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Online-Test: Test about Inert Gas Generator (CBT)
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A water column type pressure vacuum breaker device may be fitted to the deck main of an inert gas system. Which of the statements given in the options is true?
This type of device is usually designed to operate before the deck water seal reaches it’s limit.
This type of device is usually designed to operate only after the deck water seal fails.
This type of device is intended to protect individual tanks against overpressure or under vacuum.
An independent inert gas generator is supplying the inert gas during cargo discharge operations when the low pressure alarm sounds. Which one of the giving options is most likely to automatically happen when such a condition develops?
Automatic shutdown of the cargo pumps.
Deck main valve closes and the automatic vent opens.
Automatic shutdown of inert gas generator.
Pressure vacuum breaker operates on deck.
Complete the following statement to give the IMO definition of an inert condition for a cargo tank. A condition in which the oxygen content throughout the atmosphere of a tank has been:
Reduced to 8 % or less by volume by addition of inert gas.
Reduced to 20 % or less by volume by addition of inert gas.
Reduced to 16% or less by volume by addition of inert gas.
Reduced to 0 % by volume by addition of inert gas.
Considering an oil tanker fitted with an independent inert gas generator system. Which of the items identified in the options is most likely to be operating continuously when the cargo tanks are full of cargo?
Deck seal pump.
Scrubber water pump.
Combustion air blower.
Capacity control valve.
Considering the ullage space of a cargo tank containing petroleum based oil. Which of the given statements best describes the atmosphere of the ullage space?
It will contain a mixture of atmospheric air and hydrocarbon gases with an oxygen content greater than 21 % by volume.
It will contain a mixture of atmospheric air and hydrocarbon gases with an oxygen content of less than 21 % by volume.
It will contain a mixture of atmospheric air and hydrocarbon gases with an oxygen content equal to approximately 21 % by volume.
It will contain a layer of hydrocarbon gases and a layer of atmospheric air since the two cannot mix.
During loaded passage the inert gas pressure in the cargo tanks can vary due to changes in ambient temperature. Which of the given options would be the preferred way to maintain the correct pressure on a vessel fitted with an independent inert gas generator?
Continuous operation of the generator in automatic mode at a very low capacity setting using the automatic atmospheric vent to maintain the pressure.
Intermittent operation of the generator in automatic mode to top up the pressure.
Intermittent operation of the generator in manual mode to top up the pressure.
Continuous operation of the generator in manual mode to maintain the pressure with manual control of the atmospheric vent valve.
During start-up sequence of an independent inert gas generator it is necessary to allow time for a pre-purge of the furnace whether in manual or automatic mode. What is the recommended minimum time for such a pre-purge operation?
3 minutes.
1 minute.
30 seconds.
5 seconds.
During the operation of an independent inert gas generator, a problem develops with the scrubber unit effluent valves such that the water level in the scrubber unit reaches alarm condition. In addition to the alarm sounding what other action is most likely to result from this condition?
Immediate shutdown of the inert gas generator system.
The scrubber pump would immediately stop but the generator would continue.
Only the main burner would shut down.
The deck main valve would close and the automatic vent would open but the generator would continue operating.
During the start-up procedure for an independent inert gas generator when should the inert gas deck main valve be opened?
Once the measured oxygen content reaches the set point value.
Once the main burner is operating.
Once the combustion air blower is operating.
Once the deck seal pump is operating.
For an independent inert gas generator with automatic control which one of the parameters in the given options is most likely to have a controller set point that can be adjusted by the operator?
The viscosity of the fuel to the burner unit.
The pressure of the seawater to the deck seal.
The temperature of the scrubber effluent.
The pressure of the inert gas in the deck main.
For an independent inert gas generator with automatic control which one of the parameters in the given options is most likely to have a set point that can be adjusted by the operator?
The rate of water flow to the deck seal.
The temperature of the fuel at the burner inlet.
The temperature of the inert gas at the scrubber outlet.
The oxygen content of the inert gas.
For the independent inert gas generator considered in this module how is the oxygen content of the inert gas automatically controlled?
By adjustment of the automatic deck main valve.
By adjustment of the automatic atmospheric vent valve.
By adjustment of the blower capacity setting.
By adjustment of the fuel capacity control setting.
For the independent inert gas generator considered in this module how is the primary control of the deck main pressure at its set point achieved?
By the automatic operation of the atmospheric vent valve.
By varying the blower load.
By varying the fuel pressure to the main burner.
