The prime hazards associated with the shipment of solid bulk cargoes are those
- Relating to structural damage due to improper cargo distribution
Great care is required to avoid over stressing the vessel and doing structural damage. Carefully planning of the load and the discharge must be made, and at all times the maximum loading of the tank top must not be exceeded.
In tween deck vessels, high density cargoes such as iron ore should be loaded in the lower hold only to avoid damage to the tween deck.
- Loss or reduction of stability during a voyage.
The maximum loading for each hatch must not be exceeded. Care must be taken to ensure that the peak height of an untrimmed cargo is not excessive thereby increasing the tank top loading
- Chemical reactions of cargoes.
The cargo itself may be corrosive or the liquid draining out of the cargo into the bilge’s may be corrosive. In some ships severe damage has occurred. For example coal and sulphur.
Dust Very dusty cargoes may be hazardous to humans and the environment and so measures may have to be taken to control the level of dust created.
Example : stop load/discharge in high winds
Associated hazards are as follow:
Dust from cargo working:
Many bulk cargoes are dusty and some extremely so. The effects of breathing dust can never be beneficial and are probably harmful in some cases at least. Where possible it is always best to avoid exposure to cargo dust and employers and their representatives have a duty to minimise dust.
Anyone required to be on deck when a dusty cargo is being worked and anyone sweeping cargo with a brush or with air should wear a suitable respirator.
Fires account for around 25% of all losses in the containership fleet, and around 10% of the fatalities. Although most fires start in engine rooms and are contained by engine room carbon dioxide systems, hold fires tend to spread and cause more widespread damage. In many situations it is the variety of cargoes being carried that make control of hold fire difficult. Hazards are increased due to the difficulty of access once a fire has initiated.
Liquefaction results in a flow state to develop. This permits the cargo to slide and shift in one direction thus creating free surface effect and reducing the GM thereby reducing stability. Shippers declaration should be thoroughly examined by the chief officer before loading any bulk cargo.
Cargoes that are at risk of liquefaction are those containing at least some fine particles and some moisture, although they need not be visibly wet in appearance. The most widely known cargoes with this hazard are mineral concentrates, although many other cargoes can also liquefy, such as fluorspar, certain grades of coal, pyrites, millscale, sinter/pellet feed, etc.
Although they often look dry in appearance at the time of loading, these cargoes contain moisture in between the particles. At the time of loading, the cargoes are usually in their solid state, where the particles are in direct contact with each other and, therefore, there is physical strength of resistance to shear strains. During ocean transport, cargoes are exposed to agitation in the form of engine vibrations, ship’s motions and wave impact, resulting in compaction of the cargo. This leads to a reduction of the spaces between the particles. If compaction is such that there is more water inside the cargo than there are spaces between the particles, the water pressure inside the cargo can rise sharply and press the particles apart.
Cargo liquefaction will not occur if the cargo contains a sufficiently low inherent moisture content and sufficiently high interstitial air that, even in its most compacted state, there are still sufficient interstitial spaces to accommodate all of the moisture so that the increase in water pressure is inhibited
Some cargoes may have a tendency to shift across the ship in heavy weather and so correct trimming of the cargo is required. Some cargoes such as grain may need extra measures to be taken to secure the surface. For example, bulk grain may be over stowed with bagged grain.
As a general rule all cargoes should be trimmed level or nearly level. and whenever possible spaces should be filled as fully as practicable without putting excessive stress on the structure
Gas emission :
Explosive gasses such as methane and poisonous gasses such as carbon monoxide may be produced by some cargoes. For example coal
Some cargoes are liable to heat up on voyage. Temperatures should be taken and a log kept of each space. For example coal and steel swarf.