From: Debbie M. Decker <dmdecker**At_Symbol_Here**UCDAVIS.EDU>
Subject: Re: [DCHAS-L] Chemical Safety headlines from Google (13 articles)
Date: Fri, 6 Feb 2015 20:11:25 +0000
Reply-To: DCHAS-L <DCHAS-L**At_Symbol_Here**MED.CORNELL.EDU>
Message-ID: BY2PR08MB298DCCF6779D9B3B4A1A604C8380**At_Symbol_Here**

There’s a suggestion that olfactory fatigue occurs but not to the degree or as well-documented as H2S.


Here’s a tidbit I found about methyl mercaptan (


For example, because methyl mercaptan has an odor recognition threshold of only 0.0021 ppm, it is often mixed with natural gas as an indicator of leaks. However, approximately one person in 1000 is unable to detect the strong odor of this mercaptan. Impulses travel to the olfactory bulb located at the base of the front brain. At the bulb, fibers from the nose contact other nerves, which travel on to various parts of the brain. An estimated 100 million receptor cells are present in humans. For a substance to be detected as an odor by the receptor cells, several criteria must be met:

The substance must be volatile enough to permeate the air near the sensory area.

The substance must be at least slightly water-soluble to pass through the mucous layer and to

the olfactory cells.

The substance must be lipid-soluble because olfactory cilia are composed primarily of lipid


A minimum number of odorous particles must be in contact with the receptors for a minimum length of time.

An estimated 30% of the elderly have lost the ability to perceive the minute amount of this mercaptan used in natural gas.


The current OSHA PEL is 10 ppm (ceiling). The 1998 OSHA PEL is 0.5 ppm. The ACGIH TLV and NIOSH REL is 0.5 ppm. (


I’m thinking at 0.0021 ppm odor threshold, this little newspaper tidbit still seems odd.




From: DCHAS-L Discussion List [mailto:dchas-l**At_Symbol_Here**MED.CORNELL.EDU] On Behalf Of Brandon S. Chance


I did not have a lot of time to dive into the literature, but olfactory fatigue is reported for ethyl mercaptan at 4ppm.  I would suspect methyl mercaptan would also have a similarly low threshold for olfactory fatigue.


From: Ben Ruekberg <bruekberg**At_Symbol_Here**CHM.URI.EDU>
Organization: University of Rhode Island / Dept. of Chemistry


Sufficient concentration of the highly stinky gas, hydrogen sulfide, will

knock out one's sense of smell.  Is it possible that the same applied to its

methyl analog?


Ben Ruekberg


-----Original Message-----

From: DCHAS-L Discussion List [mailto:dchas-l**At_Symbol_Here**MED.CORNELL.EDU] On Behalf Of

Edward Movitz


The initial statement about the amount of Mercaptan let loose and undetected

is also at odds with common sense :


"Chemical manufacturer DuPont has reported that about 23,000 pounds of a

flammable toxic chemical escaped in the building where four of its workers

died two weeks ago at a Houston-area plant.


DuPont disclosed in a news release the quantity of the methyl mercaptan that

led to the deaths Nov. 15."






Did anyone else find this tidbit odd?  How could there be methyl mercaptan

vapor build up and no one notice it?  Around here, someone takes the sealed

jar out of the dessicator to take to the fume hood and there's howling up

and down the hall from the smell.



Debbie M. Decker, CCHO, ACS Fellow

Chair, Division of Chemical Health and Safety University of California,






Birkett's hypothesis: "Any chemical reaction that proceeds smoothly under

normal conditions, can proceed violently in the presence of an idiot."





Tags: us_TX, industrial, follow-up, death, other_chemical


HOUSTON -- It was DuPont's third deadly U.S. accident in five years and the

deadliest of them all. On November 15th, a chemical leak in LaPorte took the

lives of four workers, including two brothers.


They were inside a building that manufactured insecticides.


Federal investigators have now claimed there were problems both with the

building and with how things were done there.


"What we are seeing here in this incident in LaPorte is definitely a problem

of safety culture in the corporation of DuPont," said Rafael Moure-Eraso,

Chairman of the U.S. Chemical Safety Board.


After months of investigating, the independent agency found a ventilation

system had been broken that allowed a harmful chemical called methyl

mercaptan to build up without anyone knowing it.







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