The engine room is a potential hazards space, it contains fuel line and high-temperature heating and exhaust line. Even a small human mistake or mechanical failure may lead to a disastrous situation. That’s why ER is being provided with fixed fire fighting system to be used as a last resource for extinguishing a fire. But there are other tools to extinguish a fire at a very early stage, e.g. portable and semi-portable fire fighting extinguisher, local firefighting system(like purifier room system), high-pressure water mist system. Although high-pressure water mist system (hyper mist system) is a fixed fire fighting system, it is often called as local firefighting system because of it’s installation and extinguishing mechanism.
Before hyper mist system halon local fixed firefighting system was in commonly used. After Montreal protocol, it was declared as ozone depletion potential (ODP) and must not be specified for use in fixed fire fighting installations. As an alternative to above system high-pressure water mist system was developed. In this blog, I have explained regulations and maintenance work on hyper mist system. Before explaining that let’s read regulation for fixed fire fighting system in engine room.
Regulations for fixed fire fighting system
- Fixed firefighting system should comply as per SOLAS and Class requirement.
- Fixed firefighting system may be any of the following
- A fixed gas firefighting system complying with the FSS code. Nowadays we are using CO2 gas fixed fire fighting system. Earlier we were using halon system but it’s getting prohibited in 1994.
- A fixed foam firefighting system complying with the FSS code. For engine room, we use the high expansion foam and for deck its low expansion foam.
- A fixed water spraying firefighting system complying with the FSS code. In other words, this is known as the hyper Mist or high-pressure mist system.
- Machinery space less than 500 m³ in the volume is required additional fixed fire fighting system.
- Passenger ship less than 500 GRT and cargo ship less than 2000 GRT are mandatory to have a hyper mist or we can say high-pressure mist system onboard.
SOLAS requirement for Hyper mist (High-Pressure Mist) system
- System installation should be outside of the machinery space.
- It should be activated by 2 sensors.
- The system should be driven by independent internal combustion machinery but if it is dependent then emergency generator connection should be there.
- The effective average distribution of the nozzles shall be at least 5 litres/m²/minute.
- The system should be capable to supply water fog for the period of minimum 20 minutes to suppress the fire.
- Operating instructions should be displayed at the control station.
Areas protected by hyper mist
- Main engine space
- Auxiliary engine space
- Boiler space
- Incinerator area
- Purifier room
- The inert gas generator (IGG), in case of the tanker, fitted with IGG.
- Framo auxiliary engine, in case of the tanker, fitted with the framo system.
Advantages of hyper mist
- Automatically activation
- We can use at affected area only. Like in case of co2 we have to flood in the whole engine room but here we can use separately.
- Use water economically and water is easily available and cheap.
Working of the Hyper mist System
The main component of the system is-
- Pump and motor
- Suction valve
- Fresh water tank
- Electrical panel (Main and local control panel)
- Solenoid valve
An electrical driven vertical centrifugal, multi-stage, inline type, the pump is fitted to pump the water from F.W. tank to nozzle. Once both detectors of any protected area get activated, they send the signal to fire detection system. From the detection system signal send to the main control panel. The main control panel gives the signal to the pump starter unit and signals to open the solenoid valve of the relevant area. When the pump gets signal, will start delivering water and nozzle will release the mist(fog) to extinguishes the fire. The fresh water is always available in that fresh water tank. To ensure this suction line of hydrophore pump is connected above the suction of the hyper mist pump.
- The capacity of the pump is 200 litres/min @ 70 bar discharge pressure.
- At nozzle 12-20 litre/min @50 bar discharge pressure.
How the micro fog (mist) get generated?
Here in the system nozzle having special design having the fine hole, the water with high pressure of about 4 to 10 MPa passes through the nozzle get converted into fine particles of size about 50 to 200 µm. The diffuser action in nozzle drop in pressure at nozzle throat breaks the liquid particles into a fine mist. These fine particles are excellent fire extinguisher as it provides large surface area for cooling and of its characteristic.
