Answer SSEP Question 14
Q14.
With reference to an automatic water sprinkler, fire detecting alarm
and extinguishing system for accommodation spaces: –
A. (i) Sketch a
typical system; (ii) Describe the operation of this system;
B. State the
sources of water available
C. Describe the sprinkler head and its
operation;
D. State how the temperature rating of the sprinkler head is
determined.
Answer: A. (i) Sketch of the system.
(ii) Operation of this System
The sprinkler system is an automatic fire detecting, alarm and extinguishing system that is constantly 'on guard' to deal quickly and effectively with any outbreak of fire that may occur in accommodation or any other spaces.
Briefly the system is composed of a pressure water tank with water pipes leading to various compartments. In these compartments, the water pipes have sprinkler heads fitted which come into operation when there is an outbreak of fire. The pressure tank is half filled with fresh water through the fresh water supply line. Compressed air delivered from the electrically driven air compressor raises the pressure in the tank to a predetermined level. This should be such that the pressure at the highest sprinkler head In the system is not less than 4.8 bar. Sprinkler heads are grouped into sections with not more than 200 heads per section and each section has an alarm system.
In case the temperature rises beyond limit, the quartzoid bulb in the head bursts, the valve assembly falls permitting water to be discharged from the head which strikes the deflector plate and sprays over a considerable area. Each head showers adequately a deck area of 16 $\displaystyle \mathrm{m^2}$. At least 5 litre/$\displaystyle \mathrm{m^2}$ per minute water spray should be provided. When a head comes into operation, the non-return alarm valve for the section opens and water flows to the sprinkler head. This non-return valve also uncovers the small-bore alarm pipe lead and water passes through this small-bore alarm pipe to a rubber diaphragm. The water pressure acts upon the diaphragm and this operates switch which causes a break in then continuously live circuit. Alarms both visible and audible fitted in the engine room, bridge and crew spaces are then automatically operated. Stop Valves A and B are locked open and if either of these valves are inadvertently closed a switch will be operated that brings the alarms into operation. The alarm system can be tested by opening valve C which allows a delivery of water similar to that of one sprinkler head to flow to drain.
B. Sources of Water Available:
(1) Water is usually supplied from a hydrophore tank. This hydrophore is always filled with fresh water and pressurized by compressed air at pressure sufficient to ensure that all the water is delivered to the highest sprinkler at sprinkler head working pressure.
(2) Once this tank is emptied and eventually the pressure on the system goes down which triggers the sea water pump connected to the main sprinkler line to come online and continue feeding the water until it is required.
(3) There is also a cross Connection provided between the fire main to the sprinkler line which may be used in-case of a failure of the sprinkler sea water pump.
(4) There is a shore connection provided which is to be used in a dry dock or port.
C. Sprinkler Head and its Operation:
The sprinkler system is an automatic fire detecting, alarm and extinguishing system that is constantly 'on guard' to deal quickly and effectively with any outbreak of fire that may occur in accommodation or any other spaces.
Briefly the system is composed of a pressure water tank with water pipes leading to various compartments. In these compartments, the water pipes have sprinkler heads fitted which come into operation when there is an outbreak of fire. The pressure tank is half filled with fresh water through the fresh water supply line. Compressed air delivered from the electrically driven air compressor raises the pressure in the tank to a predetermined level. This should be such that the pressure at the highest sprinkler head In the system is not less than 4.8 bar. Sprinkler heads are grouped into sections with not more than 200 heads per section and each section has an alarm system.
In case the temperature rises beyond limit, the quartzoid bulb in the head bursts, the valve assembly falls permitting water to be discharged from the head which strikes the deflector plate and sprays over a considerable area. Each head showers adequately a deck area of 16 $\displaystyle \mathrm{m^2}$. At least 5 litre/$\displaystyle \mathrm{m^2}$ per minute water spray should be provided. When a head comes into operation, the non-return alarm valve for the section opens and water flows to the sprinkler head. This non-return valve also uncovers the small-bore alarm pipe lead and water passes through this small-bore alarm pipe to a rubber diaphragm. The water pressure acts upon the diaphragm and this operates switch which causes a break in then continuously live circuit. Alarms both visible and audible fitted in the engine room, bridge and crew spaces are then automatically operated. Stop Valves A and B are locked open and if either of these valves are inadvertently closed a switch will be operated that brings the alarms into operation. The alarm system can be tested by opening valve C which allows a delivery of water similar to that of one sprinkler head to flow to drain.
B. Sources of Water Available:
(1) Water is usually supplied from a hydrophore tank. This hydrophore is always filled with fresh water and pressurized by compressed air at pressure sufficient to ensure that all the water is delivered to the highest sprinkler at sprinkler head working pressure.
(2) Once this tank is emptied and eventually the pressure on the system goes down which triggers the sea water pump connected to the main sprinkler line to come online and continue feeding the water until it is required.
(3) There is also a cross Connection provided between the fire main to the sprinkler line which may be used in-case of a failure of the sprinkler sea water pump.
(4) There is a shore connection provided which is to be used in a dry dock or port.
C. Sprinkler Head and its Operation:
The
accommodation areas are fitted with sprinkler heads which both detect
and extinguish tires. The sprinkler head is closed by a quartzoid bulb
which contains a liquid that expands considerably on heating.
When excessively heated, the liquid expands, shatters the bulb and water will issue from the sprinkler head. A deflector plate on the sprinkler head causes the water to spray out over a large area.
D. State how the temperature rating of the sprinkler head is determined.
Generally, the operating temperature range permitted for these bulbs is $\displaystyle \mathrm{68.5^oC}$ to $\displaystyle \mathrm{93.5^oC}$ but the upper limit of temperature can be increased. This would depend upon the position where the sprinkler head or heads are to be sited. Quartzite bulbs are manufactured in different colours the colour indicates the temperature rating for the bulb; E.g. rating colour: $\displaystyle \mathrm{68.5^oC}$ - red; $\displaystyle \mathrm{80.5^oC}$ - Yellow; $\displaystyle \mathrm{93.5^oC}$ - Green
When excessively heated, the liquid expands, shatters the bulb and water will issue from the sprinkler head. A deflector plate on the sprinkler head causes the water to spray out over a large area.
D. State how the temperature rating of the sprinkler head is determined.
Generally, the operating temperature range permitted for these bulbs is $\displaystyle \mathrm{68.5^oC}$ to $\displaystyle \mathrm{93.5^oC}$ but the upper limit of temperature can be increased. This would depend upon the position where the sprinkler head or heads are to be sited. Quartzite bulbs are manufactured in different colours the colour indicates the temperature rating for the bulb; E.g. rating colour: $\displaystyle \mathrm{68.5^oC}$ - red; $\displaystyle \mathrm{80.5^oC}$ - Yellow; $\displaystyle \mathrm{93.5^oC}$ - Green
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