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    Updated: 10 May 2020



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H2S - Hydrogen sulphide
Hydrogen sulphide has a very dangerous and foul-smelling gas whose odour can be felt even at concentrations below 0.1 ppm.

However, it is very important to note that the sense of smell is not reliable when it comes to warning of hydrogen sulphide since the olifactory sense even at low gas concentrations will be stunned.

This means that you can not smell the gas after a while.

If the concentration then rises to levels harmful to health, one does not notice the danger.

Hygienic threshold limit values:

  • Level value: 10ppm

  • Maximum value: 15ppm

If the concentration increases only slightly above maximum value the gas is irritating to the eyes and at higher concentrations, it causes irritation of the mucous membranes (respiratory).

Pulmonary edema may occur.

Other symptoms that occur at higher concentrations are headache, dizziness and impaired motor activity.

Already at 800 ppm only a few minutes' exposure is deadly.

Very high concentrations will lead to immediate death.

Hydrogen sulphide detectors are used, among other things, in the paper industry, chemical industry and of and in sewage treatment plants.

Sensor Placement
Hydrogen sulphide gas has a density that is slightly heavier than the air density, but still very close.

The sensors should therefore be placed at breathing height, and at the likely leakage locations.

Explosion hazard
Sulphide in high concentrations is hazardous.

LEL = approximately 4.3%

Since hydrogen sulphide is slightly heavier than air it may be collected in locations that are low-lying and therefore cause an explosive atmosphere.

The ignition temperature is relatively low.


  • Refineries

  • Drilling platforms and rigs

  • Platforms for gas and oil production

  • Sludge Measurement Activities

  • Desulphurization plants

  • Nuclear power plants with heavy water

  • Water treatment plants

  • Chemical plants

  • Locations of wells

  • Installations for oil recovery / recycling

  • Pulp and Paper Factories


IP65, Standard - Wall design




Datasheet Modbus Address list




Press release


IP65, Duct design


IP65, Hydrogen sulphide detector with display


Compatible with different types of bus systems


Gas Central for 1-2 sensors (1 built-in) with
relay outputs for 4 alarm levels, internal
buzzer, operator panel and display












Warning lights for Hydrogen sulphide detectors

Warning Siren for Hydrogen sulphide sensors


Gas alarm plate for Hydrogen sulphide detector

Combined warning siren and flash light for
Hydrogen sulphide sensors



ATEX Gas detectors are available for 2 explosion classes as follows:

Zone 1 is available with or without display.

Gas detectors for ATEX Zone 1 are located in a flameproof enclosure, EEx d

The shell is such that ignition and combustion within the shell of a potential explosive gas mixture is not propagated to the explosive mixture outside the enclosure and the enclosure can thus endure the resulting explosion pressure without damage.

In Zone 1, one can expect an explosive atmosphere to occur during normal operation but the presence of it is relatively short.

The equipment shall not be a source of ignition in normal operation or when an error occurs.

Gas detectors for ATEX Zone 2 are of the design Non-sparking EEx nA

EEx nA is a non-sparking piece equipment.

In Zone 2, you need not count with an explosive atmosphere to occur during normal operation, and if it should occur, which is probably rare it is of short duration.

The equipment shall not be a source of ignition during normal operation.









Address list

EEx-d ATEX Protection Class


EEx-n ATEX Protection Class



E-mail: lars@fjellcom.se     

Phone: +46(0)31-287202

Mobile: +46(0)706-755561



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