Levitt-Safety Blog

What’s that smell? How you can detect gas leaks when your electronic monitor can’t

Jonathan McCallumMarket Segment Manager: Occupational Health, Industrial Hygiene & Environmental MonitoringSeptember 25, 2018

Rotten egg smell? It could be a gas leak. But, what happens when no gas is detected?

A Calgary Dairy Queen made national news recently when they finally solved the mystery of the pungent smell coming from the restaurant. The culprit? Mercaptan.

While natural gas is incredibly common in residential, commercial and industrial settings, it can also be incredibly dangerous. In fact, it is so flammable that even a small spark in the area of a leak can lead to a fire or explosion in the matter of seconds. But, it’s not the natural gas itself that smells bad. It actually doesn’t smell like anything at all. For this reason, mercaptan, a chemical compound composed of carbon, hydrogen and sulfur, is added to natural gas as an odorant to help people detect it. This is what the employees were detecting.

Since opening in 2015, the owner had called the fire department on a number of occasions to investigate where the smell was coming from but each time the gas detection tests came back negative. While the gas smell was prominent enough for the employees to pick it up with their noses, it wasn’t quite high enough to be detected electronically.

How could that be? First, many electronic gas monitors detect combustible gases in their explosive range or in per cent of Lower Explosive Limit (LEL). Natural gas is mostly methane which is lighter than air and has an LEL of 5 per cent by volume (50,000 ppm) which would equate to 100 per cent LEL.  The scale of most gas monitors will begin at 1 per cent LEL or 500 ppm in the case of methane and the gas level at customer height in the Dairy Queen was likely below that.  In contrast, the mercaptan used to add an odor to the natural gas is heavier than air and can be detected by the human nose at about 1 ppb (part per billion) in air.

So, how can one confirm their hunch when electronic tools can’t?

Gastec can do that.

A Gastec Pump with the appropriate colorimetric detector tube can be used to confirm the presence and concentration of mercaptan in our restaurant example.

Oil refinery industrial plant at night

The Gastec Detection System is easy to use, requires little training and can be used in conjunction with electronic gas monitors for an enhanced gas detection solution. Detector tubes provide fast, accurate results and are a low-cost method for routine or spot sampling of gases and vapours.

Tubes available for mercaptans include:

  • IG70 (0.35 – 84 ppm) and IG70L (0.1 – 8 ppm) – Mercaptans
  • IG72 (0.5 – 120 ppm)/IG72L (0.2 – 75 ppm) – Ethyl Mercaptan
  • IGL71H (20 – 2700)/IG71(0.25 – 140 ppm) – Methyl Mercaptan

Because of its low odor threshold, a low concentration of mercaptan is all that is required to provide the necessary warnings for natural gas users. At higher concentrations, mercaptan exposure can present some health risks such as headaches, nausea, coughing, and unconsciousness.  People working in the oil and gas industry where mercaptans are used should be aware of all precautionary measures related to this product.

The Gastec Detection System can be used to measure many other substances found in the Oil & Gas distribution, refining, and oilfield industries.  These include:

  • Hydrogen Sulfide in Production and Maintenance Operations
  • Petroleum Solvents including Benzene, Toluene, Xylene, Hexane, and Heptane
  • Liquefied petroleum Gas (LPG)
  • Formaldehyde
  • Mercury Vapour
  • Gasoline

For additional information be sure to download our Gastec Oil & Gas fact sheet and check out all of our available tubes. As always, if you have any questions about your personal exposure limits of hazardous gases, please reach out to me at [email protected].


gastec gas detection oil and gas