Gas Analysing Equipment:
5.27 Are portable gas and oxygen analyser appropriate to the cargoes being carried and are they in good order and is there a record of regular testing and calibration?
Tankers shall be equipped with at least one portable instrument for measuring oxygen and one for measuring flammable vapour concentrations, together with a sufficient set of spares. Suitable means shall be provided for the calibration of such instruments. (SOLAS II-2/4.5.7.1) Notes: Each vessel should carry at least two each oxygen, % volume hydrocarbon, LEL and toxic gas analysers. Personal oxygen and hydrocarbon analysers, which can be carried in a pocket or on a belt, should be available for tank, enclosed space or pump room entry.
The manufacturers’ recommended
intervals for servicing the equipment ashore must be observed and procedures in place for the
replacement of parts such as filters, at the manufacturers’ recommended intervals.
Use of a self-test facility does not necessarily mean that an analyser is operating correctly. An instrument may self-test satisfactorily, but then fail to register a lack of oxygen or the presence of gas. The only way to be sure that a machine is operating satisfactorily is to use a sample check gas.
5.28 Are officers familiar with use and calibration of portable oxygen and hydrocarbon analysers?
Notes: A procedure must require that all oxygen and hydrocarbon analysers are checked for correct operation before each use. Nitrogen must generally be used when calibrating oxygen analysers, but some multiple function analysers use a test gas which serves all the functions of the analyser with one sample gas and which has oxygen content of 20.9%.
In the case of hydrocarbon gas analysers, the correct test gas specified in the manufacturers’
documentation must be used and officers must know what the result of using that test gas should be. This applies to each type of analyser on board. As above, some multiple function analysers use a test gas which tests all the functions with one sample gas.
5.29 Is span calibration gas available for the types of fixed and portable analysers on board? 5.30 On vessels fitted with an inert gas system, are instruments capable of measuring hydrocarbon content in an oxygen deficient atmosphere available and in good order?
Notes: Vessels equipped with inert gas should in addition to the analysers in question 5.31 carry two analysers capable of measuring hydrocarbon content in an inert atmosphere. Personnel should ensure that the analyser being used for measuring hydrocarbon content in an inert gas atmosphere is in fact capable of doing so accurately. An example of an analyser specifically designed to do so is the MSA Tankscope. Analysers which measure hydrocarbons using an infra-red principle are designed for use in oxygen-deficient atmospheres. If this type of instrument is provided, a Tankscope is not required to be carried. In cases where a vessel is not fitted with an inert gas system, but does employ nitrogen blanketing, these instruments must be provided.
5.31 Where toxic gases may be encountered, are appropriate toxic gas detection analysers available and in good order?
Many crude oils come out of the well with high levels of H2S, but a stabilisation process usually reduces this level before the crude oil is delivered to the ship. However, the amount of stabilisation may be temporarily reduced at times and a tanker may receive a cargo with an H2S content higher than usual or expected. In addition, some crude oils are never stabilised and always contain high levels of H2S. H2S can also be encountered in refined products such as naphtha, fuel oil, bunker fuels, bitumens and gas oils. Cargo and bunker fuels should not be treated as free of H2S until after they have been loaded and the absence of H2S has been confirmed by both the results of monitoring and the relevant MSDS information. (ISGOTT 2.3.6.1) The use of personal H
2
S gas monitoring instruments by personnel engaged in cargo operations is strongly recommended. (ISGOTT 2.3.6.4) Notes: Two toxic gas detectors are required on vessels carrying noxious liquids. There should be an adequate supply of chemical indicator tubes (e.g. Draeger tubes), or other electronic equivalents specific to the cargoes being carried and they should be within their expiry date. An up to date inventory of chemical indicator tubes should be maintained. Personnel should be aware that some instrument sensors could be poisoned if exposed to high concentrations of CO
2.