The W64 Self-Rescuer is a personal rescue device that is carried on all miners while in a mine. It provides one hour of conversion from deadly CO(1% Carbon monoxide)gas to the non-fatal CO2 gas. The device produces an exothermic reaction which yields strong heat emission which is a clue to the miner that it is functioning properly. However, many uninformed miners may take the sign of its heat to mean negative functionality of the device and consequently remove it. This may quickly lead to death. The W64 Self-Rescuer is required to be carried by all people going underground in a mine by the MSHA.
The mouthpiece is self explanatory. The device you see on the left side of the photo is a nose-plug to block unintended breathing through one's nose. The green webbing goes around one's head to keep the device in place. In the background you can see the metal container the W64 is housed in to protect it from damage while the miner is working. The device is weighed at a regular interval to ensure no moisture has accumulate in the device while it's being stored on the miner's belt.