The practice of incorporating a distinct smell into natural gas began in the early 1900s, primarily for safety reasons. This crucial addition allows individuals to easily detect and avoid potential gas leaks, which can pose serious hazards. Since natural gas itself is odorless, it becomes particularly dangerous in the event of a leak, as individuals may not be aware of its presence.
Without specialized equipment, such as gas detectors, people would be unable to sense the gas, increasing the risk of accidents. Therefore, the addition of a recognizable odor serves as a vital safety measure for households and businesses alike.
Before the 1930s
Gas used for lighting and heating (like coal gas or "town gas") had a natural smell due to impurities such as hydrogen sulfide. These impurities gave the gas a distinct, unpleasant odor, so leaks were easier to detect without artificial additives.
1937 – London school explosion, Texas
A tragic explosion at a school caused by an undetected gas leak killed nearly 300 people, mostly children.
On March 18, 1937, a devastating explosion occurred at the New London School in Texas, killing nearly 300 people, most of them children. The cause was a natural gas leak in the school’s basement. At the time, natural gas was odorless, so no one noticed the leak. A spark—possibly from an electric sander—ignited the gas, resulting in one of the deadliest school disasters in U.S. history.
This tragedy had a profound impact on public safety regulations. In its aftermath, authorities made it mandatory to add odorants to natural gas, making leaks easily detectable by smell. This event marked a turning point in the history of gas safety and led to the widespread use of sulfur-based compounds like mercaptans, which give gas its distinctive "rotten egg" smell.
This disaster didn’t just change regulations—it redefined how we think about safety, prevention, and the invisible threats around us.
After 1937
This disaster led to widespread regulations requiring odorization of natural gas. Countries around the world began adding strong-smelling chemicals to gas pipelines so that even tiny leaks could be identified quickly. This practice continues today as a cornerstone of gas safety protocols.
What Is Used to Odorize Natural Gas?
Chemicals called mercaptans, also known as thiols, are the most commonly used odorants. Examples include:
- Tert-butyl mercaptan, commonly referred to as TBM, is a significant compound in various applications.
- Methanethiol, also known as methyl mercaptan, is another important sulfur-containing compound.
- THT stands for Tetrahydrothiophene, a cyclic organosulfur compound with the chemical formula C₄H₈S. By misuse of language, THT (tetrahydrothiophene) is sometimes grouped with mercaptans because it shares their strong, sulfur-like odor and is also used as a gas odorant.
- Additionally, dimethyl sulfide (DMS) may be present in certain blends, contributing to their unique properties
These sulfur-containing compounds have extremely potent odors—even at concentrations as low as 1 part per billion. The smell is often described as rotten eggs, cabbage, or skunk spray. Their strong scent helps detect leaks early, even before concentrations reach dangerous levels.
How Is Odorization Done?
Natural gas is usually given a smell at city gate stations or distribution points. Here, an odorant is added to the gas using special pumps. This process is closely monitored. It makes sure the smell is strong enough to find leaks but not too strong to cause false alarms or discomfort.
Does (Natural) Gas Smell?
No, natural gas does not smell. It is odorless in its natural state.
The smell we notice comes from a chemical called an odorant. This is added for safety reasons. These odorants are usually sulfur-based compounds like methanethiol or tert-butyl mercaptan.
They have a strong, unpleasant smell, often compared to rotten eggs smell. This helps people detect gas leaks quickly.
