Air Sampling Accessories Types of Sampling Accessories Filters
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Air Sampling Accessories
Types of Sampling Accessories Filters Sorbent Tubes Cyclones & Impactors Impingers Gas Sampling Bags
Filters are Used to Collect Many Types of Samples Dust & Respirable Dust Asbestos Silica Heavy Metals – Examples: Lead, Chromium, Cadmium Alkaline Dusts
There are Many Different Types Conductive 2 part or 3 part MCEF PVC PTFE 37 mm or 25 mm Gridded Banded
Filter Sampling Methods Sampling methods are published by NIOSH, OSHA and EPA that will describe the type of membrane used. The sample flow rate will also be described in the sampling method, along with information on run time. Filter sampling methods are normally run with high flow personal monitoring pumps in the range of 1 to 4 LPM.
Criteria Identifying Filter Membranes Diameter in mm Pore size in microns (µm) Material Example: 37 mm, 5 µm, PVC
There are Many Types of Filter Media ◉ MCE or MCEF: Mixed cellulose ester fiber ◉ PVC: Polyvinyl chloride ◉ PTFE: Polytetrafluoroethylene (Teflon) ◉ Glass Fiber ◉ Polycarbonate
A Filter Membrane May be Plain or Gridded Grid lines are often preferred for microscopic analysis Grid lines may be offered in different colors
The Filter Cassette May Have Further Description ◉ Two-Piece: Cassette consists of two press-fit parts ◉ Three-Piece: Cassette includes a center ring to allow open-face sampling ◉ Conductive: Will not build static charge ◉ Banded: Has shrink band around press joint for tamper seal
Asbestos Filters May be Described by the Test Method PCM: Phase Contrast Microscope analysis specified in the OSHA and NIOSH methods TEM: Transmission Electron Microscope analysis specified in the EPA-AHERA test method
Filter Assembly Three piece cassette: inlet is at top Center ring allows open face sampling Support pad beneath filter Filter and pad lay on vacuum disperse grid
Most Popular Filters Filter Type Sample For 37 mm, 5µ, PVC Dust, Silica, Hex Chrome 37 mm, 0. 8µ, MCE Lead, Chromium 25 mm, 0. 8µ, MCE Asbestos PCM 25 mm, 0. 45µ Polycarbonate or MCE Asbestos TEM
Sorbent Tubes
Sorbent Tube Basics Sorbent tubes are designed to collect airborne gases and vapors. They work because the target gases adhere to the surface of the collection media. They are designed for low flow rates, usually between 20 and 200 cc/minute. The target gas is recovered in the lab by desorption, either chemical or thermal.
Types of Sorbent Tubes Many types of materials have been applied to sorbent tubes. Most have been borrowed from gas chromatograph technology. Examples are Tenax, Porapack and XAD. However, the most popular type of sorbent tube contains activated charcoal.
Sorbent Tube Design A sorbent tube is usually made in two layers of unequal size. The sample is collected in a large layer, and a smaller layer serves to determine breakthrough. An arrow indicates direction of air flow.
Most Popular Sorbent Tubes Filter Type Application Activated Charcoal Hydrocarbon solvents, alcohols, acetates, ketones, methylene chloride, benzene Washed Silica Gel Acid gases Silica Gel Amines XAD-2 (Hydroxymethyl Piperidine Formaldehyde, aldehydes
Cyclones & Impactors Cyclones and impactors are used ahead of filters to provide particle size selection. Cyclones use centrifugal force to remove large particles. Impactors use small passageways to remove large particles, and can be multilayered.
Cyclones and Impactors Applications ◉ Cyclones provide respirable dust samples (e. g. , lung penetrating particles). ◉ Cyclones are suitable for sampling for inert dusts and silica dusts. ◉ Impactors can provide for PM-10 and PM-2. 5 air sampling.
Impingers allow air sampling with a liquid capture media. An older technology, most impinger methods have been replaced by sorbent tube methods.
Types of Impingers Standard impingers have a tapered end on the internal delivery tube. Bubblers have a fritted end to provide many smaller bubbles, increasing the contact surface area.
Impingers Standard impingers require a special bracket to mount them to the pump. Impingers are still used for monitoring for isocyanates like TDI, and sometimes formaldehyde.
Spill Proof Impingers Special spill proof impingers are available for convenience, but they are not specified in the test methods.
Bag Sampling Certain gases are collected in special sampling bags. From there they can be detected in a laboratory or with a portable gas monitor. The bag sampling allows an 8 hr time weighted average.
Bag Sampling The bags are made of special inert materials like Teflon® and Kynar® Tedlar®, a popular sampling material has been pulled off the sampling bag market by the supplier.
Bag Applications Carbon dioxide Ethylene oxide Nitrous oxide Sulfur Hexafluoride Trichloroethylene
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