General Questions From D022 Flashcards
How is maximum wave height defined?
The greatest wave height observed in a 10-minute period
This is a key metric in wave forecasts.
What is significant wave height?
The average height of the largest one third of all waves observed in a 10-minute period
This measurement is crucial for understanding wave conditions.
What are the prevailing winds in the polar regions?
Easterlies
What are the prevailing winds in the temperate regions?
Westerlies
What are the prevailing winds in the tropical regions?
Easterlies
What is the diameter of a typical temperate zone depression?
About 1,600 km (1,000 miles)
What are hurricanes characterized by?
Small areas of low pressure with very high wind speeds, forming only over warm seas
A typical hurricane has a diameter of about 160 km and a pressure of 950 mb in the center.
What is the diameter and wind speed of tornadoes?
Diameter of 100 m and wind speeds up to 300 knots
Tornadoes have a pressure at the center as low as 800 mb.
Define waterspout.
A rapidly gyrating vortex descending from cumulus or cumulo nimbus clouds, sucking up a column of water
Waterspouts rarely last more than half an hour.
What are the characteristics of high pressure systems?
Stable, slow moving with clear skies and low wind speeds
In summer, they are typified by bright sunshine and calm seas; in winter, they can cause low temperatures and fog.
What is the Mistral?
A powerful Mediterranean wind
It is generated by the funnelling effect of local topography.
What is haar?
Sea fog along Scottish North Sea coasts
It is caused by warm sea air in contact with cold land.
What happens when the height-to-wavelength ratio exceeds 1:13?
The wave breaks
This occurs when waves become too steep relative to their wavelength.
At what depth can wave movement typically be felt by a diver?
Down to a depth equal to about half the wavelength.
If a typical wavelength is 20 m, how deep can turbulence be felt?
Down to 10 msw (33 fsw).
What are spring tides?
Tides that occur when the sun and moon are aligned, resulting in maximum tidal range.
What are neap tides?
Tides that occur when the sun and moon are at 90° to each other, resulting in minimum tidal range.
What is the average duration of the rising tide?
Six hours and twelve minutes
This is referred to as the flood tide.
What is the typical maximum depth for air diving according to legislation?
About 50 ms (165 fsw)
Working depth may vary with tidal changes.
What are tidal streams?
Currents associated with flood and ebb tides
They change direction according to the tide.
When does the fastest tidal stream occur?
Halfway through the tide in open water
The speed of the tidal stream increases with a larger range.
What is the ‘twelfths rule’?
A method to estimate rise or fall in six hours:
* Hour 1: 1/12 of range
* Hour 2: 2/12 of range
* Hour 3: 3/12 of range
* Hour 4: 3/12 of range
* Hour 5: 2/12 of range
* Hour 6: 1/12 of range
This rule helps predict tide behavior.
What factors can produce currents besides tides?
Wind, river flow near estuaries, major ocean currents
Tidal currents can superimpose on these currents.
What percentage of wind speed typically generates a wind current?
About 3%
A Force 7 wind generates a surface current of about one knot.
How does the direction of a wind-generated current change with depth?
It turns further away from the wind direction
At 10 ms (33 fsw), it is about 90° to the wind direction.
What is the relationship between water velocity and the force exerted on a diver?
The force exerted on a diver and his equipment by the current is proportional to the water velocity squared.
If the water velocity doubles, how much does the force increase?
Four times.
List the considerations for diving in currents.
- Ability of the surface crew to recover the diver safely
- Ability of the standby diver to reach the diver in an emergency
- Physical strength and endurance of the diver
- Type of equipment being used
- Type of work being carried out
- Whether the work is being carried out mid-water or on the seabed
- Whether both hands are required to carry out the task
- Changes in strength and direction of the current
- Possibility of using an underwater tender, swim lines, etc.
What is the definition of significant wave height (SWH)?
The mean of the largest third of waves in a wave record
At what depth do only green and blue wavelengths of light remain?
About 10 msw (33 fsw)
What is turbidity a measure of?
The number of fine particles suspended in the water
What error levels have been shown in divers working in poor visibility?
Error levels as high as 30%
What can cause diving to be stopped by the master of a vessel?
Fog or mist significantly increasing the risk of collision
At what frequencies are helmeted divers safe from known sonar transmissions?
Above 500 Hz
What provides some hearing protection from sound frequencies between 400 and 500 Hz at shallow depths?
A 3mm neoprene wet suit hood
What must the diving supervisor be able to monitor at all times?
The diver’s breathing pattern
What document contains an example of a communications matrix?
IMCA D046/M205 Guidance on operational communications.
List three areas that should have dedicated voice communications in diving operations?
- bridge/DP
- engine control room
- dive control/bell dive control
What should back up dedicated communications systems on the vessel?
The ship’s telephone system and/or hand held radios operating on specified channels.
What is the requirement for voice communication with the diver?
There needs to be two-way voice communication at all times.
This is affected by noise from breathing and tools.
What is the recommended practice for recording voice communications?
Record all voice communications starting with pre-dive checks and keep recordings for at least 24 hours.
Keep recordings longer if incidents occur.
What is the purpose of document control in diving operations?
To prevent unofficial procedures and ensure out-of-date documents do not remain in circulation
Document control helps maintain safety and compliance in diving operations.
