Considering that Halon systems were banned because of their ozone depleting properties, it seems a little ironic that the more common replacement other than Novec 1230 is carbon dioxide (CO2) which is also highly criticised as a modern ‘pollutant’ and greenhouse gas.
CO2 can be used either in a hand-held extinguisher or as a flooding system. In a flooding system it is one of the most commonly used fire-extinguishing agents in ships’ engine rooms. It gas has excellent fire extinguishing capabilities and is relatively inexpensive but can pose a serious risk to personnel because it works by reducing the oxygen content in the atmosphere.
With CO2 systems, the period between detecting a fire and releasing the gas often seems quite long because crew must evacuate the area to avoid the lethal effects of the gas. As a consequence, minor fires have sometimes been allowed to escalate causing loss of life and even total loss of ships.
Issues with CO2 systems feature in many official accident investigations and advice to the industry is regularly promulgated by insurers, P&I clubs, class societies and other bodies. The concentration of CO2 above certain levels in fire-fighting applications is a major concern amongst fire safety regulators.
SOLAS does not prohibit the use of CO2 in systems protecting a ship’s engine room, or other spaces where crew has access during normal operation, but the risks to personnel are clearly recognised and SOLAS calls for various safeguards, such as two separate and interlocked controls, pre-discharge alarms and time-delays, to protect personnel in the engine room. SOLAS does not, however, allow portable CO2 extinguishers to be placed in the accommodation spaces on board ships, due to the associated risk to personnel.
For the typical engine room fire involving flammable liquids, it is important to introduce the required quantities of CO2 quickly to limit the escalation of the fire. Investigations reveal that evacuation, muster and head counts during engine room fires often take longer than expected because crew are not disciplined in mustering. Because of limited storage capacity, very few ships can carry enough gas for more than a single discharge.
CO2 has a limited cooling effect and the temperature of equipment and structures in the engine room may be very high, in particular if the time taken to release the fixed fire-extinguishing system was long. There is a further risk to fire fighters or crew who enter the space too soon, thus allowing entry of oxygen-rich air, which can cause the fire to reignite. Most advice issued with regard to CO2 systems recommends fostering awareness of the hazards related to their use through detailed and unambiguous procedures, proper training and prescribed maintenance.
The dangers of CO2 must be continuously stressed and training and experience transfer between crew should create a common understanding of the functionality, limitations and hazards associated with the ship’s specific installation.
The design of a CO2 system is covered in the FSS Code and will need to be approved by the flag state or the classification society but there are aspects which should be considered as common sense. For example, at least one engine room ventilation fan should be powered by an emergency generator so as to aid in making the engine room safe for entry after use of the system. In addition, the dangers of a CO2 system are not confined to the spaces they are designed to protect but extend to the CO2 storage area itself. It is not unknown for the cylinders to leak, creating a suffocation hazard in the CO2 store room. As a consequence, there should be adequate ventilation and the area should be considered as an enclosed space with appropriate procedures in place for testing prior to entry.