Filtered Positive-Pressure Shelter

Filtered positive pressure is an engineered method for controlling how outside air enters a protected space.

The principle

A fan supplies filtered outside air to the protected volume. If supplied airflow exceeds total outward leakage at the required pressure differential, uncontrolled inward leakage is reduced.

The key design variable

The objective is not to make a dwelling perfectly airtight. The engineering problem is the relationship between blower capacity, filter pressure drop, total envelope leakage and external pressure effects such as wind.

System chain

1. Characterise protected volume and leakage.
2. Define design airflow and pressure differential.
3. Select filtration for the relevant contaminants.
4. Account for filter loading and pressure loss.
5. Provide monitoring and backup power.
6. Commission and periodically validate performance.

What it does not solve

Positive pressure is primarily an airborne-contamination control. External gamma radiation, long-duration habitability and contamination brought in by people or objects require separate controls.