Why H2S is known as the quiet assassin

The smell of rotten eggs: this is caused by hydrogen sulphide gas, known to chemists by the formula H2S. It occurs when certain types of organic matter decompose in an environment with low levels of oxygen, such as during natural processes in soil, swamps or stagnant ditches. It can also occur in man-made environments such as sewers, water treatment works, excavations, or manure in silos or slurry pits. Because of its unpleasant odour, people avoid H2S.


But what makes it so dangerous? Our specialists in respiratory protection and gas detection explain.

Poisonous H2S

If inhaled, this gas can have extremely serious health consequences.

  • Health can be affected even at a very low concentration of 0.05 mg/m³, where it can cause eye irritation, dizziness, nausea and headaches which do, however, disappear in the fresh air.
  • At 50 mg/m³, the consequences already become much more serious and lasting. It can cause unconsciousness, and can damage eyes and skin.
  • At 100 mg/m³, the consequences can even be fatal.
  • Various institutions have reported that if concentrations exceed about 1400 mg/m³, one single inhalation already leads to unconsciousness and breathing stops immediately.

Treacherous characteristiscs of H2S

One very dangerous characteristic of H2S is that at concentrations above 150 mg/m³, it causes people to lose their sense of smell, making it undetectable without equipment. In addition, this colourless gas is heavier than air, so it always sinks to the ground.

If a personal gas detector is worn at shoulder height, it may fail to detect dangerous concentrations of H2S. If the user then bends over or kneels down, they may be suddenly put in a dangerous situation.

Any work where there is a risk that H2S will be breathed in should, therefore, be avoided, but sometimes there is no option. If that is the case, the user should be well protected!

Respiratory protection

Has exposure been checked? If so, a half mask with goggles or full-face mask with type B charcoal filter may be a solution for work to be carried out safely.

However, the use of masks with filter canisters does have its vagaries: as soon as the filter is saturated or the concentration increases to 50 mg/m³, the filter is unable to cope and the user ends up directly breathing in toxic gas.

Expert advice

An expert risk assessment and expert advice are an absolute must!

Measuring is knowledge

Gas detection systems can prevent a great deal of misery. Many devices are available, from portable (personal) gas monitors to fixed point gas detection and advanced open path systems. Such systems have an advanced meter, which emits a warning if a certain set concentration is exceeded. Advanced systems also store data about alarms, giving safety experts more information about exposure levels.

Limit value for H2S

In the Netherlands, the limit value for hydrogen sulphide – H2S – was set at 2.3 mg/m³ (1.6 ppm) based on a time-weighted average over 8 hours (TWA-8 hours) on 01/01/2007. Any higher values ​​that might appear on a MSDS (Material Safety Data Sheet) are incorrect.

Do you want to find out more?

Would you like more information on H2S gas detection? Take a look at our product page or contact our specialists on +31 (0)88 – 130 6030 or submit your question using the online contact form.

Trung Phan Thanh

Trung Phan Thanh

Sales Engineer
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