Atmospheric diving suit


An atmospheric diving suit, atmospheric pressure diving suit or single atmosphere diving suit is a small one-person articulated submersible which resembles a suit of armour, with pressure-tight joints to allow articulation while maintaining a constant internal volume and an internal pressure of one atmosphere. An ADS can enable diving at depths of up to for many hours by eliminating the majority of significant physiological dangers associated with deep diving. The occupant of an ADS does not need to decompress, and there is no need for special breathing gas mixtures, so there is no danger of decompression sickness or nitrogen narcosis when the ADS is functioning properly. An ADS can permit less-skilled swimmers to complete deep dives, albeit at the expense of dexterity.
Atmospheric diving suits in current use include the Newtsuit, Exosuit, Hardsuit and the WASP, all of which are self-contained hard suits that incorporate propulsion units. The Hardsuit is constructed from cast aluminum ; the upper torso hull is made from cast aluminum, while the bottom dome is machined aluminum. The WASP is of glass-reinforced plastic body tube construction.

Definition and classification

An atmospheric diving suit is a small one-person submersible with articulated limbs encasing the diver. Water- and pressure-tight joints allow articulation while maintaining an internal pressure of one atmosphere. Mobility may be through thrusters for mid-water operation, though this is not a requirement, and articulated legs may be provided for walking on the substrate.
Thornton distinguishes an ADS from a submersible in that the ADS has human powered articulated limbs, as opposed to remotely operated articulated limbs. It is not clear whether this would exclude servo-assisted limbs encasing those of the operator, as a powered exoskeleton, but it might be reasonable to include them as atmospheric diving suits.
An atmospheric diving suit may be classified as a crewed submersible and a self-propelled, crewed, one-atmosphere underwater intervention device, but has also been classified as an atmospheric diving system.
A characteristic of single atmosphere internal pressure is that the suit cannot passively vent gas to ambient pressure. The options are to recycle breathing gas internally, adding oxygen and removing carbon dioxide, to vent surface supplied gas back to the surface through a hose which can safely withstand the external ambient pressure, or to pump it out by compressing it to ambient pressure before venting.

Purpose and requirements

The underwater environment exerts major physiological stresses on the diver, which increase with depth, and appear to impose an absolute limit to diving depth at ambient pressure. An atmospheric diving suit is a small submersible with a pressure hull which accommodates a single occupant at an internal pressure of about one atmosphere. The provision of hollow arm spaces with pressure-resistant joints to carry manually operated manipulators, and usually separate leg spaces, similarly articulated for locomotion, makes a suit resemble a bulky suit of plate armour, or an exoskeleton, with elaborate joint seals to allow articulation while maintaining internal pressure.
An atmospheric diving suit is equipment intended primarily to isolate the occupant from the ambient pressure of the underwater environment, and provide any necessary life-support while the suit is in use. While using the suit, the diver will expect to perform useful work, and get to and from the place where the work is to be done. These functions require sufficient mobility, dexterity and sensory input to do the job, and this will vary depending on the details of the work. Consequently, the work possible in an atmospheric suit is limited by the suit construction.
Mobility at the surface and on deck can be managed by launch and recovery systems, Mobility underwater generally requires neutral or moderately negative buoyancy, and either the ability to walk or swim, or the use of finely controllable thrusters. Both walking and thruster propulsion have been applied with some success. Swimming has not been effective.
The dexterity to perform useful work is limited by joint mobility and geometry, inertia, and friction, and has been one of the more difficult engineering challenges. Haptic perception through manipulators is a major limitation on finer control, as the friction of the joints and seals greatly reduces the sensitivity available.
Operator visual input is relatively easy to provide directly by using transparent viewports. A wide field of view can be achieved simply and structurally effectively by using a transparent partial dome over the diver's head. Close-up views of the manipulators are limited by joint flexibility and geometry of the suit's arms. External sound and temperature perception are greatly attenuated, and there is no sense of touch through the suit. Communications must be provided by technology, as there is normally no-one else in the immediate vicinity.

