In a recent New York Times article(1), Dr. Joseph Allen, director of the Healthy Buildings program at Harvard T.H. Chan School of Public Health, said there is much we can do to fight against Covid-19 using tools readily available to us. We’ve all heard the admonitions to wash our hands for at least 20 seconds and to avoid touching our eyes, nose and face, but what else might we be able to do to potentially fight off viruses in the laboratory, office and in our homes? Dr. Allen points to many additional tactics that could prove useful like filtering the air in our buildings, allowing in more fresh air and keeping the humidity in a specific range to inhibit growth of the virus.
In addition to Dr. Allen’s advice, the CDC also states, "Generally coronaviruses survive for shorter periods of time at higher temperatures and higher humidity than in cooler or dryer environments. However, we don’t have direct data for this virus, nor do we have direct data for a temperature-based cutoff for inactivation at this point. The necessary temperature would also be based on the materials of the surface, the environment, etc. Regardless of temperature please follow CDC’s guidance for cleaning and disinfection."
With this in mind, we went to our database to investigate typical humidity readings in laboratories. From the article by Dr. Allen, he recommends a humidity range from 40-60%. Not surprisingly it varies widely by season and by geography.
The Element-A is a wireless, battery-powered, Internet of Things sensor used by numerous laboratories, clinics, and animal research facilities to monitor and track temperature, humidity, light levels and pressure. The Element-A takes a reading every 15 seconds and stores these data in the Cloud. Analyzing the data by region and time of year gives us some insight into typical conditions encountered in laboratories and other facilities. Many Element-A’s are deployed in cold rooms, incubators, desiccators, and environmental chambers. These were excluded from this analysis.
Not surprisingly, readings in the northern part of the USA show relatively low humidity during the winter months. It’s cold outside and cold air doesn’t hold moisture very well. Heating up the air indoors further reduces the relative humidity.
We tracked data from ambient sensors around the USA.
For each element, the daily number of hours that the average RH was below 40% or above 60% were counted.
The total number of days outside of range per month was aggregated by location (so multiple elements in the same Lab did not give that location extra weight), and finally average by region and division.
The regional and division averages per month are presented below.
The graphs below show the average daily relative humidity and temperature in each region. To calculate the averages, first, all elements from a given site are averaged to get the site average. Then, all of the site averages are averaged on the regional level. It is clear from the graphs below that temperature is typically controlled around 22°C ± 2°C, however, the humidity is not controlled. Generally, relative humidity does not exceed 60% in any region. This is due to the drying of air as it passes through the HVAC system. However, the lower bound of the relative humidity is at the mercy of the outdoor humidity, and some regions (North Central and Northeast) are more prone to exceptionally dry winters, with relative humidity consistently <40% for most of the winter and early spring.
Regional segmentation used in this analysis is shown below. All data was taken from Element-A sensors monitoring indoor ambient conditions.
Humidity by region
Indoor temperature by region
The graphs below show the average number of days in which the relative humidity falls outside the 40-60% window for at least 1 hour per day.
The graphs below show the average number of days in which the relative humidity stays inside the 40-60% window for the entirety of the day (inverse of above).
The graphs below show the average hours per day in which the relative humidity falls outside the 40-60% window aggregated by month and region.
Elemental Machines is in no way offering medical advice by presenting these data. However, based on suppositions from Dr. Allen and the CDC about survival rates of coronavirus with temperature and humidity, one can make some changes to the environment to try to maintain temperature and humidity in desired ranges. Working remotely from a laboratory can make this even more challenging. Having a robust remote monitoring system in place to continuously measure both temperature and humidity is a vital tool.