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Tanker operation : Measures for pump room inspections & gas detection equipments

A pump room contains the largest concentration of cargo pipelines of any space within the ship and leakage of a volatile product from any part of this system could lead to the rapid generation of a flammable or toxic atmosphere.

The Pump Room may also contain a number of potential ignition sources unless formal, structured maintenance, inspection and monitoring procedures are strictly adhered to.

Before Starting Cargo Operations (including Loading):

• An inspection is to be made to ensure that strainer covers, inspection plates, drain plugs and lighting are in place and in proper order.

• Drain valves in the pump room cargo system, especially those on cargo oil pumps, should be firmly closed.

• Bulkhead glands should be inspected to ensure efficient gas-tight seal between the Pump Room and the machinery space.

During Cargo Operations (including Loading):

• Inspection at regular intervals to check for leakages from glands, pipes, plugs, seals, drain valves, especially those fitted on pumps.



• Where pumps are in use, the absence of abnormal sound, the normal function of local and remote pressure gauges, the integrity of pump glands (where fitted), the bearings, casings should be checked for overheating. (Pump Glands shall never be adjusted on rotating shafts, while the pump is in service)


GAS DETECTION EQUIPMENT

Gas detection equipment is required for ensuring spaces are safe for entry, work or other operations. Their uses include the detection of:

a) Cargo vapour in air, inert gas or the vapour of another cargo.

b) Concentrations of gas in or near the flammable range.

c) Concentrations of oxygen in inert gas, cargo vapour or enclosed spaces.

d) Toxic gases

Personnel must fully understand the purpose and limitations of vapour detection equipment, whether fixed or portable.

Maintenance records for all gas detection equipment onboard are to be maintained by the Chief Officer . Onboard calibration records and shore records are to be maintained together for each meter and are to be updated on each occasion that the instrument is tested or checked. The importance of careful calibration cannot be over emphasised as the gas detection or analysing equipment will only give accurate readings if calibration is carried out strictly in compliance with the manufacturer’s instructions and using the correct calibration gases. Where calibration is carried out ashore or by shore technicians, a certificate is to be issued and retained onboard.

Instruments must always be checked, zeroed and spanned where applicable before every use as per the manufacturer’s instructions.

Where calibration is required by the manufacturer’s instructions to be carried out ashore or by shore technicians, this must be recorded within the vessel’s PMS and all certification issued. In such circumstances at least one unit for each measurement function should remain onboard available for use at all times. Where calibration is carried out ashore or by shore technicians, a certificate is to be issued and retained onboard.

Any equipment not fully operational and/or in good condition, including perished hoses, leaking aspiration bulbs and out-of-date calibration gases or Draeger tubes should be withdrawn from service and reported to the management office.

Hoses used with portable gas instruments must be of sufficient length, appropriate to the full depth of the tank or space being tested. Long hoses must clearly marked at least every 5 meters so that the user can assess the level of the hose in the space.

Where the atmosphere testing equipment is not of a uniform manufacture with identical hose fittings, a suitable system is to be created to identify and match the correct hoses with the correct equipment. Hoses compatible with the equipment should be stowed in the same location as the equipment.


OXYGEN ANALYSERS

All ships are supplied with a portable oxygen analyser. This equipment is supplied for use in checking that spaces to be entered have been properly ventilated. It is also to be used on Tankers, Gas Ships and Chemical Carriers to check that the atmosphere of inerted tanks remains below 7%.

Two tests should be carried out on the instrument prior to use and a permanent record of readings kept on board.

(a) Zero Adjustment

This is done by using an oxygen-free gas, such as Nitrogen or Carbon Dioxide. Equipment is supplied for this test. Note that CO2 is paramagnetic and therefore may not give a zero reading on certain instruments.

(b) Span Adjustment

This must be done in FRESH AIR and the instrument carefully checked that the reading has stabilised at 21% before the atmosphere of any space is tested.

The maker’s instructions for the particular instrument should be followed carefully to ensure that calibration procedures are correctly carried out. Calibration checks must be carried out every two months.


