Dry vacuum cleaner in gas hazardous areas
According to the guideline, there is a restriction on the use of vacuum cleaners in the GasEx area. When sucking in gas / dust mixtures, a hybrid mixture is created.
In this case, the following must be observed:
All dusts that are insulating in the electrostatic sense and have the limit value * mentioned below must not be vacuumed up. Non-conductive dusts 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 created by the collapse of the charged dust is not very high, but this energy can be sufficient to generate ignitable brush discharges towards the earthed container wall. Brush discharges can ignite most flammable gases and vapors, as well as hybrid mixtures. It is therefore forbidden to vacuum non-conductive dust in gas Ex areas without additional safety measures. (For more information, ask for our data sheet "Questions about non-conductive dusts".) "
* The limit value for bulk goods is a specific resistance of ≤ 1 * 10 ^ 8 Ωm (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.
The KRAHNEN models EGS for the gas Ex area of Zone 1/2 as well as the model EGS GD and DGS for the DustEx (Z21) and the GasEx (Z1) area are designed to accommodate dry, flammable, conductive and non-conductive ** Substances with a minimum ignition energy of> 0.3 mJ have been safety-tested and approved.
(** up to the specified limit value)
The suction material in the vacuum cleaner is mainly separated using appropriate filters. The vacuum cleaner should have several filters, not for zone separation with flammable substances, but also when picking up normal suction material. Danger of leakage should be avoided not because of the particle size of the pigment, but also with regard to filter breakage. Particular care should be taken when absorbing substances that are hazardous to health. Important points should be asked as a precaution: design, purpose, handling, cleaning and disposal.
Type of construction purpose
In order to avoid the risk of contamination, the appropriate filter element must be available in the vacuum cleaner for the respective application.
What is important is the manufacturer's proof of quality, fineness, class, as well as the tight fit test after installation in the vacuum cleaner.
Is the filter element resistant to the medium?
Does the filter element fulfill the purpose with regard to the degree of separation?
- Filter quality
- Filter class
- Filter surface loading
- Filter integrity before commissioning
- Filter sealing seat before commissioning
- Proof of compliance with the required OEL values 1 - 5
a) when removing the product and
b) when changing the filter
Which cleaning methods are resistant to? What must be considered when disposing of the product?
Most common mistakes in cleanroom cleaning
- How safe after a change?
- Filter integrity
- Filter seat
During cleaning work, it can happen that the suction hose and accessories are not carefully stored if there is an interruption. Reality shows that there is often no time to think about the fact that some of the dust is deposited inside the accessories and that these are contaminated. When a hand-held suction device falls over, part of the suction material emerges from the openings. In addition, the accessories are often changed during cleaning work. This usually takes place when the suction is interrupted. Hardly any attention is paid to the danger of substances hazardous to health escaping from the accessories. The risk of contamination is inevitable. The highest possible level of purity is required, especially in clean rooms. After the cleaning work has been completed, the room air is often polluted during the clean-up work without closing the suction openings of the accessories.
The use of the right accessories, based on the respective application, is an important step towards greater security. Krahnen tests different types of accessories for its customers with a special hygroscopic neon fine dust (particle size> 0.6 my) under black light. Only a video analysis with the appropriate magnification reveals hidden contamination on the components. Particularly in connection and disconnection processes, dangers arise that remain invisible to the user in daily use.
Immediately take up spilled aluminum powder 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. Do not wash away with water or aqueous cleaners.
Do not use commercially available vacuum cleaners!
The use of explosion-proof vacuum cleaners is possible, provided that they comply with the applicable regulations and guidelines and are suitable for picking up flammable conductive dusts.
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.
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".
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 assessment must be made when the minimum ignition energy of the substance is <5 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.
Flammable conductive dusts contain all of the above-mentioned hazard potentials. Flammable conductive dusts are often of metallic origin. The fineness of the dust is of particular importance. The smaller the grain size of the combustible conductive dust, the greater the possibility of improved oxygen binding, which facilitates the ignition process.
In addition, chemical reactions (base metals) in connection with other media (e.g. aluminum powder and water / see appendix) 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 dissipated.