Choosing the right dust class for the job

The letter on a dust extractor is not a quality grade. L, M and H describe which kinds of dust the machine is approved to collect, and that decides which jobs you can take it to. The filter and bag inside it matter as much as the motor.

What the three classes mean

The classes come from a European standard for extractors used with dust that is harmful to health. Each class sets how much fine dust the machine may let back into the air and how it is tested.

• L for low-hazard dust. General dust that is not classed as harmful in small amounts. This class suits cleaning up and work with materials that do not produce hazardous dust.
• M for medium-hazard dust. Wood dust, including hardwood, and mineral dust containing quartz, such as from concrete, brick, tile and render. This covers most daily work in joinery, fitting and renovation. M-class machines also warn you when the airflow drops too low.
• H for high-hazard dust. Dust with the highest health risk, including dust containing carcinogenic substances or mould spores. This class is needed for specialist remediation work and wherever the regulations require it.

Match the machine to the material

Choose for the most demanding material you expect to cut, sand or drill, not the most common one. If a day of fitting kitchen fronts ends with drilling into a concrete wall, the extractor needs to be M class for that last hour. An H-class machine makes sense when you work regularly in older buildings with unknown materials, or on jobs where the client or the regulations ask for it.

A higher class can always do the work of a lower one. The reverse is not true, however clean the room looks afterwards. The finest mineral dust is the most harmful precisely because you cannot see it.

The bag and filter count too

The class applies to the machine as tested, with the correct main filter and bag fitted. A damaged filter, a bag from another system, or working without a bag on fine dust all reduce what the machine actually holds back. Fine dust also clogs a filter quickly, which lowers suction at the tool.

• Use the bag made for the machine. A fleece filter bag takes most of the fine dust and protects the main filter.
• Check the main filter regularly. Replace it when it is damaged or when cleaning no longer restores suction.
• Set the hose diameter. On machines with airflow monitoring, this setting tells the warning system what to expect.
• Change bags with care. Close the bag before removing it so the dust stays inside.