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. The leakage of a volatile product from any part of this system could lead to the rapid generation of a flammable or toxic atmosphere. To avoid dire consequences there need to be taken some careful considerations.
Pumprooms
Ventilation Setup:
Correct use and setup of pump room(s) ventilation systems are essential to ensure that pump room(s) remain free from explosive or toxic atmospheres.
Invariably the system fans are set up to make suction from below the bottom floor plates, i.e., from the bilge area. It gives full and proper circulation of all air in the pumproom to maintain a safe atmosphere.
Additionally, middle level suctions are available above the bottom floor plates. These are for emergency use only. If flooding or saturated vapor builds up in the bilge area, they can be opened to avoid liquid or saturated gas being drawn up the fan trunk and deposited on open decks, with the consequent pollution hazard.
A notice is to be posted to each control lever for the mid-level flaps: "TO BE KEPT CLOSED EXCEPT IN CASE OF FLOODED BILGE."
Throughout cargo handling operations, the pump room ventilation system must be in continuous operation. Pumproom fans must be checked before and during cargo operations to ensure the correct direction of flow and that fans are mechanically in good condition. Noisy fans must not be operated until they have been checked to ensure that they do not generate mechanical sparks or heat at defective bearings. Defective fans must be repaired at the earliest opportunity.
How to Deal With Ventilation Failure
Pumprooms required continuous ventilation during all cargo operations and are normally fitted with an interlock to the lighting. Pumproom fan(s) are to be operated in the extraction mode, extracting from the bottom.
Normally two fans are fitted each capable of meeting the required number of 20 exchanges per hour. In the event of one failing, in this case, no special requirements are necessary.
Some vessels have a ventilation system that has been designed with one fan venting and the other extracting. This is acceptable provided extraction takes place from both sides of the pumproom bilges, and the ventilating fan delivers to the upper part of the pumproom. If one of these fans fails, then the one remaining must be capable of extracting from the bottom at the required rate.
A pumproom containes many pipeline
If the normal set up requires both fans to be running to meet the specified number of air changes, then the failure of one of these fans requires extra precautions. A risk assessment is to be completed and agreed with the office before cargo operations being carried out. This risk assessment is to consider the following.
Amount of toxic gas e.g. H2S in cargo
Vapour pressure of cargo.
Capacity of remaining fan
Enhanced controls in this risk assessment will include:
Longer ventilation time pre-entry.
Increasing frequency of atmosphere tests
Enhanced entry procedure with ELSA or EBA’s carried.
Reducing discharge rate to minimise risk of high bearing temperatures.
More frequent pumproom inspections.
Response to Pumproom Fires
Pumproom fires can originate from overheated pump bearings and pump glands, and these are to be checked at least hourly. This requirement is to be applied whenever cargo pumps and/or ballast pumps are being operated. The results of such pumproom inspections are to be recorded in the Cargo Log Book. Lubrication systems must be maintained in the pumproom as well as they are in the Engine Room.
In the event of a fire, all personnel must evacuate the space, and the CO2 smothering system to the cargo pump room must be released without delay. Before CO2 gas is released into the pumproom, space must be wholly battened down, and all ventilation stopped.
If the extinguishing system to the pumproom does not extinguish the fire at least two, preferably three, foam making branch pipes must be brought into operation from outside the pumproom, projecting foam through the pumproom door(s) against the pumproom bulkheads.
Routine Inspection
The pumproom is to be inspected as soon as possible after starting a cargo/ballast pump or commencement of loading. Inspections are to take place at hourly intervals to ensure that there are no leakages. The inspection of the cargo pumproom is to include checks of the following:
Bilges are clean, dry and free of cargo product
Cargo/ballast pump bearing and casing temperatures
Cargo/ballast pump and pipeline integrity
Operation of ventilation system
Monitoring of atmosphere.
The Pump Room may also contain several 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 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 an 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)
Sea Valves And Overboard Discharge Valves
Particular care must be taken to ensure that no leakage of oil occurs through overboard discharge or sea suction valves when starting or running cargo pumps. Manual valves are to be chained/locked. These valves are to be air pressure regularly tested for integrity and a log entry made. Officers should refer to the ICS/OCIMF Publication "Prevention of Spillages through Cargo Pumproom Sea Valves."
Requirement of 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:
Cargo vapor in air, inert gas or the vapor of another cargo.
Concentrations of gas in or near the flammable range.
Concentrations of oxygen in inert gas, cargo vapour or enclosed spaces.
Toxic gases
Personnel must fully understand the purpose and limitations of vapor detection equipment, whether
fixed or portable. Maintenance records for all gas detection equipment on board 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 overemphasized as the gas detection or analyzing
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. At least one unit for each measurement function should remain on board for
at least one group. Where calibration is carried out ashore or by shore technicians, a certificate is to be
issued and retained.
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 tank's full depth or space being tested. Long hoses must mark at least every 5 meters to assess the hose's level in the space.
Where the atmosphere testing equipment is not of uniform manufacture with identical hose fittings, a
a suitable system is to be created to identify and match the correct hoses with the proper equipment.
Hoses compatible with the equipment should be stowed in the same location as the equipment.
Use of Oxygen Analysers
All ships are supplied with a portable oxygen analyzer. This equipment is provided for use in checking
that spaces to be entered have been adequately ventilated. It is also used on Tankers, Gas Ships, and Chemical Carriers to verify that the atmosphere of inerted tanks remains below 7%.
Two tests should be carried out on the instrument before 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:
It must be done in FRESH AIR, and the instrument carefully checked that the reading has
stabilized 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 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. Any person using this instrument carefully must study 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 a 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
following manufacturers' instructions. Note that, in general, an explosimeter may be
calibrated by different gases. The correct gas must be 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 typically require a specialized attachment or tube which the gas is aspirated
. It is necessary to know in advance what gas is expected 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
Certain instruments have a combination of functions. Examples of some equipment
which may be carried are:
Draeger Combiwarn: this instrument measures and monitors flammable vapors 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.
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.
Exotox 40: this is supplied specifically for testing and monitoring the
enclosed spaces' atmosphere. It combines the functions of an
Oxygen monitor, and Explosimeter and a toxic gas monitor for either
Carbon monoxide or Hydrogen sulfide. 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.
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 sufficiently
supply of personal meters to ensure all persons working in the gas-zone are provided with a 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 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 essential to realize the length of pipe and compare it to the meter manufacturer's instructions
for the number of aspirations per meter length. If this is not done, there is a danger that the sample
gas may not reach the metering sensor and give a false reading.
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