Section 2 Principles for design and construction of diving systems

2.1 General principles

2.1.1 Wherever practically possible, diving systems are to be designed and constructed in such a way that no single point failure can lead to injuries or fatalities of the divers or operating personnel whilst working with the dive system.

2.1.2 Diving systems and their components are to be designed to meet the service conditions stated in the specification of the system.

2.1.3 Diving systems are to be constructed to ensure that persons under pressure can be safely conveyed from the surface compression chamber to the underwater work location (and back).

2.1.4 Diving systems are to be designed and built to ensure safe operation and facilitate proper maintenance and the necessary surveys.

2.1.5 All parts of a diving system are to be designed, constructed and mounted in such a way as to Facilitate cleaning and disinfection.

2.2 Environmental conditions

2.2.1 Diving systems together with their accessories and ancillary equipment are to be designed for the Environmental conditions likely to occur at the proposed Point of installation or work location. As a minimum requirement, allowance is to be made for the following conditions:

The inclined positions stated in Table 1.2.1 Design Angles of Inclination.
The other environmental conditions stated in Table 1.2.2 Environmental conditions.

Table 1.2.1 Design Angles of Inclination

Component/Systems	Angle of Inclination (Degrees)
	Athwart ship/Roll		Fore-and-Aft/Pitch
	Static	Dynamic	Static	Dynamic
PVHOs	15	22.5	10	10
Machinery	15	22.5	5⁽⁴⁾	7.5
Life Support Systems	15	22.5	10	10
Electrical/Electronic Appliances and Control Systems	22.5⁽²⁾	22.5⁽²⁾	10	10
Emergency Power Installations	22.5	22.5	10	10
Emergency Fire Pumps and their Drives	22.5	22.5	10	10
Notes:
1 Athwart ship and fore-and-aft inclinations occur simultaneously.
2 Up to an angle of inclination of 45 degrees, switches and controls are to remain in their last set position.
3 In vessels designed for carriage of liquefied gases and of chemicals, the emergency power installation is to remain operable with the vessel flooded to its permissible athwart ship inclination up to a maximum of 30 degrees.
4 Where the length of the vessel exceeds 100 m the fore-and-aft static angle of inclination may be taken as 500/L degrees, where L is the length of the vessel in meters.
For diving systems installed on column-stabilized, self-elevating or surface offshore facilities, the PVHOs, machinery and systems essential for the safe operation of the diving system are to be designed for operation under the inclinations specified Pt 5, Ch 1 General Requirements for Offshore Units of LR’s Rules for Offshore Units, Table 1.2.1 Inclination of ship units and other surface type units to Table 1.2.3 Inclination of self-elevating units as applicable.

Table 1.2.2 Environmental conditions

Location	Temperature (°C)	Humidity (%)	Other Conditions
In chambers	5 to 55	100	Salty air
Outside chambers in air ¹ ²	-10 to + 55	100	Salty air
Outside chambers in water	-2 to + 32	-	Salt water containing 3.5% salt
Control room	5 to 55	80	-
Notes
1. In the case of the facilities installed on the open deck, allowance is to be made for icing and temporary inundation with salt water and spray.
2. Other values may be permitted for installation in closed spaces.
3. The calculated inclined angles from the actual ship motion analysis can be replaced with the above accelerations.

2.3 Atmosphere conditions in the chambers

2.3.1 Diving systems are to be so equipped that a breathable atmosphere can be maintained in surface compression chambers and diving bells throughout the entire operating period.

2.3.2 Facilities must be provided for keeping the partial pressure of the CO2 in the chamber atmosphere permanently below 0,005 bar assuming a CO2 production rate of 0,05 Nm³/h per diver.

2.3.3 In the case of facilities installed on the open deck, allowance is to be made for icing and temporary inundation with salt water and spray.

2.3.4 Other values may be permitted for installation in closed spaces. In diving bells it must be possible to keep the partial pressure of the CO2 below 0,015 bar as a minimum requirement. Under emergency conditions it must be possible to hold the partial pressure of the CO2 below 0,02 bar for at least 24 h.

2.3.5 Diving systems using mixed gas and designed for operating periods of more than 12 hours at a time must be capable, under steady conditions, of keeping the temperature in the surface compression chamber constant to ±1 °C in the 27 - 36 °C range while maintaining a maximum humidity of at least 50 per cent.

2.3.6 Surface compression chambers are to be designed and equipped in such a way that a homogeneous atmosphere (CO2 and O2 concentrations, temperature and humidity) can be maintained in the chamber.

2.3.7 In the steady state, the permanent noise level (over 8 hours) in the living compartment and surface compression chamber may not exceed 65 dB(A) excluding self-induced noise.

2.4 Interface between diving system and the ship or supporting structure

2.4.1 The diving system and breathing gas facilities should be arranged in spaces or locations which are provided with adequate ventilation and lighting.

2.4.2 When any part of the diving system is sited on deck, particular consideration should be given to providing reasonable protection from the sea, from icing or from any damage which may result from other activities on board the ship or supporting structure.

2.4.3 Provision should be made to ensure that diving systems and ancillary equipment are securely fastened to the ship or supporting structure and consideration given to the relative movement between the components. In addition, the fastening arrangements should be able to meet any required survival conditions.

2.4.4 Diving systems on ships and other floating structures may only be located and operated in areas not subject to an explosion hazard. In exceptional cases, installation subject to special conditions may be permitted in zone 2 area.

2.4.5 As far as possible, the area in which the diving system is installed is to be kept free of fire loads. In addition, only those electrical cables needed to operate the diving system should be routed through this area.

2.4.6 Diving systems and breathing gas storage facilities are not to be located in engine rooms.

2.5 Chamber equipment and fittings

2.5.1 The equipment and fittings of surface compression chambers and diving bells must be suitable for operation in hyperbaric atmospheres. Under these conditions they shall not give off any toxic or strong irritant gases. The same also applies to protective coatings and paints used inside the chambers.

2.5.2 Toxicity off-gas testing is to be carried out on all PVHO’s or Pressure Hulls that have internal paint or contain non-metallic materials excluding acrylic windows.

2.5.3 Off-gas testing is not required for PVHO’s or pressure hulls where the primary means of life support is by ventilation of the atmosphere and/or by BIBS supply such that the off-gassed volatiles are continuously removed and do not accumulate within the pressure boundaries of the PVHOs or pressure hulls.

2.5.4 Gas sample analysis for the off-gas testing is to be conducted by a laboratory that is accredited by an independent third-party as being compliant with an applicable quality assurance standard for laboratories (such as ISO/IEC 17025, ANSI/ASQC Q2 or equivalent.

2.5.5 Only incombustible or at least flame and fire retardant materials should be used in the chambers.

2.6 Corrosion protection

2.6.1 Diving systems and all their accessories are to be effectively protected against corrosion, see Pt 4, Ch 3 Corrosion Protection.

2.6.2 Anti-corrosion coatings exposed to the conditions within the chambers must confirm to the requirements stated in Pt 4, Ch 3 Corrosion Protection. In addition they may not tend to blister or flake under hyperbaric conditions.