What is Inhalable Particulate?
Inhalable particulate is defined as particulate matter with a mean aerodynamic diameter of 100 microns (µm) or less and is practically defined as that size fraction of particulate which is able to enter the nose and mouth and are hazardous when deposited anywhere in the respiratory tract.
Sampling for Inhalable Particulate
Traditional total dust filter cassettes do not effectively sample inhalable particulate matter as they underestimate the concentration of larger particulate in the range of 30-100 µm (See OSHA.gov Source). The traditional 37 millimeter (mm) filter cassette inlets are small and do not allow for efficient capture of larger particles. Additionally, the particles may adhere to the 37 mm cassette walls which can cause sample loss when the filters are removed for analysis.
In the 1980’s, the Institute of Occupational Medicine (IOM) designed a sampler to meet the inhalable criterion when mounted on the body in the workers breathing zone. The sampler monitors for the same measured dust concentration and aerodynamic size distribution as that inhaled by its wearer, regardless of dust source, location and wind conditions. This device was named the IOM Sampler, and is still widely as accepted as the best inhalable particulate sampler. The IOM Sampler consists of a sampler body, cassette filter support grid, 25 mm filter, stainless steel cassette, several O-rings and a cassette front plate.
Figure 1: IOM inhalable dust sampler (parts from left to right: sampler body, body o-ring, cassette bottom, filter, cassette top, front plate o-ring, front plate)
What are the advantages of using an IOM Sampler?
Benefits of using the IOM Sampler include:
- Device performance is relatively independent of wind speed for particles with aerodynamic diameter up to and including 75 µm.
- During analysis, the cassette and filter are weighed together. This means that all particles that enter the sampler are part of the analysis.
- Particles dislodged from the filter during work activities are retained in the sample.
The American Conference of Governmental Industrial Hygienists (ACGIH) has defined Inhalable Particulate Matter (IPM) Threshold Limit Values (TLV) for those materials that are hazardous when deposited anywhere in the respiratory tract. Examples of hazardous materials for which an inhalable TLV has been developed include:
Cautionary Advice When Using the IOM Sampler
- Ensure that the outside of the sampling device has not been contaminated with excess process materials as it will overestimate the weight of captured inhalable particulate as the entire device if reweighed at the end of sampling.
- Be sure to only compare the inhalable sampling results to regulatory and recommended limits that are specified based on the inhalable method.
2015 TLVs and BEIs: based on the documentation of the threshold limit values for chemical substances and physical agents & biological exposure indices. ACGIH Signature Publications, 2015.
General methods for sampling and gravimetric analysis of respirable, thoracic and inhalable aerosols. Published by the Health and Safety Executive and licensed under the Open Government License’. June 2014. http://www.hse.gov.uk/pubns/mdhs/pdfs/mdhs14-4.pdf
Industrial Hygienist / Project Manager