SCBA set

THE ARRANGEMENT OF A TYPICAL SELF CONTAINED BREATHING APPARATUS

 

 

  • The compressed air cylinders are connected to a reducing valve which reduces the pressure of the air passing through to about 4 bars. The air then passes through a “demand valve” which further reduces the pressure and passes air to the wearer as he inhales and closes when he exhales. An automatic valve releases exhaled air from the face mask..
  • When about 10 minutes air supply remains in the cylinder a whistle sound continuously, warning the user.
  • The face mask is made of molded rubber with a series of adjustable rubber strap to secure it to the head of the wearer and fitted with quick release arrangements. The visor should have a good field of vision so that the wearer does not need to turn his head constantly.
  • A gauge should be provided to indicate the pressure of the air in the cylinder.
  • Spare cylinders should be provided for each self contained breathing apparatus. A small air compressor should be available charge the cylinders.
  • Equipment using compressed oxygen or closed circuit regenerative apparatus is not acceptable for use on board ships.

OPERATION OF A COMPRESSED AIR BREATHING APPARATUS

 The apparatus consist of a cylinder mounted on a formed stainless steel back plate secured by two quick release cylinder straps and supported on the wearer’s back by an adjustable shoulder harness and waist belt.
  • When the cylinder valve is opened, high pressure air passes through a flexible hose to a pressure reducer. From this high pressure air is fed to the whistle warning unit and via a stainless steel flexible hose to a contents gauge positioned on the shoulder harness. 
  • Low pressure air from the reducer is fed via a stainless steel flexible hose to a demand valve incorporating a positive pressure mode.
  • The demand valve is connected to the reflex face mask which incorporates an inner mask speech transmitter and fresh air valve together with a microphone port forcommunication equipment. 
  • The air supply from the demand valve, on inhalation, first passes across the visor to prevent misting and then into the inner mask.
  • On exhalation, expired air passes out through the positively closed exhalation valve situated in the front port The set should be thoroughly inspected externally after use and at regular intervals of not more than one month when not use for external damage.
  • The endurance of the set demands on the amount of work carried out Slow deep breathing is important for maximum efficiency and endurance. 
  • A fit man will use less air.
  • The whistle warning unit will operate when a predetermined pressure remains in the cylinder. 
  • This means that the wearer has approximately 10 minutes in which to reach fresh air. 
  • If the wearer considers that it will take him longer, he must constantly refer to his pressure gauge and be aware of the relationship between the pressure remaining and the breathing time available.
NOMINAL SAFE WORKING DURATION = ( fully charged cylinder / 40 ) – 10 min

CHECKING AND TESTING

Check Cylinder Pressure :

  • Open cylinder valve slowly but fully, read off pressure of the contents gauge. High pressure leak test
  • Close cylinder valve and observe pressure gauge. The pressure indicated shall not drop more than 10 bar in one minute.
  • Check whistle warning unit
  • Switch on the positive pressure facility by hand;

              To do so, seal oudet with ball hand and apply pressure briefly on the centre of the protective cap of the demand valve. Vent apparatus by carefully lifting ball of hand. Whisde must sound at a pressure appropriate to the cylinder fitted. Deactivate by depressing the red button.

PUTTING ON THE APPARATUS :

  • Done the apparatus with all straps loose and tighten by pulling on the free ends of the shoulder straps until the apparatus sits securely and comfortably. 
  • Clip the waist-belt clip together and adjust waist-belt; do NOT over-tighten the waist-belt. To loosen the waist-belt, hold buckle at right angles to belt and pull outwards at the same time check that the demand valve is deactivated by depressing the red button (Auto Demand Valve). 
  • Open the cylinder valve slowly but fully and donfthe face mask.

MASK LEAKAGE TEST :

  • Close cylinder valve, breath normally until the air in the system is exhausted. 
  • The .mask should pull onto the face: if it does not, open cylinder valve, adjust head harness, and repeat test.

       Note: The snug fit of the mask is only achieved if the mask seal makes close contact with the skin, i.e., it must be certain that there is no facial hair, stubble, side burns or the like in this area.

