The smell that keeps us safe

Dear all,

It’s been Physics and Maths Enrichment Week, and our reading in Monday’s assembly was all about a man called Peter Hansen, who most people probably haven’t heard. Now in his mid-80s, he is the man whose work in the 1970s played a key role in keeping millions of UK citizens safe. Until that time, much of the gas used in the UK came from coal, which had a distinctive smell; however, in the previous decade, new high-temperature processes began using natural gas, which has no discernible odour. Natural gas had been used by humans for thousands of years, but detecting leaks had always been difficult, relying on observation by spotting a shimmering effect or by hearing a hissing sound if gas was escaping. In both cases, by the time a gas leak was detected, it was already very dangerous, and once natural gas was being used on a mass scale, the risks to life were significant. As the rollout of natural gas continued, the number of accidents, injuries, and deaths increased.

The risk had been made clear in tragic circumstances on March 18th 1937, when a natural gas leak went undetected in the basement of the New London School in Texas, leading to a catastrophic explosion that killed nearly 300 students and teachers. Texas quickly passed a law requiring natural gas to be odorised, which began a process that eventually led the US government to pass legislation that mandated the injection of smell into natural gas pipes.

Early odorants were simple sulphur compounds, but over time, more sophisticated chemicals were developed to maximise safety, often including mercaptans, which provide that characteristic ‘rotten egg’ smell, and THT, which adds a ‘garlic-like odour’, both of which are engineered to be highly detectable, even at very low concentrations.

This is where Peter Hansen comes in – he had a start-up engineering company and was contacted in the early 1970s when natural gas was being piped to the steel works in Newport, South Wales, and from there up to the Midlands, from where it would be used to provide energy to homes and businesses across the UK. He was tasked with creating a formula that could be used at an industrial level to assist in the early detection of leaks. He began to experiment, seeking the ‘nastiest smell’ he could think of, but one that would remain stable and reliable. Eventually, his formula was used to create the smell we now associate with gas, but which isn’t natural at all. The science of gas odourisation has evolved a great deal over the past century. Nowadays, sophisticated electronic systems precisely measure the gas flow and adjust the odorant injection accordingly to ensure consistent safety levels, but the simple, unpleasant smell of gas is still the most important ingredient in keeping us safe in our homes, schools and workplaces.

Have a great weekend (and an enjoyable Pi Day tomorrow…)

Best wishes

Michael Bond