A Refresher on Mask Types, Rating, and Proper Usage
I can’t say that I love wearing face masks. Although, I have found that it keeps my face nice and warm’ now that the weather has dipped below freezing. This article is being written amidst another lockdown with rising Covid-19 cases. And much of the daily news is once again dedicated to the topic. One such topic that seems to be gaining momentum is the idea of Covid-19 transmitting as an aerosol (CBC article linked here). Not to mention that here in Ottawa, we have been asked to wear masks outdoors “as much as possible” as well (CBC article linked here). Given the current situation, I thought it might be valuable to review some of the information that differentiates medical masks.
Standards and Rating Organization for Masks
NIOSH stands for National Institute for Occupational Safety and Health. A division of the Centers for Disease Control and Prevention (CDC), this agency is responsible for conducting research and making recommendations for the prevention of work-related injury and illness.
ASTM refers to the American Society of Testing and Materials. ASTM is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, and services.
How Mask Materials Work to Trap Particles
Masks (and/or mask filters) trap unwanted particles by 2 means: The first is by the weave of material that it is made of. To be more specific how tightly that material is woven together and how large the openings are between the fibers. The bigger the opening the larger range of particles that can make it through your mask.
The other way to trap unwanted particles is via static electric charge that is built into the mask material. For the sake of this article, let’s just consider the addition of this charge as the magic of science. But similar to the way that you can pick-up dust or bend a small stream of water with a statically charged balloon, the static charge in the mask pulls particles out of the air and holds them against materials of the mask, preventing them from coming through. However, this charge does dissipate, specifically in the presence of oil. Which leads me to my next section.
Oil Resistance Ratings
Many mask types start with a letter designation. The famous N-95 mask is one of those. The other letters used are R and P. These letters describe oil resistance of the materials.
N-rated respirator masks are not resistant to oil-based substances. They should only be used in environments without oil aerosols. They protect against solid and liquid airborne particles, except those that contain oil.
R-rated respirator masks are somewhat resistant to oil-based substances. They protect against solid and liquid airborne particles, including those that contain oil. When using R-rated filters in oil-abundant environments, you should only use the respirator for 8 hours at a time. Dispose and replace the filter or mask regularly.
P-rated respirators are considered oil-proof. They go above and beyond R-rated respirators when it comes to oil resistance. They protect against all types of solid and liquid airborne particles. Just like R-rated respirators, P-rated respirators tend to degrade more quickly when used in atmospheres with oil-based particles.
Types of Medical Masks
Procedure masks- traditionally characterized by an ear loop attachment. Intended for use on hospital floors, isolation units, newborn delivery units, and a variety of other areas of the hospital. Additionally, these masks may be used in the emergency department and the intensive care unit for bedside procedures. However, they are not suitable for use in the operating room
Surgical masks- traditionally characterized by surgical ties and a closer fit than procedure masks. Recommended for use in the Operating Room. Intended to protect against a high risk of fluid exposure.
N95 respirator masks- in a hospital setting it is intended for use to filter surgical smoke created by aerosol-generating devices such as lasers and ultrasonic scalpels during invasive procedures. An N95 is also worn during higher-risk aerosol-generating procedures on patients with known or suspected aerosol-transmittable diseases such as tuberculosis, varicella and rubella.
Particulate respirators- also known as “air-purifying respirators” because they protect by filtering particles out of the air as you breathe. These respirators protect only against particles, not gases or vapors.
Level of Protection Rating: ASTM Standards
Level 1: low barrier protection for general use for low-risk, nonsurgical procedures and exams that do not involve aerosols, sprays and fluids.
Level 2: moderate barrier protection for low-to-moderate levels of aerosols, sprays and fluids.
Level 3: maximum barrier protection for any situation that has the potential for exposure of heavy levels of aerosols, sprays and fluids. Typically includes 4 layers of construction.
Level of Protection Rating: European Standards
Type I: bacteria filtering effectiveness > 95%.
Type II: bacteria filtering effectiveness > 98%.
Type IIR: bacteria filtering effectiveness > 98% and splash-resistant.
The "4 Fs" of Mask Selection
Filtration: When dealing with aerosols, which are typically smaller and lighter particles, high filtration masks will allow less particles through the mask. An N95 would be an example of a high filtration mask followed by a Type IIR.
Fluid resistance: Fluid-resistant masks do not allow fluids to be absorbed into the material. They are often chosen by medical professionals when there is any chance of blood or other bodily fluid splatter. Fluids will bead on the outside of the mask and reduce the chances of particles from the fluid to come through the mask. ASTM level 3 masks are highly fluid resistant.
Features: Mask attachment is typically either ear loop of ties. Anti-fog film, foam and tapes reduce fogging on shields and protective eyewear. Integrated shields help protect one’s eyes against droplets and fluids.
Fit: Even the correct mask could put you at risk if it is not worn correctly. The nose and mouth must be completely covered. A good seal around the face or minimal gaps will decrease the risk of inhalation exposure.
Correctly Donning a Mask
- Before putting on your mask, wash your hands with soap and water for at least 15 seconds or use alcohol-based hand sanitizer.
- Secure the elastic loops of the mask around your ears. If your mask has strings, tie them securely behind your head.
- Cover your mouth and nose with the mask and make sure there are no gaps between your face and the mask.
- Do not touch the front of the mask while you wear it. Wash your hands with soap and water for at least 15 seconds or use alcohol-based hand sanitizer if you accidentally touch your mask.
Correctly Doffing a Mask
- Wash your hands for at least 15 seconds or use alcohol-based hand sanitizer containing at least 60% alcohol.
- Don’t touch the front of the mask or your face.
- Carefully remove your mask by grasping the ear loops or untying the ties. For masks with a pair of ties, unfasten the bottom ones first, then the top ones.
- If your mask has filters, remove them and throw them away. Fold the mask and put it directly into the garbage (or laundry, if reusable)
- Clean your hands again.
Cleaning a Reusable Face Mask
You should clean your mask after every wearing. This reduces the risk of spreading the coronavirus or other germs.
- Bandannas, face scarves and masks made of fabric, such as cotton, can be washed in your regular laundry using hot water.
- You can also hand wash your mask, using hot, soapy water. Scrub the mask for at least 20 seconds, and dry them on high heat in the dryer.
- Disposable, blue surgical masks cannot be laundered or cleaned and should be thrown away and replaced at least daily.