Section 3 System arrangements

3.1.1 The design of air-conditioning and ventilation systems is to reflect the total ship design including any requirements of the System Design Description, specified subdivision and stability standard, fire safety standard or other particular features stipulated in the standards specified for the ship.

3.1.2 The design and capability of supply and exhaust systems for ventilation purposes are to address the following requirements as applicable:

1. Noxious odours, toxic and dangerous fumes or other contaminants are to be extracted, taking into account any requirements of the CBRN System Design Description.

2. Acceptable levels of fresh air are to be provided for personnel efficiency, combustion or other oxidation processes. The arrangements are to ensure that maximum CO₂ levels are not exceeded in all spaces where crew and embarked personnel are likely to be.

   1. a maximum CO₂ level of 1200 ppm is to be adopted. A gas detection system in accordance with Vol 2, Pt 9, Ch 11 Gas detection is to be provided where 100 per cent recirculation is adopted for any ship operational requirement.

   2. a minimum fresh air flow of 5 litres/s/man is to be capable of being supplied to all spaces intended for crew and embarked personnel.

3. In a fire situation within an autonomous zone, smoke migration is to be restricted to prevent ingress into compartments essential for the operational capability of the ship in a fire situation.

4. Acceptable internal ambient conditions are to be maintained for personnel comfort in manned compartments and in other compartments where required for equipment cooling. The arrangements for maintaining acceptable ambient conditions are to take account of the range of climatic conditions that the ship is required to operate within and are to be included in the System Design Description required by Vol 2, Pt 11, Ch 2, 1.3 Documentation required for design review 1.3.2.

5. Systems are to be arranged so that as far as is practicable they serve like compartments from the same sub-systems.

6. If the vessel is divided into autonomous zones, the systems are to be designed so that they do not cross over from one zone boundary to another.

7. In the case of vessels designed for CBRN Protection, the system is to be designed to maintain the vessel at an overpressure relative to the outside ambient pressure. The system is also to provide a breathable atmosphere, minimising CO₂ levels with the maximum ship's complement. Odour filtration is to be provided for all those areas that are likely to produce foul smells and are subject to recirculation in closedown, e.g. bathrooms, toilets, galleys. See Vol 2, Pt 1, Ch 3, 4.12 Guidance for CBRN protection, detection and monitoring for CBRN Protection guidance.

8. The systems are to be designed to maintain the vessel’s watertight integrity and, for ships with CBRN Protection arrangements, gastight integrity.

9. Systems are to be designed to enable inspection, cleaning and maintenance in accordance with the designer’s and equipment manufacturer’s recommendations.

3.1.3 Exhausts from clean workshops may be returned to the ship's recirculation system via suitable filter arrangements. However, the air conditioning system is not to be used for dust extraction from woodworking machinery, etc. Independent extraction systems are to be used for this purpose. Similarly, fumes from welding bays, etc. are to be exhausted to atmosphere.

3.1.4 Exhausts from sewage treatment spaces are normally to be led to atmosphere. Where identified in the System Design Description, exhausts may be led to the ship’s recirculation system but means of isolation to the recirculation system with alternative exhaust to atmosphere arrangements are to be provided to cater for abnormal plant conditions.

3.1.5 Exhausts from storerooms containing non-hazardous materials may be returned to the ship's recirculation system.

3.1.6 Exhaust arrangements from machinery spaces, pump room, aircraft and vehicle decks are to be led to atmosphere.

3.1.7 All openings in weatherdeck boundaries are to be fitted with grilles to avoid ingress of debris. Consideration is to be given to weatherdeck openings to prevent downflooding.

3.1.8 Facilities are to be provided to ensure that weatherdeck openings remain clear of ice when the ship is operating in the coldest climate for which it is designed.

3.1.9 In compartments or spaces with low noise targets or in operational spaces, accommodation, working or office areas, the design of the distribution system is to be such as to minimise noise generation.

