Term
| Thermal protection can be divided into three categories: |
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Definition
1. Operational
2. Emergency
3. Combined operational and emergency |
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Term
| Operational Thermal Protection |
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Definition
-Used day to day in any normal working situation
-Two main types of operational thermal protection:
1. Passive
2. Active |
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Term
| Passive thermal protection |
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Definition
| relies on the insulation either of the air/water trapped inside the suit, or of the suit itself |
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Term
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Definition
| means that the heat is supplied to the diver |
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Term
| When active protection is used care must be taken to avoid: |
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Definition
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Term
| Passive Operational Thermal Protection |
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Definition
A) Wet suits
B) Thermal Underwear
C) Dry Suit |
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Term
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Definition
-Close fitting garment worn next to diver’s skin
-Water enters the suit at its edges, cuff and neck
-Water is retained against the wearer’s skin by the close fit of suit |
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Term
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Definition
-Closed cell, expanded foam neoprene – a synthetic rubber like material full of minute closed cells of nitrogen gas
-Cells are not interconnected and material does not soak up water |
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Term
| Neoprene thickness varies from |
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Definition
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Term
| Wet suit Thermal Protection: |
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Definition
-The minute closed cells of nitrogen gas within the neoprene form an insulating layer
-The diver’s body heats the film of water between the diver’s skin and the wet suit and so assists in providing insulation |
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Term
| Wet suit Potential thermal protection problems |
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Definition
-Pressure of water at depth compresses the gas filled neoprene
-@ 20m wet suit is approx half its original thickness and its insulating quality is also halved
-Flushing can occur if the suit is to loose or too many tears
-Initiated by the frequent flexing of the body particularly at the waist reducing thermal protection to almost zero
-With age neoprene cells develop connections, lose gas and soak up water reducing thermal protection |
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Term
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Definition
-Fit- good fit is important
-Buoyancy- gas trapped is very buoyant,
-Can cause problems for a controlled ascent
-Overcome by use of BCD |
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Term
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Definition
-Relatively inexpensive
-Relatively lightweight
-Easy to repair
-If punctured still provides thermal protection and buoyancy
-Comfortable to wear
-Easy to swim in
-Little care and maintenance required
-Urination does not cause loss of -efficiency |
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Term
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Definition
-Good fit is essential
-Compresses with depth which reduces thermal protection
-Little thermal protection if there is a wind chill factor
-Loses buoyancy with depth |
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Term
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Definition
| Used under dry suit when conditions are cold |
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Term
| Thermal Underwear Material: |
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Definition
| Flameproof wool, synthetic fibers, foamed neoprene |
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Term
| Thermal Underwear Thermal Protection: |
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Definition
| he gas trapped in the material provides an insulating layer. The thickness of this insulating layer can be controlled by dry suit inflation and deflation facilities |
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Term
| Thermal Underwear Potential Problems: |
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Definition
| When heliox is used the gas trapped in the fibers does not provide a layer of insulation as helium rapidly conducts heat away from the divers, especially when under pressure |
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Term
| Thermal Underwear Other Considerations: |
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Definition
| Foamed neoprene underwear can be used when using hot water suits, both for added protection and for a back up in case of malfunction |
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Term
| Thermal Underwear Advantages |
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Definition
-Protection can be varied to suit the conditions
-Rugged and easy to repair
-Inexpensive enough for every diver to own one |
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Term
| Thermal Underwear Disadvantages |
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Definition
-When wet loses most of its thermal protection
-Attention must be paid to maintenance to ensure personal hygiene |
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Term
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Definition
-Diver is intended to remain dry in these suits
-Thermal underwear usually worn underneath either to provide insulation, protective layer, or to soak up sweat
-In all cases gas must be able to flow into the suit – under pressure gas is compressed until suit is squeezed against the body- restrictive, painful and causes loss of buoyancy |
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Term
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Definition
| -Rubberised canvas, foamed neoprene, reinforced rubber or various synthetic materials |
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Term
| Dry Suit Design Variations |
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Definition
1. Standard suit (canvas/rubber) is connected directly to the helmet by a breast plate so air flows from helmet to suit
2. UniSuit is a snug fitting foamed neoprene suit with inflation/ deflation facilities on the suit
3. Conventional Dry suit- loose fitting, strong, thin skin with suit inflation/deflation facilities on the suit
4. Constant Volume suit- automatically maintains a constant volume in the suit regardless of the depth of the diver |
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Term
| Dry Suit Thermal Protection |
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Definition
-Main protection comes from the layer of gas trapped between the diver’s skin, the thermal underwear and the suit.