What should be stated on a document used in diving operations?
Who it has been circulated to, who prepared it, and who can modify it
This information is crucial for accountability and traceability.
What type of systems do many businesses use to manage documentation?
Intranet systems for accessing the most up-to-date versions of company documents
Intranet systems enhance accessibility and efficiency in document management.
What components should be included in operating procedures for diving operations?
Standard procedures, site/task-specific procedures, contingency and emergency plans
These components are essential for safe and effective diving operations.
What documents must be on-site for every diving operation? (List at least 5)
- Company operations manual
- Safety management system (SMS)
- Management of change procedure
- Risk assessments
- Diving project plan
A comprehensive list ensures all necessary safety and operational protocols are followed.
What is a bridging document in diving operations?
An interface document between clients’ and companies’ SMS
It helps align safety management systems between different parties involved.
What should a diving supervisor be familiar with during operations?
Relevant legislation and guidance notes
Knowledge of legislation is crucial for compliance and safety.
What is included in the IMCA record of competence?
Documentation of a diver’s training and qualifications
This record is part of the logbook requirements.
What is the minimum number of personnel required for a surface supplied air/nitrox diving operation under IMCA D014?
Five personnel
This includes specific roles necessary for safe operations.
List the minimum personnel required for a surface supplied air/nitrox diving operation.
- Air diving supervisor
- Working diver
- Standby diver
- Tender for working diver
- Tender for standby diver
Each role is essential for maintaining safety and operational efficiency.
What is the absolute minimum number of personnel required for an offshore surface supplied mixed gas dive?
Six personnel: one supervisor and five qualified divers
The supervisor does not dive.
What is the absolute minimum team size for a closed bell diving operation under IMCA D014?
Nine personnel:
* closed bell diving supervisor
* two life support supervisors
* two life support technicians
* two divers in the bell
* surface standby diver
* tender for surface standby diver
This includes a relief diving supervisor as a provision.
What is the maximum continuous work period for a diving team member under normal circumstances?
12 continuous hours
This is followed by 12 continuous hours of rest.
What must happen if a diving team member is asked to work for more than 12 hours?
They need to have had at least eight hours off in the previous 24 hours
This is part of the IMCA international code of practice for offshore diving.
What is the longest period a member of the diving team can work in exceptional circumstances?
16 hours
This must be followed by eight hours of unbroken rest.
In saturation diving, what is the maximum duration for bell runs from seal to seal?
Eight hours
Divers must then have 12 hours of unbroken rest.
What does the dive plan need to consist of before any diving takes place?
Standard rules and procedures, task-based procedures, site-specific risk assessments, contingency and emergency procedures
All diving supervisors need to have a copy of the dive plan.
What must be included in the dive plan regarding diving procedures?
Techniques to be used and length of divers’ umbilicals
This is part of the considerations for the dive plan.
What types of locations can divers work from?
Divers may work from a variety of locations, including:
- Very small boats
- Mobile portable equipment
- Large fixed installations
- Purpose-built diving support vessels (DSVs)
Each location affects the safety and efficiency of the diving operation.
What should be considered regarding the safety and efficiency of diving operations?
Considerations include:
- Station keeping capability
- Deck strength
- Location of dive stations
- Access to the water
- External supplies
- Emergency evacuation
IMCA D035 provides guidance on selecting vessels of opportunity for diving projects.
I’m sure you are going to pass.
List some limitations of small work boats, supply boats, or standby vessels.
Limitations include:
- Lack of manoeuvrability
- Low-grade navigation systems
- Minimal deck space
- No or limited crane/lift facilities
- Low electrical power reserves
- Unsuitable propeller guards
- Limited bad weather capability
- Poor helicopter access
- Limited personnel accommodation
- Limited crew experience with diving operations
These factors should be accounted for when considering work scope and vessel location.
What are the five sections of a DP system?
- Power
- Propulsion
- Control
- Reference
- Sensors
What components are included in the propulsion system of a DP system?
- Tunnel thrusters
- Azimuth thrusters
- Main engines
Which systems are included in the reference system?
- Hydroacoustic systems
- Laser radars
- Taut wires
What is a single point failure?
Failures without a back-up or redundant system, or where the failure affects both the main and back-up systems
What design principle should be applied if a single point failure cannot be avoided?
Units should be designed to fail safe
What should every thruster have as a final back-up?
A manually operated emergency stop, normally sited close to the main DP control station
What are proving trials in DP systems?
Testing the system in all normal modes of operation and simulating failure modes
What is a polar plot used for in DP systems?
To present calculations of station keeping capability for various situations
What do capability plots show?
The likely environmental limits within which the vessel will effectively return to the wanted position
What is a critical excursion?
An excursion where personnel could be injured and/or substantial damage could be sustained
What are safe working limits?
Environmental limits within which a critical excursion caused by a single fault is very unlikely
What factors should be considered when determining safe working limits for a diving operation?
- Time taken for divers to return to the bell or basket on alert
- Likely speed of position loss
- Increased position excursion after the worst failure mode
What is the IMO recommendation regarding DP vessels built after July 1994?
They should be assigned to an equipment class
What does equipment class 1 indicate?
Loss of position may occur in the event of a single fault
What does equipment class 2 indicate?
Loss of position should not occur from a single fault of an active
component, such as a generator or thruster, but may occur after failure
of a static component such a cable, pipe or manual valve.
What is Equipment Class 3?
Loss of position should not occur from any single failure
What is the minimum equipment class required for all DP DSVs?
Equipment class 2
What are the four DP alert levels on every vessel?
- Blue - Advisory status- approaching performance limits or reportable alarm status. A failure has occurred that does not affect Dp redundancy.
- Green - normal operational status
- Yellow - degraded operational status
- Red - DP emergency status
What does the Green alert level indicate?
Normal operational status with adequate equipment on-line
What does the Yellow alert level indicate?
Degraded operational status where one or more items of redundant DP equipment has failed
What does the Red alert level indicate?
DP emergency status with a loss of position or inevitable loss of position
What is required for class 2 systems in terms of engine redundancy?
At least one redundant engine which will come on-line automatically
What should fire detection systems provide during a fire in the engine room?
Sufficient warning for the recovery of the divers before the power is lost
What is the requirement for class 3 systems regarding engine rooms?
Two independent engine rooms
What must the power distribution system ensure during diving operations?
A fault on any switchboard section should not cause the loss of the whole switchboard
What types of thrusters can be found on DP vessels?
- Gill jet
- Voith Schneider
What is the minimum control requirement for diving operations on DP vessels?
Two automatic fully redundant control systems
This allows for a smooth transfer to the other system unnoticed by divers.
How long should the period of stabilization be after establishing position on a DP vessel?
At least 30 minutes
This is after a major move, heading change, or change in environmental conditions.
What additional feature should Class 3 vessels have?
An additional DP control room
This is in case the main control room is compromised by fire or flood.
What must at least one computer on a DP vessel be able to withstand?
The worst power loss failure possible
It should continue operating with associated equipment for at least 30 minutes.
What is the requirement for position reference sensors on DP vessels?
At least three position references online, with at least two of different types
This is crucial for accurate positioning during diving work.
What should be considered when selecting position references?
Water depth, open water, proximity to other installations or vessels
No single factor should affect more than one position reference.
What are the common types of position sensors used on DP vessels?
Taut wire, hydroacoustic position reference (HPR), differential global positioning systems (DGPS), laser radar systems, FM radar systems
Examples of laser radar systems include FanBeam and CyScan.
What does HPR stand for?
Hydroacoustic Position Reference
What is the purpose of the bell transponder in an HPR system?
To provide additional positioning information and act as an emergency bell location beacon
Name potential sources of interference for HPR systems.
- Other transponders
- Water jetting equipment
- Thrusters
- Diver’s breathing exhaust gas bubbles
What does DGNSS stand for?
Differential Global Navigation Satellite System
Why are satellite-based global positioning systems generally not accurate enough?
They do not provide a usable position for the vessel on their own
How can the accuracy of satellite-based positioning be improved?
By using differential correction signals from suppliers
Another day of misery another dollar
What are two major causes of problems with DGNSS?
- Scintillation
- Shadowing of antenna
What are the names of the two laser range and bearing systems mentioned?
- FanBeam
- CyScan
How does FanBeam track a fixed target?
By producing a laser beam in a 20° vertical fan and scanning it horizontally
What is the maximum range of the FanBeam system?
2,000 m
What types of targets can be used with the FanBeam system?
- Reflective tape
- Retro prisms
What is the recommended diameter and length for the reflective tape cylinder in FanBeam?
150-250 mm in diameter and 1,000 mm long
For effective operation of FanBeam at ranges between 1,000-2,000 m, how many prisms are required?
A stack of six prisms
What are the limitations of the FanBeam system?
- Reduced operating range in fog, snow, and heavy rain
- Degraded performance in direct sunlight
What is CyScan’s operational principle?
Infrared laser ‘time-of-flight’ to pre-positioned retro-reflective targets
How fast does the CyScan rotating scanner head operate?
360° per second
What is the typical operating range of the CyScan system?
Up to 400 metres
What can increase the operating range of the CyScan system beyond 1,000 metres?
A sophisticated optical prism reflector
How many measurements can the CyScan system potentially provide for every 1° of rotation?
80 measurements
What should be ensured when selecting target locations for the CyScan system?
Unequal spacing of multiple targets and maintaining line of sight
What are the two frequency modulated microwave radar systems mentioned?
RADius and RadaScan
What is the primary function of the RADius system?
Short range and direction monitoring
How does the RADius system minimize the risk of tracking false echoes?
By using identifiable transponders
What is the typical operational range of RADius using the 500 series transponders?
Up to 350 m
What is the typical operational range of RADius using the 600 and 700 series transponders?
Up to 1000 m
What type of radar system is RadaScan?
Low power frequency modulated continuous wave radar sensor
What is the bandwidth of the RadaScan sensor?
100 MHz
In which frequency band does the RadaScan sensor operate?
9.25 GHz maritime radiolocation band
Keep going
What is the scanning frequency of the RadaScan sensor’s rotating antenna?
1 Hz
What horizontal angular separation is required for multi-target operation?
More than 7°
This is necessary between transponders.
What does the Artemis system consist of?
Fixed antenna unit and mobile antenna unit
The fixed unit is battery powered and mounted on a fixed installation.
When should the Artemis system be switched off?
During radio silence, wireline or explosive work
This should only be done after consultation with the DP operator and diving supervisor.
What can cause a system error in the Artemis system?
Obstruction
The system is limited to line of sight use.
What happens if the fixed antenna battery is low?
Signal distortion or interruption occurs
This affects the accuracy of the system.
How many fixed antenna units may vessels have?
Two fixed antenna units
This avoids delays when moving sides of a structure.
What types of additional sensors are required for diving operations?
Anemometers, gyro compasses, vertical reference unit (VRU), motion reference unit (MRU)
These measure wind speed, direction, heading, and other movements.
How many anemometers are required for diving operations?
At least two anemometers
Preferably in different locations with separate supplies and cable routes.
What is the minimum number of gyro compasses required?
At least three gyro compasses
This is important for heading control.
How many vertical reference sensors are required for diving operations?
At least two vertical reference sensors
With separate supplies and cable routes.
What is the requirement for the location of vessel sensors?
All vessel sensors need to be in separate locations
This minimizes the risk of redundant units suffering from the same physical damage.
What type of communication system must be present between the DP control room and diving operations?
A dedicated voice communication system with a back-up system
This ensures constant communication during operations.
Never forget, you are just a slave
Remember in the end we all die
True or False: Joystick control is acceptable during diving operations.
False
Joystick control is not acceptable during diving operations.
What happens to divers if the vessel changes heading and they are not at the center of rotation?
They will experience a change of position
This can have significant consequences for safety.
What should be done if a significant heading change is necessary while divers are in the water?
Recover the divers to the bell initially
Followed by assessing whether to recover them to the surface while changing the heading.
What is the maximum distance movement that can be carried out at one time?
10 meters in steps of 5 meters
How must the positions of all anchors be confirmed?
By the moored vessel and the position of the mooring lines established by two independent means.
What is the distance that mooring lines can be from the diver’s bell or basket without needing a second means of identification?
More than 250 m.
What is the minimum distance recommended between the bell or basket and any mooring line?
At least 50 m.
What factors should be considered when determining the location of the bell or basket?
Environmental conditions, height of the structure, diver’s entry point, vessel footprint, position reference systems, diver’s excursion limits.
What is the minimum diameter for a round ‘flag’ on cylinders if the shoulders are not visible?
At least 20 cm (8 inches)
What does IMCA D014 recommend for the design of the charging manifold?
Minimum volume behind the blanking plug, provision for venting, and self-draining section.
How often should bail-out bottles be checked according to IMCA D018?
Every six months.
How often do cylinders that go underwater require certification?
Every two years.
How often do surface cylinders require certification?
Every five years.
Fill in the blank: A loose end of Teflon (PTFE) tape inside a pipe can ignite easily and will burn to produce the toxic gas _______.
phosgene.
What is the maximum oxygen pressure recommended at the quad to minimize fire risk?
40 bar.
Fight to love another day
What is the purpose of a fuel cell analyser in oxygen analysis?
It generates electricity in proportion to the partial pressure of oxygen (ppO2).
What type of analysers are commonly used for oxygen analysis?
Fuel cell analysers and magneto-dynamic cell analysers.
What is a common trade name for magneto-dynamic analysers?
Servomex.
Why are fuel cell analysers preferred in diving operations?
They are robust, lightweight, and suitable for remote readings.
What must be used to calibrate a fuel cell analyser?
A zero gas and scale gas.
Fill in the blank: The oxygen percentage in a closed control room can be as low as ______.
18%.
What can cause errors in fuel cell readings?
Condensation, temperature changes, electromagnetic fields
These factors can affect the accuracy of the readings.
What is the lifespan of a fuel cell?
Approximately six months
Erratic readings indicate that the cell may need replacement.
What principle do magneto-dynamic cells rely on?
The paramagnetic property of oxygen
Oxygen molecules are attracted to a magnetic field, causing a quartz dumb-bell to rotate.
What is essential before using a carbon dioxide analyser?
It must warm up to a stable temperature
This ensures accurate readings, which are given in parts per million.
What are Dräger tubes commonly used for?
Chemical sampling and carbon dioxide analysis
They test LP air supplies for contaminants.
What is a common calibration requirement for carbon dioxide analysers?
A zero gas and scale gas
Some analysers require regular setup procedures.
What correction is needed when using a tube under pressure?
Divide the scale reading by the absolute pressure in bars
For true partial pressure, divide a percentage scale reading by 100 or a ppm scale reading by 1,000,000.
What are possible sources of contamination for gas supplies?
1) Impurities in pipework
2) Improper location of compressor air intakes
3) Oil leakage in compressors
4) Degassing of paints or resins
5) Overheating or burning of materials
6) Electrical arcing
7) Contaminants from diving operations
What standard specifies the maximum levels of contaminants in compressed air for breathing apparatus?
British and European standard BS EN 12021
What is the maximum allowable level of carbon monoxide in breathing air according to BS EN 12021?
5 ppm
What is the maximum allowable level of carbon dioxide in breathing air according to BS EN 12021?
500 ppm
What is the maximum allowable oil concentration in compressed air for breathing apparatus?
0.5 mg/m3
What are the maximum allowable water concentrations at the compressor outlet and cylinder outlet for breathing air?
