Negative Pressure Rooms
The airflow engineering that keeps infectious pathogens contained.
9 min readUpdated March 18, 20263 topics
The principle
A negative-pressure room — formally an airborne infection isolation room (AIIR) — is engineered so that air flows into the room from the corridor and never back out through the door. Any pathogens shed by the patient are captured by the ventilation system rather than escaping to shared space.
The engineering targets
| Parameter | Target | Source |
|---|---|---|
| Pressure differential vs. corridor | ≥ 0.01 in. water column (~2.5 Pa) negative | CDC / ASHRAE 170 |
| Total air changes per hour | ≥ 12 (new construction); ≥ 6 (existing) | CDC 2003 / ASHRAE 170 |
| Outdoor air changes per hour | ≥ 2 | ASHRAE 170 |
| Exhaust | Direct to outside, or through HEPA if recirculated | CDC / ASHRAE 170 |
| Anteroom | Recommended, not required | CDC |
| Verification | Continuous monitoring; daily visual/smoke check when occupied | CDC / TJC |
Airflow diagram
Interactive diagram
100%
Use the plus and minus buttons or the plus and minus keys to zoom. Drag with the mouse or use the arrow keys to pan. Press 0 to reset.
Verification in practice
The most common failure mode is drift. Filters load, dampers shift, doors are left ajar. Working AIIRs are verified:
- Continuously by a differential-pressure gauge on the corridor wall (visible to staff).
- Daily when occupied — a documented smoke or tissue test at the door.
- Every filter change, with balancing recorded in the building automation system.
Standards
- CDC Guidelines for Environmental Infection Control in Health-Care Facilities.
- *CDC Guidelines for Preventing the Transmission of M. tuberculosis***.
- ASHRAE Standard 170 — Ventilation of Health Care Facilities.
- FGI Guidelines — anteroom and space requirements.
- The Joint Commission Environment of Care (EC.02.05.01) — daily verification when occupied.
References & further reading
- 1CDC 2003 Guidelines for Environmental Infection Control in Health-Care Facilities
- 2CDC 2005 Guidelines for Preventing Transmission of M. tuberculosis in Health-Care Settings
- 3ASHRAE Standard 170 Ventilation of Health Care Facilities
- 4FGI Guidelines for Design and Construction of Hospitals
- 5The Joint Commission EC.02.05.01 — Utility systems
Help us improve
Spotted something wrong, outdated, or unclear? Let the editors know.