By automatic adjustment of the capacity control valve.
Guidance regarding the IMO requirements for inert gas systems is given in the IMO publication Inert Gas Systems, 1990 edition. Which other publication from IMO gives general guidance relating to inert gas systems?
SOLAS.
MARPOL.
STCW.
IMDG Code.
High efficiency burners are often used in independent inert gas generators to ensure good combustion and that high quality inert gas is produced. Monitoring the gases from the combustion process can give an indication of the efficiency of the combustion. Which of the given indicates good combustion?
Minimum carbon monoxide content.
Minimum oxygen content.
Minimum carbon dioxide content.
Minimum nitrogen oxide content.
How is the humidity of the inert gas supply controlled for independent inert gas generator systems fitted to gas and chemical carriers?
By cooling and then drying the gas before the inlet to the deck main.
By having a dry type scrubber unit fitted.
By using coalescer filters in the fuel supply line.
By using a demister and coalescer filters at the scrubber outlet.
How is the quantity of inert gas from an independent inert gas generator normally monitored?
By the oxygen content at the scrubber outlet.
By the pressure in the deck main.
By the blower electrical load.
By the temperature at the scrubber outlet.
In auto start mode which of the given options will start first when starting up an independent inert gas generator? Assume all normal pre-start requirements have been met:
Combustion air blower.
Scrubber pump.
Fuel pump.
Igniter.
In the event of a multiple alarm condition occurring during operation of an independent inert gas generator what will be the normal arrangement for the alarm display?
Only the last alarm to occur will be shown.
All alarms will be listed in order of priority.
Only the most important alarm to occur will be shown.
All alarms will be listed in the order they occurred.
In the event of an alarm condition occurring during operation of an independent inert gas generator how will the operator know which parameter is in alarm condition? Select the most common method from the options given:
The audible alarm will sound and the operator can then select the alarm status screen.
The audible alarm will sound and the alarm status screen will automatically display.
The audible alarm will sound and the operator will need to check the local readings to identify the cause.
The audible alarm will sound and the alarm will be indicated on the bridge which will then inform the operator.
In the event that the oxygen content of the inert gas supply from an inert gas generator exceeded the value of the set point an alarm would sound. Which one of the given options is also the most likely to occur in such a situation?
The generator would immediately shut down.
The automatic vent valve would open and the deck main valve would close.
The main burner would shutdown but the blower would continue to run.
The scrubber pump would automatically stop.
Independent inert gas generator systems fitted to gas carriers often have refrigerated type cooler dryer units fitted to control the humidity of the inert gas. Which condition of the gas is used to control entry of the gas into the drier section of such a unit?
The temperature of the inert gas.
The humidity of the inert gas.
The pressure of the inert gas.
The oxygen content of the inert gas.
Independent, oil fired, inert gas generators are usually operated on distillate fuel rather than residual fuel. What is the main reason for this?
Operating on distillate fuel normally produces a cleaner exhaust gas with a lower oxygen content due to relatively good combustion.
The inert gas plant does not require a scrubber unit since distillate fuels have a zero sulphur content.
More exhaust gas is available when burning distillate fuel.
Distillate fuel is more readily available than residual fuel.
On which one of the vessel types given in the options would a nitrogen generator most likely to be fitted for the purpose of providing inert gas to the cargo system and associated spaces?
Chemical tanker.
Crude oil carrier.
Steam ship used as a heavy fuel oil carrier.
Container vessel.
One of the main reasons for the introduction of inert gas systems onboard oil tankers was the increase in the number of explosions onboard these vessels. Which one of the given options was found to be the main ignition source for these explosions?
Build-up of static electricity during cargo and tank cleaning operations.
Overheating of fuel oil bunker tanks adjacent to the cargo tanks.
Crew members smoking on the cargo deck.
The use of unsuitable electrical equipment on and around the cargo deck.
SOLAS stimulates the maximum content of oxygen by volume that an inert gas system, including an independent inert gas generator type, must be capable of supplying. Which of the given options is this maximum value?
5 %.
3 %.
8 %.
11 %.
Select the best option from those given to complete the following statement in relation to pressure vacuum breakers as fitted to the distribution system of some independent inert gas generator systems. The correct operation of a liquid column type pressure vacuum breaker is dependent on:
The correct specific gravity of the liquid and the liquid column height.
The correct operation of the mechanical non-return device in the deck main.
The correct operation of the automatic vent to the atmosphere valve.
The correct operation of the deck water seal.
