This article is in continuation of a previous article that deals with the constructional and design aspects of the CO2 fire extinguishing system. In this article we will learn about the arrangement and working of CO2 system in the engine room and cargo spaces.
CO2 System In Machinery Spaces
A Co2 system of machinery spaces consists of a bank of Co2 bottles that can be operated from a remote place located away from the machinery spaces. The system also consists of pilot Co2 cylinders which control the activation of the bank of Co2 bottles. The Pilot cylinders are contained in a control box and are normally kept disconnected. The system is connected to the pilot cylinders and the control box with the help of steel wires or flexible pipes. All these pipes are fitted with a quick action coupling. When the system is to be activated, the coupling in plugged into the corresponding socket. The valves of the pilot cylinders will be opened with the help of the levers in the main CO2 control system.
The Co2 from the pilot cylinders will open the system’s main stop valve. The main stop valve has a piston which gets depressed due to the Co2 gas pressure and allows the pilot gas to flow to the bank of CO2 cylinders. This pilot gas operates the cylinders’ valves. These valves are known as Klem valves. All these valves have an actuator which gets operated by the pilot pressure.
The detection of fire is done by various sensors installed in the machinery spaces.Though the opening of control box operates an alarm, the main decision for Co2 flooding is taken by the Chief engineer, after due consultation with the master of the ship. Before releasing Co2 into the fire affected space, it should be made sure that everybody is out of the place and the place is fully enclosed i.e all skylights and ventilators are closed air-tight. Pumps supplying fuel oil should also be stopped in order to prevent re-ignition.
Separate levers for each and every space are present inside the main controlling cabinet. The operating of a particular lever activates the pilot bottles, which helps in releasing the complete bank of bottles designated for that place. With the opening of the master valve, Co2 is flooded inside the fire affected space, which then smothers the fire with the help of blanket effect.
Co2 System for Cargo Space
The release mechanism of CO2 system in cargo spaces is same as that of the machinery spaces. The only difference is that the cargo spaces have a different type of fire detection system.
For detection of fire in cargo hold, a sample of air is drawn from all the cargo holds by an extractor fan.This sample of air is passed through a cabinet wherein a set of smoke sensitive sensors analyze the sample. The sensors will detect any presence of smoke in the sample. As soon as the sensor detects smoke in the sample, it activates the CO2 alarm system of the ship. A part of the sample is also discharged to the wheelhouse in order to cross-check the presence of smoke in the sample. This can be done by smelling the smoke. The sample is later vented to the air.
In order to check whether the extractor is extracting samples from the holds, a small indicator propeller is fitted, which ensures that the samples are taken.
Precaution to be taken after the fire is extinguished.
After the fire is extinguished by the flooding system, all the doors,hatches,vents and other openings should be opened in order to ventilate the space properly, before any entry is made into the space.
The space should not be approached with any type of open flames as it might contain flammable vapours, which can lead to fire or explosion.
Checks on the system
- Pipes leading to the spaces should regularly be blown with air to ensure that they are not blocked.
- The level in the Co2 bottles should be checked on regular basis. If in a particular check, the difference is 10% of the total volume, the bottle should be replaced as soon as possible.
- Sensors should be checked periodically.
- Cabinet door alarms should also be checked on regular interval of time.
- All the pipings and connections at the CO2 bottles should be checked regularly.
Marine Auxiliary Machinery, 7th Edition, 1995 by McGeorge