A sad tale to TEL

You may have heard an elder asking for unleaded petrol at a pump. Do you know why lead was once added to petrol? And why it was discontinued later?

The problem of ‘knocking’ in engines
In the early days of automobiles, ‘knocking’ was a major problem. In a car’s engine, the petrol is injected into a ‘fuel chamber’, where it mixes with air. A spark plug then creates an electric spark, which causes the fuel-air mixture to burn and produce heat. This causes the air to expand and push a piston, which drives the wheel.

However, one problem was that the fuel would catch fire even when the spark was not provided. This often led to engine problems; sometimes it even exploded!

The search for an anti-knock
Many people tried to find a solution. One way was to find a chemical that could be added to petrol, so that it would not combust until the spark was provided. In 1921, Thomas Midgley discovered that a compound called tetra-ethyl lead (TEL) prevented knocking when added to fuel. Midgley is also famous as the discoverer of CFCs.

TEL was soon adopted by fuel companies around the world as an additive to fuels. However, it soon proved to be one of the world’s biggest chemical disasters.

TEL and Lead poisoning
Lead is very dangerous to human beings. It causes anaemia, memory loss, abdominal pain, bone weakening, depression and finally death. It can be identified by ‘lead hue’, i.e. pale colouration of the skin. As the use of TEL spread around the world, it led to lead poisoning among petrol pump workers as well as users.

Lead also poisons the ‘catalytic converters’ that all modern car engines must be fitted with. This is a small device that removes dangerous substances like carbon monoxide and nitrogen oxides. However, even tiny amounts of lead can damage the converter.

Sadly, TEL continued to be used for a very long time as there was no other alternative available. However, many improvements were made to engine design over the years, reducing or eliminating ‘knocking’. With the need for leaded fuel slowly decreased. Lead poisoning causes anaemia, memory loss, abdominal pain, bone weakening, depression and finally death.

A lesson learnt
has since been banned in many countries around the world. India banned the use of it in 2000. Alongside, the government introduced rules called the Bharat Stage standards. These rules require car manufacturers to implement technologies that reduce or eliminate the need for unleaded fuels.

The story of TEL highlights the nature of chemistry. What seems like a reasonable solution to a problem can unfortunately create terrible problems. Luckily, scientists today have adopted many methods to make science safer. In chemistry, such methods are called Green Chemistry.