Propane and Odor Fade |

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Propane and Odor Fade

Lisa Dejong, The Flint Journal

Six children, ranging from 2 to 19 years of age, were killed when this rural Michigan house exploded early on the morning of September 3, 2005. If you use propane in your home or business, this kind of incident could happen to you. Here’s what you need to know about propane and odor fade.

ABOUT PROPANE
ODOR FADE
PROPANE SAFETY
DOCUMENTS
NOTABLE PROPANE INCIDENTS
PROPANE NEWS

About Propane

Propane, also known as liquefied petroleum (LP) gas, is a versatile and clean-burning fuel used for a variety of home, commercial and industrial purposes.

About 7 million households, or about 6.5% of the 106 million U.S. households, depend on propane as the primary fuel for heating and cooking, according to the National Propane Gas Association. Another 10 million households have one or more propane-fueled appliance, and about 47 million homes have outdoor propane grills. Propane is also used in about 7 billion square feet of commercial space in the U.S.

PROPANE ODOR

In a natural state, propane and natural gas have no odor, taste, or color. An odorizing agent is added to the gas in order to warn consumers of a leak. The odorant in propane is ethyl mercaptan, a sulfur-based compound that gives it a distinctive rotten-egg smell (see What’s that smell?).

PROPANE AND NATURAL GAS

The properties of propane are much different than those of natural gas. It is critically important to appreciate these distinctions:

Propane has 2.5 times more energy per cubic foot than natural gas.
Propane is heavier than air, while natural gas is lighter than air.
Propane can lose its odor.

What this means: While natural gas will tend to rise into the atmosphere and disperse, propane sinks to the ground and is prone to collect in low areas and enclosed spaces. Propane behaves more like water, hugging the ground and flowing downhill toward the lowest spot it can find, such as a basement, cellar, crawl space or utility room. Propane can even flow underground if leaked from buried pipes. Like water, propane can seep through a foundation into the space beneath a home or business. It has a propensity to accumulate and pool.

When mixed in the proper proportion with air, propane is highly explosive. Propane explosions can be very powerful, causing severe structural damage and in many cases completely leveling a building. Fatalities and severe injuries are common.

Odor Fade

The odor of propane may be diminished or absent under a variety of conditions. Issues begin long before propane is delivered to the consumer (see Matters of degree).Research shows that the mercaptan can chemically react and be absorbed by other materials, significantly reducing the level of odorant in the gas.

STEEL TANKS AND LINES

Odorant can be faded by the presence of air, water or rust inside a tank or cylinder. Mercaptan chemically reacts with steel and rust in tanks and fuel lines, neutralizing the odorant over a period of days or weeks. The odorant in a common 20-pound cylinder can be completely depleted in five to seven days, resulting in gas that is essentially deodorized.

Often the tanks are new or have not been used continuously. If an empty propane tank is allowed to remain open to the atmosphere, a layer of rust can form on the inside that will result in odor fade when the tank is filled again.

The risk of odor fade varies depending on the materials and methods used in manufacture of tanks. A Canadian oil company found that the odorant in gas stored in cylinders from one manufacturer was stable, but cylinders from another manufacturer showed “rapid and complete fade” of odorant.

The odor in propane can be faded in brand new cylinders. In a survey of 1-pound cylinders purchased in retail stores, the odorant was found to be significantly depleted in six of nine cylinders.

The propensity for odor fade can vary from refill to refill. The chart below shows that in one 20-pound grill-type cylinder, the level of mercaptan dropped to zero the first and third time it was filled, but not the second or fourth time.

source

CONCRETE, MASONRY AND POROUS MATERIALS

Propane odorant is readily absorbed by concrete, masonry, drywall and other porous materials used in foundations and basements.

In a test done for the U.S. Consumer Product Safety Commission, a concrete block was placed in a chamber representing the dimensions of a typical basement, which was then filled to an explosive level with propane. In four hours, the level of ethyl mercaptan fell below the limit of detection. Two hours later, no ethyl mercaptan remained in the gas.

