Section 8 Air and Gas for Breathing Purposes

8.1.1 The breathing mixture is the mixture of gases being breathed by the occupants of a submersible or any portion of a submersible. Where occupants are breathing directly from the atmosphere in any compartment, then that atmosphere constitutes the breathing mixture.

8.1.2 All the materials used inside a submersible craft and likely to be in contact with the atmosphere, including paints, adhesives, and lubricants, should be carefully examined and where necessary subjected to tests to ensure that as far as is practicable they are unlikely to give off toxic, irritant or disagreeable gases to an undesirable level under normal operating conditions. Autonomous craft will, in addition, usually produce other contaminants (through cooking, air conditioning / ventilation, sanitary tanks, internal lead acid batteries etc.), in sufficient quantities to require further cleansing of the atmosphere. Means of removing these contaminants from the atmosphere should be taken into account when such a craft is designed and built.

8.1.3 Means are to be provided to allow the occupants to check the internal atmosphere for levels of O2 and CO2, and pressure. Other dangerous gases which may occur in autonomous craft e.g. CO, will also require to be monitored. Operation of these instruments should be ensured under all circumstances for the whole duration of the planned dive time plus the survival period.

8.1.4 Instruments to measure the temperature and relative humidity of the one atmosphere manned compartments should be provided except in the case of one-man craft.

8.2.1 Submersible unit must be provided with adequate equipment to maintain a breathable atmosphere. The equipment should provide the highest degree of reliability. It should be capable of operating with suitable efficiency during a failure of the main electrical supply.

8.2.2 Circulation of the breathing mixture should be provided as necessary to prevent any accumulation of flammable or toxic gases and to allow proper operation of the equipment.

8.2.3 Dust filtration or a fine mesh should be provided in the CO2 absorption and ventilation system.

8.3.1 Care must be taken to avoid the use of materials which are safe at atmospheric pressure but become flammable when subjected to high levels of oxygen. Similarly the use of materials which emit toxic gases or which emit toxic gases when subject to fire or excess heat, shall be avoided. The use of PVC or PVC based material should be avoided.

8.3.2 Mercury thermometers and instruments should not be used inside manned enclosures.

8.3.3 All electrical and electronic equipment should be protected and insulated with non-reactive materials.

8.3.4 The partial pressure of dangerous gases should be kept below acceptable limiting values under normal operating conditions.

8.3.5 If a desiccant is used to remove moisture from the atmosphere in a submersible, a material should be used that is non-toxic, non-corrosive and non-flammable.

8.3.6 A wide band toxic contamination level indicator should be used during initial tests and trials to ensure that there is no build-up of toxic vapours in any compartment. They should also be fitted in submersible craft which contain thermal engines or leadacid batteries which emit toxic gases within the pressure hull.

8.4.1 Isobaric diving requirements. Air supplied by bottles to be inhaled during isobaric diving at atmospheric pressure should be constituted in such a manner that a sample, at atmospheric pressure, complies with the following standard:

8.6.1 Where oil lubricated compressors are used for the compression of oxygen or mixed gases containing oxygen, the oil mist should at no time exceed 1 mg/m³ and the maximum pressure and percentage of oxygen which can be handled by the compressor should be stated by the manufacturer. A notice stating the maximum oxygen percentage and pressure is to be posted in a conspicuous position by the compressor.

8.6.2 For all oil lubricated compressors provision is to be made for intercepting and draining oil and water in the compressor discharge for which purpose a separator or filter is to be provided. A notice is to be placed adjacent to the compressor stating that the filters are to be drained before start-up and at regular intervals during running.

8.7.1 Each compression chamber living compartment is to be equipped with an oxygen dosing device and a chamber gas circulating unit in which the CO2 can be absorbed and the air temperature and humidity can be regulated. The rate of circulation shall be such as to satisfy the conditions stated in Pt 5, Ch 4, 9 Pressure, Temperature and Humidity Control.

8.7.2 Chamber atmosphere conditioning should be designed in such a way as there is 100% redundancy of each individual compartments atmospheric conditioning system.

8.7.3 Diving bells are to be equipped with a chamber gas treatment unit and also with an autonomous reserve CO2-absorption unit for emergency use.

8.7.4 Diving bells are to be equipped with a heating system provided with redundant supplies and so designed that the divers in the diving bell and in the water are maintained in a thermal balance. For diving operations at depths greater than 150 m breathing gas pre-heaters are also to be provided for the divers in the water. The heating system shall be fitted with a temperature indicator and suitable safety features are to be provided to prevent over temperature by the heating system.

8.7.5 Measures are to be taken to enable the divers within the diving bell to be maintained in a safe thermal balance for at least 24 hours in an emergency.

8.8.1 The use of closed breathing gas circuits, gas mixing systems for direct breathing gas supply and helium reclaim systems requires LR's approval.

8.9.1 The diving bell is to be provided with its own bottles so that the occupants of the chamber can in an emergency be supplied with a sufficient quantity of breathing gas mixture for at least 24 hours at the maximum operating depth. An oxygen bottle for supplementing the oxygen supply is also to be carried on the diving bell.

8.9.2 The emergency life-support systems are to be capable of operating for the following periods of time:

Special consideration will be given where it is impracticable for these requirements to be complied with.

8.9.3 Built-in breathing appliances such as BIBS with a reserve supply of oxygen or air are to be available to supply the crew and passengers for sufficient time to enable the submersible to surface and be recovered. Consideration should be given to arranging for emergency circulation of the atmosphere of manned compartments, at the rate of 30 air changes per hour for the purpose of clearing smoke, high CO2 levels, etc., following a fire or other accident. Provision is to be made for the absorption of CO2 and where possible, high speed scrubbers are preferred. Maximum partial pressures of toxic gases, equivalent to those of the national threshold limits at atmospheric pressures, are not to be exceeded.

8.9.4 In the case of a habitat the emergency life-support system should be entirely separate from the access chamber system. In one bar chambers where oxygen enrichment could occur means of preventing excess oxygen build up should be considered.