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14.4 Electrostatic Charging Data

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 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):

The previous German guidelines for avoiding ignition hazards resulting from electrostatic charge (previously ZH 1/200 "Static Electricity") from October 1989 were completely revised and replaced by the new BGR 132. German BGRs are intended primarily for the employer and provide support in avoiding work accidents, occupational diseases and work-related health hazards. BRG 132 is used to assess and avoid ignition hazards from electrostatic charge in explosion hazard areas, and it is extended by the new explosion protection guideline, BGR 104 (formerly ZH 1/10).

Definitions:

BGR 132 distinguishes between the conductivity of a particular material or an object in general

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.

and conductivity as defined particularly for hoses. According to BGR 132 a

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.

According to the implementation notes of the BG-guideline, insulating hoses consist of insulating material and they have neither conductive wires nor strands. They do not discharge any electrostatic charges.

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):

?Plastic flex hoses must be electrically conductive to discharge static electricity. If this is not the case, an electrically conductive connection must be made between the integrated steel wire and the machine extraction outlet and fixed extraction pipe.? Reference is made to BGR 132 for practical implementation.

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

?There must be an electrically conductive connection between the pipelines from the machine outlet to the collecting pipe.? Reference is made to BGR 132 for practical implementation.

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

"Grounding of conductive accessories is to be ensured. All conductive parts of the unit (including accessories) must be electrostatically grounded??

ATEX Directive 94/9/EC:

As of June 30th, 2003, only devices, components and protection systems in compliance with 94/9/EC (ATEX 100a) may be used in explosion hazard areas.

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.

The different categories are necessary to take appropriate precautions to prevent explosions.

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?

Directive 94/9/EG defines a potentially explosive atmosphere as a mixture

of combustible substances in form of gases, vapours, mist or dust
and air
under atmospheric conditions
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.)

An area in which the atmosphere can be explosive due to the local and/or operational conditions is designated as an explosion hazard area.
It is important to observe that products do not fall under Directive 94/9/EC, if they are destined for the use in or for the use in connection with areas that may have explosive hazards under some circumstances, but where one or more of the conditions 1 to 4 listed above are not met.

When is Directive 94/9/EC 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 94/9/EC
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.

Engineering modifications subject to change.