Fire Fighting

Sprinkler system maintenance
Fire Pump-test and survey
Hypermist system & maintenance
IG System
Maintenance of smoke detectors, quick closing valve and fire hydrant hoses.

Sprinkler system maintenance

Sprinkler system: - the structural fire protection is based on zones separated by fire proof bulkhead and having fire proof division within them. A network of sprinklers head is arranged throughout the spaces to be protected each sprinkler head is normally kept closed by a quartziod bulb which is almost filled with a liquid having a high expansion ratio. When liquid is exposed to abnormal heat it expands rapidly to completely fill the bulb, further expansion is sufficient to shatter the bulb. Water maintained under pressure by compressed air, is then expelled from the sprinkler head or heads in the form if a heavy spray. Each head adequately shower a deck area of 16meter square and the heads are arranged so that every part of each space requiring protection, can be covered by water spray.

The system has a pressure tank which is kept part filled with fresh water and pressurized to 8Bar by compressed air when the pressure drops below 5.5bar, a salt water pump cuts in automatically so that if the if the sprinkler operates a supply of water is maintained.

Each installation is divided into sections containing up to 200 sprinkler heads and each section has an alarm valve. When a sprinkler comes into operation, water flows through the section alarm valve. The water lifts the N/R- valve exposing an annular groove which connects to a diaphragm alarm switch. This switch is coupled to an alarm valve and to an indicator panel on the bridge which gives audible and visual warning that a sprinkler has operated and fire has probably broken out in the section indicated. Fire have frequently been found to have been extinguished by the system alone. When any occurrence has been dealt with the stop valve which is usually locked open, may be closed to replace the sprinkler head which has operated and to enable the section to be drained of salt water before filling with fresh water. Any maintenance on a section is carried out with the stop valve closed. The test valve can be opened to create flow and cause the N/R section alarm valve to open, to test the alarm.

Regular maintenance of the system consists of greasing the various valves and checking their freedom of movement, logging the pressure gauge reading, before and after each alarm valve (Thus checking the tightness of the non-return valve) and checking the alarm system. The latter is done by opening the test valves and checking that the audible and visual alarms work. The pressure tank level is checked and recharged; if necessary, with fresh water and air.

The centrifugal salt water pump should also be tested by closing the isolating valve and draining the pressure switch circuit. When the pump starts automatically the delivery pressure should be logged. In the event of fire, when a normal situation is recovered the section and system are drained and flushed out; then recharged with fresh water and air.

Isolation:-

- To isolate any section the bridge has to be informed about the intended job, time out outage and expected time of job completion.

- Close the main sectional vale (stop valve).

- The alarm from this section is disabled from local location or from the bridge.

- The sea water pump auto start has to be disabled.

- The section drain valve may be opened for draining which drains into the scupper.

Maintenance:-

- Top up fresh water and air.

- Greasing and logging gauge readings.

- Checking the alarm system by opening the test valve and checking that the audible and visual alarm working.

- Sea water pump tested by closing the isolation vale and draining the pressure switch circuit. Pump should start automatically.

- Each sprinkler head should be checked regularly for any sign of leak, corrosion of the connector, any salt deposition.

- Check and ensure appropriate bulb is fitted to different temperature zones.

- Check alarm for individual section. Indication should be checked i.e which section has operated.

- Check isolation valve for each section for operation and indication.

Return back:-

- Refill and pressurize the isolated section, first the drain is still left open and the section isolation valve is cracked open and some water is drained to flush the system out.

- Close the drain and slowly start to fill the section.

- This will cause the tank level to fall. Tank is to replenish to the required level only after atop valve is fully opened.

- Press up the tank with air up to 8-8.5 Bar.

-  Put sea water pump back to auto mode.

- Put alarm to Normal

Fire Pump-test and survey

How the fire pumps are tested:-
A. Main Fire pumps:
a. Remote/ automatic start methods are tested. Prior starting confirm that the fire line is ready, valves and hydrants are appropriately opened.

b. It is to be monitored that the pumps running efficiently, priming systems are working properly.

c. Pump must deliver correct hydrant pressures at the highest hydrant.

B. Emergency fire pump:

a. Separation from main pumps is achieved by an isolation valve located on main deck, satisfactory separation is to be checked.

b. Pump is to be test run by starting from remote power sources which is separated from machinery spaces.

c. Heating arrangements if provided should be checked satisfactory.
d. Fuel supply for the emergency fire pumps operation is to be adequate as required by the regulations.
e. Test that pump runs efficiently, priming systems work and  deliver correct hydrant pressure.

