Note: Following explanation is edited keeping general points in mind.
Part B – Prevention of Fire and Explosion
Regulation 4 – Probability of Ignition
1. Purpose
The purpose of this regulation is to prevent the ignition of combustible materials or flammable liquids. For this purpose, the following functional requirements shall be met:
1.1 means shall be provided to control leaks of flammable liquids;
1.2 means shall be provided to limit the accumulation of flammable vapours;
1.3 the ignitability of combustible materials shall be restricted;
1.4 ignition sources shall be restricted;
1.5 ignition sources shall be separated from combustible materials and flammable liquids; and
1.6 the atmosphere in cargo tanks shall be maintained out of the explosive range.
2. Arrangements for oil fuel, lubrication oil and other flammable oils
2.1 Limitations in the use of oils as fuel
The following limitations shall apply to the use of oil as fuel:
2.1.1 except as otherwise permitted by this paragraph, no oil fuel with a flashpoint of less than 60ºC shall be used;*
* Refer to the recommended procedures to prevent the illegal or accidental use of low flashpoint cargo oil as fuel adopted by the Organization by resolution A.565(14). This deals with the use of cargo oil either directly or indirectly as fuel. Ships were found using crude oil as fuel or mixing crude with fuel oil.
2.1.2 in emergency generators, oil fuel with a flashpoint of not less than 43ºC is used;
2.2.1 Location of oil fuel systems
As far as practicable, parts of the oil fuel system containing heated oil under pressure exceeding 0.18 N/mm² shall not be placed in a concealed position such that defects and leakage cannot readily be observed. The machinery spaces in way of such parts of the oil fuel system shall be adequately illuminated.
2.2.2 Ventilation of machinery spaces
The ventilation of machinery spaces shall be sufficient under normal conditions to prevent the accumulation of oil vapour.
2.2.3 Oil fuel tanks
2.2.3.1 Fuel oil, lubrication oil and other flammable oils shall not be carried in forepeak tanks.
2.2.3.4 Oil fuel pipes, which, if damaged, would allow oil to escape from a storage, settling or daily service tank having a capacity of 500 lts and above situated above the double bottom, shall be fitted with a cock or valve directly on the tank capable of being closed from a safe position outside the space concerned in the event of a fire occurring in the space in which such tanks are situated.
2.2.3.5 Safe and efficient means of ascertaining the amount of oil fuel contained in any oil fuel tank shall be provided.
Note: This deals with fuel gauges
2.2.3.5.1 Where sounding pipes are used, they shall not terminate in any space where the risk of ignition of spillage from the sounding pipe might arise. In particular, they shall not terminate in passenger or crew spaces. As a general rule, they shall not terminate in machinery spaces.
2.2.5.2 External high-pressure fuel delivery lines between the high-pressure fuel pumps and fuel injectors shall be protected with a jacketed piping system capable of containing fuel from a high-pressure line failure. A jacketed pipe incorporates an outer pipe into which the high-pressure fuel pipe is placed, forming a permanent assembly. The jacketed piping system shall include a means for collection of leakages and arrangements shall be provided with an alarm in case of a fuel line failure.
2.2.5.2 Oil fuel lines shall not be located immediately above or near units of high temperature, including boilers, steam pipelines, exhaust manifolds, silencers or other equipment required to be insulated by paragraph 2.2.6.
2.2.6 Protection of high-temperature surfaces
2.2.6.1 Surfaces with temperatures above 220°C which may be impinged as a result of a fuel system failure shall be properly insulated.
2.5.1 where daily service oil fuel tanks are filled automatically, or by remote control, means shall be provided to prevent overflow spillages. Other equipment which treats flammable liquids automatically (e.g., oil fuel purifiers) which, whenever practicable, shall be installed in a special space reserved for purifiers and their heaters, shall have arrangements to prevent overflow spillages; and
2.5.2 where daily service oil fuel tanks or settling tanks are fitted with heating arrangements, a high-temperature alarm shall be provided if the flashpoint of the oil fuel can be exceeded.
3. Arrangements for gaseous fuel for domestic purposes
Gaseous fuel systems used for domestic purposes shall be approved by the Administration. Storage of gas bottles shall be located on the open deck or in a well-ventilated space which opens only to the open deck.
