Apr. 28 2020

T-shirts and Scissors: Make a DIY Evidence-Based Protective Mask

In early April, the White House announced new U.S. Centers for Disease Control and Prevention guidelines recommending that all Americans wear cloth face coverings outside the home. But with retail inventory largely on backorder, Americans have been forced to make do with alternatives like bandanas and scarves, or take their chances and go without.

Physician Virginia Dato, MPH ’92, published an evidence-based alternative: a do-it-yourself mask that almost anyone can create with a few simple ingredients: a t-shirt, scissors, a ruler, and boiling water. No sewing required. For those without access to retail options, wearing a mask made at home—using material on hand—could help reduce viral transmission in public places. (See instructions below.)

Dato published her mask design in the U.S. Centers for Disease Control and Prevention’s Emerging Infectious Diseases Journal back in 2006. Lately, for obvious reasons, her design has received renewed attention, becoming the journal’s number-one most viewed article in March.  On April 2, the CDC interviewed her for their Emerging Infectious Diseases podcast.

Dato had already earned her MD when she enrolled in the Columbia Mailman School’s executive MPH program to bolster her capacity for health services administration. She subsequently served as a public health physician for state health departments in New Jersey and Pennsylvania, specializing in communicable disease outbreaks—roles that required her to imagine worst-case scenarios. While the idea of wearing a respiratory mask is new to most of us, Dato started thinking about the protective role of masks among the general public during the original coronavirus outbreak—the 2003 SARS epidemic.

Watching SARS spread through 26 countries in just a few months, she realized that if such a virus became a widespread pandemic, the need to wear masks on busses and other places where people are in close proximity would quickly outstrip commercial supply. So, she set out to identify a solution that nearly anyone in any country could easily implement. The resulting design can be created with components available anywhere in the world—scissors, boiling water, and a heavyweight cotton t-shirt.

An effective mask must do three things: keep a healthy person from being exposed to infected fluid particles, keep an infected person from spreading fluid particles, and allow the user to breathe sufficiently to maintain activities. “Ideally, the mask works by having material filter all of the breathable air both in and out of the nose and mouth,” Dato explains. “I say ‘ideally,’ because a good fit is needed to do that. After all, air follows the path of least resistance. And you must be able to breathe through the mask while filtering out as many virus droplets as possible.”

Top-of-the-line commercial masks, like N99 and N95 respirators, boast superior fit and can filter out very small virus droplets. Dato aimed to mimic the fitted nature and the filtration capacity of N95 respirators by incorporating multiple fabric layers in the design and boiling the mask material, a t-shirt, to shrink the tiny holes in the cotton and sterilize it.

Commercial masks are laboratory tested for fit and filtration, rated on a 100-point scale; the top-of-the-line N95 has a fit factor of 100. At home, you can test the fit of a mask by putting your hand an inch or two from the mask and feeling the airflow coming in and out. If you feel air leaking above the nose or along the sides, re-adjust the mask. To ensure the kind of snug fit needed to keep virus particles at bay, Dato’s design instructs makers to wrap the t-shirt fabric in a specific pattern around the face and head.

Dato used sophisticated methods to test her homemade mask and found it protected the wearer from aerosolized particles with minimal leakage of unfiltered air. The mask achieved fit factors of 67, 13, and 11 in three users. This means that while the DIY mask is helpful for reducing risk in everyday situations, it isn’t appropriate for a healthcare worker.

While Dato appreciates the interest in her mask, she cautions that no mask is perfect, whether her own design, alternatives with elastic bands and filters, even respirator masks for healthcare workers that must meet OSHA and NIOSH standards. No matter the mask, it won’t make us impervious to infection. Masks are no substitute for other public health measures, such as washing our hands, and social distancing.

In the midst of the COVID-19 pandemic, Dato has been wearing her own DIY mask for non-healthcare settings, such as trips to the grocery store. She has also been trying out colleagues’ designs for DIY masks, including one published by researchers at the CDC.

Dato explains: “In public health, we’ve always been creative in trying to find solutions. There’s a term called ‘quick and dirty’ that in official terms is a rapid response. An outbreak response is never perfect, but in public health, you have to think on your feet and just figure things out.”

INSTRUCTIONS

1. Choose a heavyweight 100-percent preshrunk cotton t-shirt.

2. Boil the shirt for 10 minutes (this will sterilize the shirt).

3. Use scissors, a marker, and a ruler to cut out one outer layer (≈15 x 28 in) and eight inner layers (≈7 x 7 in).

4. Assemble and fit the mask using the guide below.