When the fire pumps are tested:-

a. Fire pumps along with the fixed fire fighting appliances are inspected, weekly during Saturday routine.
b. Fire pumps are often operated during the emergency drills, fire drills are conducted at least monthly.
c. Emergency fire pumps should be kept in good working condition and test run should be done weekly without any failure.
d. Fire pumps are test run during the safety equipment surveys, Initial survey, Renewal survey and CSM surveys.

SOLAS Requirements:-

SOLAS Regulations for Fire Pumps

Maintenance carried out on the various fittings on a fire line.

Various fittings on a fire line are suction valves, fire pumps, Non-return type discharge valve, isolation valve on deck, fire hydrants, drain cock, relief valve and expansion arrangement.

Periodic inspection as per ships Plan maintenance system:-
1. Monthly inspection
a. General cleanliness of fire pumps, valves, line, hoses, hydrants and surrounding area.
b. Check the hoses and Nozzles are properly stored and ready to use.
c. Check the fire main general condition is good. Free from corrosion and any physical damage. Valves are operating freely and in open condition.
d. Test run of fire pump to be conducted, keeping required number of hydrants open. check any leakage from the fire main. monitor the pressure and flow of pump. Also monitor the motor for the any abnormal vibration or Noise. After the test the System should render ready for operation in emergency situations.
2. Quarterly inspection
a. Bearing lubrication of pump.
b. Check the condition of gland packing, check leakage and renew if required.
3. Yearly
a. Fire pumps are dismantled mechanical seal (if fitted) is checked for mating surface. Inspect the conditions of shaft, sleeve, impeller, casing, wear ring and  coupling bolts. O-rings are to be renewed.
b. Fire main are tested for leakage at maximum service pressure. Isolation valves are overhauled, maintained and working is tested.
C. Hydrants/hoses are checked for general condition. They are also checked for  correct lengths/diameters. Hydrants are accessible, properly maintained and in working condition.
D. Nozzle size/type are correct, maintained and working.
4. 5-yearly
In fire Pumps, renew ball bearing and Mechanical seal. Check shaft trueness.

Dismantle a fire pump for survey:-

Considering the fire pump is a centrifugal pump. Ensure pump is stopped, shut the suction and discharge valve. Isolate the motor electrically by control room circuit breaker. Put Man at work tag. Electric isolation permit obtained. Local panel breaker put off. Check via purging cock that the line has no pressure.

Place the dismantled part on a clean surface. When separating fit and flange faces, use jack bolts and wooden hammers, and never apply force with chisels or drivers. When removing the rotating element, take care to avoid flaw on sliding faces and machined surfaces. Particularly, never damage the mechanical seal mating faces. When removing rotating parts from the shaft, draw off each one carefully after removing the locking device. Handle the long sized-parts such as shaft carefully so that it may not bend. At overhauling, put suitable match marks as many as possible to avoid mistakes when reassembling.

Dismantling:- 

1. Remove the distant piece, fitted between the pump and motor coupling after removing both motor and pump side coupling bolts and discs.
2. Remove cooling connections to mechanical seal.
3.Remove casing top cover bolts. Once casing cover bolts are removed, pump assembly is free to remove from place along with shaft, bearing housing, bearing, mechanical seal, impeller and impeller shaft with sleeve.

4. On removing the pump assembly, slacken impeller lock nut and remove the impeller from the shaft Remove shaft key. Care should be taken for not loosing the shaft key.

5. Remove distance ring.

6. Slacken the holding screw and remove mechanical seal's rotating part

7. Slacken bearing housing bolts fitted on casing cover.

8. Remove casing cover from the shaft.
9. Remove shaft sleeve from shaft.
10. Remove bearing housing cover
11. Remove bearing retaining circlip.
12. Remove bearing housing along with bearing.

Factors which will decide replacing the parts.

The parts are to be renewed as per the manufacturers recommended period of service such as bearings and mechanical seals.

In addition to that every time upon dismantling a pump few consumable items are required to be replaced such as washers, seal rings, O-rings etc.

Further, during its inspections as per the PMS and surveys, parts are checked inspected and tested. If they are not found in satisfactory condition, must be replaced.

Cleaning and Inspection of parts:

1. Remove bearing from housing for inspection.
2. Clean impeller, bearing , shaft sleeve , casing and the shaft. Inspect and evaluate each parts for any damages, deformation, wear and tears.
3. Measure the clearance between impeller and wear rings for top as well as bottom near rings. If clearance is more than the maker's
recommendation, renew it.
4. Inspect shaft sleeve for any wear down. If sleeve found worn out , renew the same.
5. Check the condition of bearing. If found not good, renew the same.
6. Check the conditions of mechanical seal's rotary and stationary parts. If found damaged, renew it.
7. Check bearing bush at the casing bottom and confirm any wear down. If worn out beyond acceptable limits, renew It.