CHECKING THE FUNCTION OF THE APPARATUS :

  • Open cylinder valve slowly but fully. Check functioning of the demand valve and exhalation valve by breathing deeply several times. 
  • Hold breath, the unit shall be balanced i.e., no audible leak. 
  • Continue breathing, it must be possible for the expired air to flow easily out of the exhalation valve. 
  • Check the function of the supplementary supply by depressing fully the centre of the protective cap.

PAY ATTENTION TO APPROACH AND ESCAPE TIMES : 

  • Take pressure gauge reading from time to time whilst apparatus is worn. 
  • When the compressed air supply has fallen to a residual pressure of between 35 and 70 Bar, the whistle unit sounds. 
  • START ESCAPING AS SOON AS THE SIGNAL SOUNDS, j Given an average air consumption of 40 liters/min, approximately 10 minutes are available for escape.

END OF USE :

  • Take off the mask. 
  • Shut off the air supply at demand valve by pressing red button. 
  • Unfasten waist-belt by depressing two center spigots. Loosen shoulder straps by liftingbuckles in vertical direction and removing life line if used. 
  • Put apparatus down  
  • Close cylinder valve.

(DO NOT THROW DOWN OR DROP DOWN).

VENTING THE APPARATUS :

                 Vent the apparatus by activating the positive pressure facility of the demand valve. Switch positive pressure facility off again by pressing the red button.

REMOVE THE CYLINDER :

                 To remove cylinder, loosen the wing bolts. Swing the cylinder straps clear and unscrew the cylinder connector. Lift the cylinder clear of back plate.

PRECAUTION WHEN USING CABA

  • Entering into smoky atmospheres and then starting up their sets is EXTREMELY DANGEROUS AND MUST NOT BE PERMITTED.
  • The face mask is designed to prevent any external atmosphere from entering the respiratory system and it is exceedingly dangerous for the face mask to be removed when the wearer is in a smoky or toxic atmosphere. IF THE FACE MASK IS DISLODGED WHILST THE WEARER IS IN A SMOKY OR TOXIC ATMOSPHERE, IT IS VITAL THAT THE WEARER SHOULD HOLD HIS BREADTH AND IMMEDIATELY REPLACE THE DISLODGED MASK. 
  • If for any reason, there is likelihood of delay in doing so, the wearer should contact the other members of the team IMMEDIATELY and he should be evacuated to fresh air at the earliest, even though he may not feel any ill effects from the few breaths of contaminated air which he has been forced to inhale.
  • Whenever possible, working in pairs gives confidence and contact should be made by physical touch and speaking. 
  • When in strange surroundings and unable to see, the only course is to work by touch and to follow the elementary precautions of shuffling along with the feet and feeling with the back of the hand for obstructions and falling down openings in floors or stairways will be minimized. 
  • If the leading man halts for any reason, then men following will become aware of this by contact and the reason for the halt should be communicated as far as possible to others.
  • If the wearer is entrapped and unable to withdraw, then he must raise an alarm by signal on the line or a portable radio equipment (if being carried) and then he should relax in as comfortable in a position as possible, breathe shallowly and await assistance.
  • While working in areas where high expansion foam exists, it should be remembered that this foam being opaque, visibility is nil; also the audibility is greatly reduced. 
  • Immersion in high expansion foam may therefore give a feeling of complete isolation and having effects similar to claustrophobia. 
  • Men should always maintain physical touch and use the safe guards by guidelines.

CARE AND MAINTENANCE OF SCBA 

  1. The care and maintenance of all SCBA is relatively simple. 
  2. Adjustments are seldom necessary especially if the sets are regularly used and serviced. 
  3. Dismantling, assembling, testing and renewal of any of the component parts should be carried out in accordance with the manufacturers recommendations for each type of set. 
  4. After use the apparatus should be cleared as necessary. 
  5. The face mask should be washed and disinfected. 
  6. The whole apparatus should be thoroughly dried before assembly. 
  7. If the cylinder pressure is less than 5/6th of the maximum, then the cylinder should be replaced by a fully charged one. 
  8. Washers or other parts found defective during testes should be renewed. “O” rings and other seals should be renewed not less frequency than recommended by the makers. 
  9. When tightening nuts, excessive force should be avoided as this may damage the threads.