· 4-minute read
H2S: why you cannot trust your nose
Hydrogen sulphide smells of rotten eggs in small amounts and stops smelling in dangerous ones. The figures come from the US institute NIOSH.
H2S is found at wellheads, in tanks, drains and on fields with sour crude. It is colourless, heavier than air and collects in pits, well cellars and manholes. It is also flammable.
When the smell goes
According to NIOSH the smell can be noticed from about 0.13 ppm. At 100 ppm the sense of smell tires within 2 to 15 minutes: a person no longer notices the gas is still there. And 100 ppm is exactly NIOSH’s "immediately dangerous to life or health" level.
- 0.13 ppm: the smell can be noticed
- 10 ppm: NIOSH’s 10-minute ceiling limit
- 100 ppm: the smell goes, immediate danger to life
What we do on site
On every site where H2S may occur each worker wears a personal detector at the collar, and a fixed detector and windsocks stand at the wellhead. When the alarm sounds we hold our breath, put on the escape set and move upwind to the muster point on higher ground.
Most lives are lost by the person rushing to the rescue. We never go to a fallen colleague without breathing apparatus: first the alarm, then the apparatus, then a rescue by two.
The details are as of the article’s date.
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