How is clean air maintained inside a shelter?

When a shelter's internal pressure is kept controllably higher than the outside, air along any leak path flows from inside to outside. This is the first line of defence that largely prevents unfiltered contaminated air from entering.

Positive pressure is not an arbitrary value. It is calculated per project based on the leakage characteristics of door seals, transitions, service penetrations and exhaust lines.

The pre-filter captures large particles and dust; the HEPA-grade filter then handles very small aerosols; finally, impregnated activated carbon targets chemical and radioactive vapours.

These three layers are not interchangeable; each is designed against a different class of threat.

Ventilation, sewage, electrical passes, cable penetrations and door seals are the most commonly overlooked leak points.

In NUKKOR projects, these points are verified separately in the factory and on site through tightness tests.

Filter elements do not last forever. Service life, threat scenario and storage conditions must be tracked.

A long-term support contract becomes meaningful when critical spares are kept ready and a periodic replacement plan is in place.