3.14 Instrumentation and alarms ( regulation 62.16 to .19 )
Clasification Society 2024 - Version 9.40
Statutory Documents - IMO Publications and Documents - Specifications and Manuals - Inert Gas Systems - 3 Function and Design Considerations - 3.14 Instrumentation and alarms (regulation 62.16 to .19)

3.14 Instrumentation and alarms ( regulation 62.16 to .19 )

  3.14.1 Certain fixed and portable instruments are required for the safe and effective operation of an inert gas system. It is desirable that all instruments should be graduated to a consistent system of units.

  3.14.2 Clear instructions should be provided for operating, calibrating and testing all instruments and alarms. Suitable calibration facilities should be provided.

  3.14.3 All instrumentation and alarm equipment required in compliance with regulation 62 should be suitably designed to withstand supply voltage variation, ambient temperature changes, vibration, humidity, shock, impact and corrosion normally encountered on board ships.

  3.14.4 The arrangement of scrubber instrumentation and alarm should be as follows:

  • .1 The water flow to the scrubber should be monitored either by a flow meter or by pressure gauges. An alarm should be initiated when the water flow drops below the designed flow requirements by a predetermined amount and the inert gas blowers should be stopped automatically in the event of a further reduction in the flow. The precise setting of the alarm and shutdown limits should be related to individual scrubber designs and materials.

  • .2 The water level in the scrubber shall be monitored by a high water level alarm (see regulation 62.19.1.2). This alarm should be given when predetermined limits are reached and the scrubber pump shut down when the level rises above set limits. These limits should be set having regard to the scrubber design and flooding of the scrubber inlet piping from the boiler uptakes.

  • .3 The inert gas temperature at the discharge side of the gas blowers shall be monitored. An alarm should be given when the temperature reaches 65°C and automatic shutdown of the inert gas blowers should be arranged if the temperature reaches 75°C.

  • .4 If a precooler is necessary at the scrubber inlet to protect coating materials in the scrubber, the arrangements for giving an alarm in .3 above should apply to the outlet temperature from the precooler.

  • .5 To monitor the scrubber efficiency, it is recommended that the cooler water inlet and outlet temperatures, and the scrubber differential pressures are indicated.

  • .6 All sensing probes, floats and sensors required to be in contact with the water and gas in the scrubber should be made from materials resistant to acidic attack.

  3.14.5 For the deck water seal, an alarm should be given when the water level falls by a pre-determined amount but before the seal is rendered ineffective. For certain types of deck water seals, such as the dry type, the water level alarm may require to be suppressed when inert gas is being supplied to the inert gas distribution system.

  3.14.6 The pressure of the inert gas in the inert gas main shall be monitored (see regulation 62.19.1.9). An alarm should be given when the pressure reaches the set limit. The set limit should be set having regard to the design of cargo tanks, mechanical nonreturn valve and deck water seal.

  3.14.7 The arrangement for oxygen analyser, recorder and indicating equipment should be as follows:

  • .1 The sampling point for the oxygen analyser and recorder unit should be located at a position in the pipework after the blowers and before the gas pressure regulating valve specified in regulation 62. At the chosen position turbulent flow conditions should prevail at all outputs of the blowers. The sample point should be easily accessible and be provided with suitable air or steam cleaning connections.

  • .2 The sampling probe should incorporate a dust filter in accordance with the instrument manufacturer's advice. The probe and filter should be capable of being withdrawn and cleaned or renewed as necessary.

  • .3 The sensing pipe from the sampling probe to the oxygen analyser should be so arranged that any condensation in the sensing pipeline does not prevent the gas sample reaching the oxygen analyser. Joints in the pipeline should be kept to a minimum to prevent the ingress of air.

  • .4 Any coolers required in the sensing pipes should be installed at the coldest point in the system; alternatively, in certain instances it may be prudent to heat the sensing pipes to prevent condensation.

  • .5 The position of the analyser should be so chosen that it is protected from heat and adverse ambient conditions, but it should be placed as close as practicable to the sampling point to reduce the time between the extraction of a sample and its analysis to a minimum.

  • .6 The recording unit and repeater indication required by regulation 62.16 should not be located in positions subject to heat and undue vibration.

  • .7 The resistance of the connecting cables between the analyser and the recorder should be in accordance with the instrument manufacturer's instruction.

  • .8 The oxygen analyser should have an accuracy of ± 1% of the full-scale deflection of the indicator.

  • .9 Dependent on the principle of measurement, fixed zero and/or span calibration arrangements should be provided in the vicinity of the oxygen analyser fitted with suitable connections for portable analysers.

  3.14.8 A sampling point should be provided between the automatic gas pressure regulating valve and the deck water seal for use with portable instruments.

  3.14.9 The inert gas pressure sensor and recorder should obtain the signal from a point in the inert gas main between the deck isolating/nonreturn valve and the cargo tanks (see regulation 62.16.1).

  3.14.10 When the pressure in the inert gas main forward of the nonreturn devices falls below 50 mm water gauge means shall be provided to give an audible alarm or to shut down the main cargo pumps automatically (see regulation 62.19.8).

  3.14.11 The alarms required by regulation 62.19.1.7 should be given on the navigating bridge and in the machinery space.

  3.14.12 In accordance with regulation 62.17 portable instruments shall be provided for measuring oxygen and flammable vapour concentration. With regard to the hydrocarbon vapour meter, it should be borne in mind that meters working on the catalytic filament principle are unsuitable for measuring hydrocarbon concentration in oxygen-deficient atmospheres. Furthermore, meters using this principle cannot measure concentrations of hydrocarbon vapours above the lower flammable limit. It is, therefore, advisable to use meters using a principle which is not affected by oxygen deficiency and which are capable of measuring hydrocarbon concentration in and above the flammable range. For measuring below the lower flammable limit, provided sufficient oxygen is present, the catalytic filament meter is suitable.

  3.14.13 All metal parts of portable instruments and sampling tubes requiring to be introduced into tanks should be securely earthed to the ship structure while the instruments and sampling tubes are being used. These portable instruments should be of an intrinsically safe type.

  3.14.14 Sufficient tubing etc. should be provided to enable fully representative sampling of a cargo tank atmosphere to be obtained.

  3.14.15 Suitable openings should be provided in cargo tanks to enable fully representative samples to be taken from each tank. Where tanks are subdivided by complete or partial wash bulkheads, additional openings should be provided for each such subdivision.


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.