My practical experience with CBRN/NBC comes from standard military training, and a "light" exposure scenario while deployed. (Still don't now what it was didn't bother to find out.) The rest is post separation research.
Before you research anything make sure you understand the terms and concepts used in the text. While the following highlighted subjects are grouped they should be treated as their own separate hazards as one type of countermeasure will NOT protect you from all.
C.B.R.N. is the acronym used by modern military it stands for:
Chemical Chemical weapons. These include
Harassing Agents (riot gas) and
Incapacitating Agents (knock out gas) and
Blister Agents (mustard gas) and
Blood Agents (weaponized versions of arsenic & chlorine)
Choking Agents (mostly industrial & old warfare) and finally
Nerve Agents (Sarin etc...)
Biological Biological weapons / Pandemics / Waste clean up / Mold based hazards. These include viruses germs and spores spread through
Airborne Transmission (tuberculosis / influenza / weaponized anthrax) and
Blood Borne Transmission (rabies / zombies!) which is often paired with
Vector Borne Transmission (mosquito / lice) as well as the less common
Direct Contact Transmission (Warts / Syphilis)
Radiological & NuclearWhile technically the same hazard they are separated by situation and scope. Radiological covers dirty bombs nuclear power accidents. creating a dispersal of (relatively) low radioactive particulates known as
Fallout while Nuclear concerns itself with the detonation of a nuclear warhead. This includes
Blast,
EMP,
Thermal Radiation,
and the different stages of direct radiation, as well as fallout. Which in both cases causes
Radiation Poisoning.
Older terms used for this topic are "N.B.C" and "A.B.C"
While the military spectrum covers a whole host of hazards it does not cover the subject of
air displacing vapors/fumes/gas as they are not included under the choking agents. For in this situation filtration is no longer an option and would need supplied air to function in. This is mostly an industrial accidents issue but those of you living near high traffic rail lines might want to look into it.
OK now we've got that cleared up now you need to identify you Hazzard Of Choice from now on refered to as HOC.
Now that you've got your HOC you need to identify your scenario. this will determine your estimated exposure time to your HOC which will greatly affect the countermeasures needed which is the core of this discussion. Prices range from low (radiological) to (biological) to (chemical) to extremely high (Nuclear).
For instance a standard
N95 rated face mask will protect you from inhalation of 98% airborne pathogens and radiological dust (exhalation valve recommended). this does not mean you won't inhale them from your garments after removing the mask or reusing said mask.
Your selection of gas masks is almost as vast as that of n95 and would only recommend investing in these if your exposure time to them is estimated longer then an hour and to purchase one with a hydration option. Also note that these are designed to be effective for chemical warfare scenarios that don't allow for that 2-1% error. The filter you pick for your mask is critical because not all are created equal so make sure you adjust for your HOC(s) of choice. There is no such thing as a nuclear gas mask let alone for an astronaut type suit.
Now masks... Don't get a US military mask.
There i said it. while they are effective they are EXTREMELY overpriced, and by this I'm referring to the M40 by 3M and the M50 by Avon. You as a prepper can buy a just as good mask for 1/2 to 1/3 the going price of those. They will be lighter, person friendly and brand new (DON"T BUY USED) unless you're willing to test them. I'm personally in the process of replacing my M40 with an M95
Always get one with a nose and mouth cone separator. the more budget versions will exclude these and it makes your breath condense on your visor rendering yourself useless...
Rubber degrades over time if not stored properly so if buying a surplus "new" mask fro the 70's it's likely going to be useless.
Take note of what threading the mask allows and see if the filters available in it's size allow for your HOC.
On to filters... Most stand alone (can) filters utilize as their main countermeasure layers of activated carbon to absorb and neutralize your hazard of choice and allow the uncontaminated air to pass through. This process does not last for ever and filters need to be replaced after a certain time (depending level of concentration and time in environment) Activated carbon is a fragile compound and degrades in high humidity and over time. While these filters will no longer be effective for chemical agents they will still function for pathogen and particulate scenarios.
There are other options such as powered fan and UV light filters but I don't know a damn thing about them and they are uber pricy.
