DESCRIPTION

 

Description of the traditional SCUBA system

 

1.   Definition of terms:

 

A. Buoyancy "0" - Neutral buoyancy - the diver hovers in the water - the average density of the diver (specific weight - the weight of the diver divided by the volume of the diver) is equal to the density of the water.

B. Positive buoyancy - the average density of the diver is less than the density of the water, the buoyancy force acts upwards.

C. Negative buoyancy - the average density of the diver is greater than the density of the water. The buoyancy force acts downwards.

D. Pressure air tank - a compressed air balloon carried by the diver which serves as the diver's air supply tank.

E. Decompression - 80% of the air we breathe is nitrogen which is soluble in tissues and blood. The amount of nitrogen dissolved in the tissues and blood increases with the depth and time of the dive. The more nitrogen dissolved in the blood, the longer it takes for it be released. Decompression sickness happens when dissolved nitrogen is not released due to a rapid ascent. If the amount of nitrogen accumulated in the tissue during the dive is too large, some will form bubbles in the tissue and blood vessels during the ascent. These bubbles can be dangerous to the diver, as they block blood vessels (air embolism) and prevent the supply of oxygen to the tissues and brain (stroke). The way to prevent decompression sickness is to make the ascent slow and gradual, allowing the dissolved nitrogen to be released safely.

F. Ascent - The rise to the water surface at the end of the dive.

G. First degree  regulation valve - Regulates the air pressure of air tank. At the beginning of the dive the diver's air tank is filled with air at a pressure of 200 atm (2.95 Kpsi). The regulation of the first degree reduces the pressure to 10 - 8 atm (147 – 117 psi) regardless of the air pressure in the tank.

H. Second degree of regulation – also called a lung demand valve. The second regulator provides the diver with air for continuous breathing at a pressure matching the depth of the dive. The diver hold the menstrual nozzle in his mouth.

2.   Description of the traditional Scuba set

The diving kit includes:

·        Diving vest (Buoyancy Control Device - BCD) with flexible rubber bladders.

·        Compressed air tank.

·        Piping and pressure fittings.

·        Weights.

·        Diving suit.

·        Fins and diving mask.

 

The Buoyancy Control Device (BCD) includes an air balloon rack and flexible air bladders sewn inside the vest.

The tubing and pressure regulation includes:

·        An air connector that connects the tubing to the pressure tank,

·        A first-degree regulator that reduces the pressure by 8-10 atmospheres.

·        Breathing air supply hose,

·        Two second degree regulators that are part of the breathing mouthpeace (one of them is a backup – “octopus”),

·        A hose for inflating the bladders in the BCD,

·        Valves for emptying the bladders in the BCD,

·        A pressure gauge that measures the air pressure in the tank.

3.   The diving process with the traditional Scuba set

The dive process includes several stages as follows:

Calibration: After entering the water, the diver descends to a depth of 2 meters and inflates the flexible rubber bladders in the BCD to a volume that allows the diver to hover in "0" buoyancy.

Diving: After calibration, the diver starts to dive while varying the dive depth. The volume of the flexible air bladders in the BCD varies with the depth of the dive. As the diver consumes the air from the tank, the weight is reduced. The volume of the wetsuit also varies depending on the depth of the dive. To maintain a "0" buoyancy over time and at any depth the diver must inflate or empty air from the flexible bladders in the BCD. 

 When descending, the flexible bladders shrink because of the increasing water pressure. This effect causes downward acceleration, if the diver fails to inflate the bladders (positive feedback loop).  The same acceleration happens during the ascent if the diver fails to deflate the bladders, increasing the risk of decompression sickness.

 

The amount of air that is added or reduced to BCD is not measured and is not measured and is traditionally done through the process of trial and error. Experienced divers control the balancing process easily, but new divers have a hard time doing so. Divers who are not trained in balancing the BCD have trouble to maintain depth and they go up and down without control.

