Criteria for choosing a wet and dry vacuum cleaner or an industrial vacuum cleaner
The right choice of vacuum cleaner depends on the dust class (L, M, H), the required vacuum suction power and the area of use. Wet and dry vacuum cleaners are suitable for mixed substances, while industrial vacuum cleaners are designed for specific requirements such as potentially explosive dusts or liquids. This guide explains the key criteria for making the right choice when purchasing a vacuum cleaner.
Dust and dirt are unavoidable in manufacturing and processing operations, and special requirements need to be observed when cleaning them up. Over time, dust can not only affect employee health, but also have a negative impact on the quality of the end product.
The right vacuum cleaner is essential for improving working conditions and ensuring quality standards are maintained.
Not all dust is the same
While coarse dust is quick to settle, finer dust remains suspended in the air for a long time, allowing it to be inhaled and thereby cause damage to health. If the dirt being vacuumed up not only contains dust, but also coarser particles, the vacuum cleaner must be designed accordingly. If wet dust, solid particles mixed with liquids or sticky dusts (e.g. dust containing oil or paint residues) is being collected, this places even higher demands on a vacuum cleaner. Dust itself may be flammable or form an explosive mixture with the ambient air.
The different types of dust are divided into three dust classes, which provide information on how harmful each type of dust is, and provides orientation when it comes to which vacuum cleaner is suitable for which dust class.
Dust categories
The law that regulates the classification of dust categories and thereby forms the basis for the safe disposal of substances and dust is the EU standard EN 60335-2-69, which applies throughout Europe.
The applicable category is determined by the health hazards and the explosive properties of the respective type of dust. Another factor is the occupational exposure limit (OEL). The lower the OEL, the more hazardous the dust.
The transmittance describes the ratio between the quantity of dust or particles that pass through a filter and the original quantity in the air, and is expressed as a percentage or a ratio.
Additional information about materials and dusts, as well as classifications of machines to be cleaned of dust, can be obtained from the Health and Safety Executive (HSE)
Applicable dust classes in accordance with EN 60335-2-69, Annex AA
Vacuum cleaners in dust class L
Dry, hazardous, non-combustible dusts with an OEL > 1 mg/m³
Dust class: at least L
Maximum transmittance: < 1%
Examples: house dust, soil, sand
Vacuum cleaners in dust class M
Dry, hazardous, non-combustible dusts with an OEL ≥ 0.1 mg/m³
Dust class: at least M
Maximum transmittance: < 0.1%
Examples: wood, concrete, filler, paint particles
Vacuum cleaners in dust class H
Dry, hazardous, non-combustible dusts with an OEL < 0.1 mg/m³
Dust class: H
Maximum transmittance: < 0.005%
Examples: mould, very fine respirable dust
Carcinogenic hazardous substances in accordance with Section 11 of the Hazardous Substances Ordinance (GefStoffV), TRGS 905 and TRGS 906
Dust class: H
Maximum transmittance: < 0.005 %
Examples: heavy metals, mineral fibres
Asbestos in accordance with TRGS 519
Dust class: H + suitable for use in accordance with TRGS 519
Maximum transmittance: < 0.005 %
Additional suitability for combustible dusts of all dust explosion classes (excluding dusts with an extremely low minimum ignition energy < 1 mJ)
Dust class: at least L, with additional testing in accordance with EN 60335-2-69, Annex CC
Appliances of type Zone 22 (i.e. an explosive atmosphere in the form of a cloud of combustible dust suspended in the air is not normally formed during regular operation, or is present only for a short period)
Note:
Mixtures of dust and air are explosive if the dust consists of combustible material (e.g. wood, coal, cellulose, flour and other organic substances). Light metal dusts (aluminium, magnesium) can react with water to release hydrogen, thereby creating an explosive atmosphere. This is why dust collection containers must be emptied without fail every time that lightweight metal dusts are vacuumed up. There is also a risk of explosion due to any solvent vapours or gases in the air. An explosive atmosphere must be dispelled before any cleaning work by ensuring adequate ventilation. If this is not possible, special vacuum cleaners with a design that protects them from gas explosions must be used.
Wet and dry vacuum cleaners must not be used to vacuum up flammable liquids.
Vacuum suction power
It’s not just a high wattage that is decisive for optimum vacuum suction power; the right balance between vacuum pressure and air flow is also key.
A high air flow rate means the material being vacuumed up moves at high speed, and a high vacuum pressure is required for vacuuming up heavy materials or from deep spots (e.g. from hollows).
What’s more, the diameter of the hose has a decisive impact on the ratio between the vacuum cleaner’s air flow and vacuum pressure. The hose sizes supplied as standard are of an average size, which guarantees a good vacuum cleaner performance and, under normal circumstances, allows dust and dirt to be vacuumed up without any problems.
To ensure that a vacuum cleaner maintains a constant suction power, a main filter with a suitable size must be used. A pre-separator can be used to ease the load on the main filter. To keep the outgoing air as clean as possible, absolute filters (dust class H) can be fitted downstream.
Appliance components
Hose
For optimum performance, a hose is required that satisfies all requirements in terms of length, strength and connection dimensions. The hose should be long enough so that the vacuum cleaner does not need to be constantly moved around; on the other hand, a hose that is too long can be a hindrance, particularly when rolling it up and transporting it. Furthermore, vacuum suction power decreases with an increase in hose length. The hose should be flexible and have as small a bending radius as possible. At the same time, it is important that it retains its shape so that mechanical forces acting on it will not deform it.
The friction caused by the particles being drawn into the hose results in an electrostatic charge, which can trigger electric shocks and lead to injuries or explosions. This is why it is important that the suction hose on an industrial vacuum cleaner can be earthed.
