Self contained breathing apparatus:-This type of apparatus differs from the tube type in that the wearer is provided with a respirable atmosphere independent of the atmosphere immediately surrounding him.
In 1912 there were two types of self contained breathing apparatus used at Ilkeston, one using liquid air, 'Aerophor' and one using compressed oxygen contained in cylinders, 'Meco'. In the "Meco,' apparatus the oxygen feed is fixed at 2.3 litres per minute. The small apparatus cylinders are charged with 300 litres at a pressure of 120 atmospheres. The oxygen supply will thus last for 130 minutes provided there are no leakages.
The earliest types carried a supply of ordinary fresh air stored at a pressure in a suitable container, and made available to the wearer, by a system of valves according to his respiratory demand, which is greatest during periods of hard physical exertion. Since these types did not function on the regenerative principle their period of use and consequently their overall usefulness was very limited. With the incorporation of the regenerative principle into the operation of self-contained breathing apparatus, and the use of pure oxygen or liquid air the scope of their application has been very considerably increased.
||Principle of Action of Self-contained Breathing Apparatus. When considering respiration it was shown that only about 15% or less of the oxygen inhaled is consumed, and that a quantity of carbon dioxide gas, very nearly equal in volume to the oxygen used, is formed and exhaled, together with an increased amount of water vapour.
Clearly if this exhaled air has the carbon dioxide removed from it, and oxygen added to bring the oxygen content up to 21% again, it can be rebreathed. This in fact was done in the approved types of self-contained Breathing Apparatus, and it was the principle of regeneration of the air contained within the flow circuit of the apparatus.
In the Proto Apparatus the oxygen was supplied from a steel cylinder, and in the Liquid Air types by the evaporation of liquid air from a specially constructed container called the pack. The carbon dioxide was removed by passing the air over caustic soda or some other absorbent such as soda-lime.
In order to select the most efficient and the safest breathing apparatus, an invitation was sent to all makers of such apparatus, British and foreign, to compete in a series of tests lasting several days, in galleries filled with an irrespirable atmosphere, and fitted with various obstacles which the men had to surmount.
The Fluess apparatus, which had been considerably improved by Mr. R. H. Davis, and to which the name "Proto" had been given, won the competition. This was the forerunner of the "Proto Mark W, which was developed from the early design, and which is still one of the two main apparatus in use today in British mines.
The late Mr. R. H. Davis, later Sir Robert Davis, head of the firm of Siebe Gorman Ltd., the manufacturer of the apparatus, was probably the most famous designer of rescue apparatus of all kinds which the world has known.
THE SAVOX APPARATUS.
This was a short period apparatus designed for a period of wear of only 45 minutes. It comprised an oxygen cylinder, absorbent cartridge, cooling device, reducing valve, pressure relief valve and corrugated breathing tube with mouthpiece attachment. It weighed only l3.1/2 pounds and was carried wholly on the chest .
It could be used as an escape apparatus, or for inspection purposes by officials who were not necessarily in training as rescue workers.
Manufactured by Siebe, Gorman, Ltd.
This special piece of apparatus was of the gas mask type, designed to be carried by miners so that in the event of their being overtaken by fumes from a fire or explosion, they could use it to protect themselves. It contained a chemical substance named Hopcalite which changed the deadly carbon monoxide into the comparatively safe carbon dioxide. It gave protection for thirty minutes against an atmosphere containing half a per cent of carbon monoxide, where a safety lamp would burn.
Manufactured by Siebe, Gorman, Ltd.
BLACKETT'S AEROPHOR BROWN-MILLS TYPE.
This was a self-contained breathing apparatus only used on Mansfield, Ilkeston, Chesterfield, Ashby, and Houghton Le Spring and Ashington (maybe Benwell Towers, Newcastle and Crook Co. Durham too). This was the liquid air apparatus, rather than compressed oxygen Proto, which would explain their liquid air plant and Dewar Flasks. (Thanks to Brian Robinson)
The photo was probably late 1950’s to early 60s.in which the oxygen supply was provided by the evaporation of liquid air. The word Aerophor means Breathing Apparatus. It consisted essentially of a liquid air pack and a frame of solid drawn brass tubing, which carried the carbon dioxide absorbent cartridge, a breathing bag, the inhalation and exhalation valve boxes and the automatic pressure relief valve.
The Blacketts Aerorphor was last used in 1968 when it was replaced by the Aerorlox.
When the apparatus was to be used the pack was charged with 5.1/2 pounds of liquid air having an oxygen content of not less than 50% in the liquid state. Immediately on charging the liquid began to evaporate and a gaseous mixture of oxygen and nitrogen passed off from the pack, through a warming tube, to the air flow circuit. Since liquid air boils at a temperature of 77°C absolute, the warming tube was very essential to bring the temperature of the inspired air to normal,- i.e. to about 290°C absolute. The pack itself was suitably insulated to control the rate of evaporation to about 10 litres of evaporated air per minute. It consisted of the pack proper, comprising an inner perforated nickel case, tightly packed with calcined magnesite asbestos wool which absorbed and held the liquid air on charging, a middle nickel case, there being an air space between the two, and surrounding the whole a third outer nickel case, the space between this and the middle one being loosely packed with asbestos wool.
The space between the inner and middle cases had the double function of distributing the liquid air during charging, and providing an evaporating space from which the air passed to the outer space and the warming tube.
To control the rate of evaporation the pack was insulated by an asbestos mould, which itself was contained within a felt cover, the whole assembly being protected by a stout leather outer case.
The carbon dioxide absorbent cartridge was arranged in four compartments, in each of which there was a gauze pocket holding half a pound of caustic soda in three layers. The total caustic charge was therefore 2 pounds in weight.
On leaving the warming tube the evaporated air passed into the flow circuit proper on the left shoulder member, and then entered the breathing bag where it effected oxygen enrichment of air previously exhaled by the wearer. On inhalation, air was drawn from the bag placed on the wearers chest, through the inhalation valve and breathing tubes to the lungs. On exhalation it passed through the exhalation breathing tube by the exhalation valve and frame to the CO2 absorbent cartridge and back to the breathing bag. When the breathing bag was filled, partly by newly evaporated air and partly by exhaled air, any excess passed to the outside atmosphere through the automatic relief valve. Thus regeneration was effected continuously.
The frame of solid brass drawn tube served as the air flow circuit, there being two valves and two stops to maintain uniformity of direction. Provision was made for the discharge of saliva by having a collecting box and discharge valve attached to the mouth- piece. The rubber breathing bag was protected by a strong leather case having bronze springs to prevent its being unduly flattened when the wearer had to crawl in a prone position. Manufactured by Guest & Chrimes, Ltd., Rotherham.
AEROLOX LIQUID OXYGEN BREATHING APPARATUS
|1.0 Introduction Aerorlox is a two hour, closed circuit, liquid oxygen breathing apparatus which provides cool, dry air even when being used in a hot environment, Breathing resistance is so low that it is hardly noticeable under heavy work conditions. The rated duration of Aerorlox is two hours with a 25% safety factor at hard work rate and a 5.5 lb charge of liquid oxygen. As the work rate decreases so the duration increases.
|2.0 Technical data
Weight with liquid oxygen
Liquid oxygen charge
(soda lime) Oxygen flow
31 lb (13.4 kg)
failing to 26 lb (11.8 kg)
length 19.5 in (49.5 cm)
15 in (38.1 cm)
6.25 in (15.9 cm)
5.5 lb (2.5 kg)
3.5 lb (1.6 kg)
of 6-10/mesh Protosorb
3.0 Breathing circuit.
3.1 The exhaled warm saturated air passes from the mouthpiece through the exhalation valve housed in it, along the exhale breathing tube into the purifying canister.
3.2 When the air in the circuit reaches a pressure of 0.8 in (2.0 mbar) water gauge, any further exhaled air is discharged to atmosphere via the automatic relief valve.
3.3 The exhaled air passes through the radial flow purifying canister where carbon dioxide is absorbed.
3.4 The purified air passes over one end of the liquid oxygen pack into the breathing bag.
3.5 This cools the air and condenses the moisture which collects in the breathing bag.
3.6 The heat from the purified air surrounding the liquid oxygen pack stimulates the evaporation of oxygen. The oxygen gas passes from the innermost container to and fro through the outer cases, and, by so doing, slows down heat input to liquid oxygen. As the cool gaseous oxygen flows out of the evaporating tube it mixes with the purified air in the breathing bag, further reducing the air temperature and condensing more of the moisture. The condensate fails into the breathing bag where it remains trapped.
3.7 Oxygen enriched air from the breathing bag passes over the liquid oxygen pack between baffles to increase its path, and, in the process, is further cooled. 33 The now cool, fresh, dry air passes along the inhale breathing tube and through the inspiratory valve into the mouthpiece.