Assembling the pump:

Assembly
Carry out assembly, by reversing the order of disassembly and paying attention as follows.
a. Remove dust and stain from each part by washing it thoroughly with kerosene. Repair it if flaw is found.
b. Fit the locking device perfectly in each rotating part if necessary.
c. When fitting the parts with match marks, be sure no follow them.
d. Install the mechanical seal carefully and confirm its movement by hand after installation.
e. Insert each packing ring in good order softly one by one from the bottom, staggering each joint by 90° or 180°
f. Check up alignment.

g. Turn the shaft by band to see whether it tums smoothly.

Hypermist system & maintenance

Read the detailed article High Pressure Water Mist system | Hyper-Mist System 

IG System

Cargo tank protection

Fire and explosions in the cargo tank of the oil tanker can occur due to a wide variety of causes including static electricity, pyrophoric ignition, and certain metal impact if the atmosphere inside the tank is within flammable limits.

The flammable limits vary for different petroleum liquids.

In practice, the lower and upper flammable limit of oil cargoes can be taken 1% and 10% hydrocarbon by volume respectively. When an inert gas is added to a hydrocarbon gas and air mixture the result is to increase the lower flammable limits concentration and to decrease the upper flammable limit concentrations.

Hydrocarbon and their mixture without inert gas lie on line AB the slope of the line shows the reduction in oxygen content as the hydrocarbon content increases.

Points to the left of AB represent the mixture with their oxygen content for the reduction by the addition of IG.

From this figure, it is evident by adding inert gas in the hydrocarbon and their mixture the flame level range decreases until oxygen content reaches about 11% by volume at which no mixture can burn.

8% by volume specified by the IMO regulation gives a safety margin.

SOLAS regulation for cargo tank protection:

In accordance with the regulation fixed inert gas system shall be equipped on the following tankers. 

 A new tanker of 20,000 Tonnes deadweights and upward.

Tankers of 20,000 tonnes deadweight and upward constructed before 1st September 1984 which is engaged in the trade of caring crude oil shall be fitted with the inert gas system not later than

A: Tanker of 70000 tonnage deadweight and upward 1st September 1984 the date of delivery of the ship Whichever Rockers letter and

B: For a tanker of less than 70000 is deadweight 1st May 1985 of the date of delivery of the ship which never occurs later.

Tankers of 40000 tonnes deadweight and upward constructed before 1st September 1984 which are engaged in a trade of carrying coil other than crude oil and any such tanker of 20000 is deadweight and upward engaged in the trade of caring oil other than crude oil fitted with tank washing machine having individual throughput of greater than 60-meter cube per hour shall be fitted with another gas system within the allowable provided as above.

All tankers operated with a cargo tank cleaning procedure using crude oil washing shall be fitted with an inert gas system.

Method of gas replacement.

    a)   Inerting

    b)   Purging

    c)    Gas freeing

Each of these replacement operations one of two processes can predominate.

(i) Dilution which is a mixing process

(ii) Displacement which is a layering process.

Inert gas is oxygen deficient

Its main function is to inhibit fire and explosion risk by removing one side of the Fire Triangle.

Another advantage of inert gas is the reduction in pumping time as always positive pressure is maintained in the tank.

 A). Sketch a line diagram showing a typical ‘Inert Gas System’ used for inerting the cargo tanks of oil tankers, Describe the system labeling the important component parts. 

Inert gas installation for tankers from funnel gas:-

Engine exhaust is not used as it has a too high a percentage of oxygen especially at light load

(A)Boiler uptake: - point positioned

- It should not be too near to the funnel top as there is a risk of Ingress of air.

- Not too low uptake that will cause too hot gas and soot ingress, also it may cause hard deposit on the flue gas isolation valves.

Funnel gas - the temperature is 300 degrees Celsius approximately contains 12 to 14% CO2 and 2-4% oxygen 0.3 - 0.5% of SO2 (SOx and NOx unburned hydrocarbons and nitrogen).

 (B) Flue gases isolation valve:

There is an indication given for open and close for the valve. If the valve is open - the soot blower in the boiler cannot be operated. Valves provided with on-suit blowing facility.

Material: - corrosion-resistant heat resistant cast iron less than (220 degrees Celsius).

(C) Scrubber: - internal part should be constructed in corrosion-resistant material.

