How can humidity levels affect the spread of viruses?
A key study done in 1986 showed that the indoor relative humidity (RH) level, or the amount of water vapor present in air, should be kept between 40 and 60% RH to reduce the transmission of viruses. Many studies have been done since that also support this guidance.
When the relative humidity level is kept between 40 and 60% RH, viral activity, or the infectivity of a virus, is decreased. In addition, this level of humidity protects our body’s built-in barriers to illness and assists the self-clearing mechanism of the airways in our respiratory system, which is our innate antiviral defense. It even ensures proper tissue repair function, especially in our lungs.
Humidity levels also influence the effectiveness of surface cleaning. Low ambient humidity (less than 40% RH) reduces the droplet size of viruses, allowing for a prolonged airborne period, which in turn allows for further travel distance. The low weight of the virus due to loss of water allows the virus to float through air, so it can’t be cleaned up with usual surface cleaning. Keeping the humidity levels between 40-60 % RH “knocks down” airborne viruses so they can be cleaned via surface disinfection.
While this applies to all buildings, schools are obviously among those that may benefit the most from the implementation of optimal humidity levels. In contrast to the cost of single-use, disposable safeguards like soap, sanitizer, and masks, a commercial humidification system will last for over 20 years while providing broad protection for building occupants against viruses like COVID-19, the seasonal flu, and others.
Do different viruses have different humidity tolerance levels?
Studies about the impact of humidity levels on viruses have been done for many years and around many different viruses, including the seasonal flu (Influenza A), Severe Acute Respiratory Syndrome (SARS), Middle East Respiratory Syndrome (MERS), and others. The studies have all found that these viruses are less prevalent and less infective when the indoor relative humidity level is in the sweet spot between 40 and 60 % RH.
How can schools monitor and maintain optimal humidity levels?
The RH level in a school building can vary greatly depending on climate, forced-air heating, mechanical cooling, and many other factors. We would recommend an evaluation of the relative humidity in different areas of a school – like classrooms, lunchrooms, nurse’s offices, etc. – using an inexpensive hygrometer to assess and monitor RH levels.
It is important to use the right equipment to add humidity in the air of a classroom. Commercial grade humidification equipment provides the control needed to ensure proper RH levels – not too low and not too high. Simple access to power, water, and drain is all that’s needed to get a system operational – think of anyplace there is a sink nearby.
As we navigate the COVID-19 pandemic, it’s a smart idea to look for hands-off approaches to mitigate the transmission of viruses, and the addition of humidity is a safe and efficient way to protect students and teachers.
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