Le test consiste en des questions aléatoires sur un sujet sélectionné.
What is the minimum number of channels required for the portable two-way VHF's for survival craft?
*Which of the following appliances must compulsorily be found in any ro-ro cargo space intended for the carriage of motor vehicles with fuel in their tanks for their own propulsion?
One chemical powder extinguisher for each 10 vehicles the space is intended to carry
A receptacle containing sand, sawdust impregnated with soda or other approved dry material in such quantity as may be required by the Administration
At least one portable foam applicator unit
One chemical powder extinguisher for each 20 vehicles the space is intended to carry
*What precautions are necessary to prevent soot fires in the exhaust boiler ?
Hose down the smoke side at regular interval
Clean the smoke side regularly with soot blower equipment
Clean the smoke side with chemicals
All the mentioned alternatives
Under way to discharging port temperature tests indicate fire in a hold loaded with coal. What is the first action to be taken?
Call for assistance from other ships or rescue vessels
Close all air ventilators and other openings to the hold in question
Open the hatches and cover the top of the cargo by foam
The discharge arrangements for halogenated hydrocarbon total flooding systems shall be so designed that the minimum quantity of medium can be discharged in (based on the discharge of the liquid phase):
*How many fire hoses are required for general cargo ships of 1000 gross tonnage and upwards (not including hoses in any engine or boiler room) ?
At least one hose for each fire hydrant
At least one hose for every two fire hydrants
At least one hose for each 30 meter length of ship plus one spare
At least two hoses for each vertical fire zone
Regular ‘updating’ of a vessel’s position in an Inmarsat-C installation is among others things important:
To guarantee reception of NAVTEX-reports in areas where normal NAVTEX-facilities are not available
To guarantee reception of NAVTEX-reports
To guarantee assistance in emergency
To restrict NAVARAE-reports
What is the MARPOL definition of a "solidifying substance"?
A noxious liquid substance which, in the case of a substance with a melting point of less than 20°C which is at a temperature of less than 10°C above its melting point at the time of unloading, or in the case of a substance with a melting point equal to or greater than 20°C, is at a temperature of less than 15°C above its melting point at the time of unloading.
A noxious liquid which will crystallise and eventually bond into solid form at ambient, or less than ambient temperatures unless an external heat source is applied.
A noxious liquid substance which, in the case of a substance with a melting point of less than 15°C which is at a temperature of less than 5°C above its melting point at the time of unloading, or in the case of a substance with a melting point equal to or greater than 15°C which is at a temperature of less than 10°C above its melting point at the time of unloading.
A noxious liquid substance which will cystallise and eventually bond into solid form if exposed to an external heat source.
What is full form of VRP (OPA-90)
Vessel Response Procurement
Vessel Reporting Procedures
Who shall notify the cleaning up contractor (OPA-90)
Give the meaning of the following symbol
Fire main with fire valves
Fuel lubricating oil valves
Section valves drenching system
Norwegian merchant- and fishing vessels have to participate in the AMVER system. What is the purpose of AMVER?
Automatic system for plotting vessels with the purpose of rescue.
World wide telecommunication system.
A NATO reporting system in case of joining a war-convoy.
What is the correct understanding of the term "bank effect"? If a ship was approaching the bank at an angle, what would be the effect on the ship?
The vessel's stern is pushed away from the bank
The vessel’s bow is attracted by the bank.
The whole vessel would continue straight towards the bank and would require a large helm order to avoid going aground.
The vessel's bow is pushed away from the bank
If a distress signal is received on board your ship, what would you do ?
all of the alternatives together
try to make contact with the vessel in distress
contact SAR Authorities via nearest coastal Radio station
Give the meaning of the following symbol
Survival craft portable radio
Survival craft distress pyrotechnic signals
Give the meaning of the following symbol
Survival craft portable radio
Survival craft distress pyrotechnic signals
Which of the following detailed explanations should be mentioned in the Training Manual ?
The use of navigational equipment for survival crafts
The use of surface to air visual signals to be used by survivors
The use of escape routes and other escape methods
The use of helicopter rescue gear
When fighting fire, why shall you never pour water into hot fat?
The water will explode into steam causing hot fat to be thrown far away thus possibly causing severe burns or fire.
The water will turn into steam and cause the fat to explode.
The fat will not be edible any more.
The fat will stiffen immediately and need reheating.
What is the purpose of the LD (low duty) compressors on an LNG carrier?
To deliver inert gas and to aid cooling down of the cargo tanks.
To transfer cargo vapour to the shore installation during loading operations.
To handle the LNG boil-off vapour for fuelling the boiler.
To discharging the LNG cargo at a slow rate.
"A contractor is hired to install new navigation equipment onboard your ship while it’s berthed. For a period of time he’s left unsupervised and photographs schematics of the ship that he finds rolled up and stored in the corner of a nearby office. Later, from home, he hacks into the network and prints off information about the ship’s security procedures. Which of these information security measures would have prevented his unauthorized access?"
"Protective markings, reference checks, and passwords."
"Secure area, passwords, a firewall and a secure network."
"Firewall, protective markings, vetting and a secure network."
"Secure area, passwords, a firewall and protective markings."
How many rescue boats should be provided on ro-ro passenger ships of 500 gross tons and above?
Two Fast Rescue Boats, one on each side of the ship
None providing the ship has lifeboats
Two, and at least one of the rescue boats shall be a Fast Rescue Boat
When lashing general cargoes why are short lashings preferred to long ones?
Because long lashings are more prone to vibration
Because they are more easily tightened and held in tension
Because some of the ship’s lashing points may not be designed to hold long lashings
Because the safe working load of lashing materials decrease with length
What is the approximately boiling point of LNG at atmospheric pressure?
The engine turns over normally when starting air is supplied but does not fire even though normal starting rpm is achieved. What could be the probable cause to this?
The lubricating oil temperature is low.
The turning gear interlock has operated.
The turbocharger has not run up to normal full speed.
Air in the fuel oil system.
Which of the following fluids usually has the lowest density at normal ambient temperatures?
Why should wet cloths not be used for carrying hot cooking pans?
Because Health and Safety regulations prohibit the use of a wet cloth within 2.5 metres of a galley range.
Because they conduct heat quickly and may cause scalding.
Because a cloud of steam will be generated and the person carrying the pans may find it difficult to see where he is going.
Because the mositure will transfer to the pan and cool the contents.
UFL and LFL are commonly used expressions. What do they signify?
Expressions have no meaning.
Unstable Flash Level / Lower Flash Level?
Upper Fixed Level / Lower Fixed Level?
Upper Flammable Level / Lower Flammable Level of explosive atmosphere?
What is a typical composition of LNG (Arabian Gulf)?
Methane 75% - Ethane 12% - Propane 13%
Methane 80% - Ethane 15% - Propane 5%
Methane 91% - Ethane 6% - Propane 3%
You are in an area of restricted visibility. You hear this sound signal. What does it mean?
That there is a vessel engaged in underwater operations in the vicinity. She has divers down.
That there is a vessel aground in the vicinity.
That there is a vessel at anchor in the vicinity.
That there is a vessel in distress nearby.
How would you pick up a knife from a bench?
I would slide it to the edge of the bench and then pick it up by the handle.
It doesn't really matter - I would pick it up just how it was left lying by the last person who used it.
By the handle, with the blade towards me.
By the handle, with the blade facing away from me.
On a RoRo vessel, what standing instruction should be given to protect the Ramps when loading ro-ro units?
Damaged units should be rejected for loading
All ro-ro units must be thoroughly checked for damage prior to the loading ramp
Units whose weights exceed the ramp load density/SWL must not be loaded
When LNG is used as fuel a double wall piping system must be used in the engine room. What condition should the annular space between the concentric pipes be maintained in when the fuel system is in service?
Filled with nitrogen at a pressure greater than the LNG fuel pressure.
Filled with nitrogen at a partial vacuum.
Filled with nitrogen at a pressure less than the LNG fuel pressure.
Maintained at a full vacuum.
Shortly after starting up a fuel oil purifier oil is seen to be trickling out of the sludge outlet. Which of the options given is the most likely cause of this problem?
Incorrect gravity disc fitted.
Insufficient seal water supplied during start up.
Excessive back pressure in the clean oil outlet.
On the figure 4 possible definitions of the term "FREEBOARD" are given. Which one is the correct one?
Freeboard is given by A on the figure
Freeboard is given by C on the figure
Freeboard is given by D on the figure
Freeboard is given by B on the figure
How often shall drills for the operation of watertight doors, side scuttles, valves and closing mechanism of scuppers, ash-chutes and rubbish chutes take place in passenger ships?
Why does the Chief Mate have to reorder the cargo plan?
The wheels of hatchcover No. 7 came out off their tracks
Hatchcover No. 7 cannot be opened due to a defect in the hydraulic pump
Hold No. 7 is already loaded by the company ashore
The cadet disappeared with the cargo plan
Indicate the correct name for the part marked on the sketch:
A ship moving through heavy seas is affected by the water pressure at the bows causing an effect known as "Panting". What structure in the forward region of the ship combats the effects of Panting?
Double bottom tanks and floors
Collision bulkhead and deck
Panting beams and stringers
How can an approximate value of the initial transverse Metacentric Height (GM) be found from the Curve of Statical Stability (GZ curve)?
The value in metres from the X axis of the point where the curve changes from concave to convex shape.
Drawing a tangent to the curve through the origin and erecting a perpendicular through the angle of heel of 57.3 degrees
Drawing a tangent from the highest point of the curve to the X axis and measuring it in metres
It is impossible to establish the GM value from the curve of righting levers (GZ)
You are on a power-driven vessel underway in open water. You sight these lights on the port bow, on a steady bearing. The distance is closing. What are you looking at and what action will you take in compliance with the International Regulations for Preventing Collision at Sea?
This is a power-driven vessel, more than 50 metres in length or less than 50 metres in length and showing a second masthead light, restricted in her ability to manoeuvre. The sidelight of a second vessel can be seen beyond her. Under rule 18, I am obliged to keep clear of the first vessel and will therefore take appropriate avoiding action.
This is a power-driven vessel engaged in towing, less than 50 metres in length, length of tow under 200 metres and the tow, both being restricted in their ability to manoeuvre, seen from the starboard side. Under rule 18, I am required to keep clear and will take appropriate avoiding action.
This is a power-driven vessel engaged in towing, more than 50 metres in length or less than 50 metres in length and showing a second masthead light, length of tow 200 metres or more, not under command. I will keep clear under rule 27.
This is a power-driven vessel engaged in towing, more than 50 metres in length or less than 50 metres in length and showing a second masthead light and the tow, the combined length of which is under 200 metres. The towing vessel is restricted in her ability to manoeuvre. I am seeing their starboard sides. The bearing is steady and risk of collision therefore exists. I will maintain my course and speed under rule 17.
When are power-operated watertight sliding doors (class 3 doors) compulsory for all watertight doors aboard passenger ships?
Where the ship is fitted with through-going car decks
Where one or more doors are situated below deepest load line
When the ship is certified for more than 150 passengers
Where the ship has passenger spaces below the bulkhead deck
One of the crossheads on a large, six cylinder, slow speed diesel engine has been severely damaged due to bearing failure. The connecting rod for the cylinder concerned is to be removed from the engine and the piston and damaged crosshead suspended in the engine so that it can be run on 5 cylinders. Which of the methods given in the options should be used to suspend the piston and crosshead?
Remove the cylinder cover and connect the piston (with crosshead attached) to the engine room crane and position the piston so that it covers the scavenge ports.
Raise the piston sufficiently high to allow the crosshead support pins/chains to be fitted and rest the crosshead on them (with piston attached and positioned above the scavenge ports)
Raise the piston (with crosshead attached) to just above the scavenge ports and insert pieces of wood through the ports to rest the piston on
Remove the cylinder cover and lift the piston until the crown and skirt are clear of the liner and place two bits of angle iron across the liner top to rest the piston on.
On a container vessel what effects would exposure to anhydrous ammonia in moderate concentrations have?
Choking and possible loss of eyesight
How many hours before departure should the ship's steering gear be checked and tested?
Some process control systems may several inputs and controlled variables. In this context what is meant by split-range?
Several controllers are connected to the same control-valve
Several control-valves are connected to the same controller
Several control-loops for the same range
What extra precautions should be taken by the officers and crew if some of the passengers are disabled, i.e. using wheelchair, cane, blind etc.?
All passengers that will require extra assistance, also in case of an emergency situation/ evacuation, must be registered in order to allocate crew to assist them if needed.
Locate them in large cabins to ease their stay.
Passenger with some form for disability must travel with accompany, and live in same cabin or next door.
They must be placed in cabins on the same level as the muster station.
What type of sugar is commonly added to sweeten tea or coffee?
This vessel is encountered at the mouth of a river which leads to your discharge port. What do the various shapes tell you?
This is a vessel engaged in mine-clearance opetrations. The two balls in a vertical line indicate that it has a sweep mechanism deployed; the two diamonds in a vertical line indicate that the vessel should be given a clearance of at least 1000 metres; the ball / diamond / ball indicate that the vessel is restricted in her ability to manoeuvre.
This is a vessel engaged in dredging or underwater operations. The two balls in a vertical line indicate the side on which an obstruction exists; the two diamonds in a vertical line indicate the side on which it is safe to pass; the ball / diamond / /ball in a vertical line indiacte that the vessel is restricted in her ability to manoeuvre.
This is a vessel engaged on port security duties. The two balls in a vertical line indicate that the port is closed; the two diamonds in a vertical line indicate that the port is engaged in mine-clearance operations; the ball / diamond / ball in a vertical line indicate that the vessel is restricted in her ability to manoeuvre.
This is a vessel engaged in dredging or underwater operations. The two balls in a vertical line indicate the side on which it is safe to pass; the two diamonds in a vertical line indicate the side on which an obstruction exists; the ball / diamond / ball indicate that the vessel is restricted in her ability to manoeuvre.
Which electronic component is this graphical symbol illustrating:
Electric heater, 3.3 kilowatts
Inductive reactor, 3.3 kH
Vapour Leakage. A small leakage of vapour through the membrane may not be readily obvious. However, indications are likely to be:
A sudden rise in the percentage of methane vapour in one primary insulation space.
Temperature change will be obvious.
Water building up in the insulation space.
What is the meaning of organic chemistry?
Organic chemistry is substances that contain hydrocarbons and oxygen.
Organic chemistry is substances that do not contain of hydrocarbons.
Organic chemistry is substances that contain hydrocarbons.
Organic chemistry is substances that contain of hydrocarbons, nitrogen and oxygen.
Why are pure RoRo car carriers considered as being high risk design vessels where their stability is concerned.
Because they have few internal bulkheads
Because of the relatively small clearance between waterline and stern ramp sill when fully loaded
Because they can easily capsize if there is ingress of water or ballast operations are not handled correctly
A centrifugal pump is to be reassembled following overhaul and it is discovered that there are no spare gaskets for the pump housing. From the options given select the best alternative material to make a gasket from.
Reinforced pilot packing.
Thick paper (chart paper).
How many separate means of escape are provided from each fire zone above the bulkhead deck?
If conditions permit, which is the best way to board a liferaft which is floating close to the ship?
Wearing a lifejacket, jump into the water close to the raft and then swim to it
Jump onto the raft itself
Jump into the water close to the raft, without a lifejacket, as this will make it easier to swim and board the liferaft
Use a rope ladder close to the raft to climb down and board
The ship's crew are supervising the stevedores loading a non-palletized, break bulk cargo of fruit packed in cartons onto a conventional reefer vessel. Select the best type of stow to achieve good carriage conditions for the cargo from the options given.
A very loose stow leaving large gaps between the cartons for the cold air to circulate between them.
A loose stow leaving small gaps between the cartons for the cold air to circulate between them.
A very tight stow where the last few cartons are forced into existing rows to prevent any movement.
A tight stow leaving no space between the cartons so that the cold air is forced through the fruit in the cartons.
By what means can we monitor and control the integrity of the hull?
The chief officer is responsible for monitoring the integrity of the hull and superstructure at all times
Documented operating procedures
Automatic detection systems, television surveillance and patrolling
Let experienced personnel close and secure doors and ramps
Passenger ships have a normal requirement of 1 lifejacket per person + 10% for children. In addition to this, how many lifejackets have to be stowed in conspicuous places on deck or at the muster stations?
Tab washers are often fitted to bolted assemblies to prevent the nuts and bolts slackening. For an assembly where the nuts are positioned at the top select the option which describes the correct method of locating the tab washers.
Bend the inner tab up against one flat of the nut and the other tab down over the edge of the component.
Bend the outer tap down over the edge of the component and leave the other tab flat against the component.
Bend the outer tap up against one flat of the nut and leave the other tab flat against the component.
Bend both tabs up against opposite flats of the nut.
During maintenance work on a main diesel engine the fuel injection valve is found to be jammed in the pocket in the cylinder cover. Which of the procedures given in the options should be followed in order to complete the work?
With the fuel injection valve retaining nuts removed admit compressed air into the engine cylinder to try and blow the injection valve out of the pocket.
Replace the complete cylinder cover with a spare unit and land the cover with the jammed valve ashore for repair in a specialist workshop.
Remove the cylinder cover and try and drive the injection valve out of the pocket from the underside with a hammer and punch.
Wedge a bar between the piston top and the bottom of the injector and use the turning gear to force the injection valve out.
Is there any requirements regarding double bottom for large passenger ships?
No, a double bottom is not required
Yes, in ships of 76 m in length and longer, a double bottom shall be fitted amidships, and extend to the fore and aft not less that ? of the ship length.
Yes, in ship of 76 m in length and upwards, a double bottom shall be fitted amidships, and shall extend to the fore and after peak bulkheads, or as near thereto as practicable.
Yes, a double bottom shall be fitted amidship
Which of the following can be considered to be two of the main requirements for a paint coating for a cargo space of a General Cargo Vessel?
Low odour and heat resistant
Easy to clean and dark in colour
Light reflective and compatible with edible cargoes
Corrosion resistant and heat resistant
What is the correct method to use for fitting a rolling contact bearing, such as a ball bearing, onto a parallel shaft?
Use emery cloth on the inner ring (contact surface) of the bearing.
Use a hammer and a pipe with the same diameter as the inner bearing ring and knock the bearing onto the shaft.
Gently heat the bearing in an oil bath and use a bearing puller to draw it onto the shaft..
Use emery cloth on the bearing surface on the shaft.
In order to speak clearly and effectively you should:
stand tall with shoulders squared
never open your mouth too wide
open your mouth, pronounce your consonants, and shape your sounds well
If you alter the field excitation voltage (or field current) of one alternator operating in parallel, this will cause change in that alternators:
None of the mentioned alternatives
When setting the tappet clearance (rocker arm clearance) on cylinder cover valves it is important that the engine is turned to the correct position. Select, from the options given, the engine correct position for this procedure.
Each cylinder in turn should be at top dead centre position when setting the valve clearances for that cylinder.
Number one cylinder should be at top dead centre position for setting the clearance for all of the valves on the engine.
The engine should be positioned so that the cam follower for the valve for which the clearance is being set is on the cam base circle.
The engine should be positioned so that the cam follower for the valve for which the clearance is being set is on the cam peak.
Where shall you be able to activate the ship security alert system on board ro-ro passenger ships?
From the navigation bridge and in at least one other location
Captain's- and Chief Officer's office
What is the first action that should be taken by the rating on boiler watch in the event of a flame failure on the boiler?
Call the engineer on watch
Which of the following temperature sensors normally gives the highest measuring accuracy?
What does the 1 Engineer want to have done?
He wants the feed water tank cleaned
He wants the feed water tank inspected
He wants the heating coils inspected
He wants the Fitter to Check the CO 2 equipment
When operating a propulsion installation consisting of medium speed diesel engines driving a controllable pitch propeller it is possible to operate the combination of engine speed and propeller pitch in a number of different ways. What would be the main reason for operating with constant speed and variable pitch?
To allow the engine to be operated with a load sensing governor instead of a speed sensing governor.
To allow rapid load change and thrust reversal when manoeuvring.
To obtain maximum propeller efficiency over the load range of the engine.
To allow constant speed operation of a shaft generator while the engine load changes with pitch variation.
What is the purpose of the discharge booster pump?
To increase the manifold pressure.
To maintain the cargo temperature.
To compensate for friction losses in the discharge line.
Some liquefied gas carriers are classed as fully refrigerated. What is the general meaning of the term 'fully refrigerated liquefied gas carrier'?
Any vessel for carrying liquefied gas at low temperature in semi pressurised independent tanks.
A vessel which is designed to carry liquefied gases at low temperature and atmospheric pressure between terminals with fully refrigerated storage tanks and a full onboard cooling plant.
Any vessel which has thermally insulated cargo tanks.
A vessel which can load a cargo of gas at ambient temperature and cool it down to a liquid state.
A decision support system for emergency management shall be provided on the navigation bridge. What type of emergency situations shall as a minimum be identified in the emergency plans?
Fire, Evacuation, Pollution, Personnel accidents and Ship Security
Evacuation, Fire, Pollution and Man-Over-Board
Man-Over-Board, Evacuation and Fire
Fire, Damage to ship, Pollution, Unlawful acts threatening the safety of the ship and the security of its passenger and crew, Pesonnel accidents, Cargo-related accidents, Emergency assistance to other ships
What can cause crewmembers to abdicate their safety roles?
Inadequate fire-fighting training
No lifeboat drills for passengers
Inadequate fire-fighting provisions
How should a crew member on duty prevent scratching vehicles?
By removing his safety helmet when approaching a vehicle
By maintaining a safe distance from all vehicles
By wearing gloves at all times
By not wearing or carrying any external metal accessories
What is the disadvantage of using High Tensile Steel (HTS) in the construction of bulk carriers?
HTS is prone to fatigue cracking
When compared with mild steel HTS increases the lightship displacement
HTS does not form a proper bond with paint coatings
Vibration analysis is often used as a conditioning monitoring tool onboard ship as part of the approved planned maintenance system. Many vibration measuring instruments are fitted with a harmonic filter/analyser. How would these filters normally be used during vibration measurement on a centrifugal pump?
To block out any noise or vibration from the surrounding engine room.
To isolate a single frequency of vibration associated with one of the pumps components.
To sum up all the harmonics of a base frequency to give total vibration for all of the pump's components simultaneously.
To generate an audible sound signal at the same frequency and amplitude as the vibration.
Where should grease be applied to a twistlock?
Over the entire outer surface
Between the twistlock cone and associated housing
At the base of the twistlock cone
With regard to dry chemical powder fire-extinguishing systems in the cargo area, what is the required number of self-contained independent dry chemical powder units?
Sufficient number of units to cover the cargo area.
What is the definitive document which confirms whether a chemical tanker is authorised to carry a particular Noxious Liquid Substance?
Her Certificate of Fitness.
The International Pollution Prevention Certificate for the Carriage of Noxious Liquid Substances in Bulk.
Is it necessary to cool the water samples from the cooling system, before testing?
Yes, must be cooled to 25 Degr. C.
Yes, must be cooled to 50 Degr. C.
No, must be heated to about 95 Degr.C.
In the diagram, which letter is pointing at the area known as the "BOW" of the ship?
The Bow is indicated by A, in the figure
The Bow is indicated by D, in the figure
The Bow is indicated by C, in the figure
The Bow is indicated by B, in the figure
Passenger ships shall either carry automatically self-righting liferafts or canopied reversible liferafts. What does it mean that a liferaft is automatically self-righting?
The liferaft will automatically turn back into an upright position when it is empty of people
One person can manage to turn the liferaft back into an upright position
The liferaft will automatically turn back into an upright position when it is fully loaded with people
It means the same as self-righting lifeboats
Which person is qualified to carry out a five yearly thorough survey of cargo gear on a General Cargo vessel?
A classification society surveyor
A deck officer designated by the master
On the figure there are four (4) possible directions, shown by the arrowed lines, which could be the correct direction associated with the term "HEAD LINE". Which one is the correct one?
Head line is given by D on the figure
Head line is given by C on the figure
Head line is given by A on the figure
Head line is given by B on the figure
On the figure 4 possible definitions of the term "PORT QUARTER" are given. Which one is the correct one?
Port quarter is given by D on the figure
Port quarter is given by B on the figure
Port quarter is given by C on the figure
Port quarter is given by A on the figure
What was blocking the grease pipe?
The pump was blocking the grease pipe
The grease pipe was broken
Grease was blocking the grease pipe
Nothing was blocking the grease pipe
What kind of problems have they had?
The crew did not understand the 3rd Mate's order
They have had problems securing the gangway
The electrician could not repair the motor
They have had problems with the gangway net
What is the fog signal for a vessel of more than 100 meters in length when at anchor?
A rapid ringing of the bell forward followed by the gong aft for about 5 seconds at intervals of not more than 1 minute
A rapid ringing of the bell forward for about 5 seconds at intervals of not more than one minute
Two long blasts on the whistle at intervals not exceeding two minutes
A rapid sounding of the gong forward for about 10 seconds at intervals of not more than two minutes