Ethyl mercaptan is also effectively stripped from propane gas as it flows through soil, as from a leaking buried pipe. Percolating propane through soil can remove some or all of the odorant from propane, similarly to running water through an activated charcoal filter.

Olfaction

The acuity of the sense of smell varies widely among apparently healthy people, and diminishes with age. The older we get, the less we are able to detect odors. The ability to smell is affected by colds and allergies, smoking, and conditions such as Alzheimer’s disease. Millions of Americans are unable to smell mercaptan — many of whom are unaware of that fact.

More than half of people over 60 don’t recognize the smell of gas, according to a survey by Monell Chemical Senses Center. The average 70-year-old’s threshold for detecting ethyl mercaptan is 10 times higher than that of the average 18-year-old, according to investigators at the John B. Pierce Foundation Laboratory.

Smells can also be “masked” by fumes, solvents or grease, smoke, cooking and other odors.

What this means: You can’t rely on the odor of propane to warn of a leak. The odor may be very faint, or you may smell nothing unusual at all.

Documents

Odorant Depletion in Portable Cylinders. Analysis of odor fade in tanks conducted by Esso Canada.

Final Report: Characterization of LP Gas Odorant Fade. Analysis of odor fade done by Arthur D. Little, Inc., for the U.S. Consumer Product Safety Commission.

Odor Fade: Possible Causes and Remedies. Report by Michael Usher of Elf Atochem North America for the CGA Gas Measurement School.

The Smell of Danger. Article from Chem Matters magazine that provides an overview of the technical issues related to propane odor fade.

Notable Propane Incidents

W. Dayton Whittle, The Register-Herald

LITTLE GENERAL STORE, GHENT, WV

On the morning of January 30, 2007, a gas company worker encountered a problem while transferring propane from an old tank to a new replacement tank behind a rural convenience store and gas station. A component on the older tank broke, allowing propane vapor to escape. A fire crew from the Ghent, WV, volunteer fire department and an ambulance were dispatched to the scene. Within minutes, propane had seeped into the convenience store. It exploded with such force that the a fire truck and ambulance were flipped over, five homes were damaged, and windows were blown out at the Ghent Elementary School. Four people were killed and five others were seriously injured.

More information:
Investigation and report by the U.S. Chemical Safety and Hazard Investigation Board
Deadly day in Ghent
Memorial slide show from West Virginia South magazine
Google News: Ghent explosion

FALK CORPORATION, MILWAUKEE, WI

The Falk Corporation is a manufacturer of industrial gears and couplings, and one of the oldest factories in Milwaukee. On December 6, 2006, employees were testing a backup propane-fueled power system. An employee reported a leak in a 30,000-gallon propane tank, and portions of the 61-acre complex began to be evacuated when an explosion ripped through the plant. Propane gas had filled a warehouse. Three people were killed and 47 others were injured. The blast destroyed an area of about two football fields and blew debris blocks away. Windows miles away were broken. Vehicles were hurled through the air, and about thirty cars were destroyed.

More information:
Explosion at Falk Corp.
Photo gallery from the Milwaukee Journal Sentinel
Wikipedia: 2006 Falk Corporation Explosion

STOCKLINE/ICL PLASTICS FACTORY, GLASGOW, SCOTLAND

Propane from a corroded underground pipe leaked into the ICL Plastics factory building in western Glasgow. Around midday on May 11, 2004, an explosion destroyed the four-story building, which largely collapsed into a pile of rubble. Nine people were killed, including two company executives. Thirty-seven others were injured, 15 of them seriously.

More information:
Photo gallery from BBC News
The ICL Inquiry
The ICL/Stockline Disaster
Wikipedia: ICL Plastics factory explosion
Google News: ICL Plastics Factory Explosion

KELTIE’S BUM STEER, BREWSTER, NY

Propane from a single grill-type 20-pound cylinder leaked into the space beneath a restaurant, which had been built over a swimming pool. While preparing for the evening meal on July 28, 1997, a spark from a vacuum cleaner ignited an explosion that killed the restaurant’s manager and a 25-year-old woman who was there interviewing for a waitress job. Five others were seriously injured.