 

Ascent at the end of the dive: At the end of the dive, the diver ascends to the water at a set pace and must takes decompression breaks. The controlled rate of ascent and breaks are needed to release nitrogen that has dissolved in the blood and tissues during the dive. Nitrogen release is needed to prevent decompression sickness. The rate of ascent and the duration of the breaks are planned by the diver before starting the dive using a decompression table. The table takes in to account the following parameters:

• Diving depth

• Duration of the planned dive at any depth

• Dive history.

The diver can use a diving computer that advises him of the ascent plan (ascent speed and decompression breaks). The ascent to the water surface is carried out by using the fins while emptying the air bladders in the BCD.

During the ascent, the water pressure decreases and the volume of air in the flexible bladders of BCD increases and the average density of the diver decreases. For this reason, the diver is required to empty the bladders in the BCD to maintain a controlled rate of ascent. An uncontrolled increase in the volume of air in bladders will cause a growing positive buoyancy and upward acceleration, increasing the risk for decompression sickness.

4. Divers difficulties:

Different types of divers have different difficulties:

New divers - who are not trained, have difficulty in balancing themselves at the beginning and during the dive. Those divers have difficulty in regulating the amount of air in the BCD bladders according to the changes in depth. This causes them to change the diving depth in an uncontrollable manner. Having to fiddle constantly with the BCD bladders impairs the diving experience.

Note: Generally, new divers, in initial training levels, dive to shallow depths (up to 20 meters) for short duration (up to 45 min) and therefore they are less exposed to a risk of decompression sickness.

 Advanced divers are divers with a high level of training, with tens and sometimes hundreds of dives behind them. The characteristic diving depths are greater than 30 meters and the diving durations are long. This exposes them to risks:

 A. Decompression sickness risk - Generally, divers want to stay as long as possible at the diving site. On the other hand, they need to ensure that at the end of the dive they have a sufficient amount of air to make a slow and prolonged ascent that will ensure avoidance of decompression sickness. For these reasons, they must plan the dives accurately in order to safely ascend to prevent a decompression sickness while making optimal use of the air supply in the pressure tank.

These divers are equipped with a dive computer that monitors air consumption, air inventory in the dive tank, dive depths, duration at each depth (dive history). The computer warns of the danger of lack of air and instructs the diver while ascending (ascent rate and decompression breaks based on the depth of the dive, duration at each depth and the history of the dives). The diver is required to follow the computer instructions. A mistake in performing the dive plan and computer instructions endangers the diver’s health.

 B. Panic or lack of control is another problem that is characteristic of advanced divers. It happens that divers make a rapid ascent that could endanger them with lung damage and/or decompression sickness because of panic. Diving experts noted that panic ascent is caused by the following reasons:

• "Deep Blue" situation in which the diver loses spatial orientation, feels out of control and tries to ascend as fast as possible.

• When it becomes clear to the diver that he is at the limit of the amount of air in the tank.

• As a result of Nitrogen narcosis (drunkenness caused by nitrogen at high pressures).

• As a result of losing his diving partner or losing his group.

Fault in the filling valve - A phenomenon reported by several divers. In this case the filling valve of the BCD bladders remains open after pressing it (for no apparent reason) and the BCD bladders are filled up with air within seconds. In this case, the diver "shoots" up to the water surface. This fault may cause lung damage or decompression sickness.

Divers with special needs - have difficulty in operating the BCD for many different reasons. These divers are accompanied by diving instructors who help them operate the BCD. An automatic BCD would give these divers more independence and solve many of their diving issues.

 5. The proposed ScubaSafe system

The ScubaSafe system is an automated computerized diving system that gives divers support on the following topics:

 Automatic balancing - the diver is released from the need to fiddle with the BCD. The system fills and empties rigid buoys and keeps the diver balanced at any depth.

Safety supervision - the system monitors the air consumption, the amount of air in the tank, the diving depths and the length of stay at each depth.

