Main Hazards Associated with Carriage of Concentrates:
Cargo Liquefaction: Liquefaction is a phenomenon in which solid bulk cargoes are abruptly transformed from a solid dry state to an almost fluid state. Many common bulk cargoes such as iron ore fines, nickel ore and various mineral concentrates are examples of materials that may liquefy. 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.
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 conditions. The cargo holds and communicating spaces in bulk carriers are examples of confined spaces where such toxic atmospheres may develop. Several fatal accidents can occur when people enter unventilated spaces. The IMSBC code lists the following cargoes as potentially oxygen depleting: coal, direct reduced iron, sponge iron, sulphide concentrates, ammonium nitrate based fertilisers, linted cotton seed. Various gaseous products are formed including carbon monoxide, carbon dioxide, hydrogen sulphide and hydro carbons.
Precautions when loading concentrates as per “IMSBC” Code:
General Precautions:
- Bilge wells shall be clean, dry and covered as appropriate, to prevent ingress of the cargo.
- Bilge system of a cargo space to which this cargo is to be loaded shall be tested to ensure it is working.
Loading Precautions:
- This cargo shall be trimmed to ensure the height difference between peaks and troughs does not exceed 5 % of the ship’s breadth and that the cargo slopes uniformly from the hatch boundaries to the bulkheads and no shearing faces remain to collapse during voyage in particular on smaller ships, i.e., 100 m long or less.
- As the density of the cargo is extremely high, the tanktop may be overstressed unless the cargo is evenly spread across the tanktop to equalize the weight distribution.
- Due consideration shall be paid to ensure that the tanktop is not overstressed during the voyage and during loading by a pile of the cargo.
Weather Precautions:
When a cargo is carried in a ship other than specially constructed or fitted cargo ship complying with the requirements in subsection 7.3.2 of this code, the following provisions shall be complied with:
- The moisture content of the cargo shall be kept less than its TML during voyage.
- Unless expressly provided otherwise in this individual schedule, the cargo shall not be handled during precipitation.
- Unless expressly provided otherwise in this individual schedule, during handling of the cargo, all non-working hatches of the cargo spaces into which the cargo is loaded or to be loaded shall be closed.
Procedure for loading Urea in Bulk:
- Trim in accordance with the relevant provisions required under sections 4 and 5 of the code.
- Non-cohesive bulk cargoes are those listed in paragraph 1 in appendix 3 and any other cargo not listed in the appendix, exhibiting the properties of a non-cohesive material.
- For trimming purposes, solid bulk cargoes can be categorized as cohesive or non-cohesive. The angle of repose is a characteristic of non-cohesive bulk cargoes which is indicative of cargo stability and has been included in the individual schedules for non-cohesive cargoes. The angle of repose of the cargoes shall establish which provisions of this section apply. Methods for determining the angle of repose are given in section 6.
- Non-cohesive bulk cargoes having an angle of repose less than or equal to 30º:- These cargoes, which flow freely like grain, shall be carried according to the provisions applicable to the stowage of grain cargoes. The bulk density of the cargo shall be taken into account when determining:
- the scantlings and securing arrangements of divisions and bin bulkheads; and
- the stability effect of free cargo surfaces.
- Non-cohesive bulk cargoes having an angle of repose greater than 30° to 35° inclusive:- These cargoes shall be trimmed according to the following criteria:
- the unevenness of the cargo surface measured as the vertical distance (Δh) between the highest and lowest levels of the cargo surface shall not exceed B/10, where B is the beam of the ship in metres, with a maximum allowable Δh = 1.5 m; or
- loading is carried out using trimming equipment approved by the competent authority.
- Non-cohesive bulk cargoes having an angle of repose greater than 35°:-These cargoes shall be trimmed according to the following criteria:
- the unevenness of the cargo surface measured as the vertical distance (Δh) between the highest and lowest levels of the cargo surface shall not exceed B/10, where B is the beam of the ship in metres, with a maximum allowable Δh = 2 m; or
- loading is carried out using trimming equipment approved by the competent authority.