Characteristics of micro fog (mist)
- Cooling effect – As we know mist contains a water molecule, which gives the cooling effect.
- Smoke eliminating effect – The smoke particles being absorbed and settled by the mist (fog).
- Oxygen replacement effect – Mist get evaporated by taking latent heat. The water vapour is heavier than air, replace the oxygen.
- Shut off effect – The floating mist as fog forms a layer of water on fire.
Starting procedure of hyper mist
The system is provided with both automatic as well as manual starting procedure.
1. Automatic starting
Hyper mist system is provided with detectors as composed of minimum two detectors in each protected area. When perceiving a fire via one detector in any protected area, the pre-warning alarm will start. Activation of the other detector in the same protected area, it will automatically result in the release of the hyper mist system by opening the suction valve and start the pump. If the solenoid valve is not open, it can be opened by using override.
2. Manual Starting
For the manual release push button is provided on the local control panel at each section and on the main control panel at the fire control station. When the manual release push button is pressed, the fire alarm, as well as the system, will be activated in the designated area.
Stopping procedure of Hyper mist
Stopping of the system to be done manual only. The push button is provided at the local control panel as well as the main control panel. By pushing the stop button we can stop the system.
Why we can’t use sprinkler instead of hyper mist?
To avoid boilover effect in case of oil fire we can’t use the sprinkler. What is a boilover effect? An effect of the explosion, which is an extremely hazardous situation when we attempt to extinguish the semi-enclosed oil-fueled fire with water.
Mechanism of Boilover
- When we put water on an oil fire, water droplet goes to the bottom of the container, as water is heavier than oil.
- Then it takes heat energy from the oil and gets evaporated.
- As water vapours get high heat energy, spread out suddenly and carry flame and oil particle with it as a big explosion.
Onboard tests of Hyper mist
1. Operation test (pump running test and verification of discharge pressure)
- Close all the valves except the water supply valve.
- Open the pump drain valve.
- Select the switch to manual position and push the start button from the pump starter panel.
- Check the pump running condition and discharge pressure in the gauge.
- Push the stop button and drain the water remaining in the pump unit.
- Put the system back to normal position.
2. Automatic release test (without flooding)
- Close the water suction valve.
- Disconnect the motor power cable or remove the contractor from the pump.
- Open the airball valve.
- Activate both detectors by UV lamp (if flam detector) and smoke container (if smoke detector).
- Check the alarm of the main control panel, visual and audible alarm in the protected area.
- Check the air release of the nozzle in that area.
- Push the stop button from local control.
- Repeat the test with other sections. After completion put the system back to normal.
3. Actual test (With flooding)
- Select the switch to the manual potion and follow the starting procedure as above mentioned in this blog.
- For automatic activation, protect the machinery of the relevant area. Activate both detectors. Check for alarm at control panel as well as audible and visible alarm. Mist will start coming at the relevant nozzle. Once confirm the successful activation stop the system from the local control panel. After the test put the system in normal condition.
4. Alarm and other tests
- Low water level alarm test in the fresh water tank.
- Electrical source failure alarm. We can test by removing the fuse.
- Interlock (if applicable) push the start and check the ventilation cut off.
- Air blow test – blow the air of pressure 7-8 bar to ensure the line and nozzles are clear.
Note – Drain the system and put it in a normal condition after any test.
Maintenance of Hyper mist system
To avoid any malfunctioning, for better operation and efficiency the system to maintain as per makers manual. We have to follow daily and periodic maintenance. Here we are discussing few points but for maintenance on ship refer your system manual.
• Control panel to be checked for any abnormal indication.
• The alarm monitoring system to be checked for any abnormal indication.
• Pump operation to be checked. Running condition, water pressure, any abnormal noise or vibration.
• Wire disconnection check and lamp tests to be carried out.
- Every 6 month
• Various alarm to be checked
• If possible check the interlocks
- Every year
• Check the clogging of the nozzle. We can do it by air blowing.
• Overhaul the pump unit, section valve, filter etc.
Note – If having any problem with the nozzle, don’t disassemble it and send it to the manufacturer.