This model of GEP mask is not common and its manufacture date is unknown,

But, certainly at the begening of the thirties 

The facepiece is made of thick rubber sheeting and glued under the chin, the eyepieces are of the same desing as on the ARS, ANP T 31 and TC 38 masks. The filter is directly mounted on the mask and includes the exhalation valve 

The five points head harness is made of rubbr straps..