In marine practice, it is an offence to discharge smoke into the atmosphere. However, allowances are made for specific operations such as soot blowing, lighting up of boilers, and machinery breakdowns.
Since it is not practicable to impose a complete ban on smoke discharge during these occurrences, time limits have been stipulated for the emission of smoke.
Emissions from a forced draught oil-fired boiler furnace or an oil engine must not exceed 10 minutes of dark smoke in aggregate within any period of 8 hours.
If soot blowing is carried out during such a period for longer than ¼ minute in the aggregate, then that period shall be excluded from the 8-hour accounting.
The condition of gases leaving the funnel is often the best indication of combustion conditions.
- Black smoke is caused by insufficient air supply.
- CO₂ content in black smoke can be in the range of 10–14%, depending on various factors.
- Other constituents include approximately 79% nitrogen (N₂), 4% oxygen (O₂), as well as carbon monoxide (CO), sulphur oxides (SOₓ), nitrogen oxides (NOₓ), and particulate carbon.
The likely constituents of black smoke from the combustion of residual fuel in a boiler include:
- Carbon dioxide (CO₂)
- Carbon monoxide (CO)
- Nitrogen (N₂)
- Water vapour (H₂O)
- Sulphur oxides (SOₓ)
- Nitrogen oxides (NOₓ)
The contaminants likely to be found in the clear exhaust from a diesel-driven engine burning methane (a gas fuel) include:
When residual fuels are burned, the exhaust will additionally contain:
- Sulphur oxides (SOₓ)
- Nitrogen oxides (NOₓ)