Chapter 3 – Control of Ventilation
Clasification Society 2024 - Version 9.40
Statutory Documents - IMO Publications and Documents - Circulars - Maritime Safety Committee - MSC.1/Circular.1321 – Guidelines for Measures to Prevent Fires in Engine-Rooms and Cargo Pump-Rooms – (11 June 2009) - Annex – Guidelines for Measures to Prevent Fire in Engine-Rooms and cargo Pump-Rooms - Part IV – Cargo Pump-Rooms - Chapter 3 – Control of Ventilation

Chapter 3 – Control of Ventilation

Parent topic: Part IV – Cargo Pump-Rooms

1 Design criteria of ventilation systems

  .1 cargo pump-rooms should be mechanically ventilated and the capacity should be 20 air changes per hour of the total volume of the pump-room;

  .2 the position of the vent outlet should be arranged at a distance of at least 3 m measured horizontally from any ignition source and from the nearest opening to accommodation, service or machinery spaces;

  .3 an emergency intake located about 2 m above the pump-room lower grating is to be provided. This emergency intake is to be used when the lower intake is sealed off due to flooding in the bilges. The emergency intake should have a damper fitted which is capable of being closed from the exposed main deck and lower grating level;

  .4 floor gratings should not disturb the free flow of air; and

  .5 normally, the density of petroleum product vapours are heavier than air (x 2), however, the density of diluted gas/air mixture is closer to air (x 1.5). Therefore, vapour density and pump-room temperature should be carefully considered for the design of the ventilation arrangement.

2 Gas detection systems

2.1 Design requirements

  .1 sampling lines should not run through gas-safe spaces;

  .2 gas analysing units located in dangerous areas should be of the explosion-proof type;

  .3 gas sampling pipes should be equipped with flame arresters;

  .4 sampling points should be located in zones where air circulation is reduced (dead spots such as recessed corners);

  .5 the following should be considered in selecting hydrocarbon gas detector and detection positions in cargo pump-rooms:

  • 5.1 shape of the cargo pump-room; and

  • 5.2 placement of exhaust duct considering the flow characteristics;

  .6 if necessary, actual demonstration tests or computational simulation analysis should be carried out;

  .7 a hydrocarbon gas detector is recommended to be installed in the following places:

  • .7.1 (perpendicular) upper part of the main cargo pump or between two cargo pumps;

  • .7.2 one detector within 30 cm above the lowest part of the cargo pump-room bottom floor; and

  • .7.3 one detector every 10 m length or width of the cargo pump-room;

  .8 sequential sampling is acceptable as long as it is dedicated to the pump-room, including exhaust ducts, and if the sampling time is reasonably short;

  .9 sample gas should be provided with or connected to the analysing unit for regular calibration, otherwise calibration records carried out by a specialist should be kept on board; and

  .10 sampling tubing should be resistant to water and cargo vapour.

2.2 The setting value

  .1 audible and visual alarms should be activated by the hydrocarbon gas with the concentration of a pre-set level which is no higher than 10% of the lower flammable limit (LFL);

  .2 the setting value should be set carefully, because LFL of a mixture of hydrocarbon gases changes according to their mixing ratio;

  .3 in the case of a ship carrying two or more cargoes, the set value of an alarm point should be corrected based on the lowest LFL of each cargo, and the following information and equipment should be provided:

  • .1 LFL data of cargo from shippers, etc.; and

  • .2 gas detectors with function to allow adjustment of the alarm setting.

2.3 System arrangement

Copyright 2022 Clasifications Register Group Limited, International Maritime Organization, International Labour Organization or Maritime and Coastguard Agency. All rights reserved. Clasifications Register Group Limited, its affiliates and subsidiaries and their respective officers, employees or agents are, individually and collectively, referred to in this clause as 'Clasifications Register'. Clasifications Register assumes no responsibility and shall not be liable to any person for any loss, damage or expense caused by reliance on the information or advice in this document or howsoever provided, unless that person has signed a contract with the relevant Clasifications Register entity for the provision of this information or advice and in that case any responsibility or liability is exclusively on the terms and conditions set out in that contract.