4. Miscellaneous items of ignition sources and ignitability
4.1 Electric radiators
Electric radiators, if used, shall be fixed in position and so constructed as to reduce fire risks to a minimum. No such radiators shall be fitted with an element so exposed that clothing, curtains, or other similar materials can be scorched or set on fire by heat from the element.
NOTE: No open or portable heaters permitted
4.2 Waste receptacles
Waste receptacles shall be constructed of non-combustible materials with no openings in the sides or bottom.
Note: No leakages allowed
5. Cargo areas of tankers
5.1 Separation of cargo oil tanks
5.1.1 Cargo pump-rooms, cargo tanks, slop tanks and cofferdams shall be positioned forward of machinery spaces. However, oil fuel bunker tanks need not be forward of machinery spaces. Cargo tanks and slop tanks shall be isolated from machinery spaces by cofferdams, cargo pump-rooms, oil bunker tanks or ballast tanks.
5.1.2 Main cargo control stations, control stations, accommodation and service spaces (excluding isolated cargo handling gear lockers) shall be positioned aft of cargo tanks, slop tanks, and spaces which isolate cargo or slop tanks from machinery spaces, but not necessarily aft of the oil fuel bunker tanks and ballast tanks, and shall be arranged in such a way that a single failure of a deck or bulkhead shall not permit the entry of gas or fumes from the cargo tanks into main cargo control stations, control stations, or accommodation and service spaces.
5.1.4 In combination carriers only:
5.1.4.3 Hatches and tank cleaning openings to slop tanks shall only be permitted on the open deck and shall be fitted with closing arrangements.
5.1.6 Means shall be provided to keep deck spills away from the accommodation and service areas. 5.2 Restriction on boundary openings
5.2.1 Except as permitted in paragraph 5.2.2, access doors, air inlets and openings to accommodation spaces, service spaces, control stations and machinery spaces shall not face the cargo area.
5.2.4.1 in addition to the bridge operation, the watertight door shall be capable of being manually closed from outside the main pump-room entrance; and
5.2.4.2 the watertight door shall be kept closed during normal operations of the ship except when access to the pipe tunnel is required.
5.2.5 Permanent approved gastight lighting enclosures for illuminating cargo pump-rooms may be permitted in bulkheads and decks separating cargo pump-rooms
5.3 Cargo tank venting
5.3.1 General requirements
The venting systems of cargo tanks shall be entirely distinct from the air pipes of the other compartments of the ship.
5.3.2 Venting arrangements
5.3.2.1 The venting arrangements in each cargo tank may be independent or combined with other cargo tanks and may be incorporated into the inert gas piping.
5.3.2.2 Where the arrangements are combined with other cargo tanks, either stop valves or other acceptable means shall be provided to isolate each cargo tank. Where stop valves are fitted, they shall be provided with locking arrangements which shall be under the control of the responsible ship’s officer. There shall be a clear visual indication of the operational status of the valves or other acceptable means.
5.3.2.3 If cargo loading and ballasting or discharging of a cargo tank or cargo tank group which is isolated from a common venting system is intended, that cargo tank or cargo tank group shall be fitted with a means for overpressure or under pressure protection as required in regulation 11.6.3.2.
5.3.2.4 The venting arrangements shall be connected to the top of each cargo tank and shall be self-draining to the cargo tanks under all normal conditions of trim and list of the ship.
5.3.3 Safety devices in venting systems
The venting system shall be provided with devices to prevent the passage of flame into the cargo tanks.
5.3.4 Vent outlets for cargo handling and ballasting
5.3.4.1 Vent outlets for cargo loading, discharging and ballasting required by regulation 11.6.1.2 shall:
5.3.4.1.1.1 permit the free flow of vapour mixtures; or
5.3.4.1.1.2 permit the throttling of the discharge of the vapour mixtures to achieve a velocity of not less than 30 m/s;
5.3.4.1.2 be so arranged that the vapour mixture is discharged vertically upwards;
5.3.4.1.3 where the method is by free flow of vapour mixtures, be such that the outlet shall be not less than 6 m above the cargo tank deck or fore and aft gangway if situated within 4 m of the gangway and located not less than 10 m measured horizontally from the nearest air intakes and openings to enclosed spaces containing a source of ignition and from deck machinery
5.4 Ventilation
5.4.1 Ventilation systems in cargo pump-rooms
Cargo pump-rooms shall be mechanically ventilated and discharges from the exhaust fans shall be led to a safe place on the open deck. The ventilation of these rooms shall have sufficient capacity to minimise the possibility of accumulation of flammable vapours. The number of air changes shall be at least 20 per hour, based upon the gross volume of the space. The air ducts shall be arranged so that all of the space is effectively ventilated. The ventilation shall be of the suction type using fans of the non-sparking type.
