:?Smaller than 10 microns in diameter ?rate deep into thegas exchange region of the lung ?Cyclones enable collection of the respirable fraction only?Collecting larger, non-respirable particulates would inflate results of sample, overestimating exposureWHY USE A CYCLONE ??Cyclones separate larger, non-respirable particles from smaller, respirable particlesSmall particles are whirled up into the filterLarge particles fall into the red “grit pot”50% CUT-POINT:A PERFORMANCE SPECIFICATION?The 50% cut-point is often used to describe the performance of size selective samplers?It is the particle size that the device can collect with 50% efficiency ?Particles smaller than the 50% cut-point are collected with an efficiency greater than 50%.?Larger particles are collected with an efficiency less than 50% 50% CUT-POINT ON THE COLLECTION EFFICIENCY CURVE50% cut point is 4 μmTHE NEW INTERNATIONAL CRITERIA ?Specifies a 50% cut-point of 4 μm for respirable dust samplers, including cyclones?This criteria has been adopted by ACGIH, ISO, CEN, and many agencies worldwide