Section 16 Ventilation of the process plant and other spaces associated with the process plant operation

16.1.1 An efficient means of ventilation is to be provided for all enclosed compartments associated with the operation of the process plant.

16.1.2 The capacity of the ventilation systems is to comply with the requirements of Pt 5, Ch 15, 1.7 Arrangements for fixed hydrocarbon gas detection systems in double hull and double bottom spaces of oil tankers of the Rules for Ships for Liquefied Gases, or Chapter 12 of the Rules for Ships for Liquid Chemicals, where applicable, or to an acceptable Code of Practice suitably modified and/or adapted where necessary to suit the marine environment. It is to be related to the hazard and/or environmental consideration of manned spaces during normal operation, and take into account additional requirements which may be necessary during start-up procedures.

16.2.1 Hazardous compartments where flammable and/or toxic substances are being processed or produced are to be arranged for underpressure ventilation, except as stated in Pt 7, Ch 2, 10.2 Design and construction 10.2.4.

16.2.2 Safe compartments, including control rooms, are to be arranged for overpressure ventilation.

16.2.3 The number and capacity of fans are to be such that the minimum ventilation capacity required in each compartment is maintained at all times, with one unit out of service. If internal combustion engines are proposed, their fuel supply is to be kept separate from any other system. Electric motors are to be supplied by two alternative circuits, each of which is capable of supplying all the motors which are normally connected to that circuit and which are operated simultaneously.

16.2.4 The mechanical ventilation system is to be capable of being controlled from a position outside the compartment being ventilated.

16.2.5 Reduction of ventilation capacity below the required level should be indicated in the compartment and also in the control room by an audible and visible alarm.

16.2.6 The parts of the rotating body and of the casing of each fan situated in a hazardous space are to be made of recognised spark-proof materials. If non-metallic materials are used, they are to have anti-static properties.

16.2.7 Ventilation trunking or ducting is to be suitably coated or painted, or made from material suitable for the substances processed or produced, or any combination of the substances which might result from accidental admixture.

16.3.1 The air inlets for the ventilation systems are to be located in a designated safe area.

16.3.2 The air inlets and discharges of the ventilation system are to be so situated that recirculation of the vented vapours does not occur.

16.3.3 The discharges from ventilation systems which may contain vapours that present a hazard due to reaction with each other are to be effectively segregated.

16.3.4 The discharges from ventilation systems which may contain hazardous vapours are to be located not less than 10 m from the nearest air intake or opening to accommodation, service and control station spaces or other safe spaces, and from all possible sources of ignition.

16.3.5 Air intakes and openings into the accommodation spaces and all service and control station spaces are to be fitted with closing devices. For toxic gases, these devices are to be operable from inside the space.

16.3.6 Where it is impracticable to locate a plant service or control station so that any access thereto is from a safe space, the service or control station is to be maintained at an overpressure of not less than 5 mm water gauge above the surrounding spaces. Details of the arrangements to ensure that this pressure differential is maintained are to be submitted.

16.3.7 Airlocks for intercompartmental access doors and emergency escape trunks are to have separate ventilation systems so arranged that an overpressure of 5 mm water gauge is maintained above the adjacent compartments. Details of the arrangements to ensure that this pressure differential is maintained are to be submitted.

16.4.1 The ventilation systems are to be installed to the Surveyor's satisfaction.

16.4.2 The Surveyors are to be satisfied that the ventilation system is capable of maintaining a safe environment during process plant operation. This may require monitoring over an extended period to prove its effectiveness.