Section 9.2 Monitoring Cargo Condition

Once a bulk carrier is at sea, the cargo within its holds is largely hidden from direct view. However, this does not mean it can be forgotten. Many bulk cargoes are not inert and can undergo changes during the voyage due to their inherent properties or interaction with the hold environment. Therefore, a systematic program of monitoring key cargo condition indicators – primarily temperature, gas levels, and bilge soundings – is essential for ensuring the safety of the vessel and crew, preventing cargo damage, and complying with regulatory requirements. This ongoing vigilance allows for the early detection of developing problems, enabling timely intervention. The Master, through the Chief Officer and deck watch officers, is responsible for implementing and overseeing these critical monitoring routines.

1. Temperature Monitoring:

Monitoring the temperature of certain bulk cargoes is crucial for detecting self-heating, which can lead to spontaneous combustion, or for ensuring that temperature-sensitive cargoes remain within acceptable limits.

A. Why Monitor Temperature?

Detect Self-Heating: For cargoes prone to oxidation or biological activity (e.g., coal, DRI, seed cake, some fertilizers, fishmeal), a steady rise in temperature is a primary indicator of self-heating. Early detection allows for corrective action (e.g., adjusting ventilation, sealing holds, preparing fire-fighting measures) before the situation escalates to fire.

Assess Cargo Integrity: For some cargoes, temperature changes can affect quality or stability (though this is less common for typical bulk commodities than for, say, refrigerated goods, it can be a factor for some organic products).

Verify Shipper’s Information: Comparing voyage temperatures with any temperature declarations or limitations provided by the shipper.

Inform Ventilation Decisions: Temperature readings can sometimes inform ventilation strategies, especially if trying to cool a cargo or prevent condensation.

B. Cargoes Typically Requiring Temperature Monitoring:

Coal (especially lower ranks and those known to self-heat): A primary requirement.

Direct Reduced Iron (DRI – Forms A and B): Highly prone to oxidation and self-heating if wetted or not properly manufactured/aged.

Seed Cake (various types): Can self-heat due to residual oil content and biological activity.

Fishmeal (non-antioxidant treated): Prone to self-heating.

Some Fertilizers (e.g., those with organic components, or if there’s a concern about decomposition): Though gas evolution might be a more direct indicator for ANBF decomposition.

Wood Products (chips, pellets, logs if stored for long periods or loaded at high moisture): Can undergo biological heating.

Any cargo for which the IMSBC Code schedule or shipper’s instructions specifically recommend temperature monitoring.

C. Methods of Temperature Monitoring:

Sounding Pipes with Temperature Probes/Thermocouples:

Many bulk carriers are fitted with sounding pipes that extend into the cargo holds, sometimes at different levels.

Portable electronic temperature probes or thermocouples attached to a calibrated cable can be lowered into these pipes to measure temperatures at various depths within the cargo stow.

This is a common method for coal and other self-heating cargoes.

Fixed Temperature Sensors: Some vessels, particularly those designed for specific trades (e.g., dedicated coal carriers), may have fixed temperature sensors embedded within the cargo holds, providing continuous or periodic readings to a central monitoring station.

Infrared (IR) Thermometers / Thermal Imagers:

These non-contact devices can measure the surface temperature of the cargo (if accessible, e.g., during loading/discharge, or sometimes by pointing into the ullage space through an opening).

They can also be used to detect hot spots on bulkheads or decks adjacent to cargo holds.

Limitations: IR thermometers only measure surface temperature. A deep-seated hot spot may not be immediately detectable on the surface. Their accuracy can be affected by emissivity of the surface, distance, and atmospheric conditions (dust, humidity).

Manual Probes (for accessible areas): Long-stemmed thermometers can be inserted into accessible parts of the cargo stow, but this is often limited once the hold is fully loaded.

D. Frequency and Recording:

Frequency:

Daily readings are a common minimum for cargoes requiring monitoring.

For cargoes with a higher risk of self-heating (e.g., certain coals, DRI), more frequent monitoring (e.g., every 4-8 hours, or even continuously if fixed sensors are available) may be necessary, especially in the initial stages of the voyage or if temperatures start to rise.

