Its absorbent (tradename Protosorb) was loose in the bottom of the breathing bag, restrained by a perforated cloth partition, and not in a canister.

The canister seen on the front of the bag was to cool the gas in circuit, as the absorbent gets warm as it absorbs carbon dioxide, and that warming of the gas in circuit is welcome when scuba diving in cold water, but is not welcome in hot industrial situations including in deep mines.

It was used by firefighters and by rescuers in coalmines, long before open-circuit industrial breathing sets based on the aqualung became common.

In 1908 the apparatus was chosen for use by rescuers from the newly formed Howe Bridge Mines Rescue Station.

[2] These sets were used in the London fire brigade from the 1950s till the early to late 1970s, when these rebreathers were replaced by compressed air sets which use a cylinder strapped to the back of the firefighter and the air fed through a hose to the firefighter's full face mask: this is their current type of breathing apparatus.