If the hose is used to vacuum up liquids, it must be suitable for this purpose and, when relevant, be resistant to alkaline solutions and acids.
Filters
The larger the health risk presented by dust, the more effective a vacuum cleaner’s filter system must be. The most important indicator for assessing the performance of a filter system is the filtration efficiency. This indicates the percentage of the harmful substances contained in the air flow that is actually separated, and is directly proportional to the dust class.
Dust class L: filtration efficiency of 99%
Dust class M: filtration efficiency of 99.9%
Dust class H: filtration efficiency of 99.995%
However, a filter is an element that creates resistance to the air flow, and this resistance increases the smaller the filter size is and the more clogged the filter becomes. A small filter surface area also becomes clogged more quickly.
Many models use a cyclone separator system.This system makes the air flow into the container on a tangent for deflection free vacuuming. The dirt vacuumed up therefore won’t block the inlet or strike the filter directly, which could otherwise be damaged. This extends the filter’s service life, which is not only good for the environment but also saves money. Heavier particles of dirt are slowed down by the container wall and sink to the bottom of the container. The main filter therefore only needs to filter out the lighter particles of dirt, which helps to ensure a long filter service life.
Depending on the vacuum cleaner model and requirements, different main filters are used. They differ in terms of design, material and coating, and consequently in terms of dust collection capacity, tear resistance and moisture resistance.
A wet and dry vacuum cleaner is needed to vacuum up liquids or a mix of liquids and solids, for example, and it is important to ensure the filter material is tear resistant (paper filters are not suitable). Damp and wet dust clogs filters more quickly, which may mean that filters need to be changed more frequently. Dusts that swell or solidify when they come into contact with water (e.g. plaster, cement, etc.) can permanently block a filter. Washable filters, which are cleaned immediately after use, are suitable for tasks like these.
Containers / disposable bags
If the vacuum cleaner has just one dust chamber, the dirt it vacuums up ends up in a container that needs to be emptied regularly to prevent the dust that has already been collected in the container from being stirred up again and sucked back into the filter. For this reason, and to ensure efficiency, the collection container should not be allowed to fill up completely. Appliances with larger dust collection containers may therefore seem more practical, however it is important that the vacuum cleaner remains easy to handle even when the container is full (e.g. when transporting or emptying it). Vacuum cleaners for shavings also feature a sieve insert to separate solid and liquid components, so that these can be disposed of separately.
If the appliance uses a dust collection bag, then this must be used, as otherwise the collected dust cannot be removed safely. The material that the collection bag is made of must be suitable for the material being vacuumed in terms of tear resistance and moisture resistance.
The Hazardous Substances Ordinance (GefStoffV) stipulates that as little dust as possible may be released while the vacuum cleaner is in operation. Filter bags must therefore not be emptied and reused, as large quantities of dust are released when they are emptied.
To ensure safe, economical and disruption free vacuum cleaner operation, the appliance must be serviced regularly and checked to ensure it is in good working order. This includes cleaning the appliance, changing the dust collection bags and replacing parts that are subject to ear (e.g. suction hoses, filters).
Examples of use
The following examples are by no means exhaustive, and each actual case should be analysed when vacuuming hazardous substances. If a source of danger (e.g. vacuuming solvents, chemicals, asbestos, aluminium, wood dust, etc.) has been identified or is known, this must be factored in when selecting the appropriate industrial vacuum cleaner. What’s more, there are a few problematic types of dust which should only be vacuumed up using GS certified vacuum cleaners, subject to specific conditions: e.g. very fine aluminium and magnesium dust, petrol, etc. The employers’ liability insurance association can provide further assistance and relevant information in this matter.
Vacuuming of predominantly fine dust
A vacuum cleaner with moderate power and a large filter surface area is suitable for this purpose (unless the dust in question has a high specific weight, e.g. metal dust). The filter’s separation efficiency must be factored in as well to ensure that the vacuum cleaner actually collects the dust and does not release a significant amount back into the surroundings. For dusts that present a health hazard, an absolute filter must be used. If the dust is potentially explosive, the appliance must comply with Zone 22 standards.
Vacuuming a mixture of fine dust and larger particles
For this task, a vacuum cleaner with high power and a large filter size should be selected, and the appliance should also feature a mechanical pre-separator (cyclone) to protect the filter from damage. A large filter size is required to prevent the filter from becoming clogged too soon, and ensure that a good vacuum cleaner performance is maintained. In this case too, the dust class guidelines M, H and L, with design category Zone 22, must be observed.
Vacuuming of predominantly large particles
The filter system is not particularly important in this case, however the vacuum cleaner should have high suction power and a large collection capacity. As a rule, a standard appliance is usually sufficient , whereby the appliance power must suit the hose diameter, hose length and the material being vacuumed. If the vacuum cleaner is for use in a potentially explosive atmosphere, it must be ATEX approved.
Vacuuming of liquids containing chemicals (mild cleaning agents)
A wet and dry vacuum cleaner that was designed for this purpose by the manufacturer must be used. An appliance with a stainless steel container is recommended in most cases. If aggressive substances are involved, it is essential to determine precisely how the substance reacts and what requirements the vacuum cleaner must meet.
Vacuuming of oil or liquids containing oil mixed with shavings
Standard wet and dry vacuum cleaners are unable to vacuum up this material, as the way these the liquids vaporise is different to water, for example. Vacuum cleaners for shavings are fitted with a different inlet for better control over the vaporisation of liquids.
Vacuum cleaners for shavings with an integrated shaving and emulsion separation system are suitable for use with production machinery.
Vacuuming of substances in potentially explosive atmospheres
For safety reasons, an intrinsically safe compressed air vacuum cleaner (EX rated and labelled) is recommended in all cases.
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