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APPENDIX A ^
Procedures for gas monitoring of coal cargoes

A.1 Observations

Carbon monoxide monitoring, when conducted in accordance with the following recommendations, will provide a reliable early indication of self-heating within a coal cargo. This allows preventive action to be considered without delay. A steady rise in the level of carbon monoxide detected is a conclusive indication that self-heating is taking place.

All ships engaged in the carriage of coal should carry on board an instrument for measuring methane, oxygen and carbon monoxide gas concentrations (requirements for all coals, section A.7.c), so that the atmosphere within the appropriate spaces may be monitored. This instrument should be regularly serviced and calibrated in accordance with the manufacturer’s instructions. When properly maintained and operated, this instrument will provide reliable data about the atmosphere being tested. Care needs to be exercised in interpreting methane measurements carried out in the low oxygen concentrations often found in unventilated cargo holds. The catalytic sensors normally used for the detection of methane rely on the presence of sufficient oxygen for accurate measurement. This phenomenon does not affect the measurement of carbon monoxide, or measurement of methane by infrared sensor. Further guidance may be obtained from the instrument manufacturer.

A.2 Sampling and measurement procedure

A.2.1 Equipment

An instrument is required which is capable of measuring methane, oxygen and carbon monoxide concentrations. The instrument should be fitted with an aspirator, flexible connection and a length of tubing to enable a representative sample to be obtained. Stainless steel tubing approximately 0.5 m in length and 6 mm nominal internal diameter with an integral stainless steel threaded collar is preferred. The collar is necessary to provide an adequate seal at the sampling point.

A suitable filter should be used to protect the instrument against the ingress of moisture as recommended by the manufacturer. The presence of even small amount of moisture will compromise the accuracy of the measurement.

A.2.2 Sitting of sampling points

In order to obtain meaningful information about the behavior of coal in a hold, gas measurements should be made via one sample point per hold. To ensure flexibility of measurement in adverse weather, however, two sample points should be provided per hold, one on the port side and one on the starboard side of the hatch cover (refer to figure A.2.7). Measurement from either of these locations is satisfactory.

Each sample point should comprise a hole of diameter approximately 12 mm positioned as near to the top of the hatch coaming as possible. It should be sealed with a screw cap to prevent ingress of water and air. It is essential that this cap is securely replaced after each measurement to maintain a tight seal.

Due to the particular configurations of Great-Lakes self-unloaders, sampling points could be chosen in other locations provided a reasonable, logical and meaningful gas reading of the atmosphere in the hold can be obtained.

The provision of any sample point should not compromise the seaworthiness of the ship.

A.2.3 Measurement from fixed sampling point

Ensure that the instrument is calibrated and working properly in accordance with the manufacturer’s instructions. Remove the sealing cap, insert the stainless steel tube into sampling point and tighten the integral cap to ensure an adequate seal. Connect the instrument to the sampling tube. Draw a sample of the hold atmosphere through the tube using the aspirator until steady readings are obtained. Log the results on a form, which records cargo hold, date and time for each measurement.

A.2.4 Measurement strategy

The identification of incipient self-heating from measurement of gas concentrations is more readily achieved under unventilated conditions. This is not always desirable because of the possibility of the accumulation of methane to dangerous concentrations. This is primarily, but not exclusively, a problem in the early stages of a voyage. Therefore it is recommended that holds are initially ventilated until measured methane concentrations are at an acceptably low level. For Great Lakes self-unloaders operating on inland voyages only procedures as outlined in 2.7 may be followed.

A.2.5 Measurement in unventilated holds

Under normal conditions one measurement per day is sufficient as a precautionary measure. However, if carbon monoxide levels are higher than 30 ppm then the frequency should be increased to at least twice a day at suitably spaced intervals. Any additional results should be logged.

If carbon monoxide level in any hold reaches 50 ppm a self-heating condition may be developing and the owners of the ship should be notified or For Great Lakes self-unloaders operating on inland voyages only procedures as outlined in 2.7 may be followed.

A.2.6 Measurement in ventilated holds

If the presence of methane is such that the ventilators are required to remain open, then a different procedure should be applied to enable the onset of any incipient self-heating to be detected.

To obtain meaningful data the ventilators should be closed for a period before the measurements are taken. This period may be chosen to suit the operational requirements of the ship, but it is recommended that it is not less than four hours. It is vital in the interests of data interpretation that the shutdown time is constant whichever time period is selected. These measurements should be taken on a daily basis. If the carbon monoxide results exhibit a steady rise over three consecutive days, or exceed 50 ppm on any day, the owners of the ship should be notified.

A.2.7 Measurement and Reporting Procedures for Self Unloaders operating on Inland Voyages only.

For coal loaded in Great Lakes ports it is not uncommon to have CO levels reach as high as 1000 ppm in enclosed areas. Normally the concentrations will peak within approximate 12 hours of loading and gradually decrease over the next few days. Due to the short duration of these voyages reporting procedures are only required if both CO and LEL readings are simultaneously increasing, as this may indicate self heating is occurring. To establish whether such a trend is taking place readings should be taken at least every 4 hours in the first 24 hours of sailing. Otherwise CO readings should, as a minimum, be taken once per day if CO levels are under 50 ppm, at least twice per day if CO levels range from 50 to 500 ppm, and for CO levels in excess of 500ppm readings should be taken once per watch or every 4 hours.

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