Controlling the transmission of contagious diseases has always been a key issue for hospitals. Not only is this an environment that intrinsically hosts a lot of people with potential contagions, but there is also a continuous flow of visitors, new patients, and staff. Protecting people, especially those with compromised immune systems, is a universal priority and an ongoing challenge in the healthcare industry.
The Covid-19 pandemic brought the devastating potential effects of viruses to the forefront of all our minds, sparking numerous studies and overhauls of best practices to reduce transmission and prevent an outbreak such as this from occurring again. According to the Centers For Disease Control (CDC), there are three main routes of transmission:
- Direct large droplet transmission between people within close proximity
- Indirect respiratory droplet deposition on surfaces
- Airborne transmission via small-particle aerosols
The advice for staying safe was more or less universal across most industries and to the public; wear facemasks where possible, regularly wash your hands with sanitiser, keep a distance from other people, and avoid meeting in groups in indoor areas.
Covid transmission rates: indoors vs outdoors
Indoors areas were considered particularly problematic and consistently showed significantly higher rates of transmission. This is due to the fact that aerosols cannot disperse the same way that they do outdoors and instead accumulate in the air. The World Health Organisation (WHO) suggests that this is especially the case when there is poor circulation and recommended that along with other safety precautions, people should open doors and windows.
In a research article titled Sensitivity Analysis of SARS-CoV-2 Aerosol Exposure, Christian Redder, a development engineer in the field of aerosol separation at Hengst (formerly Delbag), states that: “Very good ventilation of indoor spaces is mandatory. The definition of sufficient ventilation in regard to airborne SARS-CoV-2 (Covid-19) transmission follows other rules than the standards in ventilation design. This means that especially smaller rooms most likely require a significantly greater fresh air supply than usual.”
He goes on to state that “in terms of window ventilation, it has been found that many short opening periods are not only thermally beneficial, they also reduce the exposure dose,” and “long total opening periods and large window surfaces will strongly reduce the exposure.”
In this research article, Redder draws on studies that assess the sensitivity of exposure towards Covid aerosols in the presence of one infected person in indoor environments. These studies take into consideration the effects of fresh air supply, ventilation efficiency, the volume of inhaled particles (this can be affected by factors such as increased respiration after sports, or children with smaller lungs inhaling fewer particles), the likelihood of particles penetrating masks, and the decay rate of infections particles in the air.
Ultimately, the studies found that when windows were closed, the small-particle Covid aerosol in the air would only reduce slowly over time as they decayed (along with very low leakage, as buildings are not airtight). This leads to a strong build-up of the concentration in the presence of an infected person, which is riskier in small rooms or for long periods of time.
What does this mean for ventilation in hospitals?
Hospitals encompass various types of spaces, including operating rooms, inpatient diagnostic or delivery rooms, intensive care units, protective environment rooms for high-risk immunocompromised patients, laboratories and procedure rooms, and other service rooms for administrative work, food preparation, and laundry. With rooms of various sizes, facilitating different levels of activity and for varying periods of time, methods for filtration, recirculation or ventilation of these indoor areas are going to differ.
Download the whitepaper below to read the full research article analysing SARS-CoV-2 aerosol exposure in hospitals and the effects of window ventilation. Additionally, visit Hengst’s website to find out how air filter systems have been used by the healthcare industry to maximise air purity in sensitive indoor environments.