 Material:  wash water and inlet box are of MS plate lined with two layers of glass fiber and reinforced epoxy resin coating. The flue gas from boilers is lead to the scrubber gas inlet duct where the flue gas is cleaned from sulfur oxide and suit and cool down approximately 70 degrees Celsius with a pre-cooling water spray as the first step.

Afterward the gas pass through the water sealing area in the bottom part of the scrubber where the gas is drastically cool down to normal temperature, design not more than 3 degree Celsius above seawater temperature. While the gas is coming up through this scrubber element of a corrugated plate type further cleaning and cooling of the gas takes place with the water sprays fitted at the top side.

Water sealing area serving two purposes.

-First to prevent hydrocarbon gases from flowing back to the boiler side. -Second to prevent boiler flue gases from coming into the scrubber.

The gas inlet duct is sealed with a sealing depth of 150mm. The scrubber is provided with the high-level switch of a floating type with which the high-level alarm can trip both the cooling water pump and the inert gas system operation this alarm is most important to avoid the water backflow to the boiler side.

For maximum contact between gas and water one or more arrangements adopted (i) spray nozzle (ii) tray of packed stone or plastic chippings (iii) impingement plates (iv) Venture nozzle and slot adequate opening and sight glasses (impact and heat resistance type) for inspection cleaning and observation purposes.

 (D) Demister: - the structure is made up of mild steel coated with tar epoxy greater than 250 microns thick corrosion-resistant. It removes solid and any entertained water and dried. (98.5% of suit particle larger than 1 Micron is removed as to contain reduce less than 150 PPM) demister may be corrugated plate type or vortex type with a drain. it can be cleaned by backflushing.

 (E) Inert gas blowers casing is made up of mild steel plate with epoxy coating. It is a single-stage centrifugal type, driven by an electric motor. With which inert gas or fresh air is supplied into cargo tanks under optimum positive pressure on the Deck mainline.

The impeller is made up of aluminium bronze which should be stress relieved.

Tested by overspeeding to 20% of the designed the speed of electric motor for 10% above the speed at which speed trip of turbine operate.

A freshwater washing arrangement is provided to remove deposits. Deposits can cause vibration.

Blower characteristics:- minimum pressure 200 mm-wg when cargo discharged.

At least two blowers shall be provided which together shall be capable of delivering inert gas to a cargo tank at least 125% of the maximum rate of discharge capacity of the ship by volume.

One large blower and a small blower for topping up purposes.

Or two blowers can meet the above requirement. The advantage is that change over the blower in case the blower is defective.

 

(F) Pressure control valve (gas pressure regulating valve and recirculation valve)

- Main pressure control valve regulating the flow of inert gas to the inert gas deck men.

- purge control valve automatically prevents backflow if cargo tank pressure exceeds IGI main pressure and a mechanical non-return valve and take water seal fails it also closes if inert gas blower scrubber pumps extra fails.

(G) Vent valve: - non-return valve and regulating valve vented when non-return valve/ deck isolation valve manually closed.

(H) Non-return device: - it prevents backflow of hydrocarbon vapor cargo found the cargo tank to the machinery space uptake other safe areas.

*deck water seal should present resistance to backflow of not less than the pressure setting of the pressure vacuum breaker. Water flow to be maintained, steam heating pipe provided in the tank of the Deck water seal to ensure functionality even in cold ambient condition.

- Wet type: Demister to be fitted to reduce any carry-over

- semi-dry type: Instead of bubbling through the water trap the inert gas float draws the seal water into a separate holding chamber by Venture action avoiding/ least water droplets.

- dry type: It is fitted with water when the IG plant is either shut down for the tank pressure exceeds the IG blower discharge pressure fitting and drain are performed by automatically operated valves are controlled by levels in the water seal and drop tanks by the operating state of the blower.

Advantage: - water carry-over prevented.

Disadvantage: - risk of failure of auto valves

* The Deck seal is designed so that a back seal of 2500 mm Aq. Can be maintained.

Or a mechanical non-return valve can be fitted automatically if backflow.

(I) deck isolation valve: - to be used during maintenance

(J) Pressure vacuum breaker (liquid-filled): - the pressure vacuum breaker is provided to prevent the cargo tank from being subjected to excessive positive pressure during loading and discharging operation. Capacity is equal to IG system capacity correct level of water and glycol 20% is used.

Excess pressure means positive pressure in excess of the tank test pressure. Negative pressure means -700 mm wg.

 

(k) Mast riser: - incorporated PV valve and Bypass valve. The PV valve formed of ring valve and solid valve to being superimposed and bevelled angle 45 degrees both valves fitted with light springs. Cage surrounded by gauge screen set to operate 1900 mm wg positive and 400 mm of wg negative.