-Layer can be increased or decreased with suit inflation/deflation
-When suit is made of neoprene the material also provides thermal protection from a layer of closed cells of nitrogen |
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Term
| Dry Suit Potential Thermal Protection Problems |
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Definition
-When used with heliox the dry suits protection is reduced because it conducts heat away from the body
-Dry suits usually used for shallow water cold diving up to 50m /165ft |
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Term
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Definition
1.Thermal protection can be varied to suit the conditions
2. Can be very rugged
3. Can protect the diver in polluted waters
4. Fit is not so critical |
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Term
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Definition
-If punctured, there is a loss of thermal protection, possibly some buoyancy and the dive may need to be aborted
-Blow up may be possible
-Urination leads to discomfort and loss of insulation
-Requires care and maintenance/ repair |
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Term
| Active Thermal Protection Types: |
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Definition
-Hot Water Suit
-Diver Gas Heating
-Electrically Heated Undersuit (EHS)
-Surface Hot Water Heater Unit (SHU) and Bell Gas Heater (BGH) |
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Term
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Definition
-Widely used in the commercial diving industry
-Loose fitting with tubing to distribute the heated water around the inside of the suit
-Has a control manifold so diver can regulate the amount and distribution of hot water
-Usually includes gloves and boots and should be worn with protective under suit to avoid scalding in case of malfunction |
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Term
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Definition
| Foamed neoprene insulating material with double sided nylon lining |
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Term
| Hot Water Suit Design Variations |
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Definition
-One piece suit usually includes gloves and boots
-Mixed gas suits can include a heated hood
-Hot water can either vent through the arm, leg and neck seal (open circuit)
-Recirculate (closed circuit) to the heater unit to be re warmed |
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Term
| Hot Water Suit Thermal Protection |
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Definition
-Hot water is produced at the surface and transferred, either directly or via the diving bell, through insulating tubing to the divers for use in the hot water suit
-Circulation of warm water around the divers body creates an active insulation barrier which allows the diver to easily maintain a normal body temperature and normal blood circulation.
-The hot water sacrifices its heat to the environment in place of the heat that would otherwise be drained from the divers body
-Hot water around the diver should not fall below 32c/90f or rise above 45c/113f |
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Term
| Hot Water Suit Potential Thermal Protection Problems |
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Definition
-Fit- a suit that is too tight will prevent the hot water from circulating freely. Manufacturers usually recommend around 1in between divers body and the inside of the suit
-Swimming- the average suit will hold 13-22 liters of water- can be a hindrance
-Injection Temperature- The injection temperature of the hot water into the suit should be carefully controlled as the diver is often not aware of gradual changes in water temperature. In the initial stages of both hyper and hypothermia, the diver is often not aware of his deteriorating condition.
-Heater Unit- Care should be taken to ensure that the heater is compatible with hot water suits and length and type of the umbilicals used |
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Term
| Hot Water Suit temperature is affected by: |
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Definition
-The injection temperature of the water entering the suit
-The rate at which the water flow enters the suit
The amount of water in the suit
-The exchange rate within the suit (divide l/gallons of water in the suit by the rate of flow of water entering the suit)
-The insulation of the suit material
-The depth and temperature of the water
-The amount of surrounding water which gets into the suit, causing inefficiency |
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Term
| Hot Water Suit Advantages |
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Definition
-Safe, comfortable, effective
-Diver is able to regulate the amount of thermal protection |
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Term
| Hot Water Suit Disadvantages |
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Definition
-Can be difficult to swim in
-In submersible operations, special consideration should be given to the efficiency of heat conservation
-In some open circuit suits constriction can cause burning |
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Term
| Diver Gas Heating Features: |
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Definition
-Upon inhalation the body attempts to bring the vapour content of the inhaled gas up to 100% and bring the temperature up to that of the deep core temperature.
-If gas is cold and dry it will take heat for the body to accomplish this
-If a diver breathes cold heliox he looses an enormous amount of body heat whenever he exhales
-For dives deeper than 150m the diver’s gas is usually heated to reduce this loss of body heat
-Hot water from the hot water suit supply is used to heat the breathing gas by means of a splitter block which is attached to the hot water suit inlet connection.
