More information on Shell in Nigeria here: http://www.foeeurope.org/press/2007/May3_DU_Flaring.htm
Gas Flaring is the releasing of gas and liquids associated with oil and gas production pipelines and refineries into the atmosphere. The purpose of gas flaring is to protect pipelines and infrastructure from over-pressuring .
When the gases are burned off noxious by-products are released into the surrounding air.
These by-products include nitrogen dioxide, sulphur dioxide, and volatile organic compounds like xylene and hydrogen sulfide. Carcinogens such as benzapyrene are also released. People exposed to these substances can suffer from a variety of respiratory problems, which have been reported amongst many children in the Niger Delta but have never been systemically investigated. These chemicals can also aggravate asthma, cause breathing difficulties and pain, as well as chronic bronchitis.
Benzene, which is known to be emitted from gas flares in undocumented quantities, is acknowledged as being a causative agent for leukemia.
Gas flaring of course, also contributes to global warming and climate change.
Together with oil spills, gas flaring is seen as a major cause of environmental degradation. In Nigeria, the practice is supposed to be illegal, but there is no sign of the Nigerian government being able to enforce this law.