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Safety Talk 6

Safe Operation of Storage Tanks: Decommissioning and Repair

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Decommissioning / Commissioning a storage tankstages including vapour freeing, cleaning and repair

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Standby attendant• A standby person must remain on duty outside the tank for the duration of the entry

• The site procedure shall specify the training and duties of the attendant which should include the following:

– Maintain an accurate count of all persons in the tank

– Monitor activities inside and outside the permit space to determine if it is safe

for entrants to remain in the tank

– Maintain effective and continuous contact with authorised entrants

– Order evacuation if conditions change or if any situation occurs that could

endanger entrants

– Summon rescue services in an emergency

– Assist the rescue services as necessary without entering the tank

– Ensure permit conditions are followed

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Maximum ventilation

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No hidden hazards ?

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Guidance for tank entry conditions

OXYGEN FLAMMABLE TOXIC

Without Breathing 20.8% <1% LEL <10% OELApparatus (BA)

With BA subject 19.5 - 23.5% 10% LEL to enter <STELto risk assessment 20% LEL exit

Unsafe <19.5% >20% LEL >STEL

or >23.5%

OEL (Occupational exposure limit – for 8 hours exposure)

STEL (Short term exposure limit – for 15 minutes exposure)

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Site layout drawing

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Tank cleaning protection

Appropriate PPE to be worn at various stages during cleaning

• Respiratory protection

– air-line breathing apparatus

– air fed hoods

• Body protection

– impervious clothing and footwear

– gloves

• Eye / face protection

– goggles

– face visors

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Potential hazards

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Hot work

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Recommissioning safety checkInspection

• The tank foundations have been inspected and confirmed in satisfactory condition

• The dike / bund walls have been reinstated

• The dike / bund drainage system is serviceable and clean

• All necessary repairs to the tank have been carried out

• All tank fittings and valves have been correctly reinstalled and are serviceable

Electrical

• The tank shell is grounded

• Any ground / earthing cables associated with the floating roof or internal floatingcover are securely connected and intact

• Any seal grounding / earthing shunts on a floating roof tank are correctly installedand intact

• Any tank or associated piping cathodic protection system has been reinstated

• The electrical fittings associated with any side entry mixers have been correctly installed

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Recommissioning safety check (cont’d)

Instruments

• All tank level gauging equipment has been correctly reinstalled and reconnected and is functioning correctly

• Any separate high and / or low level alarms have been correctly reinstalled and are functioning correctly

• Any tank temperature measurement instrumentation has been correctly installed

• Any instrumentation associated with the side entry mixers has been correctly replaced

Fire protection

• Any foam lines and their associated fittings have been correctly installed

• Any drencher or sprinkler system is correctly installed

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Recommissioning safety check (cont’d)

Mechanical

• That all materials and debris arising from the tank cleaning operation and subsequent inspection and any repair work have been removed from inside the tank, from the roof tank, from any internal floating cover and from the vicinity of the tank, for appropriate disposal outside the dike / bund area

• Any internal floating cover has been installed in accordance with the manufacturers requirements

• Any side entry mixers have been correctly installed

• Handrailings on stairways and around the tank roof of wind girder are intact and secure

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Recommissioning safety check (cont’d)

Mechanical (continued)

• The roof ladder is correctly positioned and intact

• The roof legs are in position and correctly set

• The automatic vent legs are all in position and correctly set

• The roof drain sumps are all clear of debris and all non-return / check valves operational

• All pontoons are clean internally and all pontoon manway covers have been replaced

• Any free vents, at the top of the shell or on the tank roof, have the correct ‘free area’ mesh / screen fitted and are clear and free from blockage

• All roof manway covers and other roof fitting covers are closed

• Primary and secondary seals are correctly installed

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Recommissioning safety check (cont’d)

Operational

• The tank has been inspected internally and is acceptable for service

• The tank has been inspected externally, including the roof and any internal floating cover, an is acceptable for service

• All roof drains, water draw-off, suction and discharge valves are serviceable and properly indentified

• All emergency roof drains, on single deck roofs, have been primed with water

• The tank drain valves are closed

• The roof drain valve is left open in accordance with local policy

• Test fixed / semi-fixed fire protection systems

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Recommissioning hazards

• Deisolate tank– Cold Work Permit– check blinds against Blind List

• When filling do not exceed inlet flow velocity of 3 ft / secs

– until inlet submerged by at least 2 ft (cone roof) if vapour space contains flammable gas /

gas mixture or mist

– roof is floated (internal / external)

– where product contains free water

• Do not jet mix if vapour space contains flammable gas / air mixture or mist

• Do not dip / sample during initial fill operation

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Flammable mixture during initial filling

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Flammable mixture will exist above internal floatingroof during initial filling it will take time to disperse