Does Your Gas Stink?

by Scott Gaudet, Bergquist, Inc.

There’s a good reason gas smells rotten

Since the beginning of odorized liquified petroleum gas (propane), the most common method to tell whether or not propane is properly odorized for its safe handling is to use the nose. The “sniff test” may reveal that propane has the odorant ethyl mercaptan mixed into the propane in question. Since the 1930s, odorant has been required to detect the presence of propane. In other words, to make your gas stink!

Certain conditions can im­pair one’s ability to detect smells. For example: sinus con­ditions, allergies, head colds, smoking, or recent use of alcohol or drugs all decrease the olfactory sense. More recently, people who have had COVID-19 can have a reduced sense of smell. Certain medications can also have an effect. Some people may also have a condition called Anosmia, the loss of the sense of smell.

NFPA58 states that the dosage of ethyl mercaptan must be at least one pound per 10,000 gallons of propane. The industry typically adds 1.5 pounds per 10,000 gallons. This is done normally at the refinery or at the end of a pipeline. Some propane for industrial use is non-odorized, and some rail terminals may inject the mercaptan after they receive it. Once propane is received at a marketer distribution facility, a sniff test is typically done during the unload process.

But what if no one is present at the plant during offload and sniff tests are not performed? Or what if sniff tests were only done on random samples? What if a load of propane, or several transport loads, does not contain any ethyl mercaptan - or not a significant amount of ethyl mercaptan? This happened to a number of marketers in Massachusetts and New England back in 2010. The inadequate amount of ethyl mercaptan was discovered after a massive explosion that caused catastrophic damage, severe injuries, and loss of life. Those of us working in the Northeast at that time quickly learned a lot about odorization. A number of propane bulk plant facilities were shut down due to under-odorized (or un-odorized) propane by local, state, and federal authorities. The facilities were not allowed to open until they could prove they had sufficient levels of ethyl mercaptan in their tanks.

So how do you know if your propane has enough odorant in it? There are several ways a marketer can test for ethyl mercaptan. First, and probably the most expensive and time consuming method is to send a sample of propane to a testing lab in an approved, properly sealed shipping vessel. Needless to say, that is not very practical. A second method is to use any one of several electronic testing devices available from a variety of manufactures. They are all fairly expensive, delicate instruments and require maintenance and recalibration over time.

The third and most cost effective way to test is the stain-tube test method. It is quick, easy, and can be performed in just a few minutes. Stain-tube testing is an approved method when done according to ASTM D5305 - Standard Test Method for Determination of Ethyl Mercaptan in LP-Gas Vapor. A number of rail terminals in the Northeast currently use this method.

A stain-tube test can also be performed at the bulk plant, off a bobtail, or at a customer end-user location. A sample of propane vapor is either collected into a special collection bag or collection bottle. Using a pump about the size of a soda can, a sample is drawn out of the collection vessel through a stain tube (similar to a test tube). After a specified amount of time, the tube is checked and a change of color inside the tube confirms the presence of ethyl mercaptan. Additionally, there is a scale on the tube to allow for adjustments in temperature of the gas and for outside air temperature. Finally, a chart provided by the manufacturer of stain tubes can determine if there is a sufficient quantity of ethyl mercaptan in the propane sample as required by NFPA58.

Over the last ten years I have assisted in stain tube testing at rail terminals and bulk plants throughout the Northeast. I even conducted stain tube training via Zoom during the COVID shutdown. Not a single person thought it was a troublesome process to perform. And, best of all, it is affordable enough to equip each facility with a test kit.

Once you have a good method for testing and someone asks if your gas stinks, you will be able to provide your answer with data!

Scott Gaudet is the Bergquist Area Sales Manager for Northeast U.S. He can be reached at 603-422-5901 or scott.gaudet@bergquistinc.com.

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