Following are the hazards of coal -
1. Coal emits methane which is a flammable gas. Methane is lighter than air and forms explosive layer in the upper part of the cargo hold. This kind of atmosphere can be ignited by a flame or spark
2. Coal loaded in a cargo hold results in oxidation of the cargo space making it unsafe for human entry
3. Coal is liable to spontaneous combustion as it can self heat. This can lead to formation of Carbon Monoxide which is poisonous.
4. Coal, sometimes, also has corrosive properties - as it reacts with the water to produce acids which may cause corrosion in hold bilges
5. Liquefaction may occur in coal cargo if the moisture content of the cargo is too high. In such conditions, the moisture may migrate to surface leading to development of flow state