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According to the requirements of the International Convention for the Safety of Life At Sea (SOLAS) chapter II-2, vehicle spaces and rollon, roll-off (ro-ro) cargo decks that cannot be closed and specialcategory spaces (defined as enclosed spaces situated above or below the bulkhead deck intended for the carriage of motor vehicles with fuel in their tanks for their own propulsion and to which passengers have access)1 must be fitted with a manually activated water-spray system. For other types of ro-ro cargo spaces, where the risk for people is lower – because passengers do not have access to them – a carbon dioxide system is normally used, although other types of inert-gas, water-spray or high-expansion foam system are permitted.

Detailed requirements for the design and installation of water-spray systems for vehicle spaces and ro-ro cargo decks are given in International Maritime Organization (IMO) Resolution A.123 (V), published in 1967.1 Some of the most important specific requirements are that:

• the system must be designed for a water discharge density of at least 3.5mm/minute for decks with a maximum height of 2.5m and at least 5mm/minute for decks with a greater height;
• the system may be divided into sections, each of which must cover the entire width of the ship (exemptions to this requirement may be admitted if the deck is separated longitudinally by ‘A’-class divisions);
• each section must be at least 20m long and the system’s pumps must have sufficient capacity for either the entire deck or at least two sections;
• section valves must be located outside the protected space; and
• at least one portable fire extinguisher must be available at each exit from the deck and at least three nozzles and a mobile foam cart must be available on board the ship.

One might well ask what the technical background material to these detailed requirements is. The answer can probably be found in a series of fire trials carried out in Denmark in 1961.

In recent years, questions have been raised as to whether a waterspray system in accordance with Resolution A.123 (V) is able to control or suppress a fire on a ro-ro deck of a modern ship with modern cars, coaches and heavy goods vehicles. Two projects funded by the Swedish Fire Research Board (Brandforsk) have looked into this: SP Report 1997:033 and SP Report 1997:15. The latter report describes a large-scale fire test in a layout that represents two trucks side by side on a ro-ro deck. Later, a feasibility study was carried out into the requirements and alternative waterextinguishing systems for cargo.

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