Face Masks: the air filters we never thought we’d be wearing

Face Masks: the air filters we never thought we’d be wearing

Pre-pandemic, I grudgingly used face masks to protect from dust and allergens, like when mowing the lawn kicked up dust, or sanding wood projects filled the air outside with dust.  I knew when I should have worn one…usually by a raging sinus headache the next morning.  Nowadays, concerns for our own or others’ health mandates wearing masks in public settings for a large portion of the year.  But–what are the risks versus rewards of masks?  What do they really do for us?

The CDC has plenty of guidelines about masks, including that masking is a “critical public health tool for preventing spread of COVID-19”.  Masks are made to contain droplets you breathe, sneeze or cough out, and provide some protection from droplets from others.  Respirators are meant to filter the air you breathe as well as contain your droplets.  It’s not hard to tell which are masks and which are respirators, according to how loosely they fit, and the materials and style in which they are made.  The CDC outlines the four types of masks and respirators: 

• Cloth: they should fit well, have a nose wire, and you should not be able to see light through the fabric.  Regulations now prohibit any “exhalation valves” that would allow droplets to escape.  Lots of innovators have offered new designs for cloth masks, even ones that filter more N95 respirators.  Most cloth masks are washable, and wearers need to have clean replacements ready if the mask gets wet or dirty.  Wet masks do not filter properly and increase the leaks around the edges of the mask. 

• Procedure masks, or “medical masks” are typically the light blue variety that are now readily available in most stores.  They are made from “non-woven” material that can be mass-produced and sold inexpensively so that dirty or wet masks can be disposed of and replaced with a clean one.  Make sure to wear them with the blue side out (or if your mask is totally white, with the soft side toward your face) and to pinch the nose wire to fit snugly.  Cloth masks should be disposed of when they are wet or dirty.

• Respirators include N95 and KN95 masks that have markings (N95, KN95) to identify their authenticity. Respirator masks should also be disposed of when they are wet or dirty, but if they are only gently used, can be reused by letting them dry out (see more at the end of this post).  It’s important to check if the N95 or KN95 mask you are using is authentic, as many fakes are being marketed and sold in the US.  There are no authorized “children’s mask” in the N95 variety; nor do they have earloops.  

One widespread concern about using masks is their propensity to increase our intake of carbon dioxide (CO2) due to retaining exhaled CO2 in the mask.  Most medical experts say that there is no increase in retained CO2 due to masks, including this video of a respiratory therapist wearing one for 6 hours, with her oxygen and CO2 levels monitored.  However, studies such as the following have shown that elevated CO2 levels are present, and even this Mayo Clinic article mentions that CO2 levels do not increase with medical and cloth masks, but does not say the same for KN95 and N95 masks. 

• This study of 11 individuals at rest shows that the levels of CO2 in their mask are elevated after only 15 minutes. The study evaluated KN95 masks, valved respirator masks, and powered air purifying respirator (PAPR, which assists in breathing by using positive pressure inside the mask).  The measurements taken for KN95 and valved respirator masks after 15 minutes showed CO2 levels above the threshold for short-term limits (TLV-STEL) which are set by the National Institute for Occupational Safety and Health (NIOSH).  They are much higher than the long-term limits (TLV-REL) set for 8 hours of exposure.   However, measurements using the PAPR were only slightly above the TLV-STEL.  The study concluded that hypercapnia was a real possibility for healthcare workers using masks for extended periods, but use of PAPR prevents relative hypercapnia.  

• This study shows levels of CO2 while volunteers are at rest sitting or standing still with a mask hovers at approximately 500-700 ppm.  While using a mask, the CO2 concentration in the mask elevates on average to 2200 ppm while sitting or standing still, approx. 2500 when walking at a pace of 3km/hr with a mask, and approx. 2900 while walking at a pace of 5km/hr with a mask.  The conclusion cites that “concentrations between 1,000 ppm and 10,000 ppm can cause undesirable symptoms such as fatigue, headache and loss of concentration”, so those who are required to wear masks for long periods like students, bus drivers or cashiers may be affected.

• Computational fluid dynamics were used in this study to show that due to the tight fit and mask composition in N95 respirator masks, CO2 levels, water vapor, and temperature are all increased inside the mask.  This leads to excessive CO2 inhalation (up to 7 times more per breath) and reduced heat transfer inside the nasal cavity (which causes the wearer to feel that they have not taken a full breath).   The authors suggested that wearers of this type of mask should limit the time the mask is worn. 

The takeaways from these studies show that it’s not advisable to wear respirator masks like the N95 unless you are in close proximity with unknown and known sources of SARS-CoV-2, and then only for shorter periods of time.  Most of us may wear well-fitting and designed cloth and procedure masks, and there are some great options for specific use out there:

• Since it’s important that masks fit everyone well, Enro has developed their mask in 6 sizes, making it exceptionally wearable, washable and durable, with an anti-microbial coating. 

• Seri face masks by Serionix are very soft, comfortable masks with refills that come in a choice of MERV 13 or MERV 16 filter material. 

• Clear masks solve the problem of not being able to see half of our faces and expressions!  ClearMask seems to be the leader for medical and professional use, but many others are offering different designs with comfort and anti-fog characteristics.  MaMo Creations is a favorite among teachers and other communicators. 

• The Vocaleasemask offers singers and performers acoustic transparency of materials for greater clarity, and a design for full range of face motion and easier breathing.  It achieves particle filtration above level 2 (the higher level) of the ASTM Standard Specification for Barrier Face Coverings (ASTM F3502-21).

• Sunnie Face Shields are not masks, but they are popular for protection against droplets as mask requirements are relaxed.  They are very light, anti-fogging, scratch-resistant and extremely durable.  

Now, how can I wear the same mask day after day, safely? 

• Sometimes, due to shortages, healthcare professionals must re-use their masks. Disinfecting N95 and KN95 masks with soap and water, bleach or even alcohol decreases their effectiveness.  The best way to disinfect these type masks is actually just to let them dry for 48-72 hours.  

• If you don’t get a chance to wash your cloth face mask everyday, we also recommend letting it dry out (don’t store your mask in a plastic bag!); 

• You can natural sprays to refresh it and remove odors, such as Cavere, which uses 70% ethanol (alcohol derived from corn or soybean), water, glycerin, peppermint oil, echinacea extract, eucalyptus oil, citric acid, and a few other ingredients.   

• Mask sanitizing sprays such as CovaGuard use Benzalkonium Chloride (BAC), which does kill viruses but have been known to induce asthma in cleaning workers, decreased lung function in farmers, and greater immune reactions and decreased fertility in mice, among other effects.  

Masks are definitely equipment that we hope will be rendered obsolete soon, but in the meantime, we can keep on innovating with them for better comfort and efficacy.

Photo by Yoav Aziz on Unsplash