Many cargo shipments transported in bulk form can suffer damage or even pose a hazard to the crew while in transit. A new guidance document from the Standard Club, INTERCARGO and DNV GL helps with practical recommendations and a better understanding of how to mitigate these risks by ensuring proper ventilation.
A number of factors can compromise the cargo integrity during normal transit. They can originate from the physical and chemical properties of the cargo itself or from changing temperature and air humidity conditions. Knowing and controlling those factors are key to avoiding hazards to humans as well as claims for cargo damage.
INTERCARGO, the Standard Club and DNV GL have jointly developed the guidance document called ‘Cargo and cargo hold ventilation’ which looks at the specific risks associated with particular types of cargo and how ventilation should be applied to mitigate them. “The guide will provide ships’ crew with a practical understanding of when to ventilate and the reasons to do so,” said Ed Wroe, Technical Manager at INTERCARGO.
“By far the most common threat to cargo integrity is ‘sweat’, the condensation of air moisture, which can cause agricultural products to spoil, steel products to rust, and other cargo types to undergo unwanted and potentially hazardous chemical reactions,” pointed out Yves Vandenborn, Director of Loss Prevention at the Standard Club. When air moisture settles on the cargo, it is referred to as ‘cargo sweat’. Condensation on the ship’s structural elements inside the cargo hold is called ‘ship sweat’. Both phenomena are directly related to the dew point, the temperature at which air becomes saturated with water, triggering condensation.
Organic matter, such as grains, animal feed, seed cake, timber or wood pulp, may decompose or ferment when exposed to sweat. Non-organic and/or hygroscopic cargo that can absorb or release moisture, such as fertilizer, salt, sugar or minerals, can react chemically with water and may self-heat and emit carbon monoxide, carbon dioxide or methane. Apart from the resulting degradation of product quality, carbon monoxide is toxic to humans, and carbon dioxide can displace atmospheric oxygen and cause asphyxiation if undetected. Both gases are odourless.
Some non-organic cargo shipments, especially silicomanganese and ferrosilicon, can emit toxic gases such as hydrogen, especially when moist. Coal and direct-reduced iron may in the same way self-heat and cause fire in the cargo hold as well as emit hazardous methane under the wrong atmospheric conditions. Both hydrogen and methane are highly explosive.
Several cargo types may pose fire, explosion and health risks. Further, non-odorous toxic gases or an oxygen-depleted atmosphere in a cargo hold pose an immediate danger to anyone entering. What is more – toxic gases exiting from cargo holds, whether by natural or mechanical ventilation or through leaks, could enter crew accommodations and in worst case cause injury or death if not detected at an early stage. Certain cargo shipments produce dust that can also pose a health hazard. Mixing hygroscopic and non-hygroscopic cargo shipments with different inherent temperatures in the same hold adds additional risks.
“Cargo hold ventilation is the established means to mitigate these risks,” explained Wroe, “The critical question is how and to what extent ventilation is advisable. In some cases, ventilation may actually aggravate the hazard by increasing the amount of moisture and oxygen interacting with the cargo, thereby accelerating the processes which taint the cargo or cause it to self-heat and emit dangerous gases.”
“Deciding when and how to ventilate can therefore be a complex task,” admits Morten Løvstad, Business Director – Bulk Carriers at DNV GL. “The ‘Cargo and cargo hold ventilation’ guidance document explains in detail what masters and crew should pay attention to, how their decisions will affect cargo quality as well as safety on board, and what the relevant codes, regulations and standards tell them to do. It also points out how operational flexibility is heavily impacted by what ventilation equipment is available on board the vessel.”
The document closes with two case studies which illustrate how improper or inconsistent application of ventilation rules can cause cargo damage and financial loss, and how proper documentation during a voyage is key to a ship’s ability to defend itself against cargo claims. A brief glossary of terms, a cargo temperature and ventilation log template, and a dew point table are included as additional practical tools.