More information:
Keltie’s blast shows dangers of propane

HUMBERTO VIDAL EXPLOSION, SAN JUAN, PUERTO RICO

On the morning of November 21, 1996, an explosion ripped through a popular department store in a busy shopping district of San Juan, Puerto Rico. Much of the first, second, and third floors of the six-story building were shattered and dropped into the basement. The blast was so powerful that authorities suspected it was a terrorist attack. Propane leaking from an underground pipe had been drifting into the building for days until apparently ignited by an air conditioner. Thirty-three people were killed and 80 were injured.

More information:
Final report of investigation by the National Transportation Safety Board
Report from Suburban Emergency Management Project
Wikipedia: Humberto Vidal Explosion

Propane News

NOTE: The author of this page has no affiliation, employment or financial relationship with any energy company, attorney or propane-related group. He is a disinterested journalist. If you are a member of the media working on a story, please let me know for my files.

This page last updated 02/26/10.

Topics: Uncategorized | 14 Comments »

14 Responses to “Propane and Odor Fade”

Bruce Goldfarb Keltie’s Blast Shows Dangers of Propane | Says:
October 29th, 2008 at 2:54 pm
[...] Propane and Odor Fade [...]
Joshua Shoulders Says:
January 12th, 2009 at 1:42 pm
Dear Sir,
I am giving a persuasive speech for competition in the NCFCA on removing propane gas from residential zones. Those six children that you mention at the beginning were very good friends of my family and mine (Joseph and Nehemiah were my best friends). Thank you for putting the dangers of propane out for the world to see. I was wondering if you could tell me what date this article (Propane and Odor Fade) was written. Also, if you have any additional information I could look at or websites, books, and articles to which you could refer me, I would be very thankful to receive that information. Thanks again!

Sincerely,
Joshua Shoulders
Bruce Says:
January 14th, 2009 at 8:26 am
The bulk of the work on this page was completed in September 2008, and it is updated as needed. I don’t know of other websites or sources of information that have not already been mentioned here. I suggest you download and read the documents linked above. I’d be very interested in hearing what you have to say about propane, and perhaps adding your material in whatever form — written, audio or video — to this page.
Eric Svensson Says:
February 15th, 2009 at 4:44 pm
Joshua should realize that propane is one of the safest and most widely used fuels on earth. One widely used altenative, charcoal, is so dangerous it should never be ued inside any buildings. The tragedy of the six children is not the gas’s fault, and “removing propane gas from residential zones” would result in the children of most parts of the world suffering from the effects of coal fumes, carbon Monoxide, oil smoke, and other pollutants created by much dirtier and more dangerous fuels. Helping people detect gas leaks, and showing how to use propane safely is a very useful way to spend his time.
Dave Says:
March 9th, 2009 at 3:32 pm
Does odorant fade occur with natural gas as well? I understand that ethyl mercaptan is used as an odorant in it, too.
Bruce Says:
March 9th, 2009 at 7:32 pm
Good question, Dave. There is nothing unique about the chemistry of natural gas versus propane. Similar mercaptan compounds are used as odorants in both. There are several related mercaptans — ethyl mercaptan, methyl mercaptan, butyl mercaptan, etc. Sometimes suppliers use a blend.

So it is theoretically possible for odor fade to happen in natural gas, such as if a slow leak percolates up through soil or gas accumulates in a concrete structure. Odor fade doesn’t seem to be as much of an issue, since natural gas is lighter than air. It tends to float up and dissipate, while propane is heavier than the air, sinking and pooling where the odorant has an opportunity to get adsorbed by surfaces.

Also, there are the same issues of impaired olfaction and odor blindness. If a person is unable to smell natural gas, he or she will be unable to smell propane. It’s a good idea for people to check their sense of smell. Your local utility company or gas supplier has free mercaptan scratch-and-sniff cards they’ll give you for the asking.

