Surface ventillation is a important necessity during the carriage of coal for two reasons:
1.To dissipate any heat which may be formed by the oxidation of the coal
2.To carry away any methane gas which may be carried away.
Through ventillation must in no way be carried out as introduction of air into the cargo promotes oxidation and thereby spontaneous combustion.
It is thus recommended that for the first five days after loading all ventillators should be utilised for removing the gas, thereafter the ventillators to the lower holds are to be plugged and opened only for 6 hours every two days.
Each hold containing coal should have atleast two ventillators one forward and the other aft. The tween deck ventillators should be independent.
Before discharging careful ventillation should be directed towards removing gases from both, the tween decks and the lower holds as a suddern influx of air before discharge into the hold may have disastrous effects. In fine weather hatches may be opened to facilitate surface ventillation. Attention to be paid to void spaces where accumulation of methane and carbon- monoxide can accumulate.
- Temperature pipes leading down to the bottom of the cargo are to be provided particularly below the hatchways. Monitoring of the temperatures at three levels in the holds to be done atleast once a day.
- Particular attention is to be paid to cargo stowed against hot bulkheads which is to be avoided if possible and the decks to be kept cool in tropical zones either by running deck water, rigging awnings or by laying out dunnage.
- Temperature pipes are to be kept covered in to prevent the ingress of air into the hold. Spontaneous heating can become accelerated in some cargoes at temperatures as low as 38 degree c.
- At temperatures around 55 degree c. And rising the existance of a fire should be strongly suspected, and in such a situation the cargo spaces should be shut down and sealed against the entry of air and the master should seek expert advice and make for a suitable port of refuge.
- A sufficient number of safety lamps should be carried on all coal carrying vessels.
- All electrical cables and components situated in the cargo spaces should be free from defects and suitable for use in methane / dust atmospheres. Points of entry and exit of cables should be sealed to prevent the passage of gas into the adjacent compartment. If necessary all electrical circuits in spaces where gas accumulation is suspected should be isolated until the space is gas-freed.
- If there is evidence of the cargo burning the space should be closed, ventillation stopped and sealed against the entry of air. Boundary cooling to be carried out but no seawater or steam to be directly applied to the coal as coal directly reduces water to hydrogen and forms carbon monoxide – both flammable gases.
- Introduction of co2, high-expansion foam into the compartments is recommended. The hold is to be kept closed at all times and specialist advise is necessary before carrying out opening of the hold. Water or steam may be used in the hold in port in copious quantities, if no co2 or inert gas is available keeping in regard at all times the stability of the ship.
- The officers on the vessel should continuously monitor the methane,oxygen and carbon-monoxideconcentrations in the holds and in the spaces where the gases could accumulate with suitably calibrated instruments.
- A certificate is obtained from the shipper regarding the moisture content of the cargo. If this figure is suspected an onboard test to be carried out in accordance with section 8 of the bulk carrier code since it should not be more than the transportable moisture limit.
- Precautions should be taken to prevent the ingress of water in the hold and cargo work should be suspended and hatches in wet weather. Stockpiles must be drained and freshly tested for moisture content before loading.
- Hold bilges should be regurly pumped out. Trimming also prevents the air from penetrating the body of the hold. And since the load of coal could turn out upto 3% less, its bills of lading should be suitably claused.