- Proper cargo ventilation prevents deterioration by reducing moisture and minimizing sweat formation.
- Two key ventilation rules: Dew Point Rule and Three Degree Rule help determine safe ventilation conditions.
- Accurate measurements and record-keeping are crucial for effective ventilation management.
Britannia P&I Club emphasizes the importance of cargo ventilation to maintain cargo integrity and prevent spoilage. Effective ventilation is essential to remove excess moisture, reduce sweat formation, and disperse hazardous gases. Implementing ventilation best practices ensures cargo safety and minimizes risks associated with improper storage conditions, reports SAFETY4SEA.
When to Ventilate?
Several factors should be assessed before ventilating cargo, including cargo properties, ambient air conditions, moisture content, seawater temperature, and exposure to external elements like rain and waves.
The Safety Management System (SMS) should provide clear guidelines to crew members based on industry best practices and company-specific requirements.
Ventilation Rules
Two primary rules guide ventilation decisions:
Dew Point Rule
“Ventilate if the dew point of the outside air is lower than the air inside the cargo hold.”
This rule relies on real-time measurements but can be difficult to implement due to restricted access, fumigation protocols, and limited personnel availability.
Inaccuracies in DP measurement can lead to ventilation log discrepancies and impact cargo claims.
Three Degree Rule
“Ventilate if the temperature of the outside air is at least 3°C lower than the temperature of the cargo.”
Primarily used for hygroscopic cargoes like grains, this rule eliminates the need for frequent cargo space access.
Requires accurate initial cargo temperature measurement at loading.
Limitations include potential temperature variations during the voyage, affecting the rule’s assumptions.
Understanding the Three Degree Rule
Hygroscopic cargoes, such as agricultural products, are dried before loading to prevent spoilage. Once loaded, cargo affects the adjacent air until equilibrium is reached.
The Three Degree Rule assumes that ambient air at least 3°C colder than the cargo will have a lower dew point, making ventilation safe. This assumption is verified through relative humidity (RH) calculations and equilibrium conditions.
Practical Verification
For example:
- Cargo hold air at 20°C with 70% RH has a dew point of 14.36°C.
- Outside air at 17°C with 80% RH has a dew point of 13.52°C, lower than the cargo hold, making ventilation permissible.
Did you subscribe to our daily Newsletter?
It’s Free Click here to Subscribe!
Source: SAFETY4SEA