Odor fade is not likely to happen within natural gas distribution systems. Natural gas flows continuously through pipes and lines, while propane is stored in tanks that are depleted and refilled.

Unlike natural gas, propane is stored in the liquid phase and used in the vapor phase. There are issues of vapor pressures and boiling points and such that affect the concentration of odorant in propane.
Ronda Eddy Says:
March 22nd, 2009 at 5:37 am
I had a propane leak in the crawlspace of my house. We have fixed the leak but the propane has sunken into the dirt, is there anything I can do to remove the odor?
Bruce Says:
March 22nd, 2009 at 6:58 am
Glad to hear the propane leak was detected in time. Dirt and porous masonry surfaces adsorb mercaptans like a sponge. The mercaptan is in the material. Once the gas is gone, the odor itself is harmless. The area smells vaguely of gas. I’m not a chemist or engineer, but if it were my home, I’d find ways to mitigate the odor. Perhaps you can remove a few inches of dirt and/or cover it with clean topsoil. If the crawlspace is open to the outside, I’d rinse what I could with a hose to remove surface dirt from the foundation, supports and beneath the beams. I’d go to Home Depot and buy a pump sprayer with a long nozzle, like the kind used by home exterminators, and fill it with a few bottles of cheap hydrogen peroxide from the dollar store. Peroxides neutralize sulfur-bearing compounds, and it may work on mercaptan. I’d spray as much as I can, and for good measure would follow up with a spray of something like Febreeze. You might also try sprinkling activated charcoal, which is sold with pool or aquarium supplies. But this stuff is jet black and messy; not a good idea if you have pets that might get in there. And as long as you’re in the crawlspace, install a propane detector — that’s the dangerous area where gas can accumulate.
C.Martin Says:
April 9th, 2009 at 11:30 am
Bruce, I was very interested in the results from the canadian study on oxide absorption and I was sad that the document you have posted doesn’t inlcude the tables. I found one that is posted on the internet that does and I thought I’d pass it along incase anyone else was interested.

http://www.cpsc.gov/library/foia/foia02/os/propanept2.PDF

Thanks for all your work on the subject!
Bruce Says:
April 10th, 2009 at 12:15 pm
Thanks for the document, Courtney. I’ve replaced yours for the inferior version I had linked. I appreciate any other documents or information you care to pass along.
Renee MacKenzie Says:
January 6th, 2010 at 10:34 am
Dear Bruce:

Just another note to say thank you again for your work in this area. I wrote you about two and a half years ago after suffering burn injuries in a house explosion. I do my own small part in educating people about the dangers of odor fade and propane but it seems So Little compared to the potential devastation.
Brooke Brockbank Says:
January 12th, 2010 at 1:39 pm
We live in a rural area and have a propane tank- only for fireplace. A few days after we installed the propane tank we smelled propane if we were standing right next to the fireplace. It was very strong. We called and had someone come check it out- when they got there the smell was not present anymore (of course), but they did many tests on all the pipes and said they were convinced there was no such leak. They also said that maybe we smelled something, but propane would sink and that it would be near the floor and not in the area around the fireplace. Well the smell keeps coming back very strong- it is the propane smell, but whenever I smell the floor, i smell nothing. Should I be concerned. Sometimes I can smell it when I walk in the room. But again it is never around the floor by the fireplace. Can you ease my worries about this?
Bruce Says:
January 17th, 2010 at 11:36 am
It’s hard to say. I’m not a propane expert or an engineer. A propane system can be tested for leaks, which I presume was done by person who came out to your house. If you aren’t confident of that person’s assessment, have your system checked by a qualified technician recommended by your propane distributor. It could be that you have a batch of propane that is heavily odorized, or that you have a very sensitive sense of smell. The best way to ease your worries is by installing a propane detector, which goes in the lowest spot in your house — a basement or crawlspace, if you have one.
Ramsey Says:
January 28th, 2010 at 6:46 am
Holy hell, Bruce. Never seen that opening photo before. Glad to know you’re on the case…..

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