EMERGENCY ESCAPE BREATHING DEVICE (EEBD)
EEBD is a part of fire fighting equipment by SOLAS II-2/4.3 ''Espcape'' section and the basic technical requirements are given in Fire Safety System Code (FSS Code 2.2). The above standards are applied depending on the type of the ship. For example, IGC Code applies to Gas Tankers. So that, the requirement of EEBD should be checked from the relevant code depending on the type of the ship.
Purpose
EMERGENCY ESCAPE BREATHING DEVICE (EEBD) is used t escape from a gas-hazardous space.
EEBD shall not be used to tackle with fire and enter in spaces where oxygen is deficient.
You may see the dilemma ''How is it possible that if EEBD is not used to fight fire, but it is included in FFS Code?''. The answer is that EEBD is under ''Escape'' section of SOLAS II/2. If fire or hazardous atmosphere occurs in an enclosed space, the victim will get the EEBD and get out of that place.
Actually, EEBD is not designed to tackle wıth fire nor enter in spaces where there is lack of oxygen because of its minimum working time requirement. (10 min by FFS Code, which is not enough o tackle wıth fire nor enter in spaces where there is lack of oxygen).
Just think that you are entering the cargo hold which is occupied by hazardous gas and has a height of 15 m. You will need to climb up & down + perform your task inside the tank within at least 10 min. It is not possible.
When you consider to tackle fire by EEBD, fire extinguishing process may take more than 10 minutes.
Working System
Once EEBD is activated, it will supply air to the hood at a pre-determined ''fixed rate'' irrespective of inhalation rate. The fixed rate is usually more than 40L/min. We will come to ''why is it 40L/m?''
The capacity of air inside the cylinder is calculated by Boyle's Law as below:
P1= 1 bar
P2= 200 barg
V1= ?
V2= 3L
(a)Working pressure of cylinder: 200 barg
(b)Capacity of air cylinder: 3 L
V1= (P2*V2)/(P1)
V1= 600L
The basic formula above dictates that what would be the air capacity at ambient pressure assuming that the temperature is constant. As you think about EEBD, the compressed air in the cylinder is reduced in pressure slightly above the atmospheric pressure. Please note that it was also assumed that 1 atm= 1 bar= 1kgf/cm2 for easing of the calculation.
40L/min consuption of air by human has been accepted in the industry. So that the working time can be calculated as (600L)/(40L/min)=15 min for the example above.
Design of EEBD
There are basically three distinctive EEBD designs as below:
Design 1: Manually Operated Cylinder Valve
 |
| EEBD PARTS |
Once the cylinder valve opened, the high pressursied air is reduced down to medium pressure (about 6.5 +/-2 barg). This rate supplies continous fixed flow of air and creates positive pressure at all times inside the hood, which prevents hazardous gas entering inside the hood.
Design 2: Auto-Operated Cylinder Valve
The only difference from manual operated cylinder valve type is that, once the EEBD bag opened, the cylinder valve automatically opens and flow of air commences. It is achieved by a hook mechanism. The anchored part is hook to the EEBD bag inside and the movable part is ınserted in the cylinder valve in a way that when it is connected, EEBD is not operational but when it is released, EEBD is operational.
 |
| Auto-activation mechanism. The hook should be fixed on dedicated location inside EEBD bag. Source: https://i.ebayimg.com/images/g/o-kAAOSw4oJeWRxO/s-l400.jpg |
Design 3: Closed-Circuit EEBD (OCEANCO)
The compressed oxygen is stored in a small cylinder.
When the cap is removed, the latch between cover and oxygen cylinder's regulator is activated and flow starts.
The regulator adjusts pressure depending on the breathing bag. If the bag flattens, the rate of flow increases.
Then, it is filtered in scrubber containing lithium hydroxide that absorbs CO2.
The regulated oxygen comes to the black Breathing Bag. If pressure exceeds the working pressure of the Breathing Bag, the excess gas is vented via relief valve fited on the bag.
Thereafter, air is delivered to the hood through mouthpiece.
During exhalation, the exhaled CO2 rich air comes to the scrubber to be absorbed. Then it goes to Breathing Bag again.
The working time is 10-15 minutes as per maker manual.
It is handy to carry and maintenance-free equipment.
Please see the parts in the picture below:
 |
| Ocenco EEBD Cover Source: https://www.ocenco.com/products/m-202/ |
 |
| Ocenco EEBD Parts Source: https://www.youtube.com/watch?v=iOVTwuav5JA |
Closer Look: Pressure Regulator
Pressure regulators in EEBD and SCBAs are ''in-line'' type. That means the regulator is integrated along the airpath.
When the clinder is turned on, high pressure air will start to flow to the valve seat. When air is passed after the spring, the air accumulated between low pressure side of the pipeline and hood will trigger the spring to close the valve.
Spring load is adjusted by maker.
Outlet pressure < spring load force: Valve Opens (spring in neutral postion) - air flows.
Outlet pressure> spring load force: Valve closes (spring is compressed) - air stops.
 |
| IN-LINE PRESSURE REGULATOR Source: https://www.youtube.com/watch?v=rd1n98Z-apg&list=LL&index=11 |
Some Important Rules Related with EEBD
- Minimum duration: 10 minutes as per SOLAS II-2/13.3.4; 15 minutes as per IGC Code 14.1.
- EEBD should be carried ''hand-free''.(MSC/Circular.849 )
- EEBD should be protected by the environment. (MSC/Circular.849 ) (That means EEBDs should be stored inside a locker).
No comments:
Post a Comment