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Let’s Talk Toilets

Preventing the spread of COVID-19 in office restrooms

We all have a lot on our minds lately. This is especially true for anyone in the office industry. Landlords and office managers around the country are trying to keep on top of the ever-changing return-to-work guidelines from the World Health Organization, the Centers for Disease Control, and local authorities. The last thing they want to think about, the last thing any of us want to think about for that matter, is toilets. But as a consulting engineer, I feel obligated to bring up this issue.  

Every presentation I make to my commercial real estate clients these days includes a slide on airborne virus transmission through two origins. The first is familiar to anyone who follows the news. The COVID-19 virus commonly spreads through droplet nuclei or aerosols that typically travel from an infected person’s cough, breath, speech, or sneeze. The other origin is less familiar: the flush of a toilet. This method of transmission tends to startle my audiences. It’s also somewhat unpleasant to contemplate. But anyone concerned with reopening of offices, has an obligation to do so. 

The Bad News

Here’s what you need to know: Studies have shown that the coronavirus can stay active in feces for more than 30 days. When people flush a toilet, the water-mixing activity creates a plume that shoots out droplets and aerosol components that can carry the virus. A recent study published in Nature measured the concentration of viral RNA in aerosols in different areas of two Wuhan hospitals during February and March. The concentration in toilet areas was far greater than the levels in isolation wards and ventilated patient rooms. 

Joseph G. Allen of Harvard University’s T.H. Chan School of Public Health mentions other relevant findings in an op-ed published by the Washington Post. One case on an airplane might have originated in the airplane bathroom, he notes. He also reports that in China, aerosols originating from flushing in a sick patient’s apartment on the 15th floor of a building were found on the vacant floor above and on 25th and 27th floors of the building, where people who had recovered from earlier bouts of COVID-19 lived. 

Yes, there are still many unknowns about the coronavirus. But these findings make it clear that restrooms warrant a place on the safety agenda. 

The Good News

The good news is that the risk of virus transmission through toilet plume is less than the risk through interpersonal interactions that take place without masks at a distance of less than six feet. Furthermore, small amounts of the virus particles are unlikely to get you sick. I’m not a medical expert, but from what I’ve learned, the danger arises from inhaling hundreds of the particles. I like to use a smoke analogy. Imagine that you’re in a room where someone starts smoking. People start coughing, demonstrating that there’s too much smoke in the room. To decrease the concentration, you can open the windows or turn on a filtering mechanism. 

Well-ventilated restrooms, like the ones you’ll find in most Class-A office buildings, decrease the concentration of virus particles. If you walk into a restroom and hear an exhaust fan running or the air moving, you are in a room where the “smoke” is being continuously exhausted. To be extra careful, wait a few minutes to enter the restroom after someone exits. If you want to be extra-extra careful, bring in a bottle of disinfectant with you and spray liberally. 

Risks increase in restrooms with little ventilation beyond a window, a common scenario in public schools or in Class B or C office space. Even in these cases, however, there are ways to mitigate the risks. One method is quite simple. Put a lid on it! Many public bathrooms have toilets without lids to streamline cleaning tasks. Now, clearly, is the time to add the lids. And restroom users should make sure to flush the toilet with the lid down. 

Kill, Capture, or Dilute 

But let’s go beyond the lid. When we assess office environments, we consider three mitigation strategies: kill, capture, or dilute. Several of these strategies apply to restrooms. 

To kill virus particles, you can turn to UVGI lighting. UVGI stands for ultraviolet germicidal irradiation, which operates on the UVC spectrum. It’s effective, but there are downsides: One, UV light is dangerous for your skin and eyes, so it’s important to make sure that there is no occupancy in the bathroom when the light is shining. Two, the more barriers there are in the bathroom, the more UVC lights are needed—all surfaces must be exposed to the light. 

One newer alternative is Xenon pulse technology, which is more compact (miniaturized) and portable than traditional UVGI lighting. This technology enables UV lighting to be placed in locations where it wasn’t previously possible. Landlords, for example, are using Xenon pulse technology to disinfect elevator cabs after each ride. You can also find this technology in the New York City subway system, where it is disinfecting cars nightly. 

Capture strategies direct air through a filter medium that simply catches virus particles as they pass through. To accomplish this in restrooms, you can introduce local air purification or air filtration units in the ceiling cavity. Both methods are effective with the proper levels of filtration. We recommend using either an electronic air purifier that filters ultrafine particles or high-efficiency particulate air (HEPA) filtration. Similar to the way in which smoke eaters of the past worked for cigarette smoke, these units placed in the ceilings recirculate air through filters that continuously scrub the air of virus particles in the restrooms. Higher-end models even have a UV light shining on the filter to kill the virus particles after they are captured. 

The third method of removing the smoke or virus particles from the air is dilution. To combat odors, restrooms are usually equipped with a form of ventilation that exhausts air to the outside. Typically, this involves the installation of a fan above the ceiling with diffusers above the toilets. We highly recommend that the system be exhausted continuously outside the building—opening a window is not sufficient. This dilution method is a straightforward fix, but it does require time and budget. 

Other precautions apply to bathrooms in general. Since the virus can live on bathroom surfaces for up to two days, frequent cleaning is essential. Ideally, restrooms should be as “touchless” as possible. Many buildings already have touchless sinks and fixtures. If the entrance/exit to the restroom is not touchless, you can compensate by putting some paper towels and a garbage can by the door. Users can dry their hands, throw one towel out, and pick up a clean one to open the door handle. 

The Future

In my experience, people have short memories. After a COVID-19 vaccine becomes available and the pandemic abates, people will probably become less concerned about the engineering of restrooms. That said, attention to indoor air quality, which was already gaining momentum before the pandemic, will persist. And COVID-19 may prompt changes in restroom design. For example, we may start to see restroom designs with ventilation in each individual toilet and closer to the toilet. 

For now, however, office landlords, property managers, and occupants have to make do with what they have. But there are many ways to minimize the risks in restrooms as employees start returning to offices. Every building is different, but most can accommodate some combination of the kill, capture, or dilute strategies outlined above. 

If you’re concerned about budget, keep in mind that any safety measures you implement can help to prevent many kinds of viruses, including the flu. And employees prefer hygienic spaces. So you will attain a long-term return on investment. Think of it this way: When it comes to restrooms, your efforts to protect against the spread of viruses in waste will not go to waste.

Propmodo is a global multimedia effort to explore how emerging technologies affect our built environment.

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