Section 5 Tank Arrangement

501. Tank Arrangement

1. Location and Separation of Recovered Oil Tanks

(1) General

Oil spill recovery vessels are not required to have double hulls.

Where double bottoms are fitted to comply with any applicable regulation or other purposes, they are to be fitted between the peaks or as near thereto as practicable. The double bottom is not be lower at any point than a plane parallel with the keel line and situated at a height not less than B/20 measured from the keel line, but in no case less than 0.76 m and need not ex- ceed 2 m.

Where wing tanks are located at a distance inboard of the molded line of the side shell plating, this distance is to be nowhere less than 600 mm to permit easy access for inspection.

The minimum size of the access openings to the double bottoms and wing tanks, where fitted,

is to be at least 380 mm × 585 mm and circular openings to be

(2) Separation of Recovered Oil Tanks

Tanks for recovered oil are not to be located below machinery stations and accommodation spaces.

at least 457 mm.

spaces, service spaces, control

Guidance for Offshore Support Vessels 2015 53

Tanks for recovered oil may be located forward or aft of machinery spaces, service spaces, con- trol stations and accommodation spaces. Recovered oil tanks are to be isolated from such spaces by means of a cofferdam. For the purposes of this requirement, void spaces, pump rooms, fuel oil tanks and compartments arranged solely for ballast may be considered cofferdams. For easy access, the minimum width of the cofferdam is not to be less than 600 mm.

Where it is impractical to meet the cofferdam requirement in above, considerations may be granted in the case of other machinery spaces. A cofferdam will not be required between the recovered oil tanks and other machinery spaces, provided the following items are met:

(a) The bulkhead plating/tank side wall is to be continuous through all joining structures to the top of the tank. Full penetration welding is required at the top of the tank and the con- tiguous boundaries.

(b) The common tank bulkhead/tank side wall is to be readily accessible under normal con-

ditions for inspection.

(c) The machinery space adjacent to the recovered oil tanks is to be provided with forced pow- er ventilation system as follows:

(i)At least twenty (20) air changes per hour, based on the gross volume of the space

(ii) The system is to be operated at all times whenever recovered oil is carried in the tanks. This is to be clearly indicated in the Operating Manual.

(iii) The ventilation system is to be designed and arranged with redundancy such that at least 100% ventilation system is still available after a single failure in any part of the

system.

(iv) Fitted with alarms to indicate ventilation failure

(v) Fitted with non-sparking fans either with the uncertified motor outside of the ventilation duct or with a certified explosion proof motor located within the duct

(d) No penetrations that create a source of hazardous vapor or oil release are allowed through the common tank boundary bulkhead. Sources of hazardous vapor or oil include any open-

ings, screwed and flanged pipe connections, valves, pumps, stuffing boxes, etc. All welded

pipe connections are not considered sources of hazardous vapor or oil.

(e) The tanks are to be hydrostatically tested at the Special Surveys.

(f) The common tank bulkhead is to be gauged at Intermediate and Special Surveys.

2. Location of Recovered Oil Tank Openings

Openings from recovered oil storage tanks including sounding pipes, vents and hatches are not to be located in enclosed spaces. For the purposes of this requirement, spaces open on one side only are to be considered enclosed.

3. Penetration of Recovered Oil Tanks

Electrical cables are not to pass through recovered oil tanks unless enclosed within an oil tight trunk or equivalent. Piping not related to the transfer of recovered oil is not to pass through recov- ered oil tanks unless the piping is made of steel, Extra-Heavy and of all welded construction, with- out valves, flanges, fittings or take-down joints.