Amid the ongoing COVID-19 coronavirus pandemic, the U.S. is facing the shortage of personal protective equipment (PPE) to avoid contamination. Face masks, including N95 that provide more protection than loose-fitting surgical masks, are becoming scarcer as the demand has increased with the outbreak.

The Federal Emergency Management Agency, which has a strategic reserve of N95 masks, distributed the safety gear to states that are especially in need. The shortage has motivated a number of DIY (do-it-yourself) efforts but the stakes are high when designing an alternative mask. Here are some qualities that N95 masks or the equivalent must have:

1. The mask has to filter out the virus:

The reason behind the mask being called N95 is that it can filter out at least 95 percent of particles of all sizes -- including something less than 0.1 microns in size -- from the air. The mask, thus, needs to keep the virus from reaching your nose and mouth. Polypropylene is a commonly used material for N95 masks.

2. More than one filtering mechanism is required:

More than one filtering mechanism is required in N95 masks to make sure if one mechanism fails, the other can help block the virus. A National Academies of Science, Engineering, and Medicine (NASEM) report described three general mechanisms that N95 masks have to pull particles from the airstream: Inertial impaction, diffusion, and electrostatic attraction.

3. The mask shouldn’t suffocate you:

It is important that the mask that you wear does not block your breathing process and the breathing resistance is in line. If you find it difficult to breathe while wearing a mask, the purpose is not solved.

4. Mask has to fit and form a seal with your face:

The mask that you wear should not be lose-fitted, and must form a tight seal with your face. A method of testing if the mask you have put on is the right fit for you is to have someone spray one of the following around you:

  • Isoamyl acetate, which smells like bananas;
  • Saccharin, which leaves a sweet taste in your mouth;
  • Bitrex, which leaves a bitter taste in your mouth; and
  • Irritant smoke, which can cause coughing.

If you are able to smell one of the first three or coughing from the fourth, the mask is not keeping out what it’s supposed to.

5. The mask shouldn’t shed:

The material used for the mask should not shed. Fibers and little particles can go straight up your nose and potentially down into your lungs.

6. The mask must be durable enough:

The mask must be reasonably resistant to situations like breathing out water vapor from your mouth or spit that may be released while you talk.

7. The airstream and filtering portion of the mask should be large enough:

Narrow passage in the mask could increase breathing resistance. It could also lead water droplets to coalesce. Coalescing water droplets can make the filter wet and thus decrease its effectiveness.

It is important to make sure the DIY mask has the mentioned qualities, else the masks are close to useless in protecting against COVID-19.

“Homemade face masks are not considered personal protective equipment [what health-care professionals call PPEs], and should be an option only when there are absolutely no respirators or face masks left, and used with other protective equipment, such as face shields,” CDC spokesperson Arleen Porcell said in an email statement to the Wire Cutter. “It’s important to note that this strategy is considered a last resort and does not adhere to the typical standards of care in the US, but acknowledges the hard realities on the ground.”