The importance of overpressure in CBRN shelters and bunkers

The overpressure in the shelter plays critical role in shelter protection and safety arrangement.

Overpressure gauges

About overpressure

Positive differential air pressure or overpressure refers pressure differences between two areas, room or other measurement points. If we are talking about the overpressure in the shelter it is a situation when the air pressure inside the shelter is higher that the pressure outside the shelter or another shelter compartment (airlock as an example). The overpressure measured always in relation to other point. This pressure difference can be used to control the airflow and prevent contaminants from entering the shelter. 

How the overpressure can be created in the shelter

In simple description if the amount of the air that is pushed into the shelter is higher than the amount pushed out thought different openings the overpressure created. Here is a good example of inflating a balloon.

There are several points required for creating overpressure in the shelter:

1. the room / protected area need to be maximally airtight - the meaning is that every structural opening have to be airtight. As an example gastight doors, hatched and windows, protected cable and pipes wall passages, air ducts and other shelter elements have to have special sealings to prevent air to be pushed our.

2. Air filtration and ventilation system have to pull or push enough air into a shelter to create an overpressure.

3. Overpressure regulation devises like overpressure valves have to be installed to maintain the overpressure level in the determined range.

   
   

Why overpressure is important

In most cases there is no possibility to make the shelter completely 100% airtight as there are different cables, pipes, air ducts and other components that penetrate the shelter perimeter as well as doors and structural openings and the air can leak through them or even small cracks in the concrete walls. When overpressure is created in the shelter it pushes the air out through the smallest openings in the protected perimeter and contamination will not enter the shelter.

Video presenting the gas tightness test for determining if the leakage withing the determined limits

Gas tightness test - the blower pulling the air into the shelter to raise the overpressure level and measure the time that the pressure reduced to zero

Video presenting the process of detecting the air leakages under overpressure with use of smoke stick.

Atmas is a Finland-based global supplier of products, technologies, project support services and complete solutions in the areas of civil defense shelters and protected spaces, facilities reinforcement against CBRN, blast, ballistic, forced entry and EMP threats, as well as security, safety and emergency response.