The IMSBC Code schedule for the specific cargo often provides guidance on monitoring frequency.

Recording:

All temperature readings, along with the date, time, hold number, and location/depth of measurement, must be meticulously recorded in a dedicated temperature log or the deck logbook.

Any trends (rising, falling, stable), unusual readings, or actions taken (e.g., changes to ventilation) should also be noted.

E. Interpreting Readings and Action Levels:

Establish a Baseline: Note the cargo temperature at loading and the initial readings after loading is complete.

Look for Trends: A steady, sustained rise in temperature is a more significant concern than minor daily fluctuations.

Compare with Ambient: Compare cargo temperatures with ambient air and sea water temperatures.

Critical Temperatures: The IMSBC Code or shipper’s information may specify critical temperature levels at which certain actions should be taken (e.g., for coal, if temperatures exceed 55-60°C and are rising, it’s a cause for concern; higher temperatures may trigger emergency procedures).

Action: If temperatures show a consistent upward trend or approach critical levels:

Increase monitoring frequency.

Review ventilation strategy (often, for self-heating, this means stopping ventilation and sealing the hold to reduce oxygen, but always follow specific Code guidance).

Alert the Master immediately.

Prepare fire-fighting equipment.

Inform the company (DPA).

Consider seeking expert advice (e.g., from P&I Club, emergency response services).

2. Gas Level Monitoring:

Monitoring the atmosphere within cargo holds and adjacent spaces for various gases is crucial for safety, particularly when carrying cargoes that can emit flammable or toxic gases, or deplete oxygen.

A. Why Monitor Gas Levels?

Detect Flammable Atmospheres: To prevent explosions by ensuring flammable gas concentrations (e.g., methane from coal, hydrogen from DRI or some scrap) remain well below the Lower Flammable Limit (LFL).

Detect Toxic Gases: To protect crew health by ensuring concentrations of toxic gases (e.g., CO from self-heating, H₂S/SO₂ from concentrates, residual fumigants) are below their Threshold Limit Values (TLVs) or Occupational Exposure Limits (OELs).

Ensure Sufficient Oxygen: To prevent asphyxiation by ensuring oxygen levels are safe (typically >19.5% or 20.9%) before any enclosed space entry and to monitor for oxygen depletion by certain cargoes.

Indicator of Cargo Condition: Rising CO levels are an early indicator of self-heating in cargoes like coal, often appearing before significant temperature increases.

B. Cargoes Typically Requiring Gas Monitoring:

Coal: Methane (CH₄), Carbon Monoxide (CO), Oxygen (O₂).

Direct Reduced Iron (DRI): Hydrogen (H₂), Oxygen (O₂).

Metal Sulphide Concentrates: Oxygen (O₂), Sulphur Dioxide (SO₂), Hydrogen Sulphide (H₂S), Flammable Gas (%LFL).

Fumigated Cargoes (e.g., Grains): Specific fumigant gas (e.g., Phosphine – PH₃), Oxygen (O₂).

Organic Cargoes (Grains, Wood Products, Seed Cake): Oxygen (O₂), Carbon Dioxide (CO₂ – though CO₂ monitoring is less common for routine safety unless specifically indicated, O₂ depletion is the primary concern).

Scrap Metal (some types): Hydrogen (H₂), Oxygen (O₂).

Any cargo listed in the IMSBC Code that specifies gas monitoring.

C. Equipment for Gas Monitoring:

Portable Multi-Gas Detectors: These are essential. Most can simultaneously measure:

Oxygen (O₂) – usually as % volume.

Flammable Gases – usually as % LFL (Lower Flammable Limit).

Carbon Monoxide (CO) – usually in ppm (parts per million).

Hydrogen Sulphide (H₂S) – usually in ppm.

Single Gas Detectors: For specific gases not covered by common multi-gas units (e.g., SO₂, PH₃).

Detector Tubes (Colorimetric Tubes): Glass tubes containing a chemical reagent that changes color when exposed to a specific gas. Used with a hand-operated bellows pump. Provide a spot reading for a wide range of gases, including many toxic ones and fumigants. Requires different tubes for different gases.

