FAQ non-conductive materials

Here you will find frequently asked questions from our customers

What should I watch out for if I want to remove minor contaminants from flammable, non-conductive dusts in everyday operations, e.g. Gas Ex Zone 1?

Immediately pick up spilled material in a dry place, avoiding the development of dust. A broom with natural hair bristles and conductive, non-sparking shovels with slow sweeping movements should be used. Avoid whirling up in the vicinity of potential ignition sources. The user should be fully equipped with conductive clothing, conductive rubber gloves and appropriate conductive footwear. In gas Ex areas, it is best to rinse away with water or aqueous cleaners.

Do not use commercially available vacuum cleaners!

The use of explosion-proof vacuum cleaners is possible as long as they comply with the applicable regulations and guidelines and are suitable for picking up flammable, non-conductive dust.
Attention, a marking e.g. Ex II 2 D T3 (suitable for use in Zone 21) does not say anything about the properties of the suction device with regard to the desired application.

We recommend industrial vacuum cleaners that have been certified or type-tested in their entirety by the notified body and explicitly permit use with flammable conductive dusts. In addition, the injection process, for example, must be used.
Because the design of the vacuum cleaner must be equipped with continuously electrically conductive components (including filter elements) on the raw gas and clean gas sides.
The vacuum cleaner must have appropriate safety devices (e.g. earthing clamp), which the device uses to maintain a fixed connection to the earth potential during use. Suction cups are recommended that do not pose a risk even in the event of a "two-fault case".
As part of a professional consultation, the industrial vacuum cleaner manufacturer should sufficiently discuss the application and the possible risks with the customer, e.g. if the vacuum cleaner is not used as intended.
Be careful if the manufacturer does not make the operating instructions available to you before purchasing and / or cannot provide you with any documentation on the mandatory electrically conductive accessories.
In the case of flammable conductive dusts, the manufacturer should always ask you about the type of application and at least about the minimum ignition energy of the suction material. Because in most cases a case-by-case consideration must be made when the minimum ignition energy of the substance is <0.3 mJ.

Further information can be obtained from the Federal Institute for Occupational Safety and Health in the technical rules for operational safety, e.g. TRBS 60335-CC, BG RCI Merkblatt 109 or 2014/34 EU.

What are other possible sources of ignition for non-conductive dusts?

  • Open flames
    z. B. match or lighter flame, firing systems, blowtorches, welding and cutting flames, internal combustion engines
  • Hot surfaces
    z. B. walls of boilers, hot pipes, soldering irons, parts of machines that run hot (bearings), hot gases
  • Electrical sparks and sources of spark
    z. B. loose contacts, overloaded lines, defective controls, tear-off sparks on switches, light bulbs,
    Flashlight, electrical devices, including battery-operated devices
  • Electrostatic discharge
    (due to non-earthed system parts or containers, unsuitable tools and furnishings, unsuitable clothing)
  • Friction or impact sparks
    z. B. grinding, hitting machine parts, tools, containers
  • lightning strike
    Strike of lightning or overvoltage caused by lightning strike in lines or systems

What should be observed in normal handling of flammable, non-conductive dust?

Dealing with flammable, non-conductive dusts almost always represents a very high risk, possibly with a risk of explosion. Therefore, these areas must be marked separately and must be free of possible potential sources of ignition. This identification is usually carried out by the relevant specialist bodies (notified bodies). All information on the relevant substances should be stored and available in the respective explosion protection document.

The usual vacuuming of non-conductive dust by / with dust-removing machines (industrial vacuum cleaners) represents a great danger.
Without additional safety devices or tools (crane injection), this is not permitted for all crane vacuums or only after a separate safety assessment.

Users and manufacturers, for example of substances, can have a free analysis and risk assessment of the substance carried out by the respective trade association.

Why are flammable, non-conductive dusts a particular hazard?

Flammable conductive dusts contain all of the above-mentioned hazard potentials. Flammable, non-conductive dusts are often of artificial origin. The fineness of the dust is of particular importance. The larger the grain size of the combustible, non-conductive dust, the greater the possibility of improved charging.

In addition, chemical reactions in connection with other media are of great importance.

It should also be noted that some of the deposited dusts have a lower ignition temperature than when they were whirled up.
In the event of improper handling and under certain circumstances, a combustible, conductive amount of dust can self-ignite when its own (built-up) energy potential is diverted.

Why are combustible dusts generally a hazard?

Combustible dusts are to be viewed differently. Depending on their nature, these are difficult or highly flammable. Flammable substances are divided into different explosion groups (see appendix). In order to ignite a substance, an appropriate ignition source is required that emits sufficient energy for the ignition process. The basic unit of energy in the SI system of units is joule. The minimum ignition energy (MIE) of a substance is given in millijoules (mJ).

The lower this value, the easier it is to ignite the product. Oxygen is of course also required for ignition.

Why are non-conductive dusts generally a hazard?

All substances that are insulating in the electrostatic sense (leakage resistance> 10 ^ 8 Ohm) or non-conductive substances build up charges during transport (suction / conveyance) with one another or in contact with conductive or non-conductive surfaces. These charges are not diverted immediately when they come into contact with a conductive connection to the earth potential; instead, for example, a very high charge potential can initially develop in a container. The charge that arises from the collapse of the charged substance is not very high, but this energy can be sufficient to generate ignitable brush discharges towards the earthed container wall.

The operator should be familiar with the type and properties of the suction medium (substance). The possible risks with regard to increased electrostatics due to the transport of substances must be known. When vacuuming these problematic substances, the vacuum cleaner must also be integrated into the operational equipotential bonding system before use.

For use in potentially explosive gas areas, it should be noted that all electrostatic insulating dusts with the limit value * mentioned below must not be vacuumed up.

* The limit value for bulk goods is a specific resistance of ≤ 1 * 108 Ω m (see also TRBS 2153, Section 6.3). For bulk goods with a higher specific resistance, the occurrence of ignitable brush discharges cannot be ruled out.