When filling both solid and ring valve lifts but when pumping out solid valve is depressed only.

Instrumentation and alarm: -

- Indicate and record gas pressure forward of non-return device and oxygen content

- indicate the temperature at the I.G fan discharge.

- Audio and visual alarm

1. Low water level in scrubber it will auto shutdown blower and gas regulating valve

2. High water level in scrubber will auto shutdown blower and gas regulator valve.

3. Highest temperature will automatically shut down the blower and gas regulating valve.

4. Fan failure automatically shut down gas regulating valve.

5. Power failure in the control system in regulating device will give alarm in machinery spaces and cargo control room.

6. Low level and Decor dress IL will auto shutdown of her go pump or independent alarm.

7. Oxygen content is between 5% to 8% will give the alarm.

8. Gas pressure lower than 100 mm of wg will auto shutdown of cargo pump or independent alarm.

9. High gas pressure will give an audible and visual alarm.

Cargo tanks must be protected against both pressure and vacuum.

Pressure vacuum valves which are set to operate at 1900 mm of wg water positive pressure and 400 mm of wg negative pressure, moderate pressure acting on the large surface area of cargo tank can cause damage either in the form of bulging or inward collapse small volume of vapor pressure caused by natural aspiration of the cargo tank and relieved by means of PV valves. They can also release moderate changes in tank pressure due to variations in temperature and vapor quantity.

High-velocity vents:

No tanks should be vented during loading or ballasting through the high-velocity vent and masthead vents as the practice of vending through an open tank is dangerous particularly during thunder conditions a simple design event has two weighted flaps which are pushed open by pressure built up to achieve ejector effect with an estimated velocity of per second will dilute the fume. Flame trap gives protection against flame travel. This gauge flame trap is to be cleaned regularly to ensure venting.

If the IG system becomes defective and repair cannot be made and another arrangement cannot be made the following is to be observed.

- For crude oil tankers cargo tank must be maintained in an inert condition to prevent pyro phosphoric oxidation which can cause exothermic oxidation can cause an explosion.

- For product tankers, detailed emergency processors are listed includes severe restrictions on tank dipping ullaging, and sampling.

b. State what oxygen content you would expect in the flue gases if good combustion is achieved. 

For good combustion the percentage by volume of the composition of the inert gas will be as follows:

(1) Nitrogen—–85 %.

(2) Carbon di oxide——11%.

(3) Oxygen—————–4%.

When the combustion is good there cannot be any carbon monoxide in the flue gases. If the combustion is good there cannot be any un-burnt hydro carbons in the flue gas

Maintenance of smoke detectors, quick closing valve and fire hydrant hoses.

(A) The smoke detection system:-

For engine room and accommodation:-

For cargo holds is simulated as follows:-

* The test is to be conducted when the holds are empty preferably during a ballast passage.
* A long pole with a tray containing a smoke test bomb lighted is raised to the vicinity of the CO2 spreader fixed on the hold ceiling. There are normally 2 or four spreaders for each hold depending on the size of the hold
* The smoke from the bomb is sucked by the sensor panel fitted on the navigating bridge and the photo electric cell gets activated giving the alarm and light signal too. This test is repeated for all the spreaders located in all the holds.
* The smoke pipes leading to the indicator on the bridge must be blown through with compressed air regularly to clear the passages.
* The photo cell may require cleaning by applying a felt cloth so that the passage of light through the lens is not restricted. Smoke adheres to the glass and hence this cleaning is necessary.

(B) Quick closing valves
Fuel oil service and some other tanks must be fitted with valves that can be
closed rapidly and remotely in the event of an emergency such as fire. Wire
operated valves are commonly fitted, with wire pull levers located externally to the machinery space.
As an alternative a hydraulically operated quick-closing valve can be fitted.

Quick-closing valves are examined and tested when installed and then periodically when the tank is not in use, to ensure that the mechanism functions correctly. Wires are sometimes found to be slack or hydraulic systems empty.

(C) Fire hydrant and Hoses:-

      1. Monthly:-Verify all the hydrants, nozzles and hoses are in place, properly placed and are in serviceable condition. Check for the damaged hoses and renew them. Check the leakage from the hydrants, that should get closed by hand tightening only. Check for glad leakages, bend spindles and gaskets etc. If found leaking that needed to be over overhauled.

      2. Quarterly:- Verify all the international shore connections are in serviceable conditions.

      3. annually:- Visually inspect all the hydrants and hoses. Test all the hydrant valves for the proper functioning. 

                       -pressure test the fire hoses at maximum fire main pressure. All the hoses are to be tested at least once in 5 years.