- 25 mg/m³ (at compressor outlet)
- 50 mg/m³ (at cylinder outlet, pressure 40-200 bar)
- 35 mg/m³ (at cylinder outlet, pressure over 200 bar)
What does BS EN 12021 state about contaminants in breathing gas?
‘Compressed gas for breathing shall not contain contaminants at a concentration which can cause toxic or harmful effects’
All contaminants should be kept to as low a level as possible.
What is the limit for all contaminants in breathing air according to BS EN 12021?
Less than one sixth of a national 8 h exposure limit
What is the required dew point for compressed air under BS EN 12021?
Sufficiently low to prevent condensation and freezing
What is the pressure dew point requirement if the temperature conditions of usage and storage are unknown?
Shall not exceed -11 °C
How often should air samples from compressors be analyzed?
Air samples from compressors should be analysed on a regular basis according to company
procedures. This is normally every three or six months, after any repair or modification to the
compressor and after any incident or accident. There should be a separate certificate for each
analysis.
What should purchased gas be provided with?
An analysis certificate and should be free of contaminants
What do diver gas recovery systems filter from the diver’s exhaled gas?
- Moisture
- Solid particles
- Carbon dioxide
- Trace gases
- Bacteria
List the IMCA DESIGN audits for diving equipment systems.
- IMCA D023 for surface oriented (air) systems
- IMCA D024 for saturation diving (bell) systems
- IMCA D037 for surface supplied mixed gas diving systems
- IMCA D040 for mobile/portable surface supplied diving systems.
What is the minimum time before flying at cabin altitude after diving with no stop dives with total time under pressure less than 60 minutes within the last 12 hours without decompression illness problems?
2 hours for 2000’ (600m) and 18 hours for all other flights
The 18-hour time applies to short flights (less than 3 hours), while for longer flights, the time is extended to 24 hours.
Waiting time before flying after air, nitrox, or trimix saturation diving (more than 4 hours under pressure)?
24 hours 2000’ (600m) 48 hours all other flights
What is the required waiting time before flying after therapy for decompression illness (DCI)?
On complete resolution- 24 hours for flights below 2000’ (600m) 72 hours for all other flights
Advice must be sought from a diving medical specialist.
No resolution- Consult medical specialist
What are the safety requirements for lift wires used in diving operations?
Non-rotating, effective safety factor of 8:1, and compact design
This minimizes the space requirements for operating winches.
Fill in the blank: The minimum time to wait before flying after heliox saturation (more than 4 hours under pressure) is _______.
12 hours (600m) 24 hours all other flights
What type of braking system is required for winches used in diving operations?
Suitable braking systems that are not fitted with a pawl and ratchet gear requiring disengagement before lowering.
What is the maximum recommended ppO2 in nitrox diving?
1.4 bar.
At what depth should air or nitrox not be used?
Below 50 msw (165 fsw).
What is the recommended minimum quantity of air required for emergency dives?
Sufficient compressed air must always be available for two emergency dives to the full intended diving depth as a reserve.
What is required for pressurizing the deck decompression chamber?
Sufficient compressed air to pressurize both locks to the maximum possible treatment depth plus enough air for three complete surface decompression cycles.
How much breathing oxygen must be available for emergency treatment procedures?
90 m3
This is a critical safety requirement for diving operations.
What are two independent sources for breathing air?
Two separate compressors operating from different power supplies or one compressor and an HP air quad
Rig air is not suitable due to its non-dedicated supply nature.
What is the minimum extension for a ladder used by divers?
At least 2 m below the surface
Divers should not have to climb more than 2 m above the water surface.
What equipment should gas cylinders on a diving stage be fitted with according to IMCA D023?
First stage regulator, double connection, contents gauge, and preferably a half mask
This setup allows for proper emergency use of the gas cylinders.
What is the maximum depth for mobile/portable surface supplied systems without decompression?
30 msw (100 fsw) with no decompression required.
Under what conditions can mobile/portable systems be used at a maximum depth of 50 msw?
Only in exceptional circumstances and after a careful risk assessment.
What is the minimum floodable volume for each cylinder in the mobile/portable system?
46 litres (1.6 ft*).
What is the minimum working pressure for the cylinders in mobile/portable systems?
150 bar (2175 psi).
How many cylinders should the mobile/portable system consist of?
At least two horizontally mounted cylinders, plus a third that can be switched on to either supply.
What is the recommended maximum time for a support vessel to return a diver to safety?
No more than 15 minutes away
What must be available to assist the small craft in case of a problem?
A second recovery craft
What are the minimum requirements for a wet bell system?
It must provide air to a manifold inside the wet bell and diver excursion umbilicals terminated at the wet bell
This is outlined in IMCA D023.
What type of air supply is acceptable as a secondary supply in a wet bell?
Onboard cylinders, provided there is a diver remaining to switch supplies or an automatic switchover system
What system should be in place if the water depth exceeds the planned maximum dive depth?
A system for preventing the wet bell from falling below this level in the event of a winch failure
What is the depth limit for using a wet bell under the IMCA International Code?
75 ms (248 fsw) using mixed gas.
For depths between 0 and 50 m, what is the maximum bottom time allowed?
