The Case for Low-Occupancy Elevators
I was listening to the Washington Post Reports on podcasts while running this morning. At the end, the podcast had a little blurb on elevators that I found interesting, but unsatisfying. In it, the reporter, Ben Guarino, talked about elevators being unique, enclosed, etc., then made reference to a few things that “we” should do (e.g. use high efficiency air filters, maintain spacing), primarily based on his opinions. That was it. If felt like the piece lacked a bit of what’s referred to as “solutions journalism”, which essentially means you report the information, but you also offer some specific (even evidence-based) advice. Here’s just a bit more on the subject of elevators, if you are returning to work in the time of COVID:
Case 1. Touching.
I’ll take the most liberties v/v science here, just based on personal experience. Most people don’t touch one another in an elevator, unless it is packed. In the era of COVID, I’m guessing people will try to avoid packing elevators. Don’t touch other people if you can help it.
Case 2. Respiration and Synchronous Occupancy.
Say you’ve been working from home and staying healthy. You wake up Monday and get to the office first. You ride the elevator alone up to your floor and begin work at your desk. That elevator ride sure seems low-risk. The chance of you giving yourself a new coronavirus infection is, um, zero. Say, instead, you arrive at the same time as another eager beaver and ride the elevator together. Now, the chance of one of you sneezing, coughing, breathing and giving the other coronavirus is non-zero. However, it’s still low, because the chance of one of you having COVID is based on two persons, conditional probabilities and the prevalence rate for your population. Say, instead, there are three of you. Not only do the risks and consequences of transmission increase because there are now three people who might pass on the virus, but because there are twice as many potential recipients as in the two-person case. The bottom line here is that you want as few people on the elevator as possible at any given time.
Case 3. Respiration and Asynchronous Occupancy.
You might also be worried about riding an elevator after an infected person rode it. If that person coughed or sneezed, are there droplets on the surfaces of the elevator? Are there still smaller droplets floating around the elevator compartment? Based on a review of some literature on the subject, I would assert that small droplets are the bigger concern. According to an article by Justin Morgenstern, found here: https://first10em.com/aerosols-droplets-and-airborne-spread/, droplets are often “divided into small droplets…and large droplets. Large droplets drop to the ground before they evaporate, causing local contamination. Disease transmission through these large droplets is what we often refer to as “droplet/contact spread”, where disease transmission occurs because you touch a surface contaminated by these droplets, or get caught within the spray zone when the patient is coughing. Aerosols are so small that buoyant forces overcome gravity, allowing them to stay suspended in the air for long periods, or they evaporate before they hit the floor, leaving the solid particulate (“droplet nuclei”) free to float very long distances, causing what we often refer to as “airborne” transmission. (Nicas 2005; Judson 2019).” Just as with other surfaces, you can wash your hands or use antiseptic after touching the surfaces of elevators (buttons, handrails, etc.). Thus, large droplets are a risk you can manage. Aerosols remain in enclosed spaces for several minutes after someone sneezes or coughs. Just how much and for how long is determined by air exchange (e.g. elevator doors opening and closing, ventilation systems, etc.). In a situation in which you enter an elevator and don’t know who was in it before you, it is hard to judge or control your aerosol risk.
Case 4. Combined Synchronous and Asynchronous Risk.
Xiaoping et al., conducted a study in which the authors simulated respiratory droplet distribution that can be found here: https://www-tandfonline-com.du.idm.oclc.org/doi/full/10.1080/10789669.2011.578699
In the study, the authors found that there were two risks to a room co-occupant – direct and indirect. The greater risk, as modeled, was direct exposure to droplets. This is when someone sneezes or coughs in your direction. The lesser risk was indirect droplets (small droplets that aerosolized and filled the room).
The following table comes from the Morgenstern article, although it’s adapted from a 2006 study by Morawska:
Note the numbers and distribution of small aerosols. While it’s highly unscientific, I draw the following conclusions from these data and my readings on this subject:
- Wear a face covering. Most people reflexively tell you to do so to protect others (which is true), but I also think it protects you in this case. Check out the simulated cough data from the Xiaoping study:
Ask yourself — would you rather have a barrier between you and the person doing the coughing? Sneezes and coughs travel, so “social distancing” in an elevator isn’t sufficient.
- Exit the elevator if someone does cough or sneeze (maybe even hold your breath?). As you can see from the time measurements above, it takes seconds for a room to fill with aerosolized particles (or carbon dioxide, as is modeled in this case), once someone coughs. Indirect exposure is inevitable, but you can minimize the time you are exposed.
- Don’t talk (or sing) in the elevator as a courtesy. You may be infected and asymptomatic, and everybody should do their part. Plus, who knows if you can carry a tune.
- Encourage your company or building manager to take steps to reduce risk. A simple rule might be to limit elevator occupancy to four people at once (if it’s an ordinary office-building sized elevator). The building manager could also conduct cleanings more frequently, take elevators out of service periodically if there’s a concern around asynchronous transmission, etc. Your employer might offer added flexibility around work hours in order to reduce peak elevator utilization.
- Pay attention and adapt. If you are worried about riding the elevator, use it at off-peak times or take the stairs. Maybe even learn a bit about the elevator’s ventilation system and whether it helps with airborne viruses.
The following two articles are interesting reads that provide some added information on the topic: