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    Updated: 10 May 2020



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Sulphur dioxide SO2
Sulphur dioxide is a colorless gas with a characteristic odour that is formed when sulphur or sulphur-containing substances (eg oil and coal) are burned.

Sulphur dioxide is emitted from boilers fired with sulphur fuel and it is partly this gas that gives rise to so-called acid rain which acidifies lakes and soils.

Sulphur dioxide, together with water forms sulphur.

Sulphur dioxide is irritating to eyes and mucous membranes.

Odour threshold is 0.5 ppm.

The first systems appear at a few ppm, and at a bit above 100 ppm it is immediately dangerous to be exposed to gas for a longer period.

Even higher concentrations are lethal after only a short time.

Poisoning symptoms may come much later why it is important that a person exposed to the gas, sees his/her doctor.

Hygiencic threshold limit values:

Level value = 2 ppm

Maximum value = 5 ppm

Alarm should be adjusted to these levels with level limit as the first alarm and maximum limit as second alarm limit.

Sensor Placement
The Sulphur dioxide is about twice as heavy as air which means that it will sink to the floor. Detectors should therefore be placed low.

Spaces in low locations should be monitored since high concentrations can be collected there.


IP65, Standard - Wall design


Address list    


Modbus Modbus Manual



IP65, Duct design


IP65, Sulphur dioxide detector with display













Low cost IP44










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 sulphur dioxide detectors


Gas alarm plate for sulphur dioxide detector


Warning Siren for sulphur dioxide sensors


Combined warning siren and flash light for
sulphur dioxide 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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