Such that the in-water decompression required is less than 100 minutes
For depths between 50 and 75 m, what is the maximum bottom time allowed?
30 minutes
Fill in the blank: Surface supplied diving mixed gas systems should conform to the requirements of _______.
IMCA D037 DESIGN for surface supplied mixed gas diving systems
What are the minimum logged offshore surface supplied dives required for working and standby divers involved in mixed gas wet bell surface supplied diving?
200 logged offshore surface supplied dives to depths greater than 30 m and at least 10 previous dives completed from a wet bell
This does not include dives during diver training.
What is the minimum onboard gas gas supply requirement for each diver in wet-bell surface supplied air/ mixed gas diving?
a minimum, there should be 7 m3 of both bottom mix and compressed air for each diver at
the maximum depth planned.
This is essential for the diver’s safety during decompression.
What are the minimum requirements for a chamber used in surface supplied mixed gas diving?
1) Two compartments
2) Minimum internal diameter of 1.37 m (54”) for one diver
3) Minimum internal diameter of 1.5 m (60”) for more than one diver
4) One mattress for medical treatment
5) One fixed bunk of minimum 1.8 m long for 1.5 m diameter chambers
6) Means to maintain thermal balance
The requirements ensure safety and medical readiness for divers.
What is the minimum internal diameter of a chamber if only one diver is in the water?
1.37 m (54”)
This is the requirement for chambers designed for single diver operations.
What is the minimum internal diameter of a chamber if more than one diver is in the water?
1.5 m (60”)
This size is necessary to accommodate multiple divers requiring decompression.
What is the minimum length of the fixed bunk required in a 1.5 m diameter chamber?
1.8 m long
This ensures adequate space for diver accommodation.
What is the minimum internal diameter requirement for chambers manufactured after January 1, 2015?
60 inches (1500 mm)
This regulation was established to improve safety standards.
What is the absolute minimum team size to support divers during a closed bell operation?
Nine: diving supervisor, two life support supervisors, two life support technicians, two divers in the bell, standby diver on the surface, tender for the standby divers
This is the minimum requirement; in practice, the team is usually larger.
What type of valve should be fitted to all external valves, except oxygen lines carrying over 15 bar absolute?
Quarter turn valve
These valves are normally open.
What type of valve should be fitted to the circuit supplying the diver’s gas?
Non-return valve
What is the minimum emergency breathing gas supply duration for each working diver?
30 minutes
How much oxygen must be available for metabolic consumption?
0.5 litres/minute per diver for at least 24 hours
What frequency should the location transponder use?
37.5 kHz
This is an internationally agreed frequency for locating the bell.
How long should onboard gas supplies and survival systems be capable of sustaining stranded divers?
At least 24 hours
This is critical for diver safety in case of emergencies.
What personal survival equipment is typically provided for each diver?
- Undersuit
- Hooded insulation suit
- Personal carbon dioxide scrubbers
- Thermal regenerators
High energy food should also be provided.
What are the criteria for using releasable weights in bell emergencies?
- At least two independent actions must be required to release the weights
- No single component failure should allow the weights to release
- Weights must not release accidentally if the bell is tilted
- They must still be capable of release if the bell is tilted
- Hydraulic or pneumatic systems should not be accidentally activated by pressure differences
The system should be inspected and tested regularly by a competent person.
What distinguishes an active cursor from a passive cursor?
An active cursor has its own winch, while a passive cursor rests on the bell and moves with it
The active cursor locks the bell during deployment and recovery.
So close to the end I can taste the freedom
I long for freedom
Who is involved in a Transfer Under Pressure (TUP) procedure?
Divers in the bell, divers in the chamber, diving supervisor, life support supervisor, deck crew
An error by any personnel could have serious consequences.
What should remain closed during a TUP procedure?
Doors to the bell trunking and transfer lock
They should only be opened when divers are moving between bell and chamber or entering/leaving the lock.
What safety measures should be in place during a TUP transfer?
A diver in the transfer lock controlling the trunking door and ensuring all doors to the transfer lock remain closed
All chamber doors should be normally closed to prevent pressure loss.
What are the conditions under which the trunking clamp may be removed?
Direct orders from the diving supervisor, pressure gauge reading zero, bleed valve opened to check pressure
Gauges can be faulty.
What does IMCA D014 state about diving operations?
No diving operation is to be carried out unless a two-compartment chamber is at the worksite or in its close vicinity
IMCA D014 is the international code of practice for offshore diving
What are the size requirements for saturation chambers manufactured after January 1, 2015?
Minimum internal diameter of 72 inches (1800 mm)
This is for surface compression chambers used for saturation diving
What does the Diving Medical Advisory Committee (DMAC) recommend for saturation chamber diameter?
Minimum of 1.8 m (72 inches) but preferably 2.15 m (84 inches)
This recommendation is for chambers where medics may have to work
Which certification societies provide standards for diving equipment?
- DNV GL
- Lloyd’s
- ABS
- Bureau Veritas
- US Coast Guard
These societies have published various standards related to diving systems
At what oxygen percentage does combustion start in a heliox environment?
6%
What is the highest fire risk scenario in diving operations?
Air range habitat welding operations
What is the minimum requirement for compressed air in air chambers according to IMCA D050?
Sufficient air to pressurise both locks to the maximum treatment depth plus air for three complete surface decompression cycles.
