Can You Smell That? The Hidden Hero of Gas Safety

Can You Smell That? The Hidden Hero of Gas Safety

Natural gas has fuelled homes and industry for over two centuries. From William Murdoch’s first coal-gas lamps in Cornwall in 1792 to today’s methane and hydrogen blends. The convenience and relative cleanliness have reshaped daily life. However pure natural gas presents a hidden danger – it is colourless and odourless. Without a warning, leaks can fill up rooms and build up to explosive levels or replace oxygen which threatens lives.

Coal gas and early hazards

In the early 1800s, Britain’s gasworks turned coal into a new fuel called “coal gas,” the first version of what later became known as “town gas,” piped to homes and streets across the country. Murdoch lit his home, and soon streetlamps and factory fires burned coal gas across the country. Coal gas was a mixture of hydrogen, methane, carbon monoxide and sulphur compounds. Its natural smell, like tar or rotten cabbage could provide a warning, however, in practice, the gas was often experienced as a silent hazard. Its smell could dissipate or go unnoticed, especially in small leaks or poorly ventilated spaces.

The poorly ventilated rooms of that era could fill with toxic carbon monoxide (CO), and leaky fittings or cracked pipes could led to devastating explosions. Without a warning smell, Victorian homeowners relied on basic methods to spot gas leaks such as listening for hissing sounds or brushing soapy water over pipe joints. If bubbles formed, it meant gas was escaping. This simple “bubble test” helped detect leaks long before modern gas detectors were available.

The New London School explosion

On 18 March 1937 in New London, Texas USA, odourless methane had been unknowingly filling the local school’s basement. After a spark from an electric sander in the school’s industrial arts shop created an ignition, the subsequent blast killed 295 pupils and teachers and injured over 300 people, destroying the building and hurling heavy debris hundreds of feet. Within weeks, the Texas state government mandated odourisation of all gas supplies. Mercaptans were added to gas supply before year’s end, and other US states and Canada followed suit.

So, what exactly are mercaptans?

Mercaptans are the smell molecules added to gas, so leaks are noticed early:

  • Detectable at tiny levels even a small leak sends enough scent to the nose
  • Harmless at household concentrations
  • Stable and non-reactive in pipelines
  • Examples include tert-butylthiol and tetrahydrothiophene, all smelling like rotten eggs or skunk spray

National regulations in the UK

British engineers paid close attention to the 1937 disaster in New London, Texas. But national gas odourisation didn’t become mandatory in the UK until nearly three decades later. Why the delay?

At the time, post-war Britain still relied on town gas,  which already had a strong natural odour due to its sulphur content. As a result, there may have been less urgency to add extra scent. But by the 1950s, things were changing. The Gas Investigation Branch and the British Gas Council began testing artificial odourants to prepare for a future using cleaner-burning natural gas. They selected alkyl-mercaptans for their strong, stable aroma and adapted American odouriser designs for UK use.

Around the same time, engineers introduced the Stretford process, a chemical method that removed toxic hydrogen sulphide (H₂S) from town gas. With the natural smell removed, artificial odourisation became essential. Once the technical groundwork was in place, legislation followed. The Gas Act 1965 made odourisation mandatory from 1 December 1965, laying the foundation for modern gas safety.

Breathing apparatus through the ages

To face the hidden dangers of gas leaks, especially in confined or unpredictable environments, firefighters have relied on breathing apparatus for over a century. The evolution of this life-saving gear tells its own story of adaptation and innovation in the face of invisible threats. These invisible threats as discussed so far include gases like methane, carbon monoxide, and hydrogen. Without proper detection or odourisation, they pose serious risks of explosion, poisoning, or suffocation.

Our Museum preserves this history through our collection of historical and modern breathing apparatus includes early woollen smoke-hoods, Siebe Gorman rebreathers, and the pioneering equipment that laid the foundation for today’s advanced gear.

  • Woollen smoke-hoods (early 1900s): Before oxygen tanks or filtration systems, firefighters relied on thick woollen hoods soaked in chemicals like bicarbonate of soda or glycerine.
  • Siebe Gorman Salvus Mk VI (1920s): A pioneering oxygen rebreather allowing entry into gas-contaminated spaces, used in WWII and by the National Fire Service.
  • Dräger PSS 7000 (2000s–present): A modern SCBA that provides breathable air, motion alarms, and real-time data for operational safety.

How Scottish firefighters detect gas today

Even with that home warning scent, firefighters do not rely on smell. When a gas leak is suspected, Scottish Fire and Rescue Service crews prioritise public evacuation. They use modern detection equipment and breathing apparatus to assess the scene safely. They also work with Scottish Gas engineers, who can shut off supply lines, and they may call in other specialists to support and manage complex incidents.

  • Smell has its limits – Mercaptans warn of methane, but carbon monoxide has no scent.
  • Essential gear on the fireground – Firefighters carry combustible-gas detectors and carbon monoxide meters to reveal hidden hazards.
  • Specialist DIM units – Detection, Identification and Monitoring teams use lab-grade analysers to pinpoint gas types and concentrations.
  • Waste-site and biogas challenges – At old landfill or anaerobic-digestion plants, gas pockets can hide underground. Anaerobic digestion uses bacteria in sealed tanks to break down waste into biogas (mainly methane and CO₂) and digestate. Methane can seep through cracks, and flames may burn clear or vanish. Firefighters use thermal-imaging cameras alongside detectors to track invisible hotspots, while DIM units analyse the gas mix before tactics begin.
  • Safety first with breathing apparatus – Before entering confined or gas-filled spaces, firefighters test their breathing apparatus to make sure it’s sealed properly and holding pressure. This ensures that toxic or flammable gases can’t leak into their air supply.

Public awareness and resources

Gas safety isn’t just the job of engineers and firefighters – it starts at home. That’s why the Scottish Fire and Rescue Service and gas experts across the UK share easy, everyday tips to help you protect your household.

  • Fit and test a carbon monoxide alarm monthly in rooms with fuel-burning appliances
  • Use only BSI-kite-marked, annually serviced heaters
  • Change LPG cylinders outdoors with good ventilation
  • Store cylinders upright outdoors away from heat
  • If you smell gas, leave immediately, avoid switches or flames, and call 0800 111 999

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