In the previous article we learned about the various features of carbon dioxide gas and the advantages and disadvantages attached to it. We also studied what is a fixed CO2 fire extinguishing system and why it is so widely used.
In this article we would go a bit more deep into the constructional and safety specifications related to the installation and design of the fixed CO2 system. A CO2 system though efficient is extremely dangerous to the people working on the ship. Safety Of Life At Sea (SOLAS), has made special regulations regarding the usage of CO2.
CO2 usage on ships has to abide by few safety regulations, as on ship there are lives at stake and measure to fight accidents are few .The main regulations are:
- If the CO2 system is installed in the cargo spaces, the quantity of CO2 available should be sufficient enough to give at least a minimum of 30% of the total volume of the largest space that is protected by the CO2 system.
- If the CO2 system is installed in machinery spaces, the quantity of CO2 available should be sufficient to give at least a volume equal to either of the following :
a)40% of the total volume of the largest machinery spaces that is protected by the CO2 system. (The volume should exclude that part of the casing where the horizontal area of the casing is 40% or less then the horizontal area of the space taken into consideration and measured midway, between tank top and lowest part of casing)
b)35% of the total volume of the largest machinery spaces that are protected by the CO2 system including the area covered by the casing.
It is also a requirement that 85% of the required quantity of gas should be released into the spaces within two minutes of evacuating the fire affected space.
Construction of CO2 bottles for fixed fire fighting system.
It is imperative that the CO2 bottles are strong and sturdy due to the high internal pressure they are going to withstand. For this reason, the bottles are made from solid drawn steel and are also hydraulically tested upto 228 bars prior to installation.
CO2 is retained inside the cylinder in the liquid form under pressure.A siphon tube is provided inside the bottle to ensure that the liquid CO2 is discharged from the bottle or else it would evaporate from the surface, giving a very slow discharge rate and taking away the latent heat would probably cause the remaining CO2 in the bottle to freeze.
Some special features are provided to the system in order to increase the safety level and also to make operation smooth.
The control cabinet doors are installed with a special signaling system. Whenever a person opens the door of the control cabinet in order to operate the CO2 system, an alarm is sounded automatically. This is done to signal crew members of CO2 flooding on ship. This is also an indication to leave the fire affected place and assemble at the muster station.
A master valve is also provided on the main pipe going to the machinery or cargo spaces, in order to stop the CO2 supply in case of accidental release.
Marine Auxiliary Machinery, 7th Edition, 1995 by McGeorge
SOLAS Regulations, Chapter II – 2 By International Maritime Organization(IMO) Publications.