Hazards of dry bulk cargo
1. Liquefaction
Liquefaction is a phenomenon in which solid bulk cargoes are abruptly transformed from a solid dry state to an almost fluid state. Liquefaction occurs as a result of compaction of the cargo which results from engine vibrations, ship’s motion and rolling and wave impact that further causes cargo agitation.
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.
2. Risk of Cargo Shift
Cargo shift has always remained as one of the greatest dangers on bulk carriers. Trimming is undertaken to reduce the danger of cargo shifting. Rolling can also cause shifting of cargo from one side to the other and reduce her positive stability resulting in the vessel to capsize.
3. Structural hazards due to improper distribution
Heavy cargoes place high loads on the structure and structural failure is therefore probable. The load density of the tank top should never be exceeded. Tank top strength is provided in the ship’s stability booklet. Exceeding the maximum permissible cargo load in any of the holds of a ship will lead to over stressing of local structure. Overloading will induce greater stresses in the double bottom, transverse bulkheads, hatch coamings, hatch covers, main frames and associated brackets of individual cargo holds. Poor distribution of and/or inadequate trimming of certain cargoes can result in excessive bending and sheer forces.
4. Chemical and Other Health Hazard
Some cargoes like coal and sulphur can cause severe damage due to corrosion. Cargoes of sulphur in bulk are normally subjected to exposed storage and are thus subjected to inclement weather thereby resulting in the increase of moisture content of the cargo. Wet sulphur is potentially highly corrosive. When sulphur is loaded, any retained free water filters to the bottom of the holds during the voyage, from where it is pumped out via
the bilges. Some water remains on the tank top and reacts with sulphur. This leads to the release of sulphuric acid resulting in the corrosion of the ship’s holds. Pond coal which is reclaimed after having been abandoned and dumped in fresh water ponds usually have high moisture content and sulphur content. This type of coal may be liable to react with water and produce acids which may corrode parts of the ship.
5. Fire
Bulk cargoes are deemed to present a great deal of fire hazards. Many bulk cargoes have a tendency to heat due to the oxidation process taking place during the voyage. Common cargoes like coal, sulphur, cotton, fishmeal are liable to spontaneus heating. Coal also emits methane which is a flammable gas. When mixed with air it can form an explosive mixture. Dust created by certain cargoes may constitute an explosion hazard.
Sulphur dust can readily ignite causing an explosion. Friction between cotton bales can cause spontaneous combustion and produce heat.
6. Oxygen Depletion
Sea transportation of bulk cargoes of an organic nature such as wood, paper pulp and agricultural products may result in rapid and severe oxygen depletion and formation of carbon dioxide. Thus apparently harmless cargoes may create potentially life threatening condition.
Ref: Polaris App
