Although never used as intended, the civilian gas masks issued in the run up to World War Two were designed to be maintained and repaired as necessary to keep them in service. Spare parts were produced and instructions given on how to dismantle and reassemble the respirators. Amongst those spare parts were replacement filter canisters that could be swapped out in the rubber face masks. Spare gas mask parts are unusual today, so it was very pleasing to be given this pair of replacement filters for civilian gas masks:Both are tin metal boxes, with a rubber inlet valve on the rear:The front has a green tin grill through which air would pass when assembled on a mask and used:Inside the canister was a particulate filter and a layer of charcoal:The official description of the canister was:
The container (known as G.C. mark II) consists of a cylindrical tin canister (lacquered black) containing activated charcoal to absorb gases such as phosgene and mustard gas, and a particulate filter which prevents the passage of finely divided smokes like the arsenical gases. The contents of the container do not deteriorate either with age or with wearing the respirator when gas is not present.
The canister itself, like so many other items made from tinplate, was manufactured by the Metal Box Company and this is indicated by the combined MB stamp on the back of the canister:To fit a new canister to a civilian gas mask, the following procedure should be observed:
(I) Replace the rubber disc valve on the stud in the container end.
(II) Grasp the container by the rim on its outer end and insert one side of the inner end into the aperture in the facepiece at a point immediately under the window. If the facepiece is a large size, the edge of the rubber should be brought just over the raised swage in the container body, and if it is either a medium or small size the edge of the rubber should be brought up to the raised swage. Hold the rubber in place of the container with the fingers, insert the fingers of the other hand inside the facepiece and stretch the rubber outwards and slip it over the container.
If the facepiece has not been slipped over the container far enough it must not be corrected by pulling the edge of the rubber; the fingers are to be inserted in the facepiece and the rubber lifted and pushed onto the container. See that the edge of the rubber is not turned in, that it is straight round the container and in the correct position according size of the facepiece.
(III) Place the rubber band in position around the container so that one half of its width lies on the rubber of the facepiece and the other half on the container.
One of these rubber securing bands is slipped around one of the canisters and has a date of 1937 stamped on it: