RESCUE BREATHING APPARATUS
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 feed of 2.3 litres per minute will permit of continuous moderate exertion for the period stated, but, if the breathing bag has been recently flushed out and allowed to fill with pure oxygen then a short spell of hard work cam be attempted. It is best not to overwork the apparatus. The Carbon dioxide is removed by the Caustic Soda peas which are arranged in the metal purifier carried o:11 the back.
DESCRIPTION OF THE "MECO" APPARATUS.
This apparatus consists of a framework holding two cylinders (a,a ) of compressed oxygen charged to 120 atmospheres, a reducing valve b) and injector c, a regenerator or purifier (d)and a cooler e) carried on the back of the wearer, supported at the shoulders by broad straps and round the body by a belt.
The breathing bag (f1,f2) is carried on the front and connected by means of flexible tubes (g, g) to the mouth attachment (m). Connections between the oxygen cylinders at the back and the breathing bag in front is made from stout india rubber pipes (g, g).
The oxygen cylinders are fitted with one valve
The reducing valve is securely fastened to the carrying frame by bolted metal clamps, and connected to the oxygen cylinders by a strong brass union.
The pressure gauge (k) is fitted between the cylinders and the reducing valve.
The regenerator or purifier is in file form of a circular curved rectangular metal case charged with a mixture consisting of caustic soda grains arranged in trays of wire gauze (t) which offer a double surface to the absorption of carbon dioxide.
In the middle of each tray is placed a strip of material impervious to air, and compels the air passing through the regenerator to travel in a Zig-zag manner.
The regenerator is supplied either with the interchangeable type which has to be thrown away after use or with the refillable type which can be refilled, and used again. The breathing bag is divided into two compartments (fl, f2) for the purposes of inspiration and expiration respectively and has fitted to it a relief valve (r) for the escape of excess air in the bag. A saliva trap (s) is also provided. This apparatus belongs to the injector type of apparatus, the injector being used to cause circulation of air up to 60 litres a minute.
ACTION OF THE MECO APPARATUS.
On opening the main oxygen valve from the cylinders, the oxygen passes through the reducing valve where it is reduced to a pressure giving 2 litres a minute. It then enters the injector where owing to the high velocity of the oxygen it sucks the expired air through the regenerator and cooler after which it mixes with the oxygen escaping through the injector and is carried along the tubes to the breathing bag and to the wearer. Experiments have proved that a negative pressure is set up in this apparatus. To reduce this the makers have introduced an equalising bag which is inserted between the cooling pipe and the injector. The relief valve has also been removed from near the saliva tap and placed near the bottom of the regenerator cartridge.