(Update 29.11.2020: added object securing) This section is about the Worst Case Scenario ‘Habitat Flooding’, its prevention and handling.
Proposals that may help to improve it are welcome.
- safety for the inhabitants of the habitat, the aquanauts
- functioning of life supporting systems for a certain period of time
- communication between habitat and surface/land support
- rescue procedures
- all parts of the habitat that could be affected by water, like electronics
- the main structure of the habitat
Thinking of an underwater habitat most people first think of an uncontrolled flooding. There are two instances carrying the risk of this event: a hull breach and a tilt of the entire structure.
In fact a breach of the habitat shell represents a major risk for the structure as a whole and its inhabitants. To formulate a prevention plan we first have to define the weakest parts of the habitat, which are:
- all seals and joints
- all openings (hatches, cable fittings…)
By implication we can say that the least risky area would be a reinforced homogeneous part without interruptions. The only area that can maintain these features is the upper part of the hull, where no openings, no windows and no hatches are necessary. In all other areas risks have to minimized technically by high standards of sealings and multiple checks before and during operation.
Today’s material quality makes a breach of a window very unlikely. The weakest point here is not the window itself, but probably the fitting and the seals. One of the factors may be the thermal expansion rate difference of the window and the hull material.
If a hull penetration is inevitable, it should it least be reinforced and kept as small as possible in order to maintain a low speed of water influx. A broken sealing will not allow a massive influx, so does the fitting of an electric cable. Breaches in those areas will grant the aquanauts enough time to investigate the cause of influx, its elimination and/or starting emergency procedures.
A tilting habitat may appear because of poor design and/or changing position of the ballast. At a certain point it could cause a chain reaction and the habitat eventually capsizes. An open hatch would cause a total flooding. It seems like there is no thinkable emergency procedure except immediate evacuation. The only solution to prevent such an incident is a clear design, that avoids movement of ballast under any circumstance and clearly defines the center of gravity. This covers not only the placement on the seafloor, but also the dynamics on the surface while under tow.
Habitat La Chalupa has a safety zone between the upper frame of the windows and the highest point of the reinforced ceiling. There are no hull penetrations higher then the upper frame of the windows, which makes this line the highest located weak point of the habitat and something we can call a “predetermined maximum flooding level”. In other words: Since La Chalupa is an ambient pressure vessel, in case of a hull penetration water would rise until this predetermined level, keeping the area above clear. In addition all vital installations are probably located above that level.
The example of La Chalupa presents an ideal approach of maintaining a safety zone within the habitat. In the worst case the habitat would be flooded to a “predetermined maximum flooding level” keeping the space between this level and the ceiling with an air pocket. All equipments to cope with that kind of emergencies should be located within that zone.
If the habitat is NOT operating under ambient pressure, but 1bar internal pressure (like a submarine), things are quiet different. In case of entire flooding the water would not stop to rise at the breach point, but would continue to rise and compress the rest air until it reaches ambient pressure. For example: in case of total flooding of a habitat with an internal pressure of 1bar at a depth of 30m (=4bars) the air inside the safety zone would be compressed to 75%. Water would fill ¾ or 75% of this zone and leave ¼ or 25% of the space with air. Since we are not planning an 1bar environment, this possibility is of less importance.
The safety zone should contain control electronics, accumulators, communication systems and emergency lighting by standard. Additionally there should be equipment to be used only in cases of emergency: fire extinguishers, emergency water and food supply, rescue blankets, first aid kits, air supply and written emergency instructions.
It can be recommended to build all other devices in a vertical shape with its vital parts or electronics in the upper areas, preferably reaching the safety zone. A proposal for the device racks was the column shape. For example: while air inlets and cooling valves of the air dehumidifier would be located in the lower part of the rack the upper part reaching into the safety zone at 2m height would contain the electronics. In the event of a hull breach through one of the window openings, water would rise until 2m height leaving the electronics unharmed.
The column racks should be mounted on a ball bearing in order to be turned for maintenance. If the racks are standardized they can be easily developed on shore and implemented into the habitat without problems. The column racks could consist of transparent areas for visual checkups. Parts of them should be watertight and only reachable from the top of the case.
- no hull penetrations in the upper part of the shell
- all cable and pipe penetrations of the hull have to be reinforced by steel rings welded around the opening
- control electronics, accumulators, communication systems and emergency lighting are located in the safety zone
- fire extinguishers, emergency water and food supply, rescue blankets, first aid kits, air supply and written emergency instructions.
- clear design of ballast compartments to prevent the habitat from capsize
- any object that could be swept away during a water ingress and cause damage to other facilities or group members should always be well stowed and/or reliably secured.
The emergency procedures for a case of habitat flooding should include:
- controlling most probable sources of influx (like list map of openings and fittings)
- optimal way of searching and detecting other potential sources
- optimal ways of over-sealing a breach
- discard water
- retreat to safe area and seal its entrance
- communication to surface/land support
- evacuation to decompression chamber
- starting decompression sequence
Please feel free do use the comment box below to contribute your idea.
Image by CalamarPark