Covid-19 and Construction #4 (May 16)

Two months ago, I first blogged about Covid-19. Since then, much has changed. Way more than I expected back then.

OpenTable has a spreadsheet for restaurant visits in 36 states, plus a few other countries. Here is their US data in chart form:

It only took two weeks to drop from normal (Mar 8) to zero (Mar 22). Many Governors shut down their states during that period, but the public was usually ahead of them by a few days. The collapse was close to simultaneous across the whole US, and also in Canada and most of Europe. Reopening started a couple weeks ago in a few states and countries, but it’s still very sparse.

What will Covid-19 do as social distancing relaxes? It may fade out for the summer as flu does. Maybe contact-tracing and moderate distancing will be enough to keep it controlled. Maybe there will be exponential outbreaks. Most people are taking it slow, which helps. Those who rush off to crowded bars and church services will be our guinea pigs.

Meanwhile, most of what I said back in March still makes sense. Here’s a slightly revised recap of my advice for construction companies:

  • Stagger work hours & locations. The less time people spend close to each other, the slower disease spreads.
  • Be clear with employees and subs. Send them home ASAP if sick, or don’t even let them come in. This might be time to start paying sick leave. Emphasize the need for testing and self-quarantine. Get a non-contact thermometer, and check people for fever.
  • Be clear with clients. If you work in client homes, let them know your plans. You might need to add plastic sheeting barriers, and sanitize more thoroughly at day’s end. Switch to outdoor work, if possible.
  • Take the usual precautions. Wash hands often. Sanitize surfaces that are touched frequently. Cancel group events. Practice social distancing. Listen to local & state health departments. Most are developing reopening guidelines now. The rules probably will be tweaked as time goes by.
  • Wear face masks. Back in March, CDC said not to use masks. Fortunately, their guidance has changed. I think masks may be the #1 way to stay safe, and still run a business. It’s worth elaborating.

Why wear face masks?

Covid-19 spreads mostly by respiratory droplets, which come in a wide range of sizes. Coughing and sneezing produce tons of them. Talking creates plenty. Even normal breathing makes some. The bigger droplets blow out a few feet, then drop quickly. They coat everything with virus gunk- that’s why it’s important to wash hands, and not touch your face.

The smaller droplets (aerosols) linger in the air. They can travel 20+ feet on air currents. Inhale, and they go straight into your airways and lungs. There is debate about how important aerosols are for Covid-19 transmission, but evidence is pretty good that they do cause many infections. Indoor spaces are more risky, especially when people are together there for hours. Air circulation (air changes per hour) makes a big difference.

Snot/saliva/ejected droplets from an infected person will have between 6 million and 2 billion viruses per cc (1 cc = 1/5 teaspoon). Fortunately, the droplets are very small, so only some contain a virus. Unfortunately, there are lots of them. Speaking produces 1,000 to 10,000 small droplets per second. Each cough makes a few thousand mostly bigger ones. Sneezes can make 40K, some of them huge.

Whether a droplet infects you is a matter of chance. Even if you inhale or ingest a virus, many of them get trapped in mucus and never reach a cell. Eventually they exit inside a booger. Others are killed by your body’s innate immune system, which has many anti-viral tricks. It takes a reasonable number of incomings, for even one to infect a cell.

Face masks work in both directions, to prevent that. Outbound, they catch virus droplets that infected people emit into the air and onto surfaces. They make other people safer. Inbound, an N95 removes 95% of aerosols, and almost all larger droplets. Surgical masks are less effective for inbound protection, but still pretty good. Even a bandana is better than nothing.

If everyone is masked, very little gets past the two different filters: one on the cougher, and one on the coughee. The risk of infection goes way, way down. Masks also reduce the odds of getting a really bad infection. I didn’t find any specific data for the effect of initial doses for Covid-19. However, almost all diseases are more deadly if you start with a lot of virus, rather than just a little.

It’s a matter of exponential growth. Once a virus invades a human cell, it starts producing duplicates. Those infect other cells, and it snowballs. The virus count zooms up inside you on a scary steep curve, just like it did globally in March.

Your adaptive immune system has many great ways to kill pathogens, but it takes time to ramp it up. If you started with one virus-infected cell, your defences probably can defeat the infection before it gets too big. You may not even notice any symptoms. Start with a few thousand, and you’ll be very sick. Start with a million or a billion, and you’ll probably die. That’s why Covid-19 kills young, healthy medical workers, especially when they don’t have proper PPE. They absorb a massive dose, the virus starts off strong, and it beats their immune response.

With masks all around, good sanitizing and careful air circulation, you probably can run safe construction projects. At least til Fall.

Dennis Kolva
Programming Director

Author: Dennis Kolva

Programming Director for Turtle Creek Software. Design & planning of accounting and estimating software.