 Controlled ascent - according to the dive data collected in the safety supervision system and according to the dive history, the system builds an ascent plan, which is updated continuously during the dive. When the diver activates an "UP" control button, the system automatically elevates him by filling a rigid buoy with the amount of air that will ascend him at the correct speed while performing decompression breaks at the required depths and duration. The diver should be at rest and allow the system to manage the ascent process without interruption.

Panic - The system is equipped with a command button "UP" to perform a controlled ascent (as described in the previous section). If the diver is accustomed to the system, he will use it in cases of distress.

Lack of air - the system monitors the air inventory in the air tank, and at the same time it calculates the amount of air needed for a regulated ascent. When the amount of air reaches a critical value, the system alerts the diver (audio or visual signal).

Depth control - the system monitors the diver's depth, alerting when descending to a greater depth than allowed according to the diver's rank.

Vocal indication - It is possible to add a vocal indication to the system using front sides attached headphones. The audible indicator will give the diver information about the depth, air pressure in the tank, various alerts.

Redundancy – A good life support system should include an independent redundant system that lacks a common failure mode. The ScubaSafe system is equipped with a manual operating system that bypasses the computerized system and will serve as a backup for the automated system. It will be possible to paralyze the operation of the automatic system and use manual backup at any stages of the dive.

 In the case of divers with special needs, the system will provide an automatic balance control solution and will exempt the accompanying guide from closely operating the BCD of the special needs diver. After discussing this with a manager of diving club for special need people, it became clear that an automatic balancing system would allow a large group of people with special needs to enjoy the diving experience.

6. Description of the ScubaSafe system

The ScubaSafe system is based on rigid buoy, computer, sensors and controller replacing the traditional BCD. The rigid buoy includes:

·        Rigid cylinder and piston - The cylinder shell and piston back are exposed to the ambient water.

·        An actuator that moves the piston to increase or decrease the volume of air in the buoy.

·        An electronic volume meter that measures the volume of air in a buoy.

·        Communication of the volume meter to an electronic controller and computer.

 

The rigid buoy is filled with air from the main air tank. The buoy’s volume is decreased by emitting air into the environment.

The rigid buoys can be controlled manually and/or by the automatic computerized system.

 Unlike the flexible bladders in the BCD, the use of a rigid buoy allows full control of the filling rate, emptying rate, and the amount of air in the buoy. Control and preservation of the volume of the rigid buoy at any depth can be easly performed. The volume of the rigid buoy can be controlled during the ascent for the purpose of controlling the ascent speed in order to avoid decompression sickness.

These features enable simple design and construction of a computerized and controlled automatic diving system. This feature is not evaliable when flexible bladders of the traditional BCD are used. Design and implementation of a control system for autonomous diving are well known in the academy and in the world of controled systems. 

7. Description of ScubaSafe's automated control system.

In addition to the rigid buoys, the ScubaSafe system includes the following components:

·        Feeding tubing for filling and emptying the rigid buoys.

·        Electrical valve for filling and emptying the buoy.

·        Depth gauge based on continuous water pressure measurement.

·        Pressure gauge that measures the air pressure in the air tank.

·        Controller.

·        Protractor, measures the angle of diver relative to water surface.

·        Computer system.

·        Battery.

·        Display unit with two or more command buttons.

Pressure gauge: Connected directly to the air tank (not via regulator) measures the air pressure inside the air tank that provides air to the diver. The air pressure in the tank is linearly proportional to the air weight inside the tank (offsetting temperature changes). The pressure gauge measures the initial pressure of the air in the tank and the pressure inside the tank during the dive. The measurement is fed to the dive computer using a wired connection or an ultrasonic transmission. The computer calculates the weight of air in the tank.

According to the change in air pressure and change in wetsuit volume (that varies with the depth) the dive computer calculates what volume of air should be reduced or added to the rigid buoy to maintain "0" buoyancy.

 

Depth gauge: Checks the depth of the diver continuously throughout the dive. The depth measurement information is fed to the dive computer.