Some oil fired, independent inert gas generators incorporate capacity control to regulate the rate of delivery of the inert gas to the distribution system. Which of the given options is the primary element regulated by such a control feature?
The combustion air blower load.
The fuel pump pressure.
The fuel recirculation valve.
The fuel rate to the main burner.
The combustion air blowers of an inert gas generator may be used to supply fresh air during venting and gas freeing operations following purging of cargo tanks and lines. What precautions must be taken when carrying out such operations with an independent inert gas generator?
Ensure all none purged tanks are properly isolated from the inert gas main.
Ensure the atmospheric vent valve is fully opened.
Ensure that the capacity control setting is at a minimum.
Ensure that the inert gas generator fuel pump is running on recirculation throughout the operation.
There are a number of different types of inert gas system in use onboard oil tankers including the so called flue gas system. What does the term flue gas normally refer to in the context of inert gas systems?
Boiler exhaust gas.
Diesel engine exhaust gas.
Incinerator exhaust gas.
Exhaust gas from an independent inert gas generator.
What effect on the upper and lower flammable limits does the introduction of inert gas into a cargo oil tank have?
It reduces the upper flammable limit and increases the lower flammable limit.
It reduces the lower flammable limit and increases the upper flammable limit.
It reduces both the upper flammable limit and the lower flammable limit.
It increases both the upper flammable limit and the lower flammable limit.
What is generally taken as the minimum amount of oxygen in a mixture of atmospheric air and hydrocarbon gases that gives a safe margin against the risk of combustion?
5 %.
8 %.
16 %.
20 %.
What is the SOLAS requirement regarding non-return devices in the inert gas main for inert gas systems on oil tankers?
There must be at least two water seal type devices fitted.
There must be at least two devices one of which should be a water seal type.
There must be at least two neither of which should be a water seal type.
As long as there is a water seal no other devices are required.
What is the approximate minimum amount of oxygen in a mixture of atmospheric air and hydrocarbon gases that will support combustion?
5 %.
11 %.
16 %.
20 %.
What is the main reason for controlling the humidity of the inert gas produced by an independent inert gas generator when fitted to a gas or chemical tanker?
To avoid corrosion problems in the cargo pipelines.
To avoid compatibility problems with the cargo.
To avoid corrosion problems in the inert gas deck main.
To avoid contamination of the deck seal water.
What is the main risk associated with dilution of a normally inerted cargo oil tank atmosphere with fresh air?
During the process the atmosphere may become over rich for some of the time.
During the process the atmosphere may be within the explosive range for some of the time.
During the process the atmosphere may become too lean for some of the time.
During the process the oxygen content may exceed the maximum limit for a flammable mixture.
What is the percentage content by volume of oxygen in atmospheric air generally taken to be?
20 %.
21 %.
79 %.
16 %.
What is the recommended interval for checking the calibration of an oxygen analyser as fitted to an independent inert gas generator system?
At least every 4 hours when the system is in use.
At least every 8 hours when the system is in use.
Once every day when the system is in use.
Once a week as part of the planned maintenance schedule.
When considering an independent, oil fired inert gas generator how is it normally protected in the event of a flame failure of the main burner?
It will normally result in audible and visual alarms and an automatic shutdown of the generator.
It will normally result in automatic ignition of the pilot burner.
The generator will automatically purge the furnace and restart.
There will be an alarm to alert the operator to manually shutdown the system.
When considering an independent, oil fired inert gas generator how is the furnace usually prevented from overheating?
By surrounding the furnace with a water jacket.
By providing a large flow of excess air to the combustion chamber.
By making the walls of the combustion chamber extra thick.
By intermittent firing of the burner.
When considering an independent, oil fired inert gas generator how is the required flow of inert gas normally generated?
The combustion air fans provide sufficient pressure to ensure the necessary inert gas flow.
Additional booster fans are fitted in the deck main.
Cargo discharge rates are kept high to create a partial vacuum in the tanks which helps to draw in the inert gas.
Main inert gas fans are fitted after the scrubber unit to increase the flow of inert gas.
When considering an independent, oil fired inert gas generator suitable for service onboard an oil tanker what are the SOLAS requirements for the oxygen content of the inert gas supply?
A maximum of 5 %.
A maximum of 3 %.
A maximum of 8 %.
A maximum of 11 %.
When considering an independent, oil fired inert gas generator suitable for service onboard an oil tanker what is the SOLAS requirement regarding the composition of the tank atmosphere to be maintained?
