Methyl mercaptan is a highly toxic and flammable gas that is naturally produced from decomposing organic matter. It has a strong unpleasant odor detectable at very low concentrations. Exposure can cause various health issues. Monitoring and preventing exposure is important, especially for workers in industries where methyl mercaptan may be present.

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Methyl mercaptan (CH3SH)
All you need to know about...

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All you need to know about Methyl mercaptan (CH3SH)WHAT IS CH3SH?
It is naturally released in the atmosphere from
microbial degradation of organic matter
It is an organosulfur volatile organic compound
(VOC). It can be easily ignited and decomposed,
emitting highly toxic fumes and flammable
vapours.
It is heavier than air and may collect in low-lying
areas. Its effective lifetime in the atmosphere is
about 1 to 26 hours.
Methyl mercaptan (CH3SH), also known as methanethiol, is a colorless, highly
flammable, toxic gas with a distinct, strong unpleasant odour.

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All you need to know about Methyl mercaptan (CH3SH)CH3SH ODOUR
The odour of methyl mercaptan can be described as that of rotten cabbage or garlic that
can be detected at a concentration of 0.0005 ppm.
Intensity Description Concentration
(ppm)
0 No odour 0.0030
1 Threshold 0.041
2 Faint 0.57
3 Median, easily
noticeable
7.9
4 Strong 110
5 Most intense 1500
Table : Odor Intensity of Methyl Mercaptan
Source: Acute Exposure Guideline Levels for Selected Airborne Chemicals: Volume 15, National Research
Council

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All you need to know about Methyl mercaptan (CH3SH)SOURCES
Natural Sources: Marshes, dump sites, underground gas
pockets, etc.
Anthropogenic / Industrial Sources:
● Manufacturing and use of methionine (i.e. poultry feed),
pesticides, jet fuels, oil shale, plastics, etc
● Sewage treatment plants,
● Petroleum refining
● Starch manufacturing
● Wood-pulp mill
● Pharmaceutical industry
● Rendering plants, etc

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All you need to know about Methyl mercaptan (CH3SH)
● Permissible Exposure Limit (PEL) given by OSHA (Occupational Safety and Health Administration)
defines the maximum concentration of H2S to which an unprotected worker may be exposed to.
● Recommended Exposure Limit (REL) and Immediately Dangerous to Life of Health (IDLH) are the
occupational exposure limit recommended by NIOSH (National Institute for Occupational Safety and
Health)
● TLVs (i.e. threshold limit values) are the exposure guidelines given by ACGIH (American Conference of
Governmental Industrial Hygienists)
PERMISSIBLE LIMITS
Recommended limits for CH3SH for occupational exposure
OSHA (PEL) For general industry : 10 ppm Ceiling
For construction industry : 0.5 ppm TWA
For maritime : 0.5 ppm TWA
ACGIH (TLV) 0.5 ppm TWA
NIOSH (REL) 0.5 ppm Ceiling
NIOSH (IDHL) 150 ppm
[Source: Acute Exposure Guideline Levels
for Selected Airborne Chemicals: Volume
15, National Research Council]

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All you need to know about Methyl mercaptan (CH3SH)
The AEGL (Acute Exposure Guideline Levels) values by EPA (Environmental Protection Agency) of
methyl mercaptan are given below. They represent threshold exposure limits (exposure levels below
which adverse health effects are not likely to occur) for the general public and are applicable to
emergency exposures ranging from 10 minutes (min) to 8 h.
PERMISSIBLE LIMITS
AEGL Values for methyl mercaptan (ppm)
Classification 10 min 30 min 1 h 4 h 8 h
AEGL-1 (non disabling) - - - - -
AEGL-2 (disabling) 40 29 23 14 7.3
AEGL-3 (lethal) 120 86 68 43 22
[Source: https://www.epa.gov/aegl/methyl-mercaptan-results-aegl-program]

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All you need to know about Methyl mercaptan (CH3SH)ADVERSE IMPACTS
HEALTH IMPACTS OF METHYL MERCAPTAN
● Headache
● Irritation in Eye, Nose and
respiratory tract
● Dizziness
● Nausea,
● Vomiting
● Seizures
● Lack of coordination
● Damage central nervous
system
● Damage liver
● Damage kidney
● Causes anemia
● Respiratory paralysis
● Coma

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All you need to know about Methyl mercaptan (CH3SH)CORRECTIVE MEASURES
The primary action is methyl mercaptan monitoring i.e. to measure how much of CH3SH
concentrations you are exposed to. In addition to this following corrective measures can be
taken:
● Avoid going to or staying in low lying areas where methyl mercaptan is produced such as
marshes, dump sites, etc.
● Avoid staying upwind of wastewater treatment plants, sewage treatment plants, landfills,
and industrial areas of starch manufacturing, wood-pulp mill, etc.
● Always use appropriate personal protective equipment (PPE) while using CH3SH
containing products or while going to places where presence of high levels of CH3SH is
suspected.
● Also, if the presence of high levels of CH3SH is detected, immediately vacant the area and
provide proper ventilation to remove the gas.

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All you need to know about Methyl mercaptan (CH3SH)MONITORING METHODS
Gas-Phase Chemiluminescence
When ambient air is mixed with ozone, the methyl
mercaptan molecules present in the air reacts with
ozone, emitting light proportional to the CH3SH
concentration present in the air sample. It is detected by
a photomultiplier tube and converted to CH3SH
concentration values.
Semiconductor
When sensor is exposed to air sample, the methyl
mercaptan molecules react on the metal oxide surface of
the sensor and dissociate into charged ions which alter
the resistance of the film which is measured and
converted to the CH3SH concentration.

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All you need to know about Methyl mercaptan (CH3SH)MONITORING METHODS
Electrochemical
Methyl mercaptan monitors working on the
electrochemical principle are operated
based on diffusion of CH3SH gas into the
sensor which results in the production of an
electrical signal proportional to the methyl
mercaptan concentration.
It allows accurate measurement of even low
concentrations, which is essential in methyl
mercaptan monitoring in the ambient
conditions.

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All you need to know about Methyl mercaptan (CH3SH)OIZOM’S PRINCIPLE
Oizom’s ODOSENSE is the real-time odour
emission tracking solution. It continuously
detects, measures and monitors the odourful
gaseous contaminants including H2S, NH3, SO2,
CH3SH, TVOC, CH2OH, and weather parameters
like temperature, humidity, wind speed, and wind
direction.
The sensor that measures methyl mercaptan work
on the principle of electrochemical sensing.
Real-time monitoring of CH3SH levels helps in
determining their source as well as formulating an
action plan to control methyl mercaptan
emissions.