Clinical Resources

ASTM refers to the American Society of Testing and Materials (ASTM). ASTM is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, and services—including those in healthcare.

The filtration efficiency and protective ability of a medical face mask is compromised when the mask becomes wet, torn or dislodged. Generally speaking, the higher protection value of a mask the longer it will maintain filtration; however, there is no set rule for how long a mask should be worn as it depends on humidity levels, respiration rate, nasal discharge, talking, etc. A medical face mask should be worn for only one patient procedure or visit. If a mask gets wet or soiled it should be replaced.

ASTM standards are referenced by the Food and Drug Administration (FDA), as the endorsed standard in the United States. The current standard ASTM F2100-11 (2011) specifies the performance requirements for Medical Face Masks with five basic criteria:

1. BFE (Bacterial Filtration Efficiency): BFE measures how well the medical face mask filters out bacteria when challenged with a bacteria-containing aerosol. ASTM specifies testing with a droplet size of 3.0 microns containing Staph. Aureus (average size 0.6-0.8 microns). In order to be called a medical/surgical mask, a minimum 95% filtration rate is required. Moderate and high protection masks must have bacterial filtration rates greater than 98%.

Some manufacturers use the Modified Greene & Vesley method to determine the BFE rating. This method is NOT recommended by ASTM for product comparison or evaluating consistency.

2. PFE (Particulate Filtration Efficiency): PFE measures how well a hospital mask filters sub-micron particles with the expectation that viruses will be filtered in a similar manner. The higher the percentage, the better the mask filtration. Although testing is available using a particle size from 0.1 to 5.0 microns, ASTM F2100-11 specifies that a particle size of 0.1 micron be used.

When comparing test results it is important to note the size of the test particles used, as use of a larger particle size will produce a misleading PFE rating.

3. Fluid Resistance: Fluid resistance reflects the surgical mask’s ability to minimize the amount of fluid that could transfer from the outer layers through to the inner layer as the result of a splash or spray. ASTM specifies testing with synthetic blood at pressures of 80, 120, or 160 mm Hg to qualify for low, medium, or high fluid resistance. These pressures correlate to blood pressure: 80 mm Hg = venous pressure (Level 1), 120 mm Hg = arterial pressure (Level 2), and 160 mm Hg (Level 3) correlates to potential high pressures that may occur during trauma, or surgeries that include high pressure irrigation such as orthopedic procedures.

4. Delta P (Pressure Differential): Delta P measures the air flow resistance of the medical mask and is an objective measure of breathability. The Delta P is measured in units of mm H2O/cm2 and the lower the value the more breathable the mask feels. The ASTM standard requires that masks have a Delta P of less than 5.0 for moderate and high barrier masks, whereas low barrier masks must have a Delta P of less than 4.0.

5. Flame Spread: As hospitals contain sources of oxygen, heat, and fuel the ASTM F2100-11 standards include testing for flame resistance. Testing dictates that all hospital masks must withstand exposure to a burning flame (within a specified distance) for three seconds. All priMED masks meet this requirement.

5.5 In addition to the above tests, all medical face masks must be tested to an international standard (ISO 10993-5, 10) for skin sensitivity and cytotoxic tests to ensure that no materials are harmful to the wearer. Tests are conducted on materials used in construction of the mask which come in contact with the user’s skin.

In the Operating Room (OR), surgical masks protect the sterile field from possible contamination, primarily as a result of coughing, sneezing or talking. A mask may also protect clinicians from the byproducts of surgical procedures such as bone chips, splashes of body fluids, and smoke plume resulting from laser or electrosurgical techniques.

Outside of the OR masks are used for standard precautions to protect clinicians and patients from pathogens that may spread by blood or other body fluids, secretions or excretions. Surgical and procedure masks are effective against droplet transmission.

A surgical mask is used inside the operating room or within other sterile procedure areas to protect the patient environment from contamination. It also protects the clinician from contaminated fluid or debris generated during the procedure. Surgical masks have ties so that they can be adjusted for fit, and are tied over top of a surgical cap or a bouffant cap.

A procedure mask is used for performing patient procedures, or when patients are in isolation to protect them from potential contaminants. Procedure masks are used to protect both patients and staff from the transfer of respiratory secretions, fluids or other debris. Procedure masks are used for generally “respiratory etiquette” to prevent clinicians, patients and visitors from spreading germs by talking, coughing, or sneezing. Procedure masks have ear loops for quick donning, and since they do not slide on the hair, they can be worn without a surgical cap.

A medical face mask is only as effective as its fit. There should be no gaps along the side, around the nose or under the chin that would allow air and droplets to bypass the filter medium. The mask should always be properly adjusted to fully cover both the mouth and nose. A well-fitting mask stays in place over the nose and cheeks and even a regular mask will prevent fogging of eyeglasses if it fits properly. Masks should not be worn underneath the nose or dangling around the neck – they should either be fully on, or disposed of.

There are several things that contribute to a good fit. The most important consideration is the nose piece. It should mold over the nose and cheeks and maintain its shape over time. It should not kink or break when adjusted. Individuals with wider faces should select a mask that ensures full coverage over the face and under the chin. The upper tie should sit at the crown of the head, and the lower tie should be tied behind the neck to hold the sides of the mask against the face to prevent any gaping.

Generally, there are three things you should look for to ensure your mask fits correctly:

1. The aluminum nose piece is at the top,

2. The white (or smoothest side) is on the inside against the wearer’s skin—the colour always faces out,

3. The pleats fall downwards and away from the nose (called a “waterfall” pleat).

Specifications developed by the American Society of Testing and Materials (ASTM) are generally accepted as the industry standard. Beware of mask ratings that do not follow ASTM guidelines. Some manufacturers may refer to “filtration rates” or the “number of layers” as an indication of effectiveness. These vendors may not be adhering to the ASTM standards and should be questioned for specific test data.