gas focus


Hydrogen Sulphide Hydrogen Sulphide (H2


S) is a


colourless, fl ammable gas that is highly toxic to organic life. Although it is fl ammable, its toxicity is so high that it causes damage to life before its fl ammable threshold is ever reached.


H2


S is produced by the anaerobic (without the presence of Oxygen) bacterial break down of organic matter and the gas is characterised by a strong smell of rotten eggs. It is slightly heavier than air making it likely to collect in low lying areas.


Sources of H2 H2


S S arises from virtually anywhere


where elemental Sulphur comes into contact with organic material, especially at high temperatures. With this in mind, volcanoes and hot springs are a natural source of H2


S.


Although crude petroleum can contain some H2


contain up to 90% H2 Because H2


S, Natural Gas extracted can S.


S is produced by anaerobic


microbial activity, there are a variety of locations it can build up in including the briny ballast tanks of ships and vessels, during water treatment processes and in a wide variety of oil rig applications such as HVAC air vents of accommodation buildings, mud return line receiver tanks and crude oil storage tanks, pipes, fl anges and valves.


The dangers of H2 Although H2


S S can be recognised by


a strong and pungent odour of rotten eggs at anywhere between a few ppb (parts per billion) and 30ppm (parts per million), at higher concentrations, it can cause severe damage or even death.


Page 10 | GasDetector | Winter 2011 Working safely with H2S:


Because of the effects of H2S and its toxicity, portable gas detection is essential to ensure adequate worker safety. Fixed gas detection should also be used to ensure that if a leak is detected, emergency procedures can be initiated.


Call: +41 (0) 44 943 4300 or visit: www.honeywellanalytics.com


Depending on its concentrations, H2 of adverse health affects including:


Exposure mg/m3 0.011 2.8 5.0 7 – 14 28 >140 >560 >700


S can cause a wide range Affect / Observation Odour threshold


Bronchial constriction in asthmatic individuals


Eye irritation Decreased Oxygen uptake


Fatigue, loss of appetite, headache, irritability, poor memory and dizziness


Olfactory paralysis (sense of smell is paralysed)


Respiratory distress Death will occur Reference Amoore & Hautala, 1983 Jappinen et al., 1990 Valhoorne at al., 1995


Bhambhani & Singh, 1991: Bhambhani et al., 1996b, 1997


Ahlhorg, 1951 Hirsch & Zavala, 1999 Spolyar, 1951 Beauchamp et al., 1984


This information is taken from Concise International Chemical Assessment Document (CICAD) 53: Hydrogen Sulphide: Human Health Aspects. Published in 2003 under the joint sponsorship of the United Nations Environmental Programme, the International Labour Organisation and the World Health Organization (WHO), and produced within the framework of the Inter-Organization Programme for the Sound Management of Chemicals (IOMC).


This table provides details of the allowed exposure to H2 Volume of H2


S 5ppm / 7mg.m-3 Relates to standard


Workplace Exposure Limit (WEL): Long-term Exposure Limit (LTEL): 8 hours Time Weighted Average (TWA) reference period (EH40/2005) in ppm


10ppm / 14 mg.m-3


Workplace Exposure Limit (WEL): Short-term Exposure Limit (STEL): 15 minute reference period (EH40/2005) in ppm


S. Description A worker can be exposed to an H2 S


concentration no greater than this during an 8 hour period


A worker can be exposed to an H2 S


concentration no greater than this during a 15 minute period


WEL information provided in the table is taken from EH40/2005 Workplace Exposure Limits. Please refer to local legislation in your country.


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