What Gas Mask filters are safe or dangerous?

What Gas Mask filters are safe or dangerous?
A look at some of the commonly available surplus gas mask/respirator filters to see what's safe to use and what's dangerous.
Study on Chromium toxicity:
https://books.google.co.uk/books?id=z5crAAAAYAAJ&lpg=PR7&ots=L9WkUBNq2n&dq=chromium%20toxicity%20gas%20mask%20study&pg=PP1#v=onepage&q&f=false

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Видео What Gas Mask filters are safe or dangerous? канала Weaponsandstuff93