A maximum of 5 % oxygen content.
A maximum of 1 % oxygen content.
A maximum of 8 % oxygen content.
A maximum of 11 % oxygen content.
When considering an independent, oil fired inert gas generator what is the main purpose of the pilot burner?
It is used to provide an ignition source for the main burner.
It is used to preheat the furnace.
It is used to establish the correct oxygen content of the inert gas before the main burner starts.
It is used to preheat the combustion air to make it easier to ignite the main burner.
When considering an independent, oil fired inert gas generator which incorporates a sea water scrubber unit. How is the water content of the inert gas normally kept to a minimum if the generator is used onboard an oil tanker?
A demister unit is fitted before the scrubber inert gas outlet.
The inert gas is passed through a series of coalescer filters after the scrubber unit.
The water flow through the scrubber unit is kept to a minimum.
The inert gas is passed through a refrigerated drying unit before it enters the deck water seal.
When considering an independent, oil fired inert gas generator, other than providing a vent to the atmosphere during start-up of the plant, what is the other main purpose of the automatic atmospheric vent valve?
It is used in conjunction with the inert gas main valve to regulate the pressure in the inert gas main.
It acts as an inlet for fresh air to the system when gas freeing.
It acts as the main relief device in the event of overpressure.
It is used to control the capacity of the inert gas generator.
When considering the automatic operation of an independent inert gas generator the start-up sequence normally has delays built in to ensure correct timing of the sequence. For example, there will be a delay in the sequence to ensure sufficient furnace purging time. How can these delays be ensured in manual mode?
By the use of timed interlocks which operate even in the manual mode.
The operator is relied upon to ensure the correct timing of the sequence.
The delays are only an extra safety precaution so it doesn’t matter if they missed out.
There is no need for any delays if the operator is in attendance during start up.
When considering the water supply to the deck water seal for an inert gas system which of the following statements is true?
There should be at least one independent pump for continuously supplying water to the deck seal.
The water supply can be taken directly from the fire man.
A water supply to the deck seal is only required during cargo operations.
The deck seal must be supplied directly from the engine room sea water main and auxiliary systems.
When gas freeing a normally inerted cargo oil tank what should be the first step in the operation?
Purge with inert gas to bring the atmosphere to below the critical dilution line.
Purge with fresh air to bring the atmosphere to below the critical dilution line.
Purge with inert gas to bring the atmosphere to below the upper explosive limit.
Purge with fresh air to bring the atmosphere to below the lower explosive limit.
Where a liquid column type pressure vacuum breaker device is fitted to the deck main of an inert gas system which liquid is normally used to fill the device?
A water glycol mix.
Fresh water.
Seawater.
Diesel oil.
Where in an independent inert gas generator system as fitted onboard a gas carrier would you expect to find a desiccant dryer unit?
As part of the humidity control system.
In the scrubber unit gas outlet.
In the deck water seal inlet.
In the combustion air intake.
Which is the best test gas to use when checking and adjusting the zero setting of an oxygen analyser as fitted to an independent inert gas generator system?
Nitrogen.
Carbon dioxide.
Carbon monoxide.
Hydrogen.
Which of the control touch screens considered in this module will allow the operator single button control of the start-up of the inert gas system if all pre-start conditions are met?
Auto-start screen.
Main screen.
Manual start screen.
Alarm status screen.
Which of the given options describes the lower explosive limit in relation to the atmosphere of a cargo oil tank atmosphere?
The least proportion of hydrocarbon gases in a mixture with atmospheric air which is flammable.
The least proportion of oxygen in a mixture of hydrocarbon gases and atmospheric air which is flammable.
The lowest amount of oxygen which will support a flame when mixed with hydrocarbon gases.
The lowest point in a cargo tank ullage space where the mixture of hydrocarbon gases and air is flammable.
Which of the given options describes the upper explosive limit in relation to the atmosphere of a cargo oil tank atmosphere?
The highest proportion of hydrocarbon gases in a mixture with atmospheric air which is flammable.
The highest proportion of oxygen in a mixture of hydrocarbon gases and atmospheric air which is flammable.
The greatest amount of oxygen which will support a flame when mixed with hydrocarbon gases.
The highest point in a cargo tank ullage space where the mixture of hydrocarbon gases and air is flammable.
Which of the given options is the main reason for ensuring that the air cone of the burner unit for an independent inert gas generator is properly positioned and maintained?
If not, it will result in overpressure in the inert gas main.
