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Follow-up Action on Product Tankers on failure of Inert gas

Tank coatings usually inhibit the formation of pyrophors in the cargo tanks of product tankert is considered totally impracticable to repair the inert gas system, discharge may thereforeesumed with the written agreement of all interested parties, provided that an external sour

of inert gas is provided or detailed procedures are established to ensure the safety ofoperations. The following precautions should be taken:1. The manual referred to in Section 7.1.12 above should be consulted. ( I G Manual)

2. Devices to prevent the passage of flame or flame screens (as appropriate) are in place an

are checked to ensure that they are in a satisfactory condition.

3.Valves on the vent mast risers are opened.

4. No free fall of water or slops is permitted.

5. No dipping, ullaging, sampling or other equipment is introduced into the tank unless essenor the safety of the operation. If it is necessary for such equipment to be introduced into theank, it should be done after at least 30 minutes have elapsed since the injection of inert gas

has ceased. (See Section 7.1.6.8 for static electricity precautions relating to inert gas andSection 11.8 for static electricity precautions when dipping, ullaging and sampling.)6. All metal components of any equipment to be introduced into the tank should be securelyearthed.This restriction should be applied until a period of five hours has elapsed since the injection nert gas hasceased.

Action to be Taken on Failure of the Inert Gas Systemn the event that the inert gas system fails to deliver the required quality and quantity of inegas, or to maintain a positive pressure in the cargo tanks and slop tanks, action must be takmmediately to prevent any air being drawn into the tanks. All cargo and or ballast dischargerom inerted tanks must be stopped, the inert gas deck isolating valve closed, the vent valve

between it and the gas pressure regulating valve (if provided) opened, and immediate actioaken to repair the inert gas system. Masters are reminded that national and local regulation

may require the failure of an inert gas system to be reported to the harbour authority, termioperator and to the port and flag state administrations.

Follow-up Action on Crude Oil TankersPyrophoric iron sulphide deposits (pyrophors), formed when hydrogen sulphide gas reacts wusted surfaces in the absence of oxygen, may be present in the cargo tanks of crude oil tan

and these deposits can heat to incandescence when coming into contact with air. In the caseankers engaged in the carriage of crude oil, the failed inert gas system must therefore beepaired and restarted, or an alternative source of inert gas provided, before discharge from

nerted tanks is resumed. (See also Section 2.6.3.)

Venting ArrangementsVenting capacity is based on the maximum volume of cargo entering a tank plus a 25% maro account for gas evolution (vapour growth). When loading cargoes having a very high vapo

pressure, gas evolutionmay be excessive and the allowance of 25% may prove to be insufficient. Actions to consideorder to ensure that the capacity of the venting system is not exceeded include a closemonitoring of vapour line

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pressures on inerted ships and limiting loading rates on non-inerted ships throughout theoading period or during crude oil washing during discharge operations. It should be noted thhe vapour growth increases

when the liquid levels in the tank are above 80%. On inerted ships, close attention should begiven to monitoring inert gas system pressures, particularly when topping-off during loadingoperations or on commencing crude oil washing during discharge operations.When calculating loading rates, a maximum venting line velocity of 36 metres per secondshould be considered. This flow rate should be calculated for each diameter of line used. Thevolume throughputs maybe aggregated where a common vent riser is used, but the maximum flow rate should not be

exceeded anywhere within the system.

Static accumulator oil

An oil with an electrical conductivity of less than 50 picoSiemens/metre (pS/m), so that it is capable etaining a significant electrostatic charge. (such as kerosene)

Liquids are considered to be non-conductors when they have conductivities less than 50pS/m (pico Siemens/metre). Such liquids are often referred to as static accumulators.

Petroleum products, such as clean oils (distillates), frequently fall into this category with a conductivypically below 10 pS/m. Chemical solvents and highly refined fuels can have conductivities of less t

pS/m.

The following additional precautions should be taken against static electricity during ullaging, dippingauging or sampling of static accumulator oils:Banning the use of all metallic equipment for dipping, ullaging and sampling during loading and for

minutes after completion of loading. After the 30 minute waiting period, metallic equipment may be or dipping, ullaging and sampling, but it must be effectively bonded and securely earthed to thetructure of the ship before it is introduced into the tank, and must remain earthed until after removBanning the use of all non-metallic containers of more than 1 litre capacity for dipping, ullaging andampling during loading and for 30 minutes after completion of loading.

Non-metallic containers of less than 1 litre capacity may be used for sampling in tanks at any time,provided that they have no conducting components and that they are not rubbed prior to sampling.

Cleaning with a high conductivity proprietary cleaner, a solvent such as 70:30% IPA:toluene mix, oroapy water, is recommended to reduce charge generation. To prevent charging, the container shounot be rubbed dry after washing.

3.2.2 BondingThe most important countermeasure that must be taken to prevent an electrostatic hazard ibond all metallic objects together to eliminate the risk of discharges between objects that mbe charged and electrically insulated.To avoid discharges from conductors to earth, it is normal practice to include bonding to earearthing or grounding). On ships, bonding to earth is effectively accomplished by connec

metallic objects to the metal structure of the ship, which is naturally earthed through the se

Some examples of objects which might be electrically insulated in hazardous situations andwhich must therefore be bonded are:Ship/shore hose couplings and flanges, except for the insulating flange or single length of n

conducting hose required to provide electrical isolation between the ship and shore. (SeeSection 17.5.)Portable tank washing machines.Manual ullaging and sampling equipment with conducting components.The float of a permanently fitted ullaging device if its design does not provide an earthing phrough the metal tape.

The best method of ensuring bonding and earthing will usually be a metallic connection betwhe conductors. Alternative means of bonding are available and have proved effective in som

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applications, for example semi-conductive (dissipative) pipes and O rings, rather thanembedded metallic layers, for GRP pipes and their metal couplings.