Gravimetric Analysis


Many airborne particulates are regulated by OSHA as “Particulates not otherwise regulated.” These are dusts for which OSHA has not established a specific permissible exposure limit (PEL). Generally the dusts are classified as INHALABLE, TOTAL, THORACIC, and RESPIRABLE based on particle size or cut point.

WOHL can provide pre-weighed, 5-micron PVC filters in a variety of filter types:

  • Two-piece, 37 mm polystyrene yellow band
  • Three-piece, 37 mm polystyrene yellow band
  • Two-piece, 37mm ESF filter black band
  • 37 mm MSA “saucer” with white band
  • 25 mm “goblet” with yellow tape for sampling behind a welding helmet

WOHL also has pre-weighed, 37 mm, 2-micron PTFE filters with blue band and green tape called WTEF cassettes which are only for oil mist/metal working fluid sampling.

It has been well documented that when dust samples are collected, some of the dusts adhere to the polystyrene cassette walls. Depending on the type of dust, its particle size and the electrostatic nature of the dust, this deposition can be substantial. ESF filters can be used to avoid this. They contain a capsule inside a standard two-piece, 37 mm polystyrene cassette ensuring all the dust collected is weighed. This filter type can be used wherever a standard two-piece, 37 mm  cassette is used. It cannot be used where additional analysis is needed, such as silica or metals, or with cyclones where a three-piece cassette is required.

Inhalable samples capture the largest-sized particulates and are collected on special IOM samplers, which can be provided by the lab with many types of media. Many current AGCIH TLV’s for particulates have an inhalable notation on them.

Total particulates are collected on pre-weighed, 5-micron pore size PVC filters using a closed faced cassette. Many current OSHA PEL’s are listed as “total”.

Thoracic samples are collected on pre-weighed, 5-micron PVC filters using a special thoracic cyclone. The laboratory can provide media but not the cyclones.

Respirable particulates are collected on pre-weighed, 5-micron PVC filters using a cyclone capable of collecting respirable particulates. The are many types of these cyclones, but the two most common are the SKC aluminum cyclone and the 10 mm nylon cyclone. The 10 mm nylon cyclones typically use two-piece, 37 mm cassettes, and SKC aluminum cyclones typically use three-piece, 37 mm cassettes.  The 10 mm nylon cyclone is available from the WOHL Pump and Equipment Loan Program. Refer to the manufacturer’s recommended flow rate for proper respirable sampling. Request the proper filter type, two-piece or three-piece polystyrene cassettes, to fit your cyclone.