Poor Ventilation May Lead to Higher Virus Infection Rates

Poor ventilation leads to increased virus transmission covid19 coronavirus offices schools

Offices and the workplace can be breeding grounds for viruses such as COVID-19. In this article, we’ll present data that shows how improving office ventilation and airflow may lower the spread of viruses like the coronavirus in the workplace.

Evidence of how Office Ventilation Affects Disease and Virus Transmission

There’s little evidence directly linking good ventilation with lower virus transmission. However, there’s a huge amount of data linking bad ventilation with higher virus transmission rates. The WHO has compiled a list of over 65 studies which show this phenomenon.

 

Poor ventilation leads to increased virus transmission covid-19

 

In this list is a study undertaken in a NY elementary school in 19070s. In the study, scientists modelled an outbreak of measles in a the school. The measles were introduced by a second-grader, and subsequently spread to over 60 other pupils within the course of a month.

Elementary School Classroom Virus Transmission

They collected data including room ventilation rates, time spent in each room, and amount of virus in the air was collected. They used this to model the probability that each student would capture measles based on various factors. The scientists  called this the Wells-Riley Equation. While not perfect, this equation can be used to show how ventilation affects the probability of catching a virus.

Wells Riley Equation shows increasing air changes per hour in school or office reduces chance of virus transmission

The Wells-Riley model shows clearly how increasing room ventilation reduces the chance of virus transmission. This, in a nutshell, is what’s important.

In the US, ASHARE recommends a minimum of 0.35 air changes per hour (ACH) for a typical home. This model shows how increasing a room’s ventilation from 0.35 ACH to 1 ACH can more than halve the probability of virus transmission. That’s huge.

Increasing air changes per hour from 0.35 to 1ACH halves the probability and chance of virus transmission

Isn’t a 30% Chance of Virus Transmission a bit too High?

Some beady-eyed readers may think that a 30% probability of capturing the virus for low ventilation levels sounds very high. The scientists who created the Wells-Riley equation noticed this too. They explained how their first model was based on the initial sick person, who may have been very infectious:

Initial infector highly infectious virus transmission schools

They used subsequent cases to adjust the model, leading to much lower probabilities of virus transmission:

Measles virus transmission second model probability of virus transmission lower than first

Despite chance of virus transmission dropping in the 2nd model, the chance in virus transmission with ventilation is the same. Re-scaling the 2nd model above shows this clearly:

Ventilation important factor on Virus transmission reduction in schools and offices

It’s clear that increasing the ventilation from 0.35ACH to 1ACH can almost halve the probability of virus transmission.

 

Caveat 1: This model is based on only a single outbreak of measles in the 70s’. Although widely used, the Wells-Riley equation can only be used as an approximation.

Caveat 2: COVID-19 has been shown to be both droplet-transmitted and airborne-transmitted. The data above covers just airborne-transmission, and doesn’t show how improving ventilation can lower the transmission of droplet-transmitted viruses.

 

Bottom Line: How Ventilation Affects Virus Transmission Rates

Ventilation can have a direct impact the probability of virus transmission for diseases like COVID-19. The Wells-Riley equation shows how increasing room ventilation from just 0.4 air changes per hour to 1 air changes per hour may lead to a halving in probability of virus transmission.

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