Tech Environmental e-Newsletter
November 2006


As public awareness of hydrogen sulfide (H2S) has grown, guidelines have been created by federal agencies, states, and municipalities, each with a different objective and perspective. Meanwhile, misinformation about H2S on the Internet and from other sources has led some citizens and legislators to pursue incorrect applications of existing guidelines. 


What is the true basis for hydrogen sulfide limits? Are they created to deal with odor nuisance concerns? Health concerns? Welfare concerns? The truth is that different concerns require radically different H2S thresholds, although today's H2S guidelines do not always address this with a clear focus.



Odors are everywhere; therefore, it is not enough to simply state that the presence of odor constitutes a nuisance. The key to determining odor nuisance is to apply FIDO - not man's best friend, but a set of factors that define whether an odor is or is not a nuisance. 


Frequency: an odor must repeatedly recur. 

Intensity: a single odor event must be very intense. Duration: an odor event must last long enough to adversely change the behavior of those affected.

Offensiveness: there is much less tolerance for more offensive odors.


All guidelines for H2S odor nuisances should consider all four FIDO factors, since nuisance determinations are subjective.



A distinction must be made between OSHA standards that are put in place to protect workers from toxic levels of H2S in the workplace and guidelines that protect sensitive citizens from acute exposures to H2S. Toxic standards are designed to prevent asphyxiation.


H2S is only toxic at levels that are hundreds of times higher than odor thresholds. Acute exposures are very different from toxic exposures - they represent mild levels of H2S exposure, and the symptoms from an acute exposure will decrease as the chemical compound is processed by the body. As such, guidelines that protect against acute exposures are extremely conservative, and represent a very low concentration of H2S. Misleading sources may mention the toxicity of H2S in the context of acute exposure levels; this often alarms concerned citizens and leads them to fear that acute exposures will have toxic effects. This unfortunate reality reinforces the need for health-based guidelines to clearly delineate the type of exposure they are designed to protect against.


H2S limits set for health purposes should not be confused with H2S limits set for odor nuisance purposes. There is no link between the odorousness of a chemical compound and its toxicity, nor does the presence of H2S odor indicate a threat to health.



Human welfare, as it relates to odorous chemical compounds like H2S, is a rather complex concept. Welfare concerns can include odor concerns, as well as protection of the natural environment, the accumulation of various compounds like H2S and sulfur dioxide in the atmosphere, the protection of wildlife from odorants, and a variety of other concerns. In addition, welfare guidelines vary wildly based on a community's odor perspective: some communities, like those in milltowns or farming areas, are sympathetic to some odorants in ambient air, while others have a much lower tolerance for odor. Each community, municipality or state should choose a welfare guideline that fits its odor perspective. 


It is crucial that guidelines enacted for welfare purposes be clear in their purpose and language. Since H2S is detectable by the human nose at extremely low, safe levels, a guideline meant to protect human welfare from H2S odors should never be confused for a guideline meant to protect human health.



H2S regulations, standards and guidelines will always be driven by local concerns. However, there is a clear need for a national framework to define the differences between H2S odor, health, and welfare concerns.  Ideally, health thresholds would be defined to protect sensitive individuals, while also considering the human body’s ability to consume and digest H2S.  It is extremely important that any standards consider that the human body can refresh its capacity to absorb H2S and that H2S does not accumulate in the body in the same manner as metals or other compounds. Health standards should differentiate between acute, subchronic, and chronic exposures, while at the same time separating themselves from odor and welfare concerns.  Presently, these appear to be blurred together.


To learn more about your specific H2S concerns, contact Dana Buske, PhD.


By the end of the year, the Massachusetts DEP is scheduled to either finalize its draft guidelines on landfill odor or re-issue them for additional comment. In June, MassDEP's Bureau of Waste Prevention requested feedback on a proposed policy guideline regarding odor nuisances and specifically addressing hydrogen sulfide. Tech Environmental has voiced a number of concerns to MassDEP regarding these draft guidelines:


> They contain only a single set of action items in response to any confirmed odor event, limiting the agency's ability to handle situations that can vary greatly. (MassDEP has confirmed that they plan to split the action items into additional tables in the forthcoming version of the guidelines.) 


> The entire set of action response items are triggered in response to a single odor event; the number of necessary action items should increase as the potential for nuisance conditions builds.


> The draft guidelines require that action be taken in response to a single odor complaint, neglecting the importance of frequency (see FIDO, at left) in determining odor nuisance. 


> It is not reasonable to require landfills to notify health agents about a "potential future health concern" in relation to a hydrogen sulfide odor complaint. As the article at left addresses, the presence of odor does not mean that health is at risk, and odor nuisances should be discussed separately from health hazards.


Michael T. Lannan, PE




Tech Environmental has presented its Odor Training seminars to many organizations, including the Massachusetts Landfill Operators, the New Hampshire Water Pollution Association, local Boards of Health, industrial clients, and groups of concerned citizens. Our introductory seminar, "Fundamentals of Odor", has been accredited by the Solid Waste Association of North America (SWANA) and by state Departments of Environmental Protection. This accreditation allows participants in TE seminars to earn continuing education credits and certifications.


The Fundamentals course includes modules that explain the basics of odor and odor science, an overview of typical odor potentials and identifiers, and a discussion of the various chemical, biological and thermal treatments available.  Further seminars use odor sampling to tailor their content to each audience - for example, operators at a treatment plant would work with sample odors from their site in order to learn how to identify and mitigate specific odors from their facility.

To learn more about our Odor Training, contact Matthew Riegert:

We are conveniently located on Trapelo Road at Reservoir Place on Route 128 at Exit 28 in Waltham, Massachusetts


1601 Trapelo Road

Waltham, Massachusetts 02451

ph. 781-890-2220

fax 781-890-9451

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TECH ENVIRONMENTAL is an environmental consulting firm specializing in air quality, odor control, noise abatement, and environmental due diligence.  General services include facility siting, licensing, permitting, compliance auditing, monitoring, and environmental impact studies.  Tech Environmental has worked for industrial, manufacturing and commercial clients in the private sector as well as municipalities and other public agencies.

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