SG350ex and SG2500ex measuring devices for hazardous substance measurement
Our devices for hazardous substance measurement in potentially explosive atmospheres, such as the measuring device SG350ex works according to this principle. All devices that feature explosion protection are certified in accordance with European Directive 94/9/EC.
Typical areas of application for our devices for hazardous substance measurement with explosion protection are mines, chemical plants or grain mills.
There is a risk of a dust explosion in the work areas there.
The finely dispersed material (dust) forms a very large surface in the ambient air. If it comes into contact with an ignition source (e.g. a spark from an electrical device), this leads to explosive combustion. The explosion protection in our appliances prevents the formation of an ignition source and ultimately prevents the explosion.
Explosion protection important for hazardous substance measurement – definition and protective measures
What is an explosion?
An explosion is a chemical reaction in which the temperature and pressure suddenly increase. This results in a sudden expansion of the volume of gases and the release of large amounts of energy in a very confined space. The sudden increase in volume creates a pressure wave.
A distinction must be made between two types:
- the heat explosion: the reaction enthalpy cannot be dissipated quickly enough so that the temperature of the system rises. This then leads to an increased reaction rate and, as a result, to further heat release (theories by Semenov, Frank-Kamenitzkii and Thomas).
- the chain branching explosion: e.g. the oxyhydrogen reaction; more chain branching than chain termination reactions take place in a certain temperature and pressure range. The radicals are recombined so that the number of radicals increases. As a result, the reaction enthalpy released increases rapidly and ultimately leads to an explosion.
Both explosions differ depending on the type of chemical reaction. However, both have the thermodynamic process in common: “The energy released leads to a rapid increase in temperature and pressure as well as volume expansion, which blows apart the surrounding material.”
Further distinctions (e.g. on a macroscopic level) will not be discussed here.
What are potentially explosive substances?
This includes all hazardous substances that “can be caused to explode by flame ignition or are more sensitive to impact or friction than dinitrobenzene (C6H4N2O4).”
Gases and fumes can only explode if a substance-specific air-oxygen-gas mixture is present. Such a concentration is also known as the “lower explosion limit”. Furthermore, a high temperature must be present or an ignition source must be present. If one of these conditions is not met, an explosion will not occur.
Protective measures
There are various ways to achieve explosion protection. One option is to limit the concentration. This involves inhibiting the supply of the hazardous substance.
There is also inertization, which means that the atmospheric oxygen is reduced/removed from the reaction. The aim of these two measures is to prevent the formation of the potentially explosive gas mixture.
Finally, there is also the option of using explosion-proof equipment. This always makes sense if one of the above measures cannot be used. However, this is a secondary measure, as it is not the concentration of the substances that is regulated, but the ignition of these substances that is prevented.
Sources:
[1] http://www.chemie.de/lexikon/Explosion.html
[2] 1×1 der Laborpraxis, Prozessorientiertes Lehrbuch für Studium und Berufsausbildung; S.Eckhardt, W.Gottwald, B.Stieglitz; Weinheim
[3] https://www.baua.de/DE/Angebote/Publikationen/Fachbuecher/Gefaehrdungsbeurteilung.pdf?__blob=publicationFile&v=4