old MSA INDUSTRIAL GAS MASK case

Here's another oddball thing that I acquired someplace years ago (presumably for cheap and because I thought it was cool?) which has otherwise now been laying around here ever since. It is a sturdy red fiberboard case with heavy duty riveted steel edges/hardware and a leather handle, which formerly held an "INDUSTRIAL GAS MASK" made by MINE SAFETY APPLIANCES CO.", a firm which apparently still remains in business today. It measures roughly 14" x 9" x 6.5". The gas mask itself is long gone, the only thing remaining inside are fiberboard dividers and the original usage/maintenance instructions card for the mask fastened to the inside of the lid. Its one likely unique feature is a small brass property tag (?) riveted to its top near the handle,which is stamped "IOWA P M A / 508 / MUSCATINE CO.". I have found online references suggesting this could date from the 1940's, but cannot confirm that...nor do I really have any idea what "IOWA PMA" is/was.