Look for a pattern, not just a number
Coal monitoring is most useful when it helps a ship’s team detect a change early and explain what that change means. The IMSBC Code identifies carbon monoxide (CO) monitoring as an early indication of self-heating when conducted according to its procedures. It also cautions that methane, oxygen and CO all matter: the atmosphere must be assessed as a whole, not reduced to a single gas reading. The Code describes a steadily rising CO level as an indication that self-heating is taking place. That makes the direction of readings over time important alongside the latest value.
Before loading, the temperature of coal identified as likely to self-heat is to be monitored; the Code says it is to be accepted for loading only when its temperature is no higher than 55°C. This pre-loading check complements, rather than replaces, voyage monitoring. A useful handoff therefore gives the ship’s team cargo information and precautions as well as an agreed way to capture and compare measurements. The Code’s broader purpose is to support safe stowage and shipment of solid bulk cargoes through information on cargo dangers and procedures for carriage.
International Maritime Solid Bulk Cargoes (IMSBC) Code · MSC.539(107): 2023 Amendments to the International Maritime Solid Bulk Cargoes (IMSBC) Code
Make each reading comparable
A trend is only meaningful if the readings are taken and recorded consistently. For coal carriage, the Code calls for an onboard instrument capable of measuring methane, oxygen and carbon monoxide, serviced and calibrated according to the manufacturer’s instructions. Its sampling procedure uses an aspirator, flexible connection and spark-proof metal tubing to draw a representative sample from the hatch area. The sample is drawn until the instrument gives steady readings; the results, cargo space, date and time are logged, and the sampling point is capped again.
Sampling-point arrangements matter too. The Code describes two points per cargo space—one on each side of the hatch cover or coaming—to provide flexibility in adverse weather, with measurement from either point considered satisfactory. The points are sealed to prevent air and water entering, and the cap is replaced after each measurement. These details help preserve comparable conditions and protect the quality of the record. The Code also warns that moisture can compromise measurement accuracy and that catalytic methane sensors rely on sufficient oxygen, so methane readings in low-oxygen holds need careful interpretation.
MSC.539(107): 2023 Amendments to the International Maritime Solid Bulk Cargoes (IMSBC) Code
Use a repeatable routine, then escalate
For unventilated holds under normal conditions, the Code describes one measurement per day as sufficient for precautionary monitoring. If CO is above 30 ppm, measurements must increase to at least twice daily at suitably spaced intervals, with additional results logged. Where methane means ventilators need to remain open, the Code describes a different approach: close them for a period before measuring so readings can help reveal developing self-heating. The selected shutdown period should be consistent; the Code recommends it be no less than four hours, and calls for daily measurements. These procedures should be applied in line with the cargo’s circumstances and the applicable requirements, rather than treated as a substitute for onboard judgment.
Escalation should not wait for a threshold if the trend is already concerning. For a cargo identified as likely to self-heat, the Code says that when CO is increasing steadily, the cargo space is to be completely closed, ventilation ceased, and the master is to seek expert advice immediately. It also says the master is to inform the shipper and company if CO reaches 50 ppm or exhibits a steady rise over three consecutive days. The information should support an accurate assessment: identify the hold; report CO, methane and oxygen results; include cargo temperature if available, where and how it was measured, sample times, ventilation times, quantity and type of coal, loading date, destination and ETA, plus the master’s observations.
A decision-ready log turns individual readings into a shared operational picture. Record results by hold and timestamp, preserve additional readings, and note ventilation changes alongside the measurements. When a trend triggers escalation, provide the supporting context promptly instead of sending a number alone. That record helps the shipper, company and expert advisers assess the situation using the same timeline and cargo details.
MSC.539(107): 2023 Amendments to the International Maritime Solid Bulk Cargoes (IMSBC) Code