The advantage here is that pressures can be monitored from outside the compartment.
It can get very confusing when a LP alarm goes off in an enclosed compartment having more than one person with SCBA sets , whose air consumptions can vary, while say doing Methanol spray of a cargo tank.
By the way NO regulation allows methanol spray with SCBA IBC sets. IBC sets are not for working in the literal sense. " Working time " relates to "lung demand" of free air, which is 10 litres / min for rest, 30 litres/ min for light work and 100 litres / min for strain of fireman's lift. Fill up a form in capital does NOT mean you have to take a flight to the capital city of your country. SCBA sets are for emergencies and must be donned by two sailors.
Air line breathing apparatus has been developed to enable compressed air equipment to be used for longer periods than would be possible using self contained equipment alone and to give easier access to confined compartments.
The apparatus consists of a face mask supplied with moisture free compressed air through a small diameter air hose. Air, from a compressor is suitably filtered and its pressure reduced to the design pressure required to supply air to the face mask.
Because of the small diameter of the air hose, it is essential that the air pressure not fall and the supply should be adjusted to maintain a constant pressure. The airhose must not be longer than 90 metres.
The airhose should be non collapsible and kept clear of sharp projections. If the compressor fails to maintain this pressure, the supply must be switched over to compressed air bottles provided for such emergency. The user should then be signalled to leave the compartment.
The air line pressure gauge and the control for changing over to an alternative supply must be under the constant supervision of a responsible person who has received instruction in the procedure required.
It is recommended that a completely separate supply of clean air should be available under the direct control of the user.
When using the equipment the following precautions are necessary:
The face mask must be checked and adjusted to ensure that it is airtight. The working air pressure should be checked before use. The audible low pressure alarm should be tested before use. The user should keep his air line clear of projections. The length of air hose used should not exceed 90 metres.
If the user has reason to suspect the efficiency of the equipment he must leave the compartment immediately, switching over to an alternative supply of air, if available.
Keep an EEBD/ ELSA handy . the hose must be attached to the wearer by a belt and must be quick disconnect system. The EEBD gives 40 litres/ min constant flow for 15 minutes and are ONLY for escape, never for working.
Airline systems must be examined and tested by a responsible ships officer at regular intervals.
Ensure that the pressure reducing systems work properly.
CAPT AJIT VADAKAYIL