Does HEPA stop gases?

No. HEPA captures particulates and aerosols; chemical gases and vapours require an activated carbon stage. Both are used together.

How often are filters replaced?

It depends on usage, ambient dust and exposure; periodic inspection and differential pressure readings determine the interval.

How is the internal air renewed?

Outside air is continuously drawn through the filter stages, while stale air is pushed out by overpressure.

What does the CO₂ collector do?

In full-sealing mode, when outside ventilation is cut off, it absorbs the carbon dioxide produced by occupants' breathing and keeps levels within safe limits.

NBC / CBRN filter unit: G4, HEPA/ULPA and impregnated activated carbon stages

SYSTEM / FILTRATION

NBC / CBRN Filtration System

A shelter is measured by the air inside it, not by wall thickness. The NBC/CBRN filtration system provides multi-layer protection against biological, radioactive, chemical and indoor-air threats through a G4 pre-filter, HEPA/ULPA particulate stage, impregnated activated carbon and a CO₂ scrubber.

NBC / CBRN filter unit: G4 pre-filter, HEPA/ULPA and impregnated activated carbon stages — NBC / CBRN filter unit: G4 pre-filter, HEPA/ULPA particulate stage and impregnated activated carbon block

Coarse Filter (G4 Class) – Pre-filtration

As soon as air is drawn from the outside, it first passes through a G4-class coarse filter. This stage captures large dust, sand, pollen, soot and coarse particles, protecting the main NBC filters downstream.

Purpose: Captures large dust, sand, pollen, soot and coarse particles from the intake air.
Benefit: Extends the life of the main NBC filters (HEPA/ULPA and activated carbon), prevents clogging and preserves system efficiency.

HEPA and ULPA Filters – Radioactive and Biological Protection

The particulate stage is responsible for retaining radioactive fallout and biological aerosols. HEPA filters operate at efficiencies above 99.99%; ULPA goes further with a much finer pore structure that catches sub-micron particles.

Biological threats: Filters bacteria, viruses, spores and microorganisms with efficiency above 99.99%, blocking biological warfare agents.
Nuclear threats (radioactive fallout): Completely retains radioactive dust and alpha/beta-emitting particles suspended in the air after a nuclear event.
ULPA support: Its finer pore structure captures sub-micron particles down to 0.12 microns and below, providing maximum physical protection.

Impregnated Activated Carbon Filter – Chemical Warfare Agent Protection

HEPA alone cannot stop chemical gases and vapours. At this stage, activated carbon impregnated with special chemicals comes into play, trapping harmful substances by adsorption on its surface.

Chemical threats: Neutralises nerve agents (Sarin, VX), blister agents (mustard gas), choking agents and blood agents through adsorption.
Toxic industrial gases: Also filters chlorine, ammonia and organic vapours that can be released during industrial accidents.

Special CO₂ (Carbon Dioxide) Collector Systems – Indoor Air Quality

In full isolation (complete sealing) mode, when outside ventilation is completely cut off, carbon dioxide rises as occupants breathe. CO₂ collector systems keep this level within safe limits.

Full isolation (complete sealing) mode: Activates when the shelter's outside ventilation must be fully closed due to extreme external contamination or blast conditions.
Purpose: Absorbs the rising CO₂ level caused by occupants breathing, keeping it within safe limits and preventing oxygen deficiency and poisoning risk.

Positive pressure (overpressure)

Filtered air keeps the interior slightly above outside pressure, so air leaks outward through unavoidable gaps and contaminated air cannot enter. This is the principle that makes filtration meaningful.

Airtightness and shell integrity

Overpressure only holds in a sealed shell. Door seals, cable and pipe penetrations, exhaust lines and blast dampers are designed as one system and verified by pressure testing at commissioning.

Operation during power loss

The system is designed to run without grid power: a backup power path and a manual or pedal-driven emergency fan maintain airflow.

Maintenance and filter life

Filter stages have a finite life. Differential pressure gauges, recorded periodic testing and spare filter stock are what guarantee the system works when it is needed.

Frequently Asked Questions

Does HEPA stop gases?: No. HEPA captures particulates and aerosols; chemical gases and vapours require an activated carbon stage. Both are used together.
How often are filters replaced?: It depends on usage, ambient dust and exposure; periodic inspection and differential pressure readings determine the interval.
How is the internal air renewed?: Outside air is continuously drawn through the filter stages, while stale air is pushed out by overpressure.
What does the CO₂ collector do?: In full-sealing mode, when outside ventilation is cut off, it absorbs the carbon dioxide produced by occupants' breathing and keeps levels within safe limits.

NUKKOR NBC Shelter Ventilation Decontamination EMP Protection Safe Room

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