-It divides the hot water flow between the suit and breathing gas systems |
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Term
| Diver Gas Heating Material |
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Definition
| Non- corrosive metals and plastic hose connections |
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Term
| Diver Gas Heating Design Variations |
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Definition
| Deep diving version supplies more hot water to provide greater heating of heliox at depths greater than 200m |
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Term
| Diver Gas Heating Thermal Protection |
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Definition
| Hot water circulates around and heats up the diver’s breathing gas as it enters the helmet |
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Term
| Diver Gas Heating Potential Thermal Protection Problems |
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Definition
| Any malfunction in the diver’s hot water supply can affect the gas heating |
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Term
| Diver Gas Heating Other considerations |
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Definition
| As the diver goes deeper the gas inhalation temperature needs to be increased to maintain a safe body temperatur |
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Term
| Electrically Heated Undersuit (EHS)Features: |
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Definition
-Rarely used in commercial diving. Light underwear may be worn underneath as it is more practical to wash than the suit. A dry suit should be worn on top
-Wearing thermal underwear between the ehs and the drysuit increases the efficiency of the thermal protection
-Material – Electric heating wires on a woolen material or proprietary conducting material |
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Term
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Definition
-One piece suit- heating elements extend over the whole body including the feet and up as far as the base of the neck but not over the shoulders where the weight of the helmet might compress it against the skin.
-Gloves are designed to function when wet. The suit is run from low DC voltage.
-Although normally dry, the heated suit is safe even when flooded and will still provide a good measure of thermal protection in this condition
-Part Body Cover- eg trunk only |
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Term
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Definition
-The EHS uses an electrical heating element to actively heat the diver
-Potential Thermal Protection Problems
-Care must be taken to hang the suit up after use
-Should never be turned on unless the suit is being worn as this might damage the heating element
-Misuse may lead to the diver suffering burns
-One electrical element in the suit should never overlap with another |
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Term
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Definition
-The EHS is used mainly by military divers
-For offshore use its main advantages would be in manned submersibles where there is already an electric power source aboard |
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Term
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Definition
-Very efficient for heat produced
-Small heater unit required for maximum heat production
-Smaller umbilicals than hot water suits
-More effective than open circuit suits at greater depths
-More versatile for setting up at remote sites where hot water equipment is too cumbersome to install |
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Term
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Definition
-Diver does not receive as much heat as with the hot water suit
-As four layers are needed for thermal protection, the divers mobility can be reduced and care is needed in dressing |
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Term
| Surface Hot Water Heater Unit (SHU) and Bell Gas Heater (BGH)Features: |
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Definition
-The SHU is placed in the ship or platform and should be near the diving spread
-BGH is usually attached outside the bell |
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Term
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Definition
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Term
| SHU and BGH Design Variations |
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Definition
-The SHU produces hot water which may be provided by steam from the ships’ supply, propane, diesel or electrical immersion systems.
-Insulated umbilicals delivers hot water to the bell gas heater.
-Most popular heating method is by electricity to heat water at the surface. |
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Term
| SHU and BGH Thermal Protection |
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Definition
-In surface supllied diving the SHU provides hot water directly to the diver for use in hot water suits and diver gas heaters
-In a diving bell the SHU sends hot water to the bell to heat the bells’ breathing gases, divers hot water and breathing gases |
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Term
| SHU and BGH Potential Thermal Protection Problems |
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Definition
-If the design of the heater is inadequate, fluctuations within the system can occur and the diver can suffer burns
-If the heater unit is unable to cope with the number of divers using the system, it may fail to heat the divers adequately, leading to hyperthermia.
-Care should be taken to provide a heater capable of providing controlled heat for the maximum numbers of divers likely to use the system |
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Term
| SHU (surface heater unit) and BGH (Bell gas heater) Advantages |
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Definition
-Simple, safe, effective
-Rugged
-Good redundancy of heat/ power supplies can be built in
-Excellent track record |
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Term
| SHU (surface heater unit) and BGH (Bell gas heater) Disadvantages |
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Definition
-If heater fails, dives would have to be terminated
-Training is required to properly maintain the unit
-Divers can be unaware of slow temperature changes |
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