The maritime industry is a mixture of numerous different spheres along with the transport of dangerous goods therefore, bringing the related issues into the equation. Safety, thus becomes a priority as even a minor error within operations can result in massive and occasionally irreversible damage to the ship and environment.
So what qualifies as “dangerous goods” at first glance when it comes to ships? Answer is fuel sources and waste products where both depend on the vessel itself. An example of this was a barge from a UK based marine firm whose barge dumped poison gas in 25th September. This barge’s function was to collect waste products from moored vessels; dumping hydrogen sulfide (H2S) later on.
Hazardous goods can also be defined as items or materials with properties which present potential damage to human health without proper control or a safety infrastructure. Therefore, introducing the 9 categories of said goods; explosives, gases, flammable liquids, flammable solids, oxidising substances, toxic and infectious substances, radioactive materials, corrosives and miscellaneous dangerous goods. Transportation of such goods should also be considered as there are 2x ways; packaged and un-packaged where packaged goods are not transformed in bulk, including dangerous goods in small packages. Bulk transports on the other hand gets loaded directly into cargo spaces or other spaces on the ship without intermediate forms of containment. Finally, there is also the presence of passengers where they are in more danger of exposure to this type of cargo therefore presenting a liability for the crew.
Beginning the analysis of dangerous cargo transportation, it is worth looking at packaging of the cargo itself where many standards should be observed for safe transport. The first thing is the compliance to the code-specific requirements as well as the cargo item itself; is it appropriate and fitting with the package itself? The substance also has to fill the package entirely. Another factor is pressure where liquid contents expand (being filled 95% capacity at 15C and heated to 55C) or the vapor pressure generated by contents heated to 55C.
Leading onto the transportation of the goods, there is a significant difference in the degree of danger between packaged goods that are not carried in bulk; goods carried in small packages, shipping containers, portable tanks and intermediate bulk containers/IBC. According to IMO, 50% of packaged goods and/or carried in bulk can be regarded as dangerous where both can be hazardous to the crew as well as to the marine environment; along with occasional threats to the vessel’s stability provided the containers are unevenly distributed or overloaded.
When is dangerous cargo the most dangerous? Answer lies within phases of loading and unloading when most interactions take place between the cargo and an array of external forces; crew, environment and possible accidents involved. External forces, on most occasions lead to chemical reactions therefore warranting a breakdown of cargo groups:
- Group A: cargo may liquefy if shipped at a moisture content exceeding THEIR transportable moist limit/TML
- Group B: cargo which possesses chemical hazards which can potentially create a dangerous situation.
- Group C: cargo not liable to either liquefy or create a chemical hazard though remaining hazardous regardless.
Liquification is basically changing state from solid to liquid therefore making solid cargo into a liquid therefore harder to control and contain as liquids always flow and can only be controlled with a closed container as liquids take shape and won’t have an exit to flow out. Liquid cargoes contain their own amount of moisture and small other particles; also giving potential for a cargo shift which will cause capsizing and loss of control aboard the vessel; possible even if the cargo in a relatively stable state. Examples of cargo with liquification potential are mineral concentrates, nickel ore and coal.
Mineral concentrates are refined ores where valuable components have been enriched by eliminating most waste material; examples include copper, iron, lead, nickel and zinc concentrate. Coal (bituminous and anthracite) is a natural, solid and combustible material which consists of carbon and hydrocarbons and is a group B cargo due to its flammable and self-heating properties; however also qualifying as group A as it also liquifies if in a fine (75% made up of particles less than 5mm size)
Group A cargo requires certain channels to be met prior to loading onto the vessel. Firstly, information that is required from the shipper himself is to determine their transportation moisture limit/TML index along with the actual moisture index BEFORE shipping out. TML is the maximum moisture content considered for safe carriage where the actual moisture content of the cargo must be below TML.
Group B cargoes are classified in 2x ways within codes “Dangerous Goods in Solid Bulk” under IMDG/International Maritime Dangerous Goods and MHB/ Materials Hazardous only in Bulk codes. MHB cargoes are materials which have potential for chemical hazards when transported in bulk while not meeting the criteria for inclusion in IMDG; presents significant risks and requires special precautions. MHB materials are as follows; combustible, self-heating, solids evolving into flammable gas when wet, solids evolving into toxic gases when wet, toxic and corrosive solids.
Fires and explosions are the types of risks that are most commonly attached to group B cargoes which in turn can release toxic and corrosive gases. Coal can create flammable atmospheres, heats spontaneously, depletes oxygen concentration and corrodes metal structures with some types capable of producing carbon monoxide and methane. Other examples include direct reduced iron/DRI which reacts with water and air to produce hydrogen and heat; increasing potential for ignition, along with depleting oxygen in closed spaces. Metal sulphide concentrates are prone to oxidation and has a tendency to self-heat also leading to oxygen depletion and toxic emissions with some sulphides potentially producing corrosion.
Organic materials and ammonium nitrate-based fertilisers support combustion; when heated, closely confined or contaminated it can explode or decompose releasing toxic fumes and gases. Finally, wood products transported in bulk where oxygen depletion and increase in carbon dioxide in cargo holds and adjacent spaces.
Group C cargoes, those which are neither liquefy or posses chemical hazard potential, present their own risks in; examples include iron ore and high density cargoes, sand and fine particles and cement. Iron ore or any other high-density cargoes which can overstress the tanktop if distribution is uneven along with affecting ship’s ballast operations during loading procedures. Sand and fine particles pose more threat to the crew as sand and silica particles, if inhaled can cause respiratory disease; affecting machinery as well in ways of clogging moving parts leading to malfunction.
Finally, it is necessary to present risk mitigation measures for the most likely circumstances of fire and explosions, corrosion and toxic incidents. Fire and explosion can be mitigated by ventilation or inertion of cargo holds. Toxic gases can also be mitigated by natural or mechanical ventilation depending on the type of cargo and properties of the gas itself. Corrosion is caused by group B and their residues where coating and barriers should be applied to the cargo space structures before loading and unloading.