Lightering and burning
Recovery at sea and onshore is always difficult and very partial. Lightering, which involves transferring the cargo of oil from a stricken vessel into another vessel or a barge, is the best way of preventing or reducing pollution.
For this, it may be necessary to call upon extra vessels or on extra equipment
airlifted by helicopter onto the vessel in difficulty. Simple transfer pump
units may be sufficient, however sometimes more complex systems incorporating
safety devices, heating mechanisms and water injection, for viscous oils
at ambient temperatures, may be necessary.
If a spill ignites during an incident, it will naturally reduce the amount of oil in the water. This phenomenon may occur naturally, when the accident results in an explosion, or when a spark produces a fire at the time of the spill. A form of spill response may involve controlling the fire without extinguishing it to reduce pollution. There have also occasionally been cases of slicks deliberately being set on fire when contained in fireproof booms (e.g. Exxon Valdez in 1989) and even of the vessel being set on fire (e.g. Torrey Canyon in 1967).
Deliberate burning remains, however, an exception. Technically, it can be applied to fresh oil before evaporation of the volatile parts and only in very particular conditions. The heat, combustion gases and soot released constitute other forms of pollution and tend to deter the decision to set the oil alight.
A slick on fire