Water mist is becoming known throughout the maritime industry as the local application systems protecting engines and other high risk objects in the engine room were introduced in SOLAS and came into force from 2002. IMO has now approved a revised standard for water mist system protecting the entire engine room.
The new standard is published as IMO MSC/Circ. 1165 (see "downloads" on the left hand side). Water mist can now be used as an alternative to for instance CO2. However, please note that all such water mist systems have restrictions with respect to volume. The systems with the largest approved volumes are at 3-4.000 m3.
DNV has trough the NMD (Norwegian flag administration) taken part in the work resulting in the new standard. Our main concern was that the old standard had almost unrealistic fire test requirements and also strict requirements with regard to back-up capability, especially when compared to other approved fire extinguishing systems. We consequently proposed to remove the requirement for the rather expensive pressure tank as the standard anyway requires a main pump and a full size back-up pump. This proposal received the necessary support and was adopted in the standard. The fire test requirements were reduced somewhat to bring it inline with other test standards, whereas the not so cost-efficient door nozzles are no longer accepted.
The new test standard has been well received in the market and the first fire tests indicate that standard water mist system can pass fire test at 4.000 m3 and maybe more, with a less complex design than we have seen in the past. Complex designs will often require more maintenance and will in worst case also reduce the reliability.
Water mist systems have proven their success in numerous test fires and also in several real fires. We expect this to continue with the new standard. There are also challenges mainly related to precision components that are not always suitable for marine operations. However, DNV does actively follow up all finding from our surveys and information brought to our attention from ship owners on these matters, in order to ensure that these important systems have a high degree of reliability.