Disposable face masks such as the Dynapro ASTM Level 2 mask have been widely used for a long time for protecting health care workers from the possibility of infection by viral or bacterial agents. Their use has become even more widespread since the advent of dangerous and infectious viruses such as SARS, Ebola, HIV and, more recently, SARS-COV-2. However, these masks offer varying levels of protection to those wearing them as well as to others in their immediate vicinity. An obvious question therefore arises – how to choose a disposable mask appropriate to the type of health care work that one does? In this post, we will try to provide some guidance to answering this question.
When considering how to choose a disposable mask, you should give priority to the guidelines provided by the regulatory and professional organizations to which you are subject. We have provided these guidelines only as an adjunct to the other legal and professional requirements to which healthcare workers may be subject.
We will also address this question only insofar as it relates to individuals involved in health care work of some kind. You should not regard the points we make below as applicable to members of the general public not involved in health care work.
Metrics Used To Measure Disposable Mask Performance
When considering how to choose a disposable face mask, it is important to understand the types of protection they offer and the metrics used to measure their protection levels. In North America, the protection standards for disposable masks are set by ASTM International (ASTM). ASTM was originally known as the American Society For Testing & Materials. It operates as an international standards organization developing and publishing international standards for materials, products, systems and services
ASTM has defined 3 performance levels for disposable masks – Levels 1, 2 and 3. It has also defined 4 areas used to measure the protective performance of these masks. We discuss each of these areas below.
Resistance To Synthetic Blood Penetration
Testers evaluate this aspect of performance by spraying synthetic blood on the mask using a specified pressure and determining whether it is able to resist penetration. ASTM defines three performance levels for this aspect of protective performance. Level 1 requires resistance to synthetic blood spray pressure of up to 80 mm Hg. Qualification for Level 2 requires resistance to 120 mm Hg and Level 3 requires resistance to 160 mm Hg. When deciding how to choose a disposable face masks, this is an extremely important metric to consider. A level 3 mask offers twice the measured protection level of one at Level 1 .
Differential pressure refers to the difference in air pressure between the internal and external surfaces of the mask. This is an indicator of how easy it is to breathe while wearing the mask. Since air will tend to flow through the mask to equalize the pressure on the two sides, a larger pressure differential is indicative of greater resistance to the passage of air. This is important as the purpose of the mask is to prevent the ingress and egress or viral and bacterial particulate matter while allowing oxygen (air) through with minimal interference.
Although this is obviously an important requirement, there is not a significant difference between masks at levels 1, 2 and 3 where this metric is concerned. Differential pressure is measured in H2O/cm2. A Level 1 mask will offer a differential pressure of up to 4.0 H2O/cm2 while one at Levels 2 or 3 will offer a differential not exceeding 5.0 H2O/cm2.
This is another important performance area of disposable masks. Testers measure filtration efficiency both for bacterial particles and for sub micron particulates with a size of 0.1 microns. A Level 1 mask will block 95% of bacterial and sub micron particles while one at Levels 2 or 3 will block 98% of these particles. There is therefore a significant difference in performance levels where is metric is concerned. This should be an important consideration to bear in mind when deciding how to choose a disposable mask.
ASTM requires disposable masks at Levels 1,2 and 3 to all demonstrate Class 1 Flame Resistance. This represents the highest possible level of resistance to both flame spread and smoke development.
Guidelines For How To Choose A Disposable Face Mask
Based on the above criteria, reasonable rules for selecting your disposable face mask might be the following:
- The protection from a Level 2 disposable mask is significantly higher than that available from a Level 1 mask. We have mentioned above that Level 2 masks offer protection against 120 mm Hg pressure level synthetic blood penetration compared to 80 mm Hg for Level 1. They also offer a 98% filtration efficiency level compared to 95% for level 1. Workers who are exposed to greater risk of infection should therefore opt for at least Level 2 masks and reject Level 1.
- Level 3 disposable masks offer an even higher protection level than Level 2 masks. However, this difference is significantly smaller than that between Levels 2 and 1. Nevertheless, whenever availability and cost permit, it is better to go up a level and choose Level 3 instead of 2. This is also a good rule to follow if the level of risk the worker is facing is uncertain. It is better to be safe than sorry.
- Healthcare workers who are in the Operating Room and are at risk of encountering splatters of blood and/or bodily fluids should wear Level 3 disposable masks. Recall that these offer protection from synthetic blood penetration at a 180 mm Hg pressure level – the maximum available. These will offer the highest possible protection from penetration by blood or other bodily fluids.
- Level 1 masks are appropriate for situations in which patient or staff isolation is the priority. These are also appropriate for patient processing, reception and other similar environments