COMPANYNAME SOLAS TRAINING MANUAL PART B – Section 10 Breathing Apparatus
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Using the same simple calculation, the working duration of 9 litre and twin 4 litre 200 bar cylinders will be found to be approximately 35 minutes and 30 minutes respectively. It must, however, be stressed that these times should be regarded as guidelines only and individuals should obtain an assessment of their own endurance capabilities by practicing under differing conditions.
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Every set of self-contained breathing apparatus must be provided with spares cylinders having a total free air capacity of 2400 litres. In practice this usually means that each set has two spare charged cylinders. There are however two exceptions: 1) in ships with five or more sets the total spare capacity (for the whole ship) need not exceed 9600 litres. 2) If the ship is able to re-charge the air cylinders with suitable breathing air, then it is necessary to carry only 1200 litres of spare breathing air per set; however the total spare storage capacity of free air provided (for the whole ship) need not exceed 4800 litres. Where ultra lightweight cylinders are carried there are restrictions concerning who may recharge the cylinders, the moisture content of the air used to recharge them, and the attention that must be given to the external cylinder protection and its condition.
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In order to minimise the amount of air used: - Train frequently, including wearing the mask in difficult circumstances. - Be very familiar with the use of the equipment. - Control breathing so that it is steady. Panting and ‘panic’ breathing will reduce the available time. - Use clean shaven personnel as a beard will often inhibit a good seal around the mask. - Do not use air unnecessarily (e.g. while waiting to enter a compartment). - Be familiar with the area to be entered.
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Other factors affecting the amount of air consumed include age, fitness, state of health, smoke/non-smoker, state of mind and overall work rate. 10.4.2.
Demand type C.B.A.
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In most types of CBA, the air passes from the cylinder to a pressure reducer where the pressure is reduced to about 10 bars (varies with type and maker) before passing to the demand regulator which is attached to the facemask. These sets are often referred to as twin-stage. In some other types, the air is led at full cylinder pressure direct to the demand regulator. These sets are known as single-stage. Essentially, from the wearer’s point of view, both types meet the same requirements though the single-stage sets are perhaps simpler to maintain. The air supply hose is attached to a demand regulator, which is often attached or screwed direct into the facemask. The flow into the mask is controlled by a tilt valve, which is actuated by a diaphragm in the demand regulator. When the wearer is not breathing, no air flows into the mask. When inhaling, however, a slight vacuum is created in the mask causing inward movement of the diaphragm, which pushes
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