From the Metal Gear Wiki

This is a a humble request, but could someone track down the model of his gas mask, if any? I would really appreciate it, I can't find anything.

There are different model Gas Masks? Surely it's just a... gas mask. --Fantomas 16:21, 21 October 2007 (UTC)

it looks like a british army S10 resporator without a S10 NBC filter (now CBR)