Introduction

The COVID-19 virus has come with many recommendations regarding the best ways to keep safe.  One common piece of guidance is that we need to wear some sort of protection, not just to protect ourselves from the virus, but also to reduce the possible spread of it to the general public.

While most of us recognize that wearing a mask is a crucial part of the response we should have to the coronavirus, there remains great deal of confusion regarding what types of protection we should wear.  

We may already know about the differences between cloth masks, surgical masks, and N95 respirators, there are further measures of the quality of a protective device, particularly within the area of surgical masks. 

Beyond the recommendations for dealing with COID-19, surgical masks have many other uses and are divided into three levels, each of which are better designed for different circumstances.  If you are looking for a surgical mask on Amazon and want to know which type is best for you, this guide should be able to assist you significantly.

ASTM Surgical Mask Levels

Let us start by taking a look at the various types of Surgical Masks that exist.    There are three levels determined by the American Standards of Testing and Measurement (ASTM).  The numbers assigned to these are related to their thickness, which demonstrate an inverse relationship between the ease of breathing through them and their ability to protect against foreign substances.

According to the American Society for Testing and Materials (ASTM), surgical masks can be divided into a number of different types, each of which are suitable for different purposes.   The higher the number a mask has, the greater level of protection it provides.

Level 1

ASTM level 1 Masks provide a relatively thin barrier and level of protection.   These types of masks are designed for general, low risk situations.   They provide fairly easy breathability but are not recommended for surgical situations.   They are not designed to protect against fluids, sprays, or aerosols.    These are one of the most commonly found types of mask, which use ear loops for attaching to a person’s head, and are designed to be worn over the nose, mouth, and lower face of the user.

Level 2

Beyond the basic protection provided by the ASTM Level 1 mask, the level 2 mask is slightly more protective, and provides some minimal protection against fluids, sprays, and/or airborne liquid particles. 

Level 3

The ASTM level 3 mask is considered to be the gold standard of surgical masks.  These are designed to be used in surgical environments, or for any situation where there is a high likelihood of exposure to any form of liquid, be it in fluid form, a spray, or an aerosol.   These are considered to be best used in environments where an individual is likely to be coughing or sneezing into the face of the wearer, or to prevent the wearer from exposing such liquids to others.   They have a tight fit and are typically affixed via straps behind the head of the wearer and should be used in any sort of sterile environment where there is a high risk of exposure to fluids. 

Other Types of Masks

Outside of the standard ASTM surgical masks there are a couple of other types that people might consider, but they are generally used for different purposes.

N95 Respirator

The N95 respirator is a highly recommended disposable mask for medical professionals who work with COVID-19 patients  These are somewhat expensive devices which are molded textiles into the shape of a shell, which fits snugly over the face of the practitioner leaving no gaps, and are lashed to the head using straps.   They provide the highest level of protection, but also can cause problems in breathing, as they are quite thick and designed to protect against pretty much any for of liquid or aerosolized particles which could transmit diseases.   These are not recommended to be used by the general public, as a) they are in short supply and should be reserved specifically for those who come directly in contact on a regular basis with those infected by the coronavirus, and b) they are not designed for easy breathing.   

Cloth Masks 

Cloth masks are not designated as Personal Protective Equipment (PPE), and are not to be used in medical settings except under the most extreme circumstances of shortage.   They are, however, recommended to the general public as a way of protecting against the spread of the virus.  The coronavirus is highly contagious and can be spread very easily through water droplets caused by coughing, sneezing, talking, or simply breathing.  By covering the nose and mouth of the wearer, a good cloth mask will prevent those who may be carrying the illness, who also may not be aware of this fact.   A good cloth mask, while it may not protect the wearer in many situations against contracting COVID-19 from an external source, will go a long way to making sure that it does not spread unchecked throughout the general population.

When selecting a cloth mask, it is important that it be worn properly, covering both the nose and the mouth of the wearer, as many particles can easily escape through the nose.  It is also not recommended to wear a cloth mask which has an exhalation vent as, while this may make breathing easier, it reduces the effectiveness of preventing the virus from being accidentally spread among the general population.

Criteria for choosing a mask

When determining what sort of mask to wear, there are four basic criteria that need to be considered.  They are filtration, fluid resistance, features, and fit. 

Filtration

When there is a high risk of communicability, such as COVID-19 or tuberculosis (or many other highly infectious diseases), those in these environments would need the highest level of mask, or typically, an N95 respirator.  Standard surgical masks may not be fully effective at protecting the wearer against these infections.   Other situations where a person may wish to wear an N95 mask might be cases where there is smoke present in the air, which could cause oxygen access to be difficult to attain. 

Fluid Resistance

If there is any risk of blood or other bodily fluids being splattered (such as mucus) it is recommended that an ASTM level 3 mask be used.   These are considered to be effective against liquids of this type. 

