ABEK filters explained

An explanation of what an ABEK filter is and what it filters out or protects against.
ABEK is a coding system for various gas/vapour threats. An ABEK filter protects against ABEK threats.
A military NBC/CBRN filter is often the same thing as an ABE-P or A2B2E1K1-P3 filter. The problem is that many NBC or CBRN filters do not specify what they can filter, meaning using the incorrect model of filter could be a fatal mistake.
ABEK filters can come in NATO STANAG, PACT GOST as well as proprietary filter connections, any filter can be an ABEK filter, it is not restricted to nation or manufacturer.