I am not an expert in this space, but my credentials are reasonable. This is my personal outlook, not that of any employer.
There are heartbreaking stories of hospitals calling for PPE – especially facemasks – and courageous stories of people cobbling together devices to reduce the likelihood that a healthcare provider could get ill while treating a patient with COVID19. This post leans heavily on information from the Smart Air Filters website written by their CEO, Paddy Robertson. I summarize those documents here.
Step 1: Reduce the Danger of the Environment; Declare War on the Droplet
The virus dies as an aerosol. It lives in droplets. When there are enough coughing patients in the room, the likelihood of infection grows because the air is full of droplets.
Before being concerned with PPE, address this issue as much as possible:
- Increase air turn over.
- Filter the air.
- Change the filters often.
- Put out specific air treatment technologies – such as room-air cleaners, ionizers and UV-C light, that are known to kill the virus.
- Add room air cleaners (Dyson, Camfil, Austin Air, etc.)
Before Improvisation – How do Masks Work?
Masks involve several layers of technical fabrics (often nonwovens or other porous materials). The performance of the mask comes from the combined performance of the materials.
Types of Masks
N95 or NIOSH masks (also N99, N100) are designed to capture particulate. They fit snug to the face, but they are not necessarily droplet proof.
Surgical masks are droplet proof, but they are exposed on the sides, so that an aerosol could get around them.
Surgical N95 Masks, or S95, have the best of both worlds. They have high capacity of an N95, but have also been through the droplet testing of the surgical standards. (Nelson Labs is the dominant provider of testing to these standards, including ASTM-F2100.)
The Ideal Mask & PPE For Corona Virus
Given the dangers of COVID19, the ideal mask would appear to be an S95 mask, that is changed out on a regular basis. All of these masks are designed to be disposable. It would be reasonable to wear more extreme protective gear – protective shielding – and perhaps even have a powered air purifier attachment.
Masks work because they have the right amount of breathability (air flow), efficiency (what % of particles do they catch), and life. Life is the easiest – masks are designed to be disposable with short lives.
Efficiency is harder. Small particles – those below 0.3 micron – the formal cut off of HEPA measurement, are often captured with charge. In filtration particles can get caught primarily by making physically small holes (mechanical filtration, where there is a physical mechanism that stops the particle), and electrostatic filtration (where the filter media – the facemask) has a charge, that is used to attract the particle. For small particles, especially below 0.3 micron, that electrostatic force is powerful enough to have a big impact on filtration. Charged filter media is widely used in facemasks.
Filtration has a lot of bad jokes – this one is about breath-ability and air permeability. A table is 100% efficient at filtering your dinner from hitting the floor. Get it? However, the breath-ability is awful. Likewise, if you make a facemask that is too efficient, it is hard for the wearer to breath. When the air flow gets too low, or when the resistance is too high, this hurts the wearer’s compliance. Healthcare workers start to slide the mask over, which defeats the whole point of the mask in the first place.
The layers of a surgical and also S95 masks, are also going to have a hydrophobic treatment to prevent droplets from passing through, and therefore be able to slow down the passage of bacteria and viruses. They do not stop the water flow forever. If we run a water hose over a surgical mask, the mask becomes inundated, and its useful life is over.
Thoughts on Mask Cleaning
There are two characteristics of the mask that are important to preserve in cleaning:
- DRY. If the mask is wet, it is likely easier for bacteria and viruses to get through the existing fluid. Make sure the mask is dry!
- CHARGE. Charge is part of the efficiency. This improves also by drying the mask out, but also look to give it some static charge. Rub it on wool, run it over an incandescent lightbulb, etc.
My personal priority would be to focus on not getting the mask too wet. I’d rather have multiple masks that I’m swapping out often, making sure that no liquid ever gets through, than to have one ‘new’ mask that I wear all day.
Masks work worse after washing. Don’t wear a wet mask! Masks depend on charge to work. Find ways to add back charge.
List of Improvisation
If I had to, I’d:
- Use a form fitting mask design.
- Use two pillow cases from the research above.
- I’d add in a pocket to put in a high air perm insert, and would use something like a swiffer dryer sheet. Modern masks work based on charge.
- I’d never wear a wet mask. A saturated mask gives disease a faster path to travel.
- I’d do everything possible to reduce the droplet danger in the room.