Breathing Apparatus [Proto Mark IV]
Siebe Gorman and Company Limited, Manufacturer
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"The Proto is a type of rebreather that was made by Siebe Gorman. It was an industrial breathing set and not suitable for diving. It was made from probably 1914 or earlier to the 1960s or later. (Distinguish from "Proton", which is another sort of Siebe Gorman rebreather).
Its breathing bag was worn on the chest. It had one or two oxygen cylinders, across the lumbar part of the back: often one, but this image shows two. Its duration in use was one or two hours, dependent on the size of oxygen cylinder fitted. Its absorbent (tradename Protosorb) was loose in the bottom of the breathing bag, restrained by a perforated cloth partition, and not in a canister. It had two wide breathing tubes running from the breathing bag to either a strapped-in mouthpiece (used with goggles) or an industrial-type fullface mask known as a Vistarama face mask, with a curved window and an inner ori-nasal mask. 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 much used by firefighters and in rescue in coalmines, long before open-circuit industrial breathing sets based on the aqualung became common. It appeared in many news images of coalmine rescue squads."
This set was designed as a rebreather, using both a breathing gas containing oxygen and recycled exhaled gas. This recycling reduces the volume of breathing gas used, making a rebreather lighter and more compact than an open-circuit breathing set for the same duration in environments where humans cannot safely breathe from the atmosphere.
The exhaled gases are directed through the chemical scrubber, a canister full of some suitable carbon dioxide absorbent such as a form of soda lime, which removes the carbon dioxide from the gas mixture and leaves the oxygen and other gases available for re-breathing.
The term "break through" means the failure of the "scrubber" to continue removing carbon dioxide from the exhaled gas mix.
Some systems have an indicating dye in the soda lime. It changes the colour of the soda lime after the active ingredient is consumed. For example, a rebreather absorbent called "Protosorb" supplied by Siebe Gorman had a red dye, which was said to go white when the absorbent was exhausted.
No H68729 / SIEBE, GORMAN & CO. LTD. / LONDON Printed
PROTO / SIEBE, GORMAN & CO LTD Embossed
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