SCBA

Compressed Air Breathing Apparatus

What is a Breathing Apparatus and where and why do we use it on board?

A breathing apparatus normally known as the BA set or the SCBA (Self contained Breathing apparatus) or CABA (Compressed air breathing apparatus) is an equipment used to supply fresh air for human breathing when a person is entering any space where the atmosphere is a suspect and may not support human life.

These include:

·         When entering into an enclosed space

·         When entering into a space to fight fire

The Self Contained Breathing Apparatus (SCBA) or Compressed Air Breathing Apparatus (CABA):

The equipment is designed on an open-circuit system.  The exhaled air is discharged to the atmosphere and the wearer of this apparatus gets his fresh air from the air cylinder attached to the equipment.

The equipment consists of:

·         One or two cylinders containing air under pressure

·         A harness to mount the cylinders on the back of the person.

·         A respiratory system which incorporates a means of reducing the pressure of the air from the cylinder and of supplying the wearer on demand with air according to his requirements, and

·         A facemask attached to a demand valve, which maintains a positive pressure inside the mask at all times.

The arrangement of a typical apparatus is as follows:

·         The cylinders contain approximately 1240 litres of free air compressed to give approximately 31 minutes of full air usage time and 21 minutes of working duration under normal circumstances.  Please note that the usage time greatly varies from person to person and the workload the person is performing.

·         A reducing valve is connected after the cylinders to reduce the pressure to approximately about 4 bars.  This pressure is further reduced by the demand valve, which is attached to the mask of the wearer.  The demand valve supplies air to the wearer when he inhales and closes when he exhales.

·         An Exhalation valve releases the exhaled air from the facemask.

·         When approximately 10 minutes of air is left (air cylinder pressure about 50 bar), a warning whistle will sound continuously – warning the user that his air supply would soon be over and he has to move out.  This warning signal will sound continuously till the air in the cylinder is over.

·         The facemask is made of moulded rubber with a series of adjustable rubber straps to secure it to the head of the wearer and fitted with quick release arrangements.  The user should have a good field of vision so that the wearer does not need to turn his head constantly.

·         A gauge is provided to indicate the pressure of the air in the cylinder.

·         Spare cylinders should be provided for each set of breathing apparatus and a small air compressor to charge these cylinders is provided.

If the facemask is dislodged whilst the wearer is in a smoky or toxic atmosphere, it is vital that the wearer should hold his breath and immediately replace the dislodged mask.  If for any reason, there is likelihood of delay in doing so, the wearer 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.    

An approximate Consumption and duration table:

Degrees of work	Air consumption (Ltrs/minute)	Duration of cylinder having 1200 ltrs capacity (minutes)	Duration of cylinder having 1800 ltrs capacity (minutes)
Resting	8 – 12	150 – 100	225 - 150
Light Work	12 – 20	100 – 60	150 – 90
Moderate Work	20 – 40	60 – 30	90 – 45
Heavy Work	40 – 60	30 – 20	45 – 30

Please note in the above table the total full duration is given.  Reduce the safety margin from the above table to get the working duration.

Nominal Working Duration  = (fully charged cylinder capacity) minus 10 minutes.

                                                            (40)

Here we have taken an average consumption of 40 litres of air per minute being required by human being when doing heavy work.

Hence if we have a cylinder of 1200 litres capacity fully charged then

Nominal working duration = 1200/40 = 30 minutes – 10 minutes (period for which the alarm whistle will blow and time required for the wearer to get back to safe atmosphere) = 20 minutes.

Pre-Operational Checks:

High Pressure Leak Test:

1. On the lung demand valves, press reset lever to switch ‘Off’ positive pressure mechanism.

DO NOT press center of rubber cover while pressing reset lever, or force lever against stop. See Figure below.

WRONG WAY

CORRECT WAY

2. Open cylinder valve slowly, but fully, to pressurize system.

3. Close cylinder valve and observe pressure gauge.

4. Gauge reading shall not decrease more than 10 bar in 1 minute.

Note:   If a leak is indicated from the demand valve proceed as follows:

Press center of rubber cover to release positive pressure mechanism - press re­set lever to lift positive pressure mechanism. Repeat action two or three times to eliminate leak.

If leak not eliminated, do not attempt repairs on board. Send for service ashore.

Whistle Warning Unit Test:

1. Cover demand valve outlet with ball of hand, press center of rubber cover (as shown in figure below)

2. Turn ‘On’ positive pressure switch.

3. Slowly vent system by carefully lifting ball of hand maintaining a slow de­crease in pressure.

4. Observe gauge. Whistle should sound at pre­set pressure of 55 bar +/- 5bar.

5. Following satisfactory whistle test, press reset lever to switch ‘Off’ posi­tive pressure.

Should whistle not sound at required pressure, whistle can be reset using manufacturers instructions AND with Master or Chief Officer help.

DO NOT ATTEMPT TO ADJUST WHISTLE ON YOUR OWN.