 

The controller is activated by the dive computer and connected to the volume gauge of the rigid buoy and the depth gauge alternately. In the calibration phase (see below). The controller changes the air volume of the rigid buoy and brings the diver to a state of constant depth (levitation) at 2 meters below the water surface. The volume of the rigid buoy in the end of the calibration phase defined in the system as V₀ the "control volume".

During the dive phase, the controller reads the volume gauge of the rigid buoy. The controller maintains a constant V₀ "controlled volume" of air in the rigid buoy and implements corrections signaled by the dive computer according the changes in weight of air in the air tank and volume of the diving suit. The controlled volume in the rigid buoy preserves the diver's density equal to the water density.

 Protractor measures the diver's angle relative to the surface of the water. The diver's angle has an effect on the drag force in the ascent process. The drag force is developed while ascending and affects the air volume in the rigid buoy required to obtain a stagnation speed that corresponds to the desired ascent speed. If the diver is in a horizontal position, its vertical drag is large and therefore a larger amount of air is required to add into the rigid buoy. If the diver is perpendicular to the surface of the water, its vertical drag is smaller and therefore a smaller amount of air is required to be added to the rigid buoy.

Note: Stagnation speed is the constant speed developed when the drag force is equal to the buoyancy force. The drag force is proportional to the speed of the diver squared.

 

 Display and control panel displays the information about the depth of the diver, the pressure in the air tank, the duration of the dive and more. The panel includes two command buttons:

 

"C" Button ("C" for calibration): Activates "Calibration" mode. The diver presses the "C" button at the beginning of the dive when the diver is on the water surface. As a result of a single press, the system lowers the diver to a depth of 2 meters and stabilizes them at this depth for 240 seconds. At this stage the diver is in "0" buoyancy state. The system measures the volume of air in the rigid buoy after calibration. This volume is the "control volume" (V₀). This is the air volume needed to keep the diver's density equal to the water density. From this stage on the computer will maintain the control volume (V₀) in the buoy while correcting the volume resulting from the decrease in air weight in the air tank and the changing volume of the wetsuit depending on the depth.

Note: If it were not necessary to compensate for a change in the air weight and the volume of the wetsuit, it would be possible to fix the position of the piston inside the rigid buoy and thus ensure that the control volume would not change.

 

"U" button (U for up) – Activates "ascent" mode - In this mode the system raises the diver to the water surface according to an ascent plan. The ascent plan includes a controlled ascent rate and decompression breaks as calculated. This button is pressed when the diver wants to ascend or when diver is in "panic" state.

 

Simultaneous pressing of the "U" and "C" buttons - disables the automatic system and allows the diver to operate the rigid buoy manually. Another simultaneous press resumes the automatic dive.  

 

The display unit gives the diver indications about the system state like "calibration", "dive" and "up" status.

 

Computer: Receives data from the depth gauge, the pressure gauge (which measures the pressure in the tank), the time clock and signals from the "U" and "C" buttons. The computer monitors the change in pressure in the air tank and calculates the diver's air intake rate.

 

When entering the water, the computer samples the pressure gauge of the air tank, translates the pressure to air weight and determines the initial air weight as (M₀).

 

As mentioned before a single press of the "C" button puts the computer in "Calibration" mode. In this mode, the computer activates the controller for depth control as indicated by the depth gauge. If the "C" button is pressed when depth is less than 2 meters the controller is required to stabilize the diver at 2 meter depth while filling or emptying the rigid buoys. If the "C" button is pressed when depth is greater than 2 meters, the controller is required to stabilize the diver at the current depth by filling and emptying the rigid buoy. During the calibration process, the computer displays a "calibration mode" message in the display unit.

 

After stabilizing at the required depth, the computer samples the volume of the buoy and determines this volume as the "control volume" (V₀).