Calibration and Bump Testing: All electronic gas detectors must be regularly calibrated according to manufacturer’s instructions (often every 3-6 months, or as specified) using certified calibration gas. Bump testing (exposing the sensor to a known concentration of gas to verify alarm function) should be done before each day’s use. Records of calibration and bump tests are critical. Detector tubes have expiry dates.

D. Sampling Points and Procedures:

Hold Ullage Space: Samples are typically taken from the air in the space above the cargo, often via sounding pipes, dedicated gas sampling ports, or by briefly opening a small access hatch (with extreme caution if flammable/toxic gas is suspected).

Ventilation Outlets: Can give an indication of the general atmosphere being exhausted.

Adjacent Enclosed Spaces: Forecastle store, mast houses, cofferdams, or any space that could be contaminated by leakage from cargo holds.

Procedure:

Use appropriate sampling lines/probes to draw air to the detector. Ensure lines are clean and not kinked.

Allow sufficient time for the detector to stabilize and give a true reading.

Purge lines with fresh air between sampling different locations if cross-contamination is a risk.

Always follow manufacturer’s instructions for the specific gas detector.

E. Frequency and Recording:

Frequency:

Daily readings are a common minimum for cargoes requiring gas monitoring.

For cargoes with high gas emission rates or developing problems (e.g., rising CO or CH₄), more frequent monitoring (every few hours) is necessary.

IMSBC Code schedules often provide specific guidance.

Recording:

All gas readings (date, time, hold number, location of sample, O₂%, %LFL, CO ppm, H₂S ppm, etc.) must be meticulously recorded in a dedicated gas log or the deck logbook.

Note any trends, alarms, or actions taken (e.g., changes to ventilation).

F. Interpreting Readings and Action Levels:

Oxygen (O₂):

Normal air: ~20.9%.

Safe for entry: Generally >19.5% (some authorities say >20.5% or 20.8%).

Deficient: <19.5%. Entry prohibited without SCBA.

Increased fire risk: >23.5%.

Flammable Gas (%LFL):

LFL (Lower Flammable Limit) is 100% LFL. This is the minimum concentration at which the gas can ignite.

Action levels are usually set well below 100% LFL (e.g., alarm at 10-20% LFL, consider increased ventilation; evacuate/stop hot work at 40-50% LFL or as per company policy).

Never enter a space if LFL is >0-1% without specific authorization and precautions.

Carbon Monoxide (CO):

TLV/OEL varies (e.g., 25-50 ppm over 8 hours TWA – Time Weighted Average). Short Term Exposure Limit (STEL) may be higher.

Rising CO levels are a strong indicator of self-heating/fire, even if no smoke or temperature rise is evident.

Hydrogen Sulphide (H₂S):

Extremely toxic. TLV/OEL is very low (e.g., 1-10 ppm TWA). STEL may be 5-15 ppm. Immediately Dangerous to Life or Health (IDLH) level is around 100 ppm.

Sense of smell is unreliable (paralyzed at higher concentrations).

Sulphur Dioxide (SO₂):

Toxic and irritant. TLV/OEL typically 2-5 ppm TWA. STEL 5-10 ppm.

Action: If gas readings exceed safe limits or show worrying trends:

Implement ventilation strategy as per IMSBC Code/cargo requirements.

Alert Master immediately.

Prohibit entry into affected spaces.

Prepare emergency equipment if necessary.

Inform company.

3. Bilge Soundings (Hold Bilges):

Regularly sounding the bilge wells in cargo holds is a fundamental aspect of good seamanship and cargo care.

A. Why Monitor Bilge Levels?

Detect Water Ingress: An unexpected increase in bilge levels can indicate:

Leakage through hatch covers (due to poor sealing or heavy weather).

Hull damage/leakage (e.g., from collision, grounding, or structural failure).

Leakage from ballast tanks or pipelines into the hold.

Condensation (ship’s sweat) running into bilges.

Monitor Cargo Sweat/Drainage: Some cargoes naturally release moisture during the voyage, which collects in the bilges. Monitoring helps quantify this.