Design constraints

The main environmental factors affecting design are the ambient hydrostatic pressure of the maximum operating depth, and ergonomic considerations regarding the potential range of operators. The structure and mechanics of the suit must reliably withstand the external pressure, without collapsing or deforming sufficiently to cause seals to leak or joints to experience excessive friction, and the full range of movement must not change the internal or external displaced volume, as this would have consequences for the amount of force required to move the joints in addition to the friction of the joint seals. Insulation is relatively simple, and can be applied to the inside of the suit and in the form of clothing on the diver. Active heating and cooling are also possible using well established technology. Mass changes can be used to provide initial and emergency buoyancy conditions by way of fixed and ditchable ballast weights.
Ergonomic considerations include the size and strength of the user. The interior dimensions must fit or be modifiable to fit a reasonable range of operators, and operating forces on joints must be reasonably practicable. The field of vision is constrained by the helmet design or viewport positioning, though closed circuit video can extend it considerably in any direction. General underwater conditions of visibility and water movement must be manageable for the range of conditions in which the suit is expected to be used. Marine thrusters may be mounted on the suit to help with maneuvering and positioning, and sonar and other scanning technologies may help provide an augmented external view.
Factors affecting the design and construction:
  • Pressure hull form – Sufficient volume for necessary internal systems, constrained by size and shape of human operator, and by shapes with high resistance to collapse under external pressure.
  • *Displacement – Need for neutral buoyancy at work and positive buoyancy in emergencies
  • *Hydrodynamics – cruise speed
  • *Propulsion – Thruster type and arrangement
  • *Ergonomics – Anthropometry, joint design for limb articulation under external pressure.
  • Working depth rating – Strength, rigidity and density of materials. Buckling, constant volume, and joint friction limiting factors
  • *Construction materials
  • *Safety .

    Systems

Systems usually include:
On-board life-support:
  • Breathing gas supply, monitoring and recycling
  • *Monitoring of oxygen partial pressure, carbon dioxide level
  • *Carbon dioxide scrubbing
  • *Oxygen replenishment, oxygen storage cylinders
  • *Emergency rebreather circulation systems.
  • Thermal management
Buoyancy and trim ballast systems:
  • Control of basic buoyancy
  • Adjustment of trim – control of the positions of centre of gravity and centre of buoyancy.
  • Compensating trim and buoyancy for payload effects.
  • Achieving stability when submerged and in emergency Compensation for variations in water density due to stratification.
  • Compensation for pressure effects.
  • Adjustable and ditchable ballast systems.
Movement, propulsion, and navigation systems:
  • Propulsion systems, thrusters.
  • Control of vertical, lateral and forward movement, and rotation and orientation in three dimensions.

    Safety and emergencies

Classes of emergency:
  • Fires and fire extinguishing methods.
  • Leaks and flooding.
  • Entanglement.
  • Life-support system failures, toxic hazards.
  • Loss of communications and emergency communications options
  • Loss of power and sensors.
There are also physiological and psychological effects of prolonged isolation underwater due to sensory deprivation and thermal stress.

Operating skills and procedures

Operator skills:
  • Standard operating procedures:
  • * Buoyancy set up of the suit
  • * Flying in and around underwater structure
  • * Reporting life support system readings while hovering
  • * Through-water communications protocols
  • * Rigging preparation and rigging work
  • ** Connecting the umbilical to a down-line
  • ** Attaching a shackle to work on the bottom and in mid-water
  • ** Use of buoyant lifting bags
  • * Carrying loads and managing a tool basket
  • * Use of powered underwater tools
  • * Underwater measurement
  • Emergency procedures:
  • * Climbing the umbilical in the event of power loss, entrapment)
  • * Emergency jettison systems

    Work skills

These may include submarine rescue, salvage, inspection and non-destructive testing, and typical oilfield construction and maintenance tasks, or a range of scientific observation and sampling activities.

Operator requirements

  • The operator must fit inside the suit, be able to move their limbs effectively, and be able to get out again.
  • The operator must be able to reach and to operate electronics panels and life support systems, be able to jettison ballast, operate umbilical and thruster cable cutters.
  • The operator must be physically, medically and psychologically fit for the work.