99.6%

Innovation

There's a helmet for dentist appointments that blocks 99.6% of Covid-19 air droplets

Venturing outside your home is an inherently risky endeavor these days. But perhaps no necessary trip inspires more anxiety right now than your routine visit to the dentist.

Not only do you need to take off your mask in a room with a relative stranger, but you also need to open your mouth and keep it open for extended periods of time, all while someone works mere inches from your face. Going to the dentist is an essential aspect of good healthcare and hygiene. But in the time of coronavirus, it is an inherent truth that both patients and practitioners are at risk of transmitting infections to one another via airborne droplets.

Instead of skipping your twice-yearly cleaning — and potentially paying the price in cavities or worse down the road — a team of engineers from Cornell University has designed a transparent helmet to be worn during procedures that would create an internal vacuum to stop droplets exhaled by patients from reaching the open air.

In their simulations, the researchers found this helmet would prevent the spread of 99.6 percent of coughed droplets in only .1 seconds, or 100 milliseconds.

Why it matters — The researchers report the helmets would even be slightly more effective than entire room filtration systems, which can take up to 45 minutes to capture 99 percent of airborne droplets. The helmets could be a cheaper and more easily accessible alternative to expensive filtration systems, increase patient and practitioner safety, and get more people back into the dentist's chair faster than remodeling an entire building's air systems to suit our new needs.

"It would have a similar feel as driving with the windows down."

See also: Video of sneeze vortex shows a critical flaw in face shields

Here's the background — Telemedicine has exploded as Covid-19 made it increasingly difficult and risky to attend medical appointments in-person. But even routine dental work like a cleaning or check-up doesn't quite translate to video chat.

Using vacuum pressure, small droplets can be captured within the helmet and sucked up into a filtration nozzle.Jia et al. / Physics of Fluids

To get care, you need to go in-person. And, obviously, these appointments involve poking around patients' mouths, noses, or throats — areas which are essentially ground zero for the spread of Covid-19.

Screening people prior to their appointments and requiring practitioners to wearing N95 masks and gloves does help limit the transmission of the virus, but only to such a degree. Installing high-tech filtration systems in offices to create "negative pressure rooms" to stop droplet spread can help halt the spread, but they can also be prohibitively expensive.

To solve this problem in a more cost-effective way, this research team decided to focus on neutralizing virus transmission at the source: the nose and mouth.

In research published Tuesday in the journal Physics of Fluids, the researchers lay out their innovative, if a bit strange, design.

How it works — The helmet design itself looks like a futuristic clash between a deep-sea diver's helmet and the Cybermen in Doctor Who. In the simulated prototype, the helmets are made of a 1-millimeter thick transparent plastic with one opening at the top for an air-filtration nozzle, and one at the mouth and nose for medical access. The helmets were also designed with padding around the neck to create an air-tight seal.

The way it works is this: Once a vacuum seal is established, droplets from the mouth and nose are sucked up into the filtration nozzle before being expelled back into the air. Some droplets may become stuck inside the helmet, so it will require disinfection for repeated use.

Using computer models, the researchers investigated how droplets of varying sizes expelled during a cough might be captured by negative pressure created in the helmet by gentle vacuum pressure.

Dongjie Jia is a postgraduate student of mechanical engineering at Cornell University and first author on the paper. He tells Inverse the experience of wearing this PPE helmet would be similar to wearing a motorcycle helmet on the open road.

"It would have a similar feel as driving with the windows down," Jia explains. "The drop in pressure is relatively small, so there shouldn't be any discomfort."

During these simulations, the researchers observed the trajectory of 400 different droplets (divided evenly into four different droplet sizes).

In simulations, their helmet captured 99.6 percent of droplets in under one second.Jia et al. / Physics of Fluids

What they discovered — After analyzing the simulation results, the researchers report close to 100 percent — 99.6 percent to be exact — of exhaled droplets during simulated coughs were captured by their helmet and filtered.

Importantly, not all droplet sizes were impacted equally by this device. The heaviest droplets were more likely to escape the vacuum created in the helmet. Capturing these rogue droplets would require vacuum pressures too high for a wearer's comfort, according to the researchers. But, the researchers write, this shouldn't necessarily be cause for panic. The reason why is to do with Covid-19 itself.

Smaller droplets, which the helmet did capture, are more likely to linger in the air and increase Covid-19 transmission. Heavy droplets on the other hand tend to fall to the ground in 0.2 seconds, meaning they are less likely to transfer infection.

What's next — Next on these researchers' to-do list is to begin developing a physical prototype of this helmet to see how its effectiveness stands up to the real world.

"This proposed design is still at its very early stage if we are considering turning this into an actual product," Jia says. "The access port — face opening — shape is only for proof of concept and it would take intensive collaboration with field practitioners to come to a final design for the best accessibility and efficiency."

The team also plans to continue tweaking this helmet design's efficiency to broaden its clinical impact in the future. Such a helmet could make other procedures, like intubation, safer, too.

Abstract: Clinic encounters of dentists and otolaryngologists inherently expose these specialists to an enhanced risk of SARS-CoV-2 infection, thus threatening them, their patients, and their practices. In this study, we propose and simulate a helmet design that could be used by patients to minimize transmission risk by retaining droplets created through coughing. The helmet has a port for accessing the mouth and nose and another port connected to a vacuum source to prevent droplets from exiting through the access port and contaminating the environment or clinical practitioners. We used computational fluid dynamics (CFD) in conjunction with Lagrangian point-particle tracking to simulate droplet trajectories when a patient coughs while using this device. A range of droplet diameters and different operating conditions were simulated. The results show that 100% of the airborne droplets and 99.6% of all cough droplets are retained by the helmet.
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