Envent Engineering Ltd. Page 51 Revision 2.4
Risk Assessment - Safety Information
Hydrogen Sulfide Properties
Usually encountered as a gas
Color Colorless - No visible sign of H2S to warn you of its presence
Odor Characteristic smell of rotten eggs at 0.5 ppb; paralyzes the olfactory nerve
around 100 ppm
Vapor Density Heavier than air (1.19 compared to 1.0 for air)
> In gas mixtures, it will be present wherever the gas mixture is found
> Gas mixtures may be heavier or lighter than air, depending upon their vapor
density and temperature compared to the ambient atmosphere (i.e. usually air)
> In its pure state, or as a high proportion of a gas mixture, it may flow or settle
into low-lying areas, such as pits, trenches and natural depressions
Flammability Flammable
Flammable at 4.3 - 46 percent vapor concentration in air, by volume
Burns with a blue flame and gives off Sulphur dioxide (SO2) gas SO2 is also
hazardous and irritates the eyes and the respiratory system
Solubility Soluble in water and oil, solubility is inversely proportional to fluid temperature
Common
Locations for H2S
Piping systems, pipelines, wellheads or wellbores, vessels, production
facilities, tanks, pits and low spots, confined or enclosure spaces, shacks or
buildings, bermed or diked area, sour spills.
Table 6. Hydrogen Sulfide Properties
Hydrogen Sulfide Quantities and Health Effects
Less than 1 ppm
you can smell it
10 ppm > No known health effects for most people
> For 10 ppm or less, the exposure limit is 8 hours - Check your local legislation
as they vary.
> For 15 ppm, the exposure limit is 15 min with 60 minutes breaks. Check your
local legislation as they vary.
20-200 ppm > Eye and respiratory tract irritation and loss of smell
> Headache and nausea - loss of smell after 2 - 5 min
> Respiratory Protection is required beyond this level such as SCBA (Self-
contained Breathing Apparatus) and SABA (Supplied Air Breathing Apparatus)
200 - 500 ppm > Above effects, but sooner and more severe
> Loss of breathing and death in 30 min to 1 hour
500 - 700 ppm > Affects the central nervous system
> Rapid unconsciousness, cessation of breathing, and death
700 ppm and
above
> Immediate loss of consciousness
> Permanent brain damage and death in a few minutes even if removed to fresh
air at once
Table 7. Hydrogen Sulfide Quantities & Health Effects
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