Fire Suppression: Performance without the Delay
Alternatives to Carbon Dioxide fire suppression systems can provide the performance without the activation delay according to Kristin Øgaard of Norway’s Autronica Fire and Security AS.
With the phase out for environmental reasons of fire suppression systems using Halon gas starting in 1994, the use of Carbon Dioxide (CO2) as a fire suppressant has become typical both on land and at sea. Today, CO2 fire suppression systems can be found in engine rooms and cargo areas on board, and whilst proving effective in extinguishing flames without causing significant residual damage to critical and expensive equipment, this method of fire fighting brings with it inherent complications.
Whilst in low quantities, CO2 can actually be beneficial to humans, in the quantities required to successfully suppress a fire, it can quite literally be as dangerous to life as the fire itself. In order to discharge CO2 into the atmosphere of an engine room or cargo area on board, the system and its operators have to be 100% certain that the area has been fully evacuated. Which means a delay of no less than 20 seconds has to occur before total flooding of the area with CO2 can occur.
In reality, at sea, the 20 second delay is usually much longer. From the point of detection and alarm, oil pumps and remote trips have to be manually shut down and vents and doors have to be closed. Personnel need to evacuate often confined and hazardous areas, possibly under duress and only when they are confirmed as evacuated with a manual head count can the Master or Chief Engineer grant permission to activate the system. CO2 is then released into the pilot system where a mandated delay, with an audible (CO2 powered) alarm that usually lasts for three minutes occurs. Only once this delay is complete will the stop valve in the CO2 suppression open to discharge CO2 into the protected space. [Source for above process: Gustafson 1998 ]. In some cases, the entire process has been known to take up to 20 minutes, which gives a serious fire plenty of time to take hold and cause local damage, or in extreme cases, vessel wide catastrophe.
Another issue caused by the nature of CO2 fire suppression systems on board, is that of accidents during repair and maintenance, especially with untrained personnel being allowed into the pump room, or signage in a language that engineers not familiar with the system may not understand. This has been the cause of several accidents and fatalities at sea, and is an inherent problem with the use of CO2 as a fire suppressant.
There are some circumstances where no alternative can provide as effective protection against fire as CO2 and for large cargo vessels and tankers, CO2 is still the best option for cargo hold protection. The possibility of using an alternative method is usually based on the size of area to be protected, but on many offshore vessels and some passenger vessels with smaller machinery and engine room spaces, the development of systems using alternative gasses and water mist total flooding systems is providing a suitable and safer alternative to CO2. Water based systems are divided into various types such as water mist, deluge, foam deluge and sprinkler systems. Among the gas based gaseous systems are NOVEC 1230, FM200 and Argonite.
Several large supply vessels have changed spec from CO2 to Novec 1230 – a much safer gaseous suppression system for use in machinery spaces, engine control rooms, switchboard rooms and cargo pump rooms – during building in the last three years. The benefits of Novec 1230 include that its release does not necessarily damage expensive equipment. For use in accommodation and public areas, high risk areas and engine rooms, water mist based fire suppression is becoming more typical, such as the Autronica developed FlexiFOG, which cruise operator Hurtigruten in Norway changed to from the originally specified CO2 system aboard the vessel 'M/S Nordlys' in February 2012. Also of note are three new fishing trawlers being built in Norway, where one is using Novec 1230 and the other two have chosen FlexiFOG, making them the two first trawlers in the world equipped with water mist total flooding suppression systems.
FlexiFOG low pressure water mist is mainly used to replace CO2 systems in machinery spaces. The fire suppression capability is equal as the system has to fulfil the test requirements set in the MSC Circulars.
However, the safety is better with water mist because it isn’t hazardous to crew whilst it can be activated as soon as the fire is detected, without concern that there are personnel still left inside the protected space.
As a modern fire suppression system, water mist brings with it further benefits in terms of size and weight, so less space is required to install it. FlexiFOG system performance is optimised towards regulations with performance balanced against power consumption, size and weight. Power use is low by keeping pressure and flow at a reduced level. Recent developments have got the pressure down from 10.7 bar to 8 bar at the nozzle, reducing the requirement for emergency power even more when compared to high pressure systems.
Also, weight, size and space restrictions can be overcome by optimising the system design towards the vessel. As an example, Autronica was tasked with developing suppression for a number of small coast guard vessels. The spec called for 6% foam liquid, with total of 2 x 6000 litre tanks to be welded to the hull, with a total weight of 14 tons. Because the FlexiFoam system allows for customization in the same way as FlexiFOG, a proposal to change to 1% foam liquid based on 2 x 1000 liter LLD plastic tanks was made. The total weight was three tons, so the new suppression system design managed to save 11 tons per vessel and a huge amount of space.
Today it is just as critical to have focus on safety and work environment on board ships as it is in any other Industry, so having alternatives to CO2 fire suppression systems such as water mist and Novec 1230 gaseous system is a positive development for the industry. Ship-owners can now install safe fire suppression systems in all machinery spaces, which can be activated as soon as a fire is detected, rather than waiting for crew to evacuate the area.
And that will save lives and vessels.
(As published in the December 2012 edition of Maritime Reporter - www.marinelink.com)