  

After completing the calibration process, the diver can dive freely. The display panel indicates the transition from "calibration" mode to "dive" mode. The controller then adapts volume of the buoy according to the indication obtained from the volume meter in the rigid buoy. The computer updates the required rigid buoy volume during the dive according to the air pressure in the air tank and wetsuit volume (that varies with depth) in order to maintain “0” buoyancy.

 

Throughout the dive the computer collects the dive data, duration and depth and updates the "ascent" plan according to these parameters.

 

Pressing the "U" button - the computer will enter "ascent" mode. The computer instructs the controller to increase the volume of the rigid buoy. The increase of buoy volume is pre calculated and depends on the diver's angle. The computer signals the controller to control the ascent speed according to the information obtained from the depth gauge. The controller adjusts the amount of extra volume in the rigid buoy to match the required speed of ascent. According to the depth gauge and according to the ascent plan, the computer instructs the controller to reduce the volume of the rigid buoy to allow for decompression breaks.

Note: In the ascent process the diver is required to be passive and motionless, without making swimming motions, to not foil the ascent plan.

8. The diving process with ScubaSafe

The following is the diving process with the ScubaSafe system.

 

A. Before entering the water - the diver feeds the computer with the following parameters:

·        Diver rank, diving permissions (maximum depth allowed).

·        Breathing system type (closed, open).

·        Volume and pressure of the air tank.

·        Data on the wetsuit such as the weight of the dry suit, the type of suit (full, short, thickness), the type of fabric (4 types of fabrics).

·        Diver Height and Weight (BMI) - needed to determine the conservatism coefficient of decompression plan software.

 

The data is transmitted using a mobile phone application that is connected via Bluetooth to the system computer.

 

B.  Upon entering the water, the diver fills air in the rigid buoy and presses the "C" button. The system will lower the diver to depth of 2 meters, balance him and calibrate the air volume in the buoy (V₀).

 

C.  Once the diver has received a display indication about the end of the calibration process he can start diving freely. The system monitors the change in depth, air pressure in the tank and adjusts the volume of the rigid buoy to ensure a "0" buoyancy.

D.  At the end of the dive the diver presses the "U" button and stops swimming. The system will raise the diver according to an ascent plan while performing decompression breaks.

E.  Reaching the surface, the diver will fill the the rigid buoy and swim to the ship or shore.

F. On shore, the diver will be able to download the dive log to an external computer, or smartphone using the bluetuth or line connection.

 

9. ScubaSafe and Safety

The sport of diving is involved with many safety risks; there are many good reasons why it is necessary to take a 5-day diving course to get a diving a license at the lowest level (one star). Many divers are concerned about safety, so in addition to the operational benefits of the system, ScubaSafe provides a number of safety benefits as follows:

·  The system alerts the diver if he descends to a greater depth than is permitted according to his training level.

·  The system monitors the amount of air in the tank and the rate of air consumption and alerts shortage for air.

·   The system plans the ascent plan at the end of the dive in real time. The plan is based on the depth of the dive, the duration at any depth and the dive history.

·  The computerized system calculates the duration needed for a safe ascent (according to the ascent plan). The system "learns" the diver's air consumption. According to these two parameters, the system determines what is the minimum amount of air required for a safe ascent. When the amount of air in the tank reaches 1.5 of the critical value, the system alerts the diver.

·  The system does not allow to start the dive if the battery that feeds the system is not charged.

·  Throughout the dive the system gives the diver visual indication of the dive parameters. Audial indication is also possible.

·  The dive computer stores all the information about the dive and at the end of the dive the information can be downloaded to an external computer for later review. 

·  The system includes a manual valve for filling or emptying the rigid buoys. The manual valve is used as a backup for the automatic system.

 10. Geometry

Divers uses two kind of BCD

a. Vest BCD - bladders inside the vest

b. Wing BCD - bladders attached to the diver's back

ScubaSafe was built inspired by a Wing BCD. Volume control cannot be performed on the flexible bladders of Wing BCD. Volume control can be performed on ScubaSafe rigid buoys.