Some Soviet armored vehicles, including the PT-76B and the BTR-50K, were fitted with Nuclear Biological Chemical systems. As those dated from the early 1960's, I cannot help wondering how well these things actually worked.

If it's anything like the systems we used on cvrt ..it works on positive pressure ..
Seal up the vehicle ie hatched shut down etc the system powers up and creates a higher air pressure inside the veh...thus keeping the nasty stuff out..the vehicle all so has a system of filters fitted...
May be of some use
Terry

I have the ZSU-23-4 V1 to Silka can comment.
Was in automatic monitoring system, Gas, Biological, Nuclear radiation in case of danger, all openings closed, positive pressure created in the air was passed through separate filters in the system.
These filters were placed on top of the tower (oval-shaped, three items), the lower part of the tower air through an opening in the back left.
The system (without the expensive filters, except) high temperatures are also welcome used instead of air conditioning.
The size made ​​sharp overpressure situation, the staff clogged ears, off (like when you go to a high place), shooting at the closed lids were important, protecting the personnel may be the shrapnel from exploding munitions.