3.2.1 The design of ventilation arrangements to magazines is to minimise the risk of explosion. Where fitted, exhausts from magazines are to be led to atmosphere.

3.2.2 Systems serving compartments containing flammable stores (e.g. paint stores) or potentially explosive gases (including battery charging rooms, oxygen bottle stores and magazines) are to be fitted with flameproof gauzes and isolating valves in these branches. The systems serving such compartments are to be independent of those supplying other spaces. Fans supplying and extracting air to/from such compartments are to be spark resistant as a minimum, see Vol 2, Pt 7, Ch 4, 3.3 Non-sparking fans for hazardous areas. Exhausts are to be led to atmosphere away from other outlets, i.e. fuel tank vents.

3.2.3 Exhausts from compartments containing hazardous materials, including dangerous or noxious gases (e.g. refrigeration machinery), are to be led to atmosphere.

3.2.4 Electrical equipment (including any heating arrangements) for magazines, stores and spaces containing flammable gases and vapours is to comply with Vol 2, Pt 9, Ch 5 Hazardous Areas.

3.3.1 The following arrangements are to be incorporated in ventilation systems within galleys:

1. All trunking is to be of steel or stainless steel.

2. Exhaust terminals above equipment such as fryers, grills, etc, are to be fitted with grease filters that can easily be removed and cleaned.

3. Exhaust branches, fitted with grease filters, are to be protected by fire flaps within the galley. The flaps are to be sited in the exhaust trunking between the canopy and the exit from the galley, arranged to close in the direction of air flow and be readily operable from both within and outside the galley.

4. CO₂ injection or other fire extinguishing means facilities are to be fitted.

Exhaust systems from galleys are normally to be led to atmosphere. In the case of ships fitted with CBRN Protection and when identified in the System Design Description, the galley ventilation system may be designed to recirculate air and, to limit food smells, odour filtration is to be provided. If the exhaust is led to atmosphere in ships fitted with CBRN Protection, the air loss is to be considered when assessing the CBRN arrangements.

3.3.2 In addition to those fitted in galley systems, fire flaps are also to be fitted:

1. In ventilation trunks that pass through designated fire barriers.

2. In ventilation trunks that pass through watertight bulkheads where this penetration occurs within the lines of weathertight and watertight integrity as defined in Vol 1, Pt 3, Ch 2 Ship Design.

3.4.1 Sick bay complexes are to be provided with a dedicated air treatment unit with trunked distribution, fresh air, recirculation and where necessary, exhaust systems.

3.4.2 The arrangements for ventilation of medical compartments are to be such that they are capable of maintaining a positive pressure in relation to the surrounding complex to prevent the ingress of any contaminated air. Similarly, any operating theatres are to have arrangements for providing a relative positive pressure to the adjacent medical spaces.

3.5.1 Welldeck spaces are to be designed with ventilation systems that provide a safe working environment for a defined period of time which in general should be not less than 8 hours.

3.5.2 Guidance for the design of ventilation systems for welldeck spaces can be found in IMO MSC/Circular 729 – Design Guidelines and Operational Recommendations for Ventilation Systems in Ro-Ro Cargo Spaces.

3.6.1 In addition to the requirements in Vol 2, Pt 11, Ch 2, 3.1 General, where the Owner has specified the installation of a smoke clearance system. The design of such a system is to be based on the declared operating philosophy identified in the System Design Description required by Vol 2, Pt 11, Ch 2, 1.3 Documentation required for design review 1.3.2 which, in general, should recognise that smoke clearance is only undertaken when a fire has been extinguished since any attempt to clear smoke before a fire has been extinguished could introduce more air to the fire. Dedicated fixed smoke clearance trunking is to be of steel construction and both this and the fans are to be capable of operating at the temperatures of the exhaust gas from the extinguished fire but, in any case, not less than 250°C. Portable fans of suitable design may also be used with temperature resistant flexible trunking. Clearance of smoke is to be such that unaffected parts of the ship are not contaminated with smoke.