The COVID-19 pandemic has forced us to re-evaluate our understanding of indoor safety. While we've traditionally relied on physical barriers like walls and doors to keep us safe, a recent outbreak in Spain has revealed a hidden vulnerability: airborne viruses can travel between apartments through vents. This revelation has significant implications for building design and safety protocols, and it's time we take a closer look at the science behind it.
The outbreak in Santander, Spain, occurred in a seven-story residential building where 15 residents across four apartments tested positive for COVID-19 within days. The pattern of infections was unusual, as the apartments were stacked vertically and not next to each other. This led resident engineer David Higuera to suspect that the connection was not social, but structural.
Upon further investigation, researchers discovered that the building's ventilation system was the culprit. Each apartment had a small bathroom vent connected to a shared vertical shaft that ran from the bottom floor to the roof. This system relied on natural airflow, with warm air rising and exiting the building. However, it also created a shared air pathway between homes.
The key to understanding the outbreak lies in the fact that airflow inside buildings is not constant. It shifts with temperature, weather, and human activity. Opening a window or turning on a fan can change pressure inside a room, causing airflow to reverse. In this building, that meant air from one apartment could enter another through the bathroom vent.
Researchers studied the airflow in detail, monitoring pressure, airspeed, and carbon dioxide levels. They found that in one test, an empty apartment had increasing carbon dioxide levels throughout the day, as if there was a ghost in the room. This indicated that the air was not coming from outside, but from other apartments.
The virus spread through vents under certain conditions, with airflow reversing strongly when a kitchen exhaust fan ran at full power. This reverse flow reached about 42 liters per second, carrying virus-carrying aerosols from other homes. The building's design allowed air to move both ways, making it possible for infection to travel vertically.
The study's findings have broader implications for building design and safety protocols. Many older buildings still use shared ventilation shafts, which were designed for efficiency, not infection control. This means that even if you're far from the source of the virus, if your air is connected, you can still get sick.
The solution is surprisingly simple: installing a small exhaust fan with a one-way flap can stop reverse airflow. The flap blocks incoming air when the fan is off, and when the fan runs, it pushes air out safely. Another measure is to allow fresh air to enter while using kitchen fans, such as opening a window to balance pressure and reduce the chance of pulling air from other apartments.
This outbreak changes how we think about indoor safety. Walls and doors do not always isolate air, and hidden pathways can connect spaces in unexpected ways. Building inspections need to consider airflow systems more carefully, as shared ducts, pipes, and cavities can act as channels for airborne particles. In Santander, a simple ventilation shaft became the link between households, showing that infection can move through buildings in ways people rarely consider.
In conclusion, this outbreak has revealed a hidden vulnerability in our understanding of indoor safety. While we may have thought that our homes were safe havens, the truth is that airborne viruses can travel between apartments through vents. It's time we take a closer look at the science behind building design and safety protocols, and make the necessary changes to protect ourselves and our loved ones.
