This page contains all known information about Helly Hansens model IMB gas mask.
The History of the IMB Model
The IMB is very similar to the IMA. The IMB does appear to have somewhat of a lighter colour to it, but technically the masks are very similar. The mask has a 40mm filter tread and it is most likely that it was issued with the light brown Helly Hansen filter, as seen in the photo. The mask was made for the Norwegian military, but it is unknown which branch they were issued to, or if they were even issued at all.
The carrier for the IMB model is made out of dark green PVC, and closes with a small velcro patch. The bottom of the carrier has a simple piece of cardboard to keep the carrier in shape. Unlike the carriers for the LF-62 and A59, etc. The IMB carrier has a silver colored inside material and has a string which can be tied around the leg to keep the carrier in place.
The filter for the IMB is most likely the light brown Helly Hansen filter seen in the first photo. But it has never been confirmed what filter this mask was issued with.
The manual for the IMB is built up in the same way as the other Helly Hansen masks, with full instructions and sketches to make use easier.