Article: Design Principles for CBRN-protected Vehicles Mobile Platforms & Containers

“Preparation is better than panic”

 

The question I have been asked frequently is “why equip the vehicle with CBRN (Chemical, Biological, Radiological and Nuclear) protection systems, if the chance for CBRN event is very low”

The answer is the same as for other protection systems… we add ballistic or mine protection for even the smallest of chances that you may need it.

 

Chemical, Biological, Radiological and Nuclear (CBRN) Threats
 

Military, Police and other Special Purpose Vehicles need to function in very different conditions and fast changing environments. It is crucial that the crew and the sensitive equipment inside the vehicles will safely continue performing their mission even in a contaminated environment following a CBRN event. We can find many examples in the modern History of CBRN events like industrial hazards or transport accidents with Toxic Industrial Chemicals (TIC) release, war scenarios or terror attacks with use of Weapon of Mass Destruction (WMD), as well as epidemics, fires, natural hazards and many others. 

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Critical components for vehicle protection

 

Vehicle design and the life support systems are the main components that are critical for building an efficient CBRN protected vehicle. Let’s talk about every part in more details:

1. Vehicle Design:

In the design of CBRN protected vehicle, we need to take into consideration the following:

Possibility to create a "Toxic Free Area (TFA)" inside the crew compartment
The use of the right materials that are resistant to the toxic environment
correct air supply and distribution inside the compartment
 

2. Design of the crew compartment as a Clean & Toxic Free Area:

For creating a TFA inside the crew compartment, we will need to seal the crew compartment… sounds easy, but on the practical side, to seal the compartment 100% is just “Mission Impossible”. Every small opening can cause an air leakage that may not allow creation of overpressure (pressure higher than atmospheric pressure) that is critical for creating a TFA.

When designing a CBRN protected vehicle the approach has to be different than to “regular” vehicle, as the vehicle has to be airtight. This can be created with careful design of the compartment structure, sealing technical openings and pass-through (for cables, hoses etc.), doors and hatches sealing, and even bolt threads need to be sealed, as they can be a source for air leakages.

To create overpressure inside the compartment, the volume of air that is “pushed” into the compartment has to be higher that the volume of air that “pushed” outside (the same principle as inflating balloon). When the compartment is airtight, the air supply system by pushing fresh air to the compartment will create an overpressure inside. This will prevent contaminated air from entering the compartment and in case of small leakages to push the air out.

An important consideration when the vehicle is on the move, the external air pressure on the vehicle is rising and the level of the overpressure inside the compartment needs to be sufficiently high to prevent the air from entering through the small openings.

 

3. Using the right Materials:

Materials, coating and seals have to be durable and resistant to chemicals. Following exposure to war chemicals or toxic industrial chemicals, as well as to chemicals used in the decontamination process, the rubber seals and other surfaces could be damaged or degraded. The rubber parts have to be very durable and resistant to different environmental conditions, as they effect the sealing and airtightness of the complete compartment.

 

4. Air distribution inside the compartment:

Effective air distribution that will “flush” the compartment with fresh air will allow to control the CO2 levels. In the CBRN mode the fresh air have to be filtered with CBRN filtration system and the AC system will work in re-circulation mode. The easiest way to insure the air flushing effect is to place the overpressure valve in the opposite corner to the CBRN filtration system and the air inlet. 

Life support systems:
CBRN filtration system is considered a life support system and has a critical role in protecting the crew and allowing continuous work of the people and the equipment in CBRN contaminated environment. 

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There are two main types of CBRN filtration systems:

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• Air Pushing system – is installed outside the TFA and pushes the air into the compartment. This type of systems is usually used in armored vehicles. 
  The main advantages of the pushing system, is that the filter can be changed from outside the TFA without contamination and the compartment will be kept “clean”. Additional advantage it extra protection in case of leakage from the CBRN filter, the filters installed outside and will not contaminate the cabin.

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• Air Pulling system – that is usually used in bomb shelters and pulls the air from outside. The filters usually placed inside the TFA or in additional room connected to the TFA area. 
  In both cases the pushing and pulling systems needs to filter the dust and CBRN particles to the safe levels. The safety level usually determined by the user or according to the standards, like the AEP-54 or others.

 

The other role of the air filtration systems is to create an overpressure inside the vehicle introducing air into the protected TFA area and to perform complete air changes in the compartment to prevent raising of the CO2 concentration levels.

 

It is important to emphasize that CBRN filters are usually designed to deal with certain CBRN threats and with certain capacity but can be ineffective for some Toxic Industrial Chemicals (TIC) or substances released in burning of different materials. The ability to absorb different chemicals is dependent on the formula of the carbon used in the filter and can be different in different types of filters.

 

The overpressure in the vehicle compartment is usually controlled by an overpressure valve that has a blast protection mechanism, that locks the valve if the air pressure suddenly rises outside and prevents contamination entering the TFA area.

In case the vehicle cannot be sealed and it is impossible to create a TFA inside the vehicle, there are several solutions based on face-masks that can be applied. Although this solution may be simpler and less expensive, the use for the crew is more complicated and may affect their operational capabilities.

 

As you can see, to create a CBRN protected vehicle you need to take into consideration many different aspects starting from design of the vehicle and choosing the right systems for the purpose and protection needs.