Fire and explosion risks posed by carriage of


scrap metal


The NorthStandard P&I Club presents the risk involved with bulk shipments of scrap ferrous metal, as explained by Dr Neil Sanders of Burgoynes Consulting Scientists and Engineers.


According to NorthStandard, bulk shipments of scrap ferrous metal (iron and steel) bring risks involving heating, flammable gas production and fires. Dr Neil Sanders of Burgoynes Consulting Scientists and Engineers shares the potential problems with all types of scrap ferrous metals in this article.


1


Self-heating, possibly to ignition


In practice, self-heating has occurred in cargoes that were declared as scrap metal, Group C, as well as in ferrous turnings etc., Group B. Self- heating occurs because iron and steel oxidise (rust) by reacting with oxygen in air, or oxygen in water. Oxidation reactions produce heat, which tends to be retained due to the insulating effect of surrounding cargo. The oxidation reactions become exponentially faster at higher temperatures, so self-heating can worsen, sometimes to the point of ignition, depending on the circumstances and actions taken.


Freshly exposed iron and steel surfaces have a high tendency to oxidise, whereas ‘aged’ surfaces that are already oxidised react more slowly, or insignificantly. Fresh surfaces may occur because the metal has been recently shredded, or because it has been stored after shredding in a way that avoids exposure to air, e.g., within a large stockpile or coated in oil that drains off.


2


Hydrogen, produced by water oxidation of scrap


iron and steel


Hydrogen is highly flammable over a wide range of


concentrations of hydrogen and air/oxygen. It is also extremely easy to ignite, odourless and colourless. We have seen cargoes declared as scrap metal, Group C, producing problematic amounts of hydrogen which, if allowed to build up and ignite, would cause an explosion in ship’s holds.


Although the IMSBC Code entries mention trying to keep these cargoes dry, in practice scrap iron and steel cargoes are often stored in outside stockpiles in the rain, and terminals use water sprays to suppress dust. Therefore, iron and steel scrap may be wet, potentially producing hydrogen.


Seawater has a greater tendency than fresh water to oxidise iron and steel, producing hydrogen, but fresh water can also produce hydrogen, depending on the circumstances. The IMSBC Code does not indicate measuring gases in holds, so hydrogen production may go unnoticed.


58 | ISSUE 107 | MAR 2024 | THE REPORT 3


Combustible materials in the cargo, such as cardboard, rags, plastics from recycled


items, oils, and flammable gases from cylinders or aerosols.


Some of these combustible materials can be ignited at temperatures from roughly 250°C upwards, which is much lower than the ignition temperature of the scrap iron and steel. Fires in scrap metal (Group C) cargoes usually involve combustibles in the cargo and only rarely the scrap metal itself.


4 5


Ignition sources in the cargo, such as batteries and cylinders with flammable gases.


These items are of course contaminants, but they may be present due to the source of the scrap, e.g., household recycling. They may cause ignition during handling or shifting of cargo, or spontaneously. Burning material may also be loaded with the cargo.


Asphyxiating atmospheres due to oxidation of iron and steel cargo


removing oxygen from the hold gases.


Oxygen may also be removed from adjacent spaces, if there are any gaps in bulkheads. In the case of self-heating or fire, carbon monoxide and carbon dioxide will be produced, which can also cause asphyxiation. Therefore, thorough risk assessments and precautions are needed before entering holds containing iron and steel scrap, and the same applies to adjacent spaces.


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