NIOSH Funds Study to Examine Filter Efficiency for Nanoscale Particles

Aug. 2, 2005
Some see the field of nanotechnology as having the potential to yield exciting medical, environmental and consumer product breakthroughs. EHS stakeholders may very well share in that excitement, but they also see some important unanswered questions pertaining to the safety of the workers who are and could be exposed to nanomaterials.

A NIOSH-funded study being conducted by scientists at the University of Minnesota aims to answer one of those questions: Will the same respirator filters that protect against silica and other traditional airborne containments be sufficient to capture materials that can be tens of thousands of times smaller than a single human hair?

Preliminary findings from the study are expected to be presented at the second International Symposium on Nanotechnology and Occupational Health in Minneapolis on Oct. 3-6.

Conventional knowledge, based on a substantial body of evidence, holds that airborne particles 0.3 micrometers (µm) in size are more likely to penetrate a filter than particles of other sizes, according to NIOSH. Particles larger than 0.3 µm will be blocked by filter fibers. Those smaller than 0.3 µm will be stuck on and among the fibers through a process called "diffusional capture," NIOSH says.

Consequently, if a filter captures particles 0.3 µm in size, scientists could be confident that the filter would capture particles of any size.

However, little experimental work has been done to quantify the performance of filters against particles in the nanometer size range. (A nanometer is one-billionth of a meter.) The NIOSH-funded study aims to determine if the accepted theory of filtration remains valid for particles on the borders of nanosize and below. If the study finds that the effectiveness of filters begins to decrease for nanosize particles, it will attempt to identify at what size this decrease is likely to occur.

"NIOSH's support for this study is part of our commitment with many partners to address current questions about nanotechnology and occupational health, and to design exemplary research to help answer those questions," said NIOSH Director John Howard, M.D. "In so doing, we will help to ensure that the U.S. remains strong and competitive in the dynamic global nanotechnology market."

Nanomaterials currently can be found in consumer products such as sunscreens, coatings for bowling balls and stain-resistant clothing. Their potential medical applications are being introduced at a rapid pace, according to Emory Knowles III, M.S., CSP, CIH, manager, industrial hygiene and safety, for Baltimore-based Northrop Grumman Corp. Electronic Systems. Knowles recently led a seminar on the emerging EHS issues associated with nanotechnology at the American Society of Safety Engineers' annual conference in New Orleans.

New Nanotechnology Resources from NIOSH

Showing that the emergence of nanotechnology is a rising concern in the EHS community, NIOSH earlier this summer launched a new Web topic page addressing frequently asked questions regarding nanotechnology. The topic page answers basic questions, defines nanotechnology, identifies nanomaterials, addresses the worker health effects and outlines the NIOSH research program. The topic page can be accessed at

The agency also has launched a Web newsletter called "Focus on Nanotechnology." The newsletter provides a regularly updated electronic report on new NIOSH developments related to research on nanotechnology and occupational health.

The Web newsletter is at

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