If not, it will result in a low carbon monoxide content of the inert gas.
If not, it will result in a high oxygen content of the inert gas.
If not, it will result in poor combustion.
Which of the given options is the one that will most influence the combustion efficiency for the burner type described in this module?
Distance from pilot burner tip to edge of air cone.
Distance from pilot burner tip to igniter.
Distance from main burner tip to pilot burner tip.
Distance from the main burner tip to the edge of the air cone.
Which of the given options represents the approximate percentage content by volume of nitrogen in atmospheric air?
21 %.
50 %.
70 %.
79 %.
Which of the given ranges of oxygen content by volume is likely to be achieved when supplying inert gas from an independent inert gas generator operation on distillate fuel?
5 % to 8 %.
3 % to 5 %.
Less than 0,5 %.
0,5 % to 3 %.
Which of the given statements best describes the operation of gas freeing when considering oil tankers fitted with inert gas systems?
The introduction of nitrogen into a tank to remove all toxic, flammable and inert gases and reduce the oxygen content below 21 %.
The introduction of oxygen into a tank to remove all toxic, flammable and inert gases and increase the oxygen content to 100 %.
The introduction of inert gas into a tank to remove all toxic and flammable gases to reduce the oxygen content to zero.
The introduction of fresh air into a tank to remove all toxic, flammable and inert gases and increase the oxygen content to 21 %.
Which of the statements given in the options best describes the SOLAS requirements for inert gas systems fitted to a gas carrier?
Water seal type non-return devices are prohibited for use in the deck inert gas main on gas carriers.
At least one of the non-return devices fitted in the inert gas main must be a water seal type.
There must be at least one non-return device fitted in the inert gas deck main.
There must be two non-return devices fitted in the inert gas deck main.
Which one of the alarm conditions given in the options would result in shutdown of the burner unit and the blower continuing to run for a cooling down period when considering the operation of an independent inert gas generator?
Scrubber pump low discharge pressure.
Deck inert gas main high pressure.
High oxygen content of inert gas.
Combustion air blower low load.
Which one of the given options is the most likely type of fixed gas measuring device to be fitted for monitoring and control of the quality of the inert gas produced by an independent inert gas generator?
A paramagnetic type oxygen analyser.
A heated filament combustible gas analyser.
A carbon monoxide monitor.
A carbon dioxide monitor.
Which one of the statements given in the options is the most accurate in respect of control of oil fired, independent inert gas generators?
The generators are usually automatically controlled but normally also have a manual control facility.
The generators are normally started in the manual mode but can be changed to automatic mode once inert gas production has started.
There is normally only one control station for the generator which is situated locally to the generator.
If a second control station for this type of inert gas generator is provided it is normally situated on the bridge.
Which one of the vessel types given in the options is most likely to be fitted with an independent inert gas generator?
A motor ship designed to carry petroleum product cargoes.
A steam ship designed to carry crude oil cargoes.
A motor ship designed to carry high grade lubricating oil cargoes.
A steam ship designed to carry high grade chemical cargoes.
Which parameter is normally used as the main indicator of the quality of inert gas supply for the cargo system of an oil tanker?
Oxygen content.
Humidity.
Temperature.
Pressure.
Which term is used to identify the operation whereby fresh air is introduced into a cargo tank in order to remove toxic, flammable and inert gases and to increase the oxygen content of the tank to 21 % by volume?
Gas freeing.
Diluting.
Purging.
Inerting.
Which term is used to identify the operation whereby inert gas is introduced into a cargo tank in order to reduce the oxygen content throughout the atmosphere of the tank to 8 % or less by volume?
Gas freeing.
Diluting.
Purging.
Inerting.
While operating an independent inert gas generator during cargo discharge it is noted that the automatic vent valve is continuously 50 % open. Which of the given options would be the best adjustment to make in order to minimize the gas being lost to atmosphere whilst maintaining the inert gas main pressure?
Reduce the fuel pressure to the generator burner.
Increase the set point setting for the deck pressure control.
Increase the cargo discharge rate.
Reduce the system capacity control setting.
With reference to the adjustment of the set points for the process controllers and the alarm for an independent inert gas generator which one of the statements given in the options is the most accurate?
Normally only the alarm settings can be adjusted on this type of inert gas generator by ship’s staff.
The settings are factory set and cannot normally be adjusted.
Any of the settings can be adjusted by anyone operating the generator.
There is usually some in build security feature to limit access to these settings.
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