Negative pressure rooms use a vacuum effect to trap airborne germs and prevent them from spreading.

Negative pressure rooms are a critical engineering control used in hospitals to manage Airborne Infection Isolation Rooms (AIIR). The system works by maintaining a lower air pressure inside the room compared to the adjacent hallways or rooms. This pressure differential is achieved by mechanically exhausting air at a higher rate than the supply air enters the space.According to the Centers for Disease Control and Prevention (CDC) guidelines, these rooms must maintain a minimum pressure difference of 0.01 inches of water column relative to the corridor. This ensures that when a door is opened, air flows into the room rather than out into the hospital. This mechanism is essential for treating highly contagious diseases such as tuberculosis, measles, and COVID-19.The exhaust system typically utilizes High-Efficiency Particulate Air (HEPA) filters. These filters are standardized by the Department of Energy to remove at least 99.97% of dust, pollen, mold, bacteria, and any airborne particles with a size of 0.3 microns. This filtration process ensures that the air vented outside the building does not pose a risk to the public or the environment.The concept of isolation rooms dates back to the early 20th century, but modern standards were significantly refined following the 2003 SARS outbreak. Today, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Standard 170 provides the specific ventilation requirements for healthcare facilities. These standards mandate at least 12 air changes per hour for new or renovated isolation rooms to ensure constant air purification.