The IP-4M is a closed circuit rebreather that was issued to military personnel that were working in environments with a low oxygen concentration. It was produced in the mid 1980's and was made in both black and grey rubber with either a grey or light green bag.
The lenses of these masks were crimped onto the rubber facepiece by a metal ring. It also features a voice diaphragm so that the wearer could communicate with other personnel (an improvement from the earlier IP-4 model). The rebreather uses the RP-4 oxygen generating cartridge and a small air bladder to recycle the oxygen. The wearer exhales, and the exhaled air passes through the RP-4 canister, releasing oxygen from a chemical reaction as it passes through, and then inflates the air bladder. Then when the wearer inhales, the air bladder is deflated and recycled again, This occurs in a continuous loop until the canister is depleted. The usage times for the rebreather are listed below:
- Heavy Labor: 30-40 minutes of oxygen
- Light Labor: 60-75 minutes of oxygen
- Resting: 180 minutes of oxygen
You can tell whether the canister has been used/depleted by looking at the rectangular strip across the top of the canister. If the strip is white, the canister has not been used. If the strip is tainted blue, the canister has been used. To activate the canister in order for use, pull the pin out of the screw-plunger and twist the plunger clockwise, then insert the canister into the bag (connecting the air tubes), and finally put on the mask and start breathing. The canister becomes extremely hot during use due to the chemical reaction occurring inside. The carrying bag is very insulated on the top to prevent burns/scalding from the heat. The carrying bag and breathing hose cover are made of heavy duty chemical resistant plastic in case of chemical splash.
This mask was issued with lens outserts to further prevent damage to the eyes.