General:

1. The occurrence of discharges that can ignite the explosive mixtures of gas, vapour, mist and dust.
2. Dangerous or unpredictable behaviour caused by shock when this discharge takes place via the human body.
3. Process disruptions caused by the medium sticking to the hose wall.
4. Malfunction of measuring devices and controllers.

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:

1. Grounding of the hose over its entire length.
2. Connectors can be included in the grounding on both sides
   (saves additional ground connections).
3. The embedded wire has maximum contact area with the plastic (in contrast to externally-applied copper strands).
4. Spiral construction covers the greatest possible portion of the surface (in contrast to axial surface-mounted wires).
5. Antistatic or electrically conductive plastics can be used in manufacture if required.

The evaluation of the particular application and the choice of protective measures to be taken can only be made by the person responsible for design engineering and operation. Here are the most important domestic and international regulations and their implementation:

German Employers' Liability Insurance Association guidelines 132 and 104 (BGR 132 and 104):

Definitions:

• A substance or material with a surface resistance of ?10⁴ ? is conductive.
• An object or device is capable of discharge if its surface resistance is between 10⁴ ? and 10⁹ ? measured at 23°C and 50% relative humidity. The characteristic of being able to discharge is also referred to as being "antistatic".
• A material or substance that is neither conductive nor capable of discharge is insulating.

• conductive hose is a hose with a resistance of less than 10³ ?/m.
• hose capable of discharge is a hose with a resistance of more than 10³ ?/m and less than 10⁶ ?/m

• insulating hose is a hose with a resistance of more than 10⁶ ?/m.

The definitions for hoses do not come from BGR 132 but were defined or adopted from the PTB (German Federal Institute for Physics and Technology) with reference to the cited standards for hoses for liquids (e.g. DIN EN 12115, under which many ?rubber hoses? fall for reasons of design).

Application of the BG-guideline to NORRES hoses: For hoses, the ratio of resistance between the fittings and the length is what always counts. Independent of this is the selection of material used to make the hose (conductive, static discharging or insulating).
According to this definition and the presence of conductive wires, all NORRES hoses with steel reinforcement are to be considered to be at least electrically groundable. This is also the case if the hoses have been manufactured from insulating or antistatic wall material. The maintenance of a maximum spiral distance and a maximum wall thickness under the wire are the only requirements for that, as well as grounding of the hose by the exposing of the steel wire, which is then to be connected to the conductive fittings.

NORRES hoses capable of discharge are designated by the following symbol in the header line: Despite of the principal suitability of these NORRES hoses for use in explosion hazard areas, depending on the flammability of the medium and the existing hazard zones, the following measures among others are recommended for increasing levels of protection:

• In most cases, the following is sufficient: Use of a hose capable of grounding, manufactured with an insulating wall (surface resistance > 10⁹ ?), which must be grounded via the metal support wire. For this purpose, part of the wire must be stripped free and connected to conductive fittings. The spiral distance of the metal wire must be no greater than 20 mm. It must be considered here that the spiral distance increases in the outer radius of a bent hose.
• Higher protection: Use of a hose capable of grounding, manufactured with a non-chargeable (antistatic) wall (surface resistance < 10⁹ ?), which must be grounded via the metal support wire.
• Maximum protection: Use of an electrically conductive hose with a specific resistance ?10³ ?, which must be grounded via its support wire.
• Additional grounding options, such as an external ground cable, are available on request.

German Employers? Liability Insurance Association Guideline ZH 1/730 (fire and explosion protection in systems for the extraction and separation of wood dust and chips):

German Employers? Liability Insurance Association Guideline ZH 1/739 (Wood dust ? handling and safe work):

BIA (BG Institute for Occupational Safety and Health) regulation for industrial vacuum cleaners and dust extractors:

ATEX Directive 94/9/EC:

Device categories: Directive 94/9/EC defines three device categories in Devices Group II, which are intended for use in explosion hazard areas with different probabilities of occurrence for potentially explosive air mixtures.

• Category 1: There is a constant hazard of explosion in the environment.
• Category 2: There is a probable hazard of explosion in the environment.
• Category 3: The probability of an explosion hazard in the environment is low, but it may occur for short periods.

Zones: Since explosive areas for gases, vapours and mists as well as for dust are uniformly defined in the guideline, this also means a ?three zone division? for dust in practice. The implementation of 94/9/EC, the standard DIN EN 1127-1 ?Explosive atmospheres - Explosion prevention and protection - Part 1: Basic concepts and methodology? has been developed. It already considers the new ?zone concept? and it defines the zones 20, 21 and 22 for dust explosion hazard areas.

What is a potentially explosive atmosphere according to ATEX?

1. of combustible substances in form of gases, vapours, mist or dust
2. and air
3. under atmospheric conditions
4. in which the combustion process is propagated to the entire mixture after the ignition has succeeded. (It must be noted that with dust the entire amount of dust is not always burned.)

When is Directive 94/9/EC applicable?

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.