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Glossary / Cars and engines

Tetraethyl lead

A lead compound added to petrol to suppress knocking. It spread lead into the air with the exhaust and was banned worldwide once the harm to health became clear.

In 1921 Thomas Midgley at GM found that a very small amount mixed into petrol stops knocking. It was cheap and effective, and for more than half a century it was added to petrol everywhere. The lead, once burnt, went straight out into the air with the exhaust.

In 1965 the geochemist Clair Patterson showed that lead in modern people and their surroundings was far above natural levels[1]. In 1979 children with more lead in their bodies were reported to do worse in learning and classroom behaviour[2]. That evidence, together with the fact that lead destroys exhaust catalysts, led country after country to phase it out. It is a case showing that a technology working well and a technology being safe are different things.

Related terms

  • KnockingAbnormal combustion in an engine in which the fuel-air mixture explodes before the spark ignites it, with a metallic knocking sound.
  • Three-way catalystA device fitted to the exhaust of a petrol car that turns three kinds of harmful component in the exhaust gas into harmless gases at the same time.

On the timeline

Sources

  1. C. C. Patterson, “Contaminated and Natural Lead Environments of Man,” Arch. Environ. Health 11, 344–360 (1965).
  2. H. L. Needleman, C. Gunnoe, A. Leviton, et al., “Deficits in Psychologic and Classroom Performance of Children with Elevated Dentine Lead Levels,” N. Engl. J. Med. 300, 689–695 (1979).