Putting on equipment:

1. Extend shoulder straps and waist belt. Put on equipment.

2. Fasten buckle (See figure below). Pull ends of waist belt away from buckle until secure and comfortable on hip. Tuck ends in belt loops.

3. Pull down shoulder straps (See figure below) until equipment is secure and comfortable. Tuck strap ends under waist belt.

Putting on Face piece:

Preparing the mask:

1. Open the straps as far as they will go.

2. Place the carrier strap around your neck.

Fitting the mask:

Beards and sideburns in the sealing area of the facemask will cause leaks. Therefore the facemask should not be used by anyone with facial hair of this sort. Spectacle frames in the sealing area also cause leaks.

Insert chin in chin-piece.

Tighten both lower (1), then upper straps (2) evenly towards back of head. (See figure below). Only tighten center strap (3) if necessary.

Connecting Demand Valve to Face piece:

1. Check face piece port and demand valve O-ring, are clean and undamaged.

2. Push demand valve into face piece port until it clicks into position.

3. Check attachment is secure. Pull demand valve away from face piece - there should be no axial movement.

4. On achieving face seal positive pressure de­mand valves will automatically activate on first inhalation.

5. Breathe normally.

6. Before use perform function checks.

Function Checks:

1. Close cylinder valve.

2. Breathe normally to vent system.

3. During vent­ing observe gauge - whistle alarm should sound at preset pressure of 55bar +/-5bar.

4. When gauge indicates zero, hold breath. Face piece should hold onto face indicating positive seal.

5. Open cylinder valve slowly, but fully to pressurize system.

6. Inhale and hold breath. Unit must balance, i.e. no audible leak.

7. Continue breathing. Expired air should eas­ily flow out of exhalation valve.

8. Press center of rubber cover on demand valve checking supplementary supply.

Note: If leak detected, open cylinder valve, readjust head harness and retest.

During Use:

1. Cylinder pressure must not be less than 80% full.

2. Check gauge reading regularly. Whistle will sound at 55 bar +/- 5 bar.

3. When whistle sounds, exit and go to safe area, by shortest and safest route.

4. Do Not remove equipment until in safe area, clear of hazard.

After Use:

1. Press reset lever to switch ‘Off’ positive pressure.

2. Press and hold down the button and remove the demand valve.

3. Removing mask: Insert index finger behind the tabs on the neck straps and press the buckles forwards with thumb, pulling the mask forward off your face and then up and back over your head.

4. Close cylinder valve and remove face piece.

5. Unbuckle waist belt, lift shoulder strap buckles to loosen, remove equipment.

Maintenance on facemask:

Cleaning: The mask must be cleaned after every use. Do not use any organic solvents such as acetone, alcohol etc.

Clean the mask with a cloth and lukewarm water mixed with all-purpose detergent. Rinse thoroughly under running water.

Disinfecting: Disinfect mask after every use. Place mask in disinfectant bath. Only use approved disinfectants - e.g. DAlSYdes. (R54 125)2). Excessive disinfectant concentrations and over-long disinfecting times can damage the mask. Rinse thoroughly under running water.

Drying: Leave to dry in air. Maximum temperature 60°C. Keep out of direct sunlight.

Testing: The mask must be tested every time it has been used, repaired or serviced as per manufacturers instructions.

Visual inspection of the speech diaphragm: The speech diaphragm and O-ring must be clean and undamaged. If not, clean or replace.

    

Visual inspection of inhalation valve: The inhalation valve is visible in the mask connector. Check by blowing into it that both wings of the valve disc move freely. Replace if seized.

Visual inspection of exhalation valve: Remove the protective cap from the connector. Press one arm of the spring clamp inwards and remove the clamp. Hold valve disc by the nipple and lift out of guide. The valve disc and seat must be clean and undamaged. Clean or replace if necessary. Moisten valve disc with water and refit. When the seat is

horizontal, the valve disc must slide into the guide under its own weight. Fit spring clamp and spring so that both clamp arms engage at the sides. The clamp is marked “L”= left and “R” right and fits at an angle.

      

      

Additionally, Maersk requires following checks to be carried out:

1. Every month the air bottles, bottle valves, reduction valve, intermediate hose, manometer, carrying back plate, the lung demand regulator, the warning alarm for withdrawal, and the breathing mask shall be examined and checked in accordance with the manufacturer's manual.

2. Every year all valves, sealing and speech membranes shall be checked.

3. Every second year the exhalation disc must be replaced. This should be done even if the mask has not been used.

4. Every five years the complete breathing apparatus shall be submitted to a major service check, which should include a major overhaul of the reduction valves in an authorized workshop and a pressure test of the air bottles.

5. Pressure test of the air bottles shall be carried out by an approved service company.

6. If an air bottle shows any sign of corrosion or if it has been exposed to damage or overheating it shall be replaced instantly.

Charging Cylinders:

Charge cylinder to pressure stamped on neck, or shoulder of cylinder.

Refer notes on Breathing Air Compressor.