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Elektrostatický náboj
General
When solid and liquid materials are conveyed through chargeable tubes or hoses, electro-static charging (separation of charged particles) occurs due to the friction of the material against the wall and the friction within the medium. The primary hazards are:
- The occurrence of discharges that can ignite the explosive mixtures of gas, vapour, mist and dust.
- Dangerous or unpredictable behaviour caused by shock when this discharge takes place via the human body.
- Process disruptions caused by the medium sticking to the hose wall.
- Malfunction of measuring devices and controllers.
Whereas countermeasures for the points 2 - 4 are left largely to the discretion of the user, there are a number of regulations and guidelines for assessment and avoidance of fire hazards and the protective measures to be taken.
The most reliable protective measure is to prevent electro-static charging in the first place by selection of the proper hose. Our products have proven their worth in application in this regard for a number of reasons:
- Grounding of the hose over its entire length.
- Connectors can be included in the grounding on both sides (saves additional ground connections).
- The embedded wire has maximum contact area with the plastic (in contrast to externally-applied copper strands).
- Spiral construction covers the greatest possible portion of the surface (in contrast to axial surface-mounted wires).
- Antistatic or electrically conductive plastics can be used in manufacture if required.
The ATEX Directive 2014/34/EU
Since June 30 2003, only devices, components and protective systems intended for use in potentially explosive atmospheres that comply with the 2014/34/EU Directive can be placed on the market.
Device categories: The Directive ATEX 2014/34/EU determines three device categories in the Equipment Group II, which are intended for use in hazardous areas with different probabilities of occurrence of an explosive atmosphere.
- Category 1: An explosive atmosphere is always present.
- Category 2: The emergence of an explosive atmosphere is probable.
- Category 3: The emergence of an explosive atmosphere is improbable, but can be present for a short time.
The different categories are required to take appropriate precautions for the prevention of explosions.
Areas: Because of a uniform definition in the directive, regarding the explosion hazard areas for gases, fumes and mists, as well as dusts, it also means in principle a “three zone classification” for dusts. For the implementation of the Directive 2014/34/EU (the norm) DIN EN 1127-1 „Explosive atmospheres, explosion protection, Part 1, Basic concepts and methodology“ was elaborated. This standard already considered the new "zone concept" and defined the zones 20, 21 and 22 for explosive dust zones.
What is an explosive atmosphere according to ATEX?
For the purposes of the Directive ATEX 2014/34 / EU an explosive atmosphere is defined as a mixture
- of combustible materials in the form of gases, fumes, mists or dusts
- and air
- under atmospheric conditions
- in which the combustion after occurred ignition is transferred on the entire mixture. (Note that in the presence of dust not always the whole quantity of dust burns.)
An area in which the atmosphere can become explosive due to local and/or operational conditions is described as an explosive area.
It is important to note, that products are not covered by the Directive 2014/34/EU, if they are intended for use in or in conjunction with areas that can be explosive under certain circumstances, but in which one or more of the requirements mentioned from 1. to 4. are not met.
When is Directive 2014/34/EU applicable?
| Analysis | Result | ||
|---|---|---|---|
| Devices with an inherent potential ignition source | Devices that should be used in or in connection with explosion hazard areas | Devices containing an internal atmosphere defined as capable of explosion | Devices that fall in the area of application for Directive 2014/34/EU |
| YES | YES | YES | YES |
| NO | YES | YES | NO |
| YES | NO | YES | NO |
| YES | YES | NO | YES |
| NO | NO | YES | NO |
| YES | NO | NO | NO |
| NO | YES | NO | NO |
| NO | NO | NO | NO |
Application of the BG guideline to NORRES hoses:
In all categories, the standard specifies the use of electric conductive components and the connection and grounding of all electric conductive components as the most important protective measure to avoid electro-static charge build-up and the associated discharges capable of causing ignition. Such products are designated in the header line by the following symbols for grounding capacity and electric conductivity:
Since June 30th, 2003, only devices, components and protective systems with an appropriate CE marking may be put into service in explosion hazard areas.
As the operating conditions of the user are outside our direct control and the constructive variety is too large, we can not guarantee the accuracy of the data.
New Technical rule TRGS 727 replaces TRBS 2153
Explosion protection measures are regulated by the TRGS 727 "Avoiding ignition hazards due to electrostatic charges".
The Technical rule TRGS 727 is based on the TRBS 2153 and BGR 132 of the Technical Committee Chemistry of the German Social Accident Insurance (DGUV).
The currently frequently used insulating plastic and rubber hoses with conductive metal inlays may no longer be used.
Another important innovation is the hose selection for pneumatic transport of flammable bulk materials, as this strongly charge-generating process with the TRGS 727 has been re-evaluated.
For characterizing the wall material as conductive (EC) or antistatic (AS) the volume resistivity RGES may only be used and not the surface resistance, as before.
As part of electrostatic studies and reviews in collaboration with a specialized department for explosion protection, hoses of different types were categorized regarding the use in hazardous areas.
The certificate can be found here:
Engineering modifications subject to change.