Features

One of the most important features that a mask should have in surgical settings is one that has two tie offs behind the head.   ASTM level 3 masks are considered to be effective, particularly if used with any film that prevents fogging, and various tapes to reduce any visual interference from fogging.    In these settings, it is also recommended that users wear protective eyewear as well as shields to protect other parts of the face against any sort of splashing or aerosol disbursement of fluids. 

Fit

Extremely important when choosing a mask is that it fits properly.  Regardless of whether the correct mask-type is worn, if it is affixed incorrectly, it may not be effective and could put users at risk.   It is important that the mouth and nose of the wearer be completely covered, and there should be a seal around the face to prevent any risks of inhaling any vapors from the patient. 

Further Criteria

There are a set of measurements that are used when determining the quality of a mask.  These are divided into 5 distinct categories.  The Food and Drug Administration (FDA) sets these guidelines for testing and measuring materials which go into surgical masks. 

Bacterial Filtration Efficiency (BFP)

 This is a measurement of the percent of bacteria that is filtered out if aerosolized.    Within the ASTM guidelines, tests are performed using a droplet size of .3 microns containing a bacteria of .6-.8 microns.   For a mask to reach medical or surgical grade, (ASTM level 3) at least 95% of materials should be filtered, with the highest quality masks being able to filter out at least 98%.

Particulate Filtration Efficiency (PFE)

PFE is a measurement of the percentage of particles of submicron size that will be filtered out.   The designation of a higher PFE number indicates better filtration.   The size of the particles used in testing is important, because if one uses a particle size that is too large, it may not be effective at reducing access to very small particles.  Tests are available that will range up to 5.0 microns, however the ASTM specifies that the particle sizes that are used are typically at .1 micron.

Fluid Resistance

Fluid resistance is a measurement of what percentage of the above particles that will be filtered.  In other words, this is a measurement of the ability to minimize any type of liquid or fluid that can transfer from the outer layer of the mask to the inner layer from any sort of spray, splash, or aerosol.  These correlate to the ability to provide a barrier against fluids at a range of different pressures.

The tests that are performed use synthetic blood at varying pressures.   For level 1 masks, they should be able to withstand 80 mmHg of pressure, are about the amount of pressure from a vein,   For level 2 the amount is 120 mmHG or about the pressure typically given off by an artery, and for level 3 surgical masks, they must be able to withstand 160 mmHG of pressure for the highest fluid resistance, such as in high pressure irrigation dental procedures.


Delta P (Differential Pressure)

The Delta P is considered to be an objective measure of the breathability of the mask.   It measures the resistance of airflow.   There is an inverse relationship between the level of filtration and the level of breathability.  In other words, the higher the number, the better filtration the mask provides, but the more difficult it may be for the wearer to breathe through it.  ASTM requires that the Delta P be 5 or lower for high quality masks. 

Flame Spread

Flame spread is a measurement of the flammability of a mask.  Because hospitals may have sources of heat, oxygen and additional fuel, there’s always a risk of an open flame appearing near a mask. Flame spread determines whether or not the mask can withstand an open flame for at least three seconds, and not combust or melt. 

Skin Sensitivity

Beyond the above criteria, for ISO certification, the masks should be tested for skin sensitivity to the wearer, to make sure no one wearing such a mask is harmed during the process.     Tests are conducted using materials that are involved in creating the mask for any parts that come in contact with the skin of the user. 

What procedures are ASTM level 3 masks recommended for?

There are a wide range of different medical and dental procedures where a person is recommended to wear at least an ASTM level 3 surgical mask.

These include everything from Abdominal Aortic Aneurysm repair (AAA), or any other major or minor abdominal procedure. This can include Colonoscopies, or any other type of endovascular procedures.   They should be used in Bone Marrow transplants or biopsies, as well as any plastic surgeries.

In Obstetric/Gynecological settings, they should be used for C-Sections, hysteroscopies, vaginal hysterectomies, and any other procedure which is likely to produce fluids of any significant pressure.

Head-based surgeries, such as craniotomies, or any other general neurosurgeries, should require level 3 masks.    

Beyond these and many other obviously intrusive surgical situations, they should also be considered for arthroscopies, knee, shoulder, and hip surgeries.   Even if dealing with something as simple as general basic surgeries, or operations on a hand or extremity, there is always a risk of arterial or venal exposure.  It is wise to always wear the highest quality mask available. 

Conclusion

The sheer number of types and variations of masks can be somewhat confusing, and all masks are not created equal.  This guide should help you make the correct decision when deciding what circumstances to wear the highest level of surgical mask (ASTM level 3).  If you work within the medical or dental field, it is wise to have a good supply of this type of mask on supply to ensure that you and your staff are adequately protected.