The Smell of Safety

Fire Safety

It’s the smell that gets all of us worried and makes us cautious. It’s acutely distinctive and foul smelling, quite similar to that of rotting cabbage, and it’s hard to miss. It’s the smell of safety and the chemical that produces this smell is Ethanethiol, most commonly referred to as Ethyl Mercaptan. Ethanethiol is an odorant that is added to LPG (Liquefied Petroleum Gas) and natural gas so that a gas leak can be easily detected. The primary constituents of LPG are hydrocarbon gases such as butane and propane and these are colorless and odorless in their natural state. If these gases are used as is, it would become extremely difficult to detect gas leaks with our sense of smell. The potential fallout of such undetectable gas leaks would be disastrous, to say the least. This is why Ethyl Mercaptan is added to LPG and natural gas so as to make it safe for use in households, industries, and other places.

When was Ethyl Mercaptan discovered?

The credit for discovering Ethyl Mercaptan goes to William Christopher Zeise, a Danish organic chemist who discovered the mercaptans (thiols) in 1832. At that time, Zeise created Mercaptan using chemicals such as calcium ethyl sulfate, barium sulfide, and hydrogen sulfide. Since then, various new variations have been produced. However, Ethyl Mercaptan remains to be the top choice globally for its use as an odorant.

Key properties of Ethyl Mercaptan

Ethyl Mercaptan is produced through a chemical process wherein ethylene is mixed with hydrogen sulfide. To support the chemical reaction, a catalyst is used. The most common catalyst used for the production of Ethyl Mercaptan is alumina. Ethyl Mercaptan has the chemical formula C2H6S, which makes it quite similar to ethanol. The only difference is that Ethyl Mercaptan has sulfur instead of oxygen. The sulfur in Ethyl Mercaptan is the thing that gives the odorant its distinctive foul smell. Ethyl Mercaptan is highly inflammable and burns at almost the same rate as other hydrocarbon gases such as butane and propane. When it burns, it loses its foul smell. This is another reason why Ethyl Mercaptan is preferred. If the foul smell would emanate even after burning, it could not have been used as an appropriate gas leak odorant.

Ethyl Mercaptan has a high detection rate. Even minute quantities of  gas can be detected by the human sense of smell. As per research studies, humans can detect the gas even when it’s present in the ratio of 1:2.8 billion parts of air. This is advantageous from a safety perspective, as the probability of the gas being undetected is extremely low.

Some exceptions to detecting the foul smell

There can be some exceptions to the human ability to detect the foul smell of Ethyl Mercaptan. For example, if a person has cold or some other ailment that has affected their sense of smell, they may not be able to detect the gas leak. In such cases, the consequences could be disastrous. The risk of an accident would increase if the person is alone. If you are facing a similar situation, it is recommended that you install a gas detector. These devices will activate and sound an audio alarm if gas is detected. If your sense of smell has been compromised for any reason and if you are staying alone, you can consider installing a gas detector.

Overexposure to other odorant gases or stench can also affect an individual’s ability to detect Ethyl Mercaptan. For example, people living near to a landfill or garbage processing plant may experience a constant stench. This might make them immune to the smell of Ethyl Mercaptan.

The foul smell of Ethyl Mercaptan can also be affected due to the phenomenon called ‘odorant fade’. This can occur if the gas reacts with other substances and goes through the process of oxidation. For example, if the inside wall of the gas cylinder is corroded or if there is presence of water or air, it will react with Ethyl Mercaptan. This will result in the phenomenon of ‘odorant fade’, wherein Ethyl Mercaptan will lose much of its foul smell. The process of ‘odorant fade’ can also occur due to adsorption, wherein Ethyl Mercaptan sticks to the inside walls of the gas cylinder. However, the occurrence of odorant fade is rare since LPG companies take adequate precautions to prevent such outcomes. The standard practice is to use dry and inert nitrogen gas inside the gas cylinder, which keeps away moisture and prevents rust and corrosion.

Is Ethyl Mercaptan toxic?

The toxicity of Ethyl Mercaptan depends on the quantum of exposure. Only a small amount of Ethyl Mercaptan is added to LPG, and at this ratio, it is considered to be safe. In case of a gas leak, people would inhale minute quantities of Ethyl Mercaptan, which is within the mandated safety levels. However, if Ethyl Mercaptan is inhaled directly, it can cause various problems such as shortness of breath, dizziness, headache, nausea, convulsions, fatigue, etc. In extreme cases, it can damage the liver and kidneys, resulting in coma and even death. Exposure over longer durations can lead to anemia, as Ethyl Mercaptan can damage the red blood cells. However, LPG and natural gas users do not face such risks since the amount of Ethyl Mercaptan added to these products is minuscule.

What to do when you notice the smell of safety?

The moment you smell Ethyl Mercaptan, it would indicate that a gas leak has occurred. It could be coming from your gas stove, gas pipe, gas regulator or the gas cylinder. The first thing you need to do is to turn off your gas burner. Next, you need to turn off the regulator and replace it with the safety cap. You need to open all doors and windows and if possible, move the cylinder outside your home. You should not operate any electrical switches or appliances at this time, as it may create a spark and ignite the gas. You need to move out of the house and call the gas distributor for emergency assistance.

The smell of safety, aka Ethyl Mercaptan, must have prevented thousands of accidents. It continues to save lives across households, industries and all other places where LPG and natural gas are used. This is one foul smell that you cannot live without.

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