What is the typical maximum treatment depth for air chambers?
Normally 50 metres.
What equipment should chamber control be equipped with?
One or more sets of breathing apparatus and communication systems
This is necessary to ensure continued operation in case of fumes in the control room.
What is required for each chamber’s control panel?
A separate control panel and separate depth gauge
This prevents any crossover connections and allows for isolation of valves.
What must be fitted to prevent accidental leakage between mixes at the control panel?
Non-return valves and vents
These are necessary if several mixes are connected to a common pressurisation-line.
Minimum gas before commencing saturation diving operations?
Sufficient gas, in the event that the chamber atmosphere becomes contaminated, to allow
each diver four hours’ breathing on BIBS masks at the deepest storage depth in addition
to other gas reserves.
* Sufficient quantities of treatment gas for the depths involved to carry out any foreseeable
treatments as detailed in the company’s rules.
* Sufficient mixed gas available to be able to pressurise the system (all deck chambers/HES
involved in the saturation) required for the envisaged operation to the maximum
intended storage depth, plus at least an equal amount as a reserve.
− During the operation, the reserve of mixed gas should be sufficient to completely
repressurise the system, should be maintained at all times;
*Sufficient oxygen to allow for:
− metabolic consumption by each diver
− any oxygen make-up prior to decompression, and
− that required to maintain the ppO2 during decompression.
- This quantity should be doubled for safety reasons and held in two separate
banks.
*Sufficient quantities of calibration and zero gas to provide a minimum of three weeks’supply for the analysers
− This reserve needs to be maintained during the saturation.
In addition, sufficient mixed gas should always be available at the start of a bell run to carry
out the intended bell run, or for both intended bell runs if conducting bottom turn-
rounds/continuous diving, plus the same quantity of gas should be held as a reserve. This gas
will be in addition to the gas requirements in the above paragraphs. Gas carried onboard the
bell or hyperbaric evacuation system (HES) in cylinders should not be included in these
calculations.
Back-up supplies must be immediately available. For chamber use this means that they must
be at sufficient pressure to go directly into the chamber. Gas at a pressure of less than 20 or
30 bar cannot be considered as part of the reserve.
Minimum quantities of other consumables like soda lime and Purafil will normally be specified
in company manuals. Typically, they will be sufficient to continue operations for about two
weeks without further supplies being received.
What is the minimum supply duration for calibration and zero gas for analysers?
Three weeks
This ensures that analysers can function properly throughout the saturation period.
Should gas carried onboard the bell be included in calculations for gas reserves?
No, gas carried onboard the bell or hyperbaric evacuation system (HES) should not be included in these calculations.
What is the minimum pressure for backup gas supplies to be considered usable?
Gas at a pressure of less than 20 or 30 bar cannot be considered as part of the reserve.
How long should minimum quantities of consumables like soda lime and Purafil last?
Typically, they should be sufficient to continue operations for about two weeks.
What types of infections are commonly caused by gram negative bacilli?
Ear infections and wound infections.
What types of infections can be detected using swabs?
Gram negative bacilli and fungal infections.
What should be done if a chamber gas reclaim system is used?
The reclaim bag should be swabbed on a regular basis.
Regular swabbing helps monitor for potential contamination.
What are the components of prophylactic ear drops?
Silver acetate, salicylic acid, or aluminium acetate solution.
These solutions make the ear canal too acidic for bacteria.
How often should prophylactic ear drops be administered?
Usually every eight hours.
Regular use helps prevent ear infections in divers.
What is the maximum carbon dioxide level in heliox saturation?
Equal/less than 5 mb (0.005 atm)
High CO2 levels can lead to respiratory issues for divers.
What should be the temperature range for saturation environments?
25-33 °C (77-92 °F)
Comfortable temperatures are essential for diver wellbeing.
What is the minimum internal diameter recommended for a medical treatment chamber in saturation systems?
1.8 m (6 ft)
Preferably, the chamber should be 2.15 m (7 ft) or more for better accessibility.
List three specifications required for the bunk in the medical treatment chamber.
- Waist high
- Access from at least one side and one end
- Firm base for tilting the patient
The bunk must facilitate proper patient positioning and treatment.
What diameter should the medical lock in the treatment chamber be at a minimum?
300 mm
This ensures that medical personnel can efficiently access the chamber.
What is the minimum duration the HRU should maintain divers with life support?
72 hours
According to the IMO Guidelines and Specifications for Hyperbaric Evacuation Systems Resolution A. 692(17)
What is the maximum time allowed for the transfer of divers into the HRU?
15 minutes
What is the maximum time allowed for the launch of the HRU once instructed?
30 minutes
What should be the distance of the HRU from the vessel/installation after launch?
100 meters
What is the target time for the HRU to reach a safe haven after launch?
Within 75% of the HRU designed endurance
Which IMCA documents relate to hyperbaric evacuation systems?
- IMCA D02459
- IMCA D053
- IMO Guidelines and Specifications for Hyperbaric Evacuation Systems Resolution A.692(17)
These documents outline the design and operational requirements for saturation diving systems.
How often should hyperbaric rescue drills be conducted?
Regularly, with practice deployment and recovery every six months
These drills are part of the regular on-board fire and boat drills.
