I recently obtained an Israeli civilian mask with a 40mm filter. I tried the filter with both the mask it came with and with my GP-5 as I heard they were threaded for them, and I noticed a smell of ammonia (piss). This doesn't seem right to me, and I thought I'd check to see if it was likely to be an issue and whether it was safe to use. Google wasn't the most helpful. The Filter has some Hebrew (I presume) writting on it, but the writting I can read says (In standard direction you would read): UM01 14:37 03/04/13 12/13 200051-8000569-1312-6
Any help anyone can offer would be extremely helpful and appreciated.