Section 23(1)(iv) in The Merchant Shipping (Fire Appliances) Rules, 1969
(iv)one extinguisher of at least 45 litres capacity or an equivalent carbon dioxide extinguisher in each boiler room if the number of burners therein is five or more, provided that if the number of such burners is less than five, one portable froth fire extinguisher for each such burner may be carried.