Section 42(2) in The Merchant Shipping (Fire Appliances) Rules, 1969
(2)Every fixed area fire extinguishing installation fitted in lieu of a fixed fire smothering gas installation required by these rules to be provided in the oil cargo spaces of any tanker shall be capable of distributing on the decks over the oil cargo tanks through fixed discharge outlets in not more than 15 minutes, a quantity of foam sufficient to cover to a depth of at least 5 centimetres the whole of tank deck area. Such installation shall be capable of generating foam suitable for extinguishing oil fires and means shall be provided for the effective distribution of the foam through a permanent system of piping and control valves or cocks to discharge outlets. There shall be sufficient mobile foam sprayers capable of being connected to the installation whereby foam can be directed into any tank.Explanation. - For the purpose of this sub-rule, "tank deck area" means an area equivalent to the extreme length of the cargo tanks multiplied by the breadth of the ship.