When should bell diver rescue drills be conducted?
Early in the saturation period (first two to three bell runs) and every 14 days thereafter
These drills should include recovery of a completely incapacitated saturation diver.
What is a potential circumstance for accelerated emergency decompression from saturation?
When the HRU is out of action, weather conditions prohibit HRU launch, or reception facilities are unavailable
DMAC guidance on emergency decompression should be consulted in such cases.
What is the construction of most wire ropes?
Most wire ropes are constructed from six strands laid around a fibre core
The fibre core allows the strands to bed in and take up their natural positions when the rope bends or stretches, and it acts as an absorbent for lubricating oil.
What is the safety factor for general working of a wire rope?
A wire rope should have a safety factor of 5
This means the rope should not be used for loads greater than one-fifth of its breaking strain.
What is the required safety factor for wire ropes used for man-riding?
The safety factor for man-riding wire ropes should be 8: 1.
What is the fleet in relation to a winch?
The fleet is half the length of the drum and is the distance moved by the rope from the centre to the edge of the drum as it winds or unwinds.
What is the maximum fleet angle to minimize abrasion on the sheave and drum?
1.5°
The fleet angle is measured by comparing the fleet with the lead.
What is the required lead for every meter of fleet?
At least 38 m of lead for every metre of fleet.
What is the recommended distance between the top layer of wire and the edge of the drum flange?
About 2.5 times the diameter of the winch wire.
What is the minimum number of offshore commercial dives required for a Trainee Air Diving Supervisor?
100
What is the minimum number of lockout hours required for a Trainee Bell Diving Supervisor?
400
What are the minimum requirements for an Air Diving Supervisor?
- Logged at least 200 panel hours and 100 surface dives over 60 days
- Demonstrated competence as an offshore air diver
- Recommended by a company
- Passed the IMCA Air Diving Supervisor examination
Up to 60 panel hours and 30 surface dives can be gained through simulator experience.
What is the required experience on a class A simulator for an Air Diving Supervisor?
30 hands-on hours gaining up to 60 panel hours and 30 surface dives
Alternatively, 20 hands-on hours can gain up to 40 panel hours and 20 surface dives on a class B simulator.
What is the minimum panel hours and bell runs for a Bell Diving Supervisor?
350 panel hours and 50 bell runs
Must be logged under direct supervision over a minimum period of 90 days.
What is the requirement for acting as a trainee air diving supervisor for Bell Diving Supervisors?
At least 10 offshore commercial air dives
Includes simulator experience under specific conditions.
What is one of the specific simulator requirements for a Bell Diving Supervisor?
10 hours on a class A simulator
One simulator dive must include the emergency recovery of a closed bell within the air range.
How many panel hours and bell runs can be gained from a class A simulator?
Up to 105 panel hours and 15 bell runs can be gained by 53 hands-on hours’ experience.
Simulators provide a controlled environment for trainees to practice skills.
How many panel hours can be gained from a class B simulator?
Up to 70 panel hours and 10 bell runs can be gained by 35 hands-on hours’ experience.
Class B simulators may provide a different level of training and experience compared to class A.
What is the minimum panel hours requirement for trainees working as an LST or assistant LST?
At least 360 panel hours at any time.
LST stands for Life Support Technician, a crucial role in diving operations.
What Beaufort scale category describes calm conditions?
Beaufort scale 0 - Calm, sea like a mirror.
At what wind speed (in knots) does the Beaufort scale categorize light air?
Beaufort category 1 = 1-3 knots.
What is the visibility range classified as ‘Poor’?
Visibility less than 1000m.
What does ‘veering’ refer to in wind direction terminology?
The changing of the wind in a clockwise direction.
What is indicated by the term ‘backing’ in wind direction?
The changing of the wind in an anti-clockwise direction.
What visibility range is classified as ‘Good’?
Visibility more than 5 n.miles.
What is the wind speed associated with a ‘light breeze’ on the Beaufort scale?
4-6 knots.
What is the visibility range classified as ‘Moderate’?
Visibility between 1000m and 2 n.miles.
What is the wind speed associated with a Gale warning?
Winds of at least Beaufort force 8 (34-40 knots) or gusts reaching 43-51 knots
Gale warnings indicate severe weather conditions that can impact diving operations.
What wind speed is classified as a Severe Gale?
Winds of force 9 (41-47 knots) or gusts reaching 52-60 knots
Severe Gale conditions can pose serious risks to marine activities.
Define the wind speed for a Violent Storm.
Winds of force 11 (56-63 knots) or gusts of 69 knots or more
Violent Storm conditions require immediate attention and action in diving operations.
What wind speed is classified as Hurricane Force?
Winds of force 12 (64 knots or more)
The term hurricane on its own refers to a true tropical cyclone.
What does ‘Imminent’ indicate in weather terms?
Expected within 6 hours of time of issue
Imminent conditions require prompt action to ensure safety.
What does ‘Soon’ indicate in weather terms?
Expected within 6 to 12 hours of time of issue
Soon conditions still require monitoring and preparedness.
What is the Beaufort scale force associated with winds of 34-40 knots?
Beaufort force 8
This scale is used to estimate wind speeds and associated conditions.
Fill in the blank: Winds of force 9 are classified as _______.
[Severe Gale]
