Hydrogen Sulphide H2S

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H2S-HYDROGEN SULPHIDE:

Swedish chemist Carl Wilhelm is considered to be the inventor of H2S (Hydrogen Sulphide) in the year 1777.

H2S (Hydrogen Sulphide) is often evolved from the bacterial break down of organic matter in the absence of oxygen such as swamp and sewers. This process is generally known as anaerobic digestion.

Sulphur is significant ingredient in certain types of fossil fuel like natural gas and hydrocarbon wells. At high temperature those hydrocarbons give off free hydrogen which reacts with the existing sulphur contents in the fossils to form H2S (Hydrogen Sulphide)

The human body also generates H2S (Hydrogen Sulphide) in small amount and uses it as signalling molecule. There is always a bacterial breakdown of organic matter within our body while we consume and digest the food which contains carbohydrates. A part of it also goes out as urine and excreta waste.

H2S (Hydrogen Sulphide) is highly toxic, flammable, poisonous, heavy, hazardous and corrosive gas.

The various hazard related glossaries are given below

  1. 1} TLV-TWA(THRESHOLD LIMIT VALUE-TIME WEIGHTED AVERAGE) cum PEL(PERMISSIBLE EXPOSURE LIMIT:

It is the maximum permissible exposure limit of a hazardous chemical expressed either as parts per million {(ppm) (by volume in air) with respect to entry through inhalation} or milligrams(mg) per litre {with respect to entry through ingestion or skin contact} below which there is no reported adverse health effects on humans throughout his occupational life considering a 40 hours’ work schedule per week .This is legally enforceable level as established by OSHA ,It is also defined as the concentration that a worker may be exposed for 8 hours a day, 5 days a week, for 30 years of an occupational spell with no ill effects related to that chemical.

Accordingly the PEL for H2S (Hydrogen Sulphide) is 10 ppm

Formula to be applied:

Normal TLV-TWA cum PEL*8/n

Where n is the actual number of hours to be spent regularly

E.g. Accordingly with respect to H2S (Hydrogen Sulphide) exposure duration wise values are as shown below:

a) For 10 hours: (10*8/10) =8 hours

b) For 12 hours: (12*8/10) =6.6 hours

c) For 14 hours: (14*8/10) =5.7 hours

  1. 2} STEL(SHORT TERM  EXPOSURE  LIMIT)-TLV:

It refers to an exposure limit higher than PEL-TWA with the limits placed on the same time one can be exposed. STEL values are limited to 15 minutes followed by a gap of one hour in fresh air. This cycle can be repeated for maximum four times during 8 hours work

STEL TLV for H2S (Hydrogen Sulphide) is 15 ppm

3}IDLH (Immediate Dangerous to Life and Health):

It represents an atmosphere that poses an immediate threat to life or would cause irreversible adverse health effects, or would impair an individual’s ability to escape from a dangerous situation.It is also termed as an acute respiratory exposure that poses an immediate threat resulting into loss of life, immediate or delayed irreversible and adverse effects on health, acute eye exposure which may hamper an escape from a hazardous atmosphere.

IDLH for H2S (Hydrogen Sulphide) is 100 ppm.

 4} INTERPRETATION OF LETHAL (LIFE THREATENING) CONCENTRATION LEVELS OF TOXIC CHEMICALS: 

a)Toxic Doze Lo(Td-Lo)

It is the lowest dose of a material introduced by any route other than inhalation over any given period of time and reported to produce any toxic effect on humans or to produce carcinogenic, neoplastigenic or tetragenic effects on animals or humans.

b)Toxic concentration Low(Tc-Lo)

It is the lowest concentration of material in air to which animals or humans have been exposed for a given period of time and have produced any toxic or carcinogenic, neoplastigenic effect on animals or humans.

c)Lethal Doze Low(Ld-Lo)

It is the lowest doze (other than LD-50) of a material introduced by any route other than inhalation over any given period of time in one or more divided portions and reported to have caused death among animals or humans

d)Lethal Doze -50

It is calculated doze of material that is expected to cause death of 50% of an entire defined group of experimental animal population. It is determined from the exposure to the material by any route other than inhalation of a significant number from that population. Other lethal dose percentage such as LD-1, LD-10, LD-30 and LD-99 as may be published in scientific literature for the specific purpose of the author.

e)Lethal concentration (LC-50)

It is the lowest concentration of a material in air exposure to which for a specified length of time is expected to cause the death of 50% of an entire defined experimental animal population. It is determined from the exposure to the material of a significant number from that population.

f)Lethal concentration –Low (Lc-Lo)

It is the lowest concentration of a material other than the Lc-50 that has been reported to have caused the death in humans or animals. The reported concentration may be entered for periods of exposure that are less than 24 hours (acute) or greater than 24 hours (sub acute or chronic)

PUBLISHED VALUES FOR H2S

Lc-Lo for H2S: Human 600ppm/30 minutes;

Duration: (800ppm/5minutes duration)

Same is the value with reference to mammals that is 800ppm/5 minutes duration.

Ld-Lo: 5, 700pg/kg body weight (cynus, pulmonary)

Lc-50(Rat) : 444 ppm; Mouse 634 ppm/1hour

  1. 5} FLAMMABLE CHARACTERISTICS OF H2S (Hydrogen Sulphide): 

     Flash Point: -12 degree centigrade

     Flammable limits of H2S (Hydrogen  Sulphide):

     Lower: 4.3% by volume of air

    Upper: 46% by volume by air

    Auto Ignition point : 260 degree cent

    Classification of fire: C (gas)

    NPFA rating :

     Health: 4(Extreme)

     Fire: (4) Extreme

Hydrogen-Sulfide-Chemical-Label-LB-1592-071

A sample M.S.D.S is as shown below

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For industrial safety related topics click on the links below

https://kishorekaruppaswamy.wordpress.com/2012/04/04/chemical-hazard-pictograms/

 

https://kishorekaruppaswamy.wordpress.com/2012/01/18/ingress-protection/

 

https://kishorekaruppaswamy.wordpress.com/2017/02/23/safety-integrity-level-sil/

 

https://kishorekaruppaswamy.wordpress.com/2017/11/20/hydrogen-sulphide-h2s/

 

https://kishorekaruppaswamy.wordpress.com/2017/12/17/hazardous-area-classification/

 

 

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