When carrying coal cargoes, it is vital to obtain accurate gas measurements to determine the correct ventilation requirements, and in this video West P&I Club explains the proper way for gas measurement of coal cargoes.
According to West Club, coal may self-heat or emit significant amounts of methane, and occasionally, it may do both. Incorrect ventilation can also lead to cargo fire or cargo explosion, which makes it crucial to obtain accurate gas measurements to determine the correct ventilation requirements.
While this may appear straight forward, West Club’s experience is that these measurements are often not taken correctly.
To enable accurate readings the multi-gas detection meter must be correctly serviced calibrated and regularly bump tested, and gas readings must be taken via the fitted sampling points.
Operators should follow these steps to get an accurate gas reading:
- Insert the spark proof metal tube into the sampling point and ensure an airtight seal;
- Connect the sampling tube;
- Draw a sample until steady readings are obtained;
- Record the results;
- Replace the sealing cap;
- Oxygen carbon monoxide and hydrogen sulfide levels can be read directly with any meter and at any hold atmosphere.
What is more, methane levels can be unreliable if the hold atmosphere oxygen level falls to 10 or less, so the following steps need to be taken to ensure a correct methane reading:
- If your meter has an infrared sensor you can be assured that the methane reading will be correct at all hold oxygen levels and you can rely on the normal sampling results for all gases;
- If your meter has a catalytic sensor fitted you must check the hold oxygen level; if this is 10 or less then it is necessary to take dilution readings for oxygen and methane;
- For oxygen take both normal and dilution readings;
- For methane only dilution readings are required. If a diluted fitment is provided follow manufacturer’s instructions alternatively dilution readings can be taken using a splitter.
To use a splitter follow this procedure:
- Ensure all connections are airtight;
- Keep both tubes in the fresh outside air and draw a sample until the reading is steady at zero percent;
- Connect one tube to the sampling point and leave the other tube in fresh air run until a steady reading of methane level is obtained;
- Record the dilution readings for methane level and oxygen level;
- Remove the splitter and connect a single tube between the meter and the sampling point;
- Draw a sample until gas levels are steady;
- Record the whole atmosphere oxygen carbon monoxide and hydrogen sulfide levels to correct the methane reading.
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