Prevent Cargo Damage: If water accumulates in the bilges and rises above the level of the strum box or tank top ceiling (if fitted), it can come into contact with and damage the cargo, especially bottom tiers.

Maintain Stability: Large unpumped quantities of water in bilges can create a free surface effect, reducing stability.

Verify Bilge System Integrity: Regular soundings confirm that bilge suctions are clear and that water is not accumulating due to a blocked line or faulty non-return valve.

B. Frequency and Procedure:

Frequency:

At least once daily is standard practice.

More frequently (e.g., once per watch, or every 4 hours) during periods of heavy weather, if there are known issues with hatch cover weathertightness, or if carrying cargoes known to produce a lot of sweat.

Procedure:

Sound all cargo hold bilge wells (port and starboard if separate wells exist).

Use a calibrated sounding tape/rod with water-finding paste if necessary (especially if the cargo itself is dark or could be mistaken for water).

Record the soundings accurately in the deck logbook or a dedicated bilge sounding log.

Note any water pumped out, including quantities and overboard discharge position (if permissible and recorded as per MARPOL if any sheen is possible, though hold bilge water is usually considered clean unless contaminated by cargo).

C. Interpreting Bilge Soundings:

Establish a Baseline: Note soundings after loading is complete.

Look for Changes: A sudden or unexplained increase in soundings is a cause for immediate investigation.

Distinguish Sources: Try to determine the source of any water:

Freshwater: Likely condensation or rain ingress.

Saltwater: Likely hatch cover leakage in heavy seas or hull leakage.

Cargo Drainage: Some cargoes (e.g., some ores, logs) may drain water.

Consider Weather Conditions: Expect higher potential for ingress during heavy rain or rough seas.

D. Action if Excessive Water is Found:

Pump Bilges: Pump out the accumulated water as soon as practicable, ensuring discharge is compliant with MARPOL (hold bilge water is generally considered “clean” unless contaminated by specific cargo residues or chemicals).

Investigate the Source: Determine why the water is accumulating (e.g., inspect hatch seals, check for hull damage if suspected, check ballast tank levels).

Take Remedial Action: If a leak is found, take steps to stop or minimize it (e.g., re-secure hatch cleats, effect temporary repairs if safe and possible).

Protect Cargo: If water is nearing cargo level, try to pump it out urgently.

Inform Master and Company.

Log all findings and actions.

4. Importance of Accurate Record-Keeping for All Monitoring:

Meticulous and contemporaneous records of all temperature readings, gas measurements, and bilge soundings are crucial for:

Demonstrating Due Diligence: Shows that the vessel is actively monitoring cargo condition and taking appropriate care.

Early Trend Detection: Allows for early identification of developing problems by comparing current readings with previous ones.

Incident Investigation: Provides vital data if an incident (fire, cargo damage, personnel exposure) occurs.

Supporting Claims/Disputes: Can be essential evidence in commercial disputes or insurance claims.

Compliance with SMS and Regulatory Requirements.

5. Master’s Role in Overseeing Monitoring Programs:

Establish Clear Procedures: Ensure there are clear, written procedures in the SMS for temperature, gas, and bilge monitoring, including frequencies, recording methods, and action levels.

Ensure Equipment Availability and Calibration: Verify that all necessary monitoring equipment is onboard, in good working order, and properly calibrated.

Crew Training and Competency: Ensure officers and crew responsible for monitoring are properly trained in the use of equipment, sampling techniques, interpretation of readings, and safety precautions.

Review of Records: Regularly review monitoring logs to stay informed of cargo conditions, identify any trends or anomalies, and ensure records are being maintained correctly.

Decision Making: Based on the monitored data, make informed decisions regarding ventilation, emergency actions, or seeking external advice.

Promote a Culture of Vigilance: Encourage all crew members to be observant and report any unusual conditions related to the cargo or holds.

Diligent and systematic monitoring of cargo conditions during the voyage is a fundamental responsibility of the Master and crew. It is a proactive approach to safety and loss prevention, ensuring that potential hazards are identified early and managed effectively, leading to a safer voyage and the delivery of cargo in good order.