Face masks: Selection criteria and choices

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by John A. Molinari, PhD

The use of face masks by health-care workers (HCW) initially was considered an infection-control precaution aimed at protecting patients from bacteria and viruses that were aerosolized during treatment. Later, studies dating back to the 1940s showed that properly worn masks prevented patient exposure to exhaled droplets from HCW during coughing, sneezing, and speaking.

As more knowledge about respiratory infections and their control was reported, the rationale for wearing masks expanded to include HCW protection against exposure from potentially infectious microorganisms in aerosols, spatter particles, and splashes. This was reinforced in the latest CDC Guidelines for Infection Control in Dental Health-Care Settings – 2003. The guidelines state:

“Wear a surgical mask and eye protection with solid side shields or a face shield to protect mucous membranes of the eyes, nose, and mouth during procedures likely to generate splashing or spattering of blood and other body fluids.”

While surgical masks serve as a primary component of personal protective equipment, many HCW do not think about important mask features and limitations. The following discussion addresses the application of certain selection and use criteria that can affect mask protection capabilities.

Specific features should be evaluated when selecting these disposable items. These include ensuring that the mask:

• Does not come into contact with the wearer’s nostrils or lips
• Has a high bacterial filtration efficiency (BFE) rate
• Fits snugly around the entire periphery
• Does not cause fogging of eyewear
• Is made of a fabric that does not irritate skin or induce an allergic reaction
• Is comprised of a material that does not collapse when worn or when wet
• is easy to put on and remove

First and foremost, masks must effectively filter out airborne particles. The filtration capabilities for these FDA-regulated medical devices are determined by two factors:

• The size of the pores in the mask material as measured in microns (µ)
• The filtration efficiency, measured as the percentage of particles filtered out by the mask. A practitioner should know the percentage and size of particles filtered by his or her mask.

The American Society for Testing Materials is responsible for “medical face mask” performance classification, and defines terms used to describe the key features. Tested and approved information is described on the product box using the terms bacterial filtration efficiency and particle filtration efficiency (PFE). BFE is measured by using viable particles (bacteria) that range in size from 1µ to 5µ. PFE is measured by using nonviable particles fixed in size from 0.1µ to 1µ.

This latter feature refers to the filtration of smaller particles, thereby translating into better protection. With the reemergence of tuberculosis (TB) as a major public health and health professional concern, specialized masks also have been developed to protect a HCW’s respiratory system from infectious TB droplet nuclei. An example of these disposable particulate respirator masks is the N-95 mask.

These particulate respirators, which are designed to provide a tighter face seal than regular masks, can filter out more than 95% of the particles less than 0.1µ. They are appropriate for HCW who require extraordinary respiratory protection, such as when treating patients with active TB.

As with any infection-control practice, the key for achieving maximum mask effectiveness is compliance. A few common issues that may require your attention are:

Masks worn longer than 20 minutes in an aerosol environment lose their protective quality, and can allow microorganisms to penetrate through wet material by a process called “wicking.” Thus, masks should be changed every 20 minutes during procedures that generate heavy fluid exposure. A new mask should be worn for each patient.

A mask should conform to the shape of a HCW’s face to provide a more effective seal. Thus, use of a “one size fits all” philosophy may not provide multiple users with the expected protection.

Masks are effective when covering the HCW’s nostrils. If a person is not covering his or her mouth with the mask because “it is too hot,” the person should look for a more comfortable mask so it can be used properly. Some HCW also develop a facial skin rash when using certain masks. They should consider using masks with a softer inner lining to minimize this problem. Masks developed for sensitive skin are available.

Remember, no face mask can filter out 100% of aerosolized particles. Yet, when basic criteria are applied, HCW will be better protected to minimize occupational airborne infections.

About the Author

John A. Molinari, PhD, is director of Infection Control for THE DENTAL ADVISOR. Previously, he was professor and chairman of the department of biomedical sciences at the University of Detroit Mercy School of Dentistry. Contact him at [email protected].