The alternatives of filter overloading and electrostatic effects as explanations for results of inaccurate asbestos (1332214) fiber measurements using NIOSH Method 7400 were discussed, with reference to a report by Seixas and colleagues on electrostatic effects. In the original report using Method 7400, all the samples were indicated to be significantly overloaded with dust due to high background levels, so that one could expect the filters to become overloaded in a short time period. This would obscure fibers. A second effect when samples were overloaded was that the particles collected on top of each other rather than directly on the filter, making them prone to redistribution on the cowl surface during sample handling and shipment. Fiber counting could also be biased positively with lightly loaded filters, which might have occurred for filters used to collect fibers found on the cowl surface. The author's research on electrostatic effects involved the question of cowl deposition. The electrostatic field was highest at the inlet of the conductive cowl, lower at its outer surfaces, and least on its interior. Any deposit due to oppositely charged particles would be primarily on the inlet edge and outer surfaces of the cowl. Identically charged particles would be completely repelled or propelled toward the center of the filter. Thus, deposits measured in the Seixas paper, which were collected from the cowl interior, were not likely to have come from electrostatic sampling effects but rather from redeposition of losses from the overloaded filter surfaces. The author concludes that electrostatic effects can bias measurements under certain conditions, but that other recognized sources of bias, such as those discussed above, need to be eliminated as well.
Links with this icon indicate that you are leaving the CDC website.
The Centers for Disease Control and Prevention (CDC) cannot attest to the accuracy of a non-federal website.
Linking to a non-federal website does not constitute an endorsement by CDC or any of its employees of the sponsors or the information and products presented on the website.
You will be subject to the destination website's privacy policy when you follow the link.
CDC is not responsible for Section 508 compliance (accessibility) on other federal or private website.
For more information on CDC's web notification policies, see Website Disclaimers.
CDC.gov Privacy Settings
We take your privacy seriously. You can review and change the way we collect information below.
These cookies allow us to count visits and traffic sources so we can measure and improve the performance of our site. They help us to know which pages are the most and least popular and see how visitors move around the site. All information these cookies collect is aggregated and therefore anonymous. If you do not allow these cookies we will not know when you have visited our site, and will not be able to monitor its performance.
Cookies used to make website functionality more relevant to you. These cookies perform functions like remembering presentation options or choices and, in some cases, delivery of web content that based on self-identified area of interests.
Cookies used to track the effectiveness of CDC public health campaigns through clickthrough data.
Cookies used to enable you to share pages and content that you find interesting on CDC.gov through third party social networking and other websites. These cookies may also be used for advertising purposes by these third parties.
Thank you for taking the time to confirm your preferences. If you need to go back and make any changes, you can always do so by going to our Privacy Policy page.