Article: Equipment Required for CBRN Shelter
Author: Andrey Shpak | LinkedIn >​
CBRN Shelter – definition
A CBRN shelter is a structure, or a chamber designed to protect people and equipment from airborne chemical, biological, radiological and nuclear (CBRN) contaminants. Such shelters must have a gas tight perimeter and different integrated systems for creating safe and toxic free area (TFA) inside the shelter. The “clean” CBRN protected space called a CBRN protected perimeter.
Important notice: CBRN shelters can have additional layers (perimeters) for protecting from blast, ballistic, EMP, fire and other types of threats but they do not necessarily have to be integrated with the CBRN perimeter and can be separated. One example of such is the generator room that in most cases protected from blast and other threats but usually placed outside the CBRN protected perimeter.
CBRN Shelters Main Types:
1. Airtight shelters with external air supply
2. Autonomous shelters isolated from external environment
Type 1 – Airtight shelters with external air supply
This is the most common type of shelter where the air supply and air quality management (CO2 and O2 levels, overpressure and other critical functions) are provided by the CBRN air filtration system and other shelter components presented below.
Main equipment required for shelters with external air supply:
1. CBRN air filtration system – the system is required for supply of fresh air (external) and its filtration from dust and different types of airborne chemical, biological, radiological and nuclear (CBRN) contaminants. Additionally, the system should be able to create overpressure (positive air pressure) by bringing the air into the sealed shelter. The system is usually selected according to number of occupants, shelter space and in some cases by air leakage rate.
2. Overpressure valve – normally closed air control valve which installed on the external perimeter to maintain the pre-defined levels of overpressure in the shelter by allowing pressure release in case the overpressure in the shelter rises beyond the required levels. Additional type of overpressure valves are differential pressure valves which manually set for determining airflow direction and creation of the different overpressure levels in separated areas of the shelter like multilevel airlocks. *As the overpressure valves used for air release from the shelter, it is recommended that some of them to be placed in toilets, kitchens or other regions to prevent smells spreading in the shelter.
3. Gas tight doors and escape hatches – doors and hatches have an important role in sealing the perimeter and must be design for maximum air tightness, preventing the CBRN contaminants entering the shelter and the internal filtered air to be pushed outside when overpressure level rises. In most cases the doors and the hatches are integrated with chemical resistant seals which are pressed by the door leaf and the locking mechanism to the frame, which allows to seal them.
4. Gas tight cable transits – cable transits installed on the external CBRN protective perimeter to allow safely bringing the electric and communication cables as well as different hoses into the shelter. Some cable transits offer a blast protection rating as well.
5. Overpressure gauges – devices for measuring and presenting the overpressure levels in the shelter or in different areas of the shelter. Overpressure gauges measuring the relative pressure between two areas and presenting the difference in pressure between them. This is required to ensure correct levels of overpressure, which helps to prevent the contaminated air from entering the shelter.
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Type 2 – Shelters which are completely or partially isolated from external environment (lockup mode)
This type of shelter is more common in special applications, strategic facilities and shelters located in areas where potentially the safe external air supply may be not possible in time of emergency. Some of the reasons for insufficient fresh air supply can be high concentration of toxic industrial chemicals, fires which create heat, smoke and lack of oxygen and high levels of carbon monoxide, floods which can block the air supply and other factors.
Main equipment required for shelters which completely or partially isolated from external environment:
The main difference in this type of autonomous shelter is that the air management is performed by the closed circle of air regeneration systems. In this case the CBRN air filtration system is not required, and the air regeneration is made by the following systems. Because of lack of fresh air supply and constant air exchanges in the shelter the levels of carbon dioxide (CO2) and oxygen (O2) must be controlled and maintained in the safe range. In addition, the overpressure which is required for preventing contamination entering the shelter needs to be maintained by adding compressed or filtered air.
1. CO2 Removal System (scrubber) – scrubbers are designed to scrub the air and remove the caron dioxide (CO2) from the air, which is created in normal breathing of people staying in the shelter. The systems can be automatic or manually operated and the removal made by CO2 filter filled with special absorbing material.
2. O2 Supply system – there are several types of systems for oxygen supply in the shelter, but the main ones are based on automatic or manual release of oxygen from cylinders. Such systems are usually equipped with oxygen monitoring units and can add oxygen to maintain safe levels in the air. Another source of oxygen can be chemical reaction-based oxygen candles, but they are used as an emergency means for fast release of a large amount of oxygen.
3. Overpressure maintenance system – such systems required for compensating the loss of air volume and maintaining positive pressure in the shelter. There are two main approaches for overpressure maintenance, one is based on a release of compressed air from the cylinders placed in the shelter, the system is regulating the air release based on the pressure reading. The other is based on use of small amount of external fresh air filtered by the CBRN filtration system and/or carbon monoxide (CO) removal system (in case of fire outside). Usually there is no need to install the overpressure valve in this type of shelters as the positive pressure level maintained by the automatic system or manually.
4. Gas Detection and Monitoring Systems - gas monitoring is an essential for maintaining a life supporting atmosphere within the shelter. During the stay, occupants consume oxygen and expire carbon dioxide (CO2) and carbon monoxide (CO) as part of their normal respiration. CO can also enter the chamber during occupant entry and if the compressed air intake is compromised. Closely monitoring gas levels in the shelter allows occupants to take corrective actions to maintain a safe and inhabitable environment.