EXPLOSIMETER

The Explosimeter is the name normally associated with the instrument for measuring hydrocarbon gas in air at concentrations below the Lower Flammable Limit. Its full name is a Catalytic Filament Combustible Gas Indicator.

A full understanding of the construction and principle of an Explosimeter is essential for its safe and efficient use and it is essential that any person using this instrument carefully studies the operating manual. There is also a detailed explanation in the ISGOTT carried on tankers.

The Explosimeter measures from 0 to 100% of the Lower Explosive Limit (1.4% by volume). If the gas to air mixture is above the upper explosive limit (6% by volume) the meter reading will initially rise to give a reading of 100% or above, but will rapidly fall towards zero because the mixture of gas and air in the combustion chamber is too `rich' to sustain combustion.

The meter must therefore be constantly observed for this phenomenon, as an apparently safe reading may be obtained when the atmosphere is in fact highly dangerous.

Calibration checks must be carried out at two monthly intervals and when a filament has been changed in accordance with manufacturers’ instructions. Note that, in general, an explosimeter may be calibrated by different gases. It is essential that the correct gas is used otherwise an error may result. Explosimeters will not read hydrocarbon levels in an inert atmosphere.


TANKSCOPE

Although similar to the Explosimeter, the `Tankscope' (or Non-Catalytic Heated Filament Gas Indicator) measures hydrocarbons in an inert atmosphere. It indicates their presence as a percentage proportion of the whole atmosphere. The instrument is especially useful during purging with inert gas. It will indicate when the proportion of hydrocarbons has fallen to a level whereby the atmosphere will remain below the Lower Explosive Limit (LEL) on the introduction of fresh air. Calibration checks must be carried out at two monthly intervals.


TOXIC GAS DETECTORS

These detectors measure relatively low concentrations of toxic gases. Such gases may include Carbon Monoxide or Hydrogen Sulphide.

The type of instrument will normally require a special attachment or tube which the gas is aspirated through. It is necessary to know in advance what gas is expected in order to choose the correct detection tube. The readings are to be compared with the occupational exposure limits or threshold value limits.

A minimum list of tube types required for specific vessels is included at the end of this section however additional tubes must be carried appropriate to the hazards identified within the MSDS for the cargo carried.


COMBINED FUNCTION METERS

There are certain instruments which have a combination of functions. Examples of some equipment which may be carried are:
  1. Draeger Combiwarn: this instrument measures and monitors flammable vapours as a percentage of LEL in the range of 0 - 50% LEL. It also measures oxygen concentrations. This instrument can be preset to give audible and visual alarms at specific levels.
  2. Digiflam 2000: this combines the functions of the Tankscope and an Oxygen meter, its main use being the monitoring of COW and Inert Gas operations.
  3. Exotox 40: this is supplied specifically for the use in testing and monitoring the atmosphere of enclosed spaces. It combines the functions of an Oxygen monitor, and Explosimeter and a toxic gas monitor for either Carbon monoxide or Hydrogen sulphide. It provides continuous monitoring of all three functions and has visual and audible alarms.
As with all other instruments the manufacturer’s instructions regarding operation and calibration must be followed at all times.


PERSONAL MONITORING METERS

Some instruments can be carried in a pocket such as a Personal Oxygen Meter, used for entry into enclosed spaces. Such instruments are intended only as a personal monitor and will give an audible and visual alarm if the Oxygen content falls below its preset level.

As monitors, they are not designed (and therefore not to be used) for testing the atmosphere for oxygen or other gases.

A vessel carrying H2S cargo must maintain sufficient supply of personal meters to ensure all persons working in the gas-zone are provided with detection equipment.

Zero and alarm checks are to be made before each use.


SAMPLE LINES

The material and condition of sample lines can affect the accuracy of gas measurements. Sample tubing which is cracked or blocked or which has become contaminated with oil or other substances may seriously affect instrument readings.

The tubing must always be checked before and during use and if necessary be cleaned or replaced. It is also important to realise the length of tubing and compare to the meter manufacturer’s instructions as to the number of aspirations per metre length. If this is not done there is a danger that the sample gas may not reach the meter sensor and therefore give a false reading.



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