(SELF CONTAINED BREATHING APPARATUS) - SCBA
SCBA is a Respiratory Protective Device used by Fire Fighters to have pure air supply (BREATHABLE AIR) continuously by the air cylinder attached to the backpack.
Firefighters are continuously exposed to
1. Toxic combustion products
2. Oxygen deficient atmosphere
3. Superheater air
4. Dangerous gases
5. Airborne contaminants
6. Smoke particles
To protect themselves from the above situations they use OPEN CIRCUIT TYPE SCBA (self-contained breathing apparatus.
WHAT IS SCBA:
A self-contained breathing apparatus (SCBA) is a type of respiratory device/ Breathing apparatus that contains breathable compressed air in a cylinder and delivers air in the required quantity for breathing purposes. This apparatus/equipment is carried along with the firefighter/rescue workers
TYPES OF SCBA:
They are two types of SCBA
INDIAN STANDARDS
The Indian standard ( IS 10245) on BREATHING APPARATUS is provided in four parts.
· Part 1: Dealing with closed-circuit breathing apparatus.
· Part 2: Dealing with open-circuit breathing apparatus
· Part 3: Dealing with fresh air hose and compressed airline
· Part 4: Dealing with escape breathing apparatus.
Part 2: Open-circuit self-contained breathing apparatus type (SCBA) is used by firefighters/rescuers working in toxic atmospheres,
OPEN TYPE SELF CONTAINED BREATHING APPARATUS
The open-circuit breathing apparatus is widely used by firefighters to have a continuous supply of air.
The three most important parts of the SCBA are
1. BACKPACK WITH HARNESS
2. CYLINDER WITH CYLINDER VALVE ASSEMBLY
3. FACE MASK WITH HARNESS
The compressed air carried in the cylinder is fed either via a First stage pressure reducer followed by a lung-governed demand valve connected to the facepiece to enable the wearer to breathe air. The Exhaled air passes through the non-return valve to the atmosphere.
SEQUENCE OF OPERATION OF THE ENTIRE BA SET
UNDERSTANDING THE PARTS OF SCBA
1) BACKPLATE HARNESS ASSEMBLY: It is a rigid frame with adjustable straps (2 shoulder straps, 1 waist strap, 1 cylinder strap to hold the cylinder) to fit properly and secured onto the firefighters back. The straps are designed to stabilize the unit and carry the weight and providing the wearer with a comfortable fit and required safety.
2) AIR CYLINDER ASSEMBLY: The air cylinder contains breathing air under pressure. It is constructed of steel, aluminium wrapped in fibreglass or Kevlar. The weight of the apparatus as ready for use with facepiece and fully charged cylinder should not exceed 18 kg as per standard. The Colour of the cylinder is as per IS 3933: 1966.
IMPORTANT: The cylinder valve should be designed in such a way that, the valve spindle cannot be unscrewed completely from the assembly as well as valve should not close when it comes accidentally with any surface
3) CYLINDER WORKING DURATION: This is used to calculate the time in minutes a wearer can use, this is done by dividing TOTAL VOLUME OF AIR IN LITRES IN CYLINDER / 40 (40 Is the average air intake by personnel engaged in firefighting /rescue operations)
4)
PRESSURE GUAGE / LUNG DEMAND VALVE: The cylinder outlet is connected to PRESSURE REGULATOR UNIT (this is called the 1ststage pressure reducer which reduces the pressure coming from the cylinder to around 8 bar). From this Pressure regulator unit, two hoses are drawn which are HIGH-PRESSURE HOSE and LOW-PRESSURE hose
i. To the end of the high-pressure hose, a PRESSURE GUAGE with WARNING DEVICE (alarm/whistle) is connected. The function of the PRESSURE GUAGE is to show the working pressure of air present in the cylinder. The function of WARNING DEVICE is to get activated and give out a sound (alarm/whistle) If the pressure in the cylinder drops to 50-55 bar, this is a warning indication to the firefighter/rescuer to stop the operation and immediately evacuate the premises to the safe point.
ii. To the end of the low-pressure hose, a LUNG GOVERNED DEMAND VALVE which in turn is connected to the facepiece at the point of INHALATION VALVE. This LUNG GOVERNED DEMAND VALVE will ensure that only the required pressure of air is built up at its INLET such that the wearer can continue breathing.
5) FACE PIECE ASSEMBLY: The facepiece assembly is manufacture as per IS:14166/70. It consists of HARNESS with adjustable straps for proper tightening and these should not be of size less than 19 mm. The facepiece is provided with Important parts along with HARNESS
a. FACEPIECE LENS
b. EXHALATION VALVE,
c. LUNG GOVERNED DEMAND VALVE INLET
d. NOSE CUP.
e. SPEAKING DIAPHRAGM.
DONNING OF SCBA
There are two methods of Donning (steps to wear SCBA)
1. Over the head method
2. Coat method
STEP 1: The cylinder is fixed with straps to the backplate harness assembly (ensuring proper fitment to the outlet of cylinder and pressure reducer valve) and the entire set of cylinder and backplate harness assembly is mounted on the back of the rescue personnel either through 1st or 2nd method with valve assembly pointing downwards.
STEP 2: Open the valve assembly and check the pressure gauge reading connected to the HIGH-PRESSURE hose, the reading on the pressure gauge should be equivalent to the PRESSURE of the cylinder with a small margin for error.
STEP 3: Check the working of the warning device which will give an alarm if 1/5th of the total volume of the breathing air volume is left (or) at least 250 litres should be still left in the cylinder.
STEP 4: Don the face mask by keeping the chin in the centre of the chin cup and the harness has to be centred, once the face mask is fitted properly, all the straps should be tightened for a proper fitment leaving no chance of external air getting into the face mask. Check the exhalation valve and ensure proper fitment of LUNG GOVERNING DEMAND VALVE. Slowly open the cylinder valve and take the first breath to activate the LUNG DEMAND VALVE
SAFETY CHECKS OF SCBA
1. Observe for any leaks during opening the cylinder valve, the leak can happen anywhere in the entire circuit ( i.e. from the cylinder outlet – hoses – pressure gauge/ demand valve)
2. Check the working of warning device/alarm
3. Check the fitment of straps/buckles, any loose/improper fitment can cause serious injuries
4. Check the proper fitment of the mask by doing a MASK LEAKAGE TEST
5. After closing the cylinder valve observe the pressure gauge, the pressure indicated shall not drop more than 10 bar in one minute
PERSONAL ALERT SAFETY SYSTEM (PASS)
A PASS device (Personal Alert Safety System device) also known as a Distress Signal Unit (DSU) which is used by FIREFIGHTERS as a safety device along with SCBA apparatus. It is powered by a battery and can be attached to the harness belt around the shoulder/ waist belt and activated before commencing the rescue/firefighting operating operations. In some cases, the PASS device is integrated into the SCBA, so that when air is opened this PASS device automatically kept in working condition.
There are two situations where firefighters can face danger
1) Firefighter falling unconscious/incapacitated and can remain motionless
2) Firefighter getting stuck up under falling debris, a situation where he is conscious but cannot move.
In both, the situations PASS Device will help firefighters to get rescued in time.
· In the first case if the firefighter remains motionless for 30 seconds, then the device sends a reduced volume continuous pre-distress signal and after 7 seconds a louder pulsating signal is sent
· In the second case, the firefighter can manually trigger an alarm and send a distress signal for help.
____________________________________________________________________________
Article by PJ Mohan
Sr.Faculty, NIFS
No comments:
Post a Comment