Vessels equipped with vapour collection systems must be fitted with a pressure sensing device that senses the pressure in the main vapour collection line, which:
(a) Has a pressure indicator located on the vessel where the cargo transfer is controlled; and (b) Has a high pressure and a low pressure alarm that:
(1) Is audible and visible on the vessel where cargo transfer is controlled;
(2) Alarms at a high pressure of not more than 90 percent of the lowest pressure relief valve setting in the cargo tank venting system; and
(3) Alarms at a low pressure of not less than four inches water gauge (0.144 psig) for an inerted tankship, or the lowest vacuum relief valve setting in the cargo tank venting system for anon-inerted tankship. (CFR 46 39.20-13)
Note: Particular attention should be paid to monitoring the pressure in the cargo tanks and the associated line system. P/v valves, the ullaging system and the level alarms should have been thoroughly tested prior
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to the transfer commencing and there should be awareness of the initial transfer rate and maximum allowable transfer rates.
Static Electricity Precautions
Notes: ISGOTT Chapter 3 addresses the hazards associated with static electricity. ISGOTT Chapter 11 addresses the precautions that must be taken when handling static accumulator cargoes in more detail. Provided that a tank is maintained in an inert condition, when static non-accumulator cargoes are being handled, or when it can be guaranteed that the tank atmosphere is non-flammable, no anti-static precautions are necessary.
Questions 8.63 to 8.71 should only be completed for vessels carrying static accumulator cargoes in non-inert tanks. If the cargo is not a static accumulator or if the tanks are inerted, answer these questions ‘NA’.
Static accumulator petroleum cargoes are all those except crude oils, residual fuel oils, black diesel oils and asphalts (bitumens). Some chemicals are known static accumulators and examples are Cumene, Cyclohexane, Diethylether, Heptanes, MTBE, Nonene, Octenes, Styrene, Toluene and Xylene. In case of doubt it should be assumed that a product is a static accumulator and the appropriate precautions should be taken.
8.63 Are precautions relating to maximum flow rates during initial loading being observed?
The generally accepted method for controlling electrostatic generation in the initial stages of loading is to restrict the velocity of oil entering the tank to 1 metre/second until the tank inlet is well covered and all splashing and surface turbulence in the tank has ceased. The 1 metre/second limit applies in the branch line to each individual cargo tank and should be determined at the smallest cross-sectional area including valves or other piping restrictions in the last section before the tank's loading inlet. (ISGOTT 11.1.7.3)
8.64 Are required settling periods being observed?
There should be a delay of 30 minutes (settling time) after the completion of loading of each tank before commencing these operations. (dipping, ullaging or sampling with metallic equipment) This is to allow the settling of gas bubbles, water or particulate matter in the liquid and the dissipation of any electrical potential
(ISGOTT 11.8.2.3) Note: If the vessel is fitted with a fixed tank level gauging system, but is not fitted with IG and not fitted with full depth sounding pipes, the Operator’s policy relating to actions to be taken in the event of failure of the primary fixed gauging system must be reviewed.
8.65 Where vapour locks are fitted to cargo tanks that are not fitted with full depth sounding pipes, are static electricity precautions taken to ensure that the appropriate relaxation period elapses prior to ullaging or sampling?
Operations carried out through sounding pipes are permissible at any time because it is not possible for any significant charge to accumulate on the surface of the liquid within a correctly designed and installed sounding pipe. A sounding pipe is defined as a conducting pipe which extends the full depth of the tank and which is effectively bonded and earthed to the tank structure at its extremities. The pipe should be slotted in order to prevent any pressure differential between the inside of the pipe and the tank and to ensure that true level indications are obtained (ISGOTT 11.8.2.3)
8.66 Are metal tapes and other gauging or sampling devices effectively bonded before being introduced into tanks?
Note: UTI tapes must be bonded before being introduced into tanks. UTI tapes which have quick couplings to connect the unit to the vapour lock will possibly not require bonding wires. However, the internal bonding of such units should be checked every six months in accordance with the manufacturer’s requirements.
8.67 If portable tank cleaning hoses are used, are continuity tests carried out and the results recorded?
Bonding wires should be incorporated within all portable tank washing hoses to ensure electrical continuity. Couplings should be connected to the hose in such a way that effective bonding is ensured between them. Hoses should be indelibly marked to allow identification. A record should be kept showing the date and the result of electrical continuity testing. (ISGOTT 11.3.6.2)
All hoses supplied for tank washing machines should be tested for electrical continuity in a dry condition prior to use, and in no case should the resistance exceed 6 ohms per metre length. (ISGOTT 11.3.6.3)
8.68 Are personnel aware of the hazards associated with tank cleaning after the carriage of volatile products?
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8.69 Are personnel aware of the hazards associated with steaming cargo tanks after the carriage of