5.5 Inert gas systems
5.5.1 Application
5.5.1.1 For tankers of 20,000 tonnes deadweight and upwards, the protection of the cargo tanks shall be achieved by a fixed inert gas system in accordance with the requirements of the Fire Safety Systems Code.
5.5.1.2 Tankers operating with a cargo tank cleaning procedure using crude oil washing shall be fitted with an inert gas system complying with the Fire Safety Systems Code and with fixed tank washing machines.
5.5.1.3 Tankers required to be fitted with inert gas systems shall comply with the following provisions:
5.5.1.3.1 double-hull spaces shall be fitted with suitable connections for the supply of inert gas;
5.5.1.3.2 where hull spaces are connected to a permanently fitted inert gas distribution system, means shall be provided to prevent hydrocarbon gases from the cargo tanks entering the double hull spaces through the system;
5.5.3 General requirements for inert gas systems
5.5.3.1 The inert gas system shall be capable of inerting, purging and gas-freeing empty tanks and maintaining the atmosphere in cargo tanks with the required oxygen content.
5.5.3.2 The inert gas system referred to in paragraph 5.5.3.1 shall be designed, constructed and tested in accordance with the Fire Safety Systems Code.
5.5.3.3 Tankers fitted with a fixed inert gas system shall be provided with a closed ullage system.
5.6 Inerting, purging and gas-freeing
5.6.1 Arrangements for purging and/or gas-freeing shall be such as to minimize the hazards due to dispersal of flammable vapours in the atmosphere and to flammable mixtures in a cargo tank.
5.6.2 The procedure for cargo tank purging and/or gas-freeing shall be carried out in accordance with regulation 16.3.2.
5.7 Gas measurement
5.7.1 Portable instrument
Tankers shall be equipped with at least one portable instrument for measuring flammable vapour concentrations, together with a sufficient set of spares. Suitable means shall be provided for the calibration of such instruments.
5.7.2 Arrangements for gas measurement in double-hull spaces and double bottom spaces
5.7.2.1 Suitable portable instruments for measuring oxygen and flammable vapour concentrations shall be provided. In selecting these instruments, due attention shall be given to their use in combination with the fixed gas sampling line systems referred to in paragraph 5.7.2.2.
5.7.2.3 The materials of construction and the dimensions of gas sampling lines shall be such as to prevent restriction. Where plastic materials are used, they shall be electrically conductive.
5.8 Air supply to double hull spaces and double bottom spaces
Double hull spaces and double bottom spaces shall be fitted with suitable connections for the supply of air.
5.9 Protection of cargo area
Drip pans for collecting cargo residues in cargo lines and hoses shall be provided in the area of pipe and hose connections under the manifold area. Cargo hoses and tank washing hoses shall have electrical continuity over their entire lengths including couplings and flanges (except shore connections), and shall be earthed for removal of electrostatic charges.
5.10 Protection of cargo pump-rooms
5.10.1 In tankers:
5.10.1.1 cargo pumps, ballast pumps and stripping pumps, installed in cargo pump-rooms and driven by shafts passing through pump-room bulkheads shall be fitted with temperature sensing devices for bulkhead shaft glands, bearings and pump casings. A continuous audible and visual alarm signal shall be automatically effected in the cargo control room or the pump control station;
5.10.1.2 lighting in cargo pump-rooms, except emergency lighting, shall be interlocked with ventilation such that the ventilation shall be in operation when switching on the lighting. Failure of the ventilation system shall not cause the lighting to go out;
5.10.1.3 a system for continuous monitoring of the concentration of hydrocarbon gases shall be fitted. Sampling points or detector heads shall be located in suitable positions in order that potentially dangerous leakages are readily detected. When the hydrocarbon gas concentration reaches a pre-set level, which shall not be higher than 10% of the lower flammable limit, a continuous audible and visual alarm signal shall be automatically effected in the pump-room, engine control room, cargo control room and navigation bridge to alert personnel to the potential hazard; and
5.10.1.4 all pump-rooms shall be provided with bilge level monitoring devices together with appropriately located