The recent concerns and complaints over the natural gas storage well leak in the Porter Ranch area of Los Angeles has been a big news story. However, most if not all of the symptoms that people reported don’t match the known symptoms of exposure to the chemicals involved.  Methane – the main ingredient in natural gas – is not toxic.  Meanwhile, tert-butyl mercaptan, the odorant added to the gas (so you know when you have a gas leak, so you don’t have an explosion and/or fire), is not known to cause bloody noses or most all of the symptoms reported by the residents there.  The remainder of the chemicals of potential concern from the leak (notably benzene) were at insignificant, trace levels.

The level of tert-butyl mercaptan that most people can smell is less than 1 part per billion (ppb), whereas the level that NIOSH says is safe for the workplace to avoid chronic disease (meaning, for an over 30 year career length exposure), is 500 ppb.  I’m sure that the level public health officials were using to gauge the safety of the Porter Ranch leak was lower than this (I believe I saw 100 ppb at one point and have not been able to relocate that info).  In any event, the monitoring found that the levels weren’t unsafe and were reportedly at very low levels, albeit levels that were high enough that people could still smell it, which is really quite low (<1 ppb).

So what gives?  How come people report all these symptoms at such low levels?  A Ph.D. toxicologist from UCSD once gave me the very memorable example of the smell of vomit.  When people smell vomit, they want to vomit.  It’s a disgusting, rank smell.  But it’s not toxic.

Something happens in our brains that when we smell something awful or unusual – we react.  The worse the smell, the worse the reaction.  It doesn’t mean it’s necessarily toxic, like in the case of Porter Ranch.  It’s part of our programming (probably with a natural selection benefit) to be grossed out by a nasty odor – even to the extent of having symptoms.  Some people might call this “psychosomatic,” which Webster’s defines as “of, relating to, involving, or concerned with bodily symptoms caused by mental or emotional disturbance,” but I tend to think this is a little insulting to the poor person experiencing the symptoms – more or less telling them that it is all in their mind and that they are crazy.  I think I like the term “sub cognitive” or “instinctive” reaction better.  Maybe we need to coin a whole new term to define the phenomenon.

Years ago, when I was employed as a Health and Safety Manager in aerospace, I dealt with a frustrating mercaptan problem that was part of a manufacturing process.  Whenever the employees used the compound containing mercaptans, people would freak out and walk off the job.  They’d claim we were trying to kill them and give them cancer.  Emotions ran high, and some employees reported experiencing symptoms, which similar to that discussed here – were not related to the mercaptan’s known toxicology.  Meanwhile, all our monitoring showed that levels were far below any level of concern. We were transparent about our sampling process and the results, but the employees were still not satisfied about the safety of the work.  In the end, we ended up moving the work to the graveyard shift when less people were around, and asking only volunteers to do the smelly work.  That seemed to work and production was able to continue.

Throughout my practice, I’ve had to deal with several situations where folks have reacted to bad smells that have made them feel sick at levels far below that known to be toxic.  At the end of the day, if you are the employer, landlord, or gas company that owns the source of the smell, you’ve got a problem.  Regardless if it is not at toxic levels, you’ve still got people upset, non-productive, and screaming at you that they are ill.  You need to deal with it and work with people best you can to minimize concerns and allay fears.

In any event, I’ll never forget the example of “the smell of vomit.”