On Tue, 08 Sep 2020 15:02:42 +0700, John B. Slocomb
wrote:

If your mask has the standard 40 mm filters then you can easily change
them.

It's 40 mm. I didn't realize that they were standardized and commonly
available:
https://www.ebay.com/sch/i.html?_nkw=40mm+gas+mask+canister

As for length of service it depends on what is being filtered.
In some cases, filtering Chlorine for example, filter life is measured
in minutes and 3M recommends changing a filter that is opened and not
used after 6 months.

OSHA filters N, P or R designate particulate filters. N series filters
are used for any solid or non-oil-containing particulate, and R and P
series filters are used for any particulate, including aerosols.

According to OSHA, the filter needs to be replaced when:

The user has difficulty breathing comfortably or notices an
increase of breathing resistance resulting from particle buildup.
The filter becomes visibly dirty.
The filter is physically damaged.

Respirator filter selection is something I haven't investigated and
therefore know nothing about the topic. I'm mostly interested in
whatever a fireman uses, but that may change later. I have a 3M mask
with P100 filters that I think will suffice:
http://www.learnbydestroying.com/jeffl/crud/jeffl-dust-mask.jpg


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558