Table 4.
Differences Between Positive and Negative Pressure Areas
| Engineering Characteristic | Positive Pressure Areas (eg, PE) | Negative Pressure Areas (eg, AII) |
|---|---|---|
| Pressure differential | > +2.5 Pa (0.01-in. water gauge) | > −2.5 Pa (0.01-in. water gauge) |
| Air changes per hour | >12 | ≥12 (for renovation or new construction) |
| Filtration efficiency | ||
| Supply: 99.97% at 0.3 μm DOP | Supply: 90% (dust spot test) | |
| Return: none required (if patient requires both PE and AII, return air should be HEPA-filtered or otherwise exhausted to outside) | Return: 99.97% at 0.3 μm DOP (HEPA filtration of exhaust air from AII rooms should not be required, provided exhaust has been properly located to prevent re-entry into building) | |
| Room airflow direction | Out to adjacent area | In to room |
| Clean-to-dirty airflow in room | Away from patient (high-risk patient, immunosuppressed patient) | Toward patient (airborne disease patient) |
| Ideal pressure differential40 | > +8 Pa | > −2.5 Pa |
Note: Adapted from Streifel.40
Abbreviations: AII, airborne infection isolation; DOP, dioctylphthalate particles (0.3 μm in diameter); HEPA, high-efficiency particulate air; PE, protective environment.