M-Class: the minimum standard for construction dust

M-Class (Medium hazard) is the baseline requirement for hazardous construction dust, including silica. To qualify as M-Class, a vacuum must:

  • Achieve airflow greater than 20 m/s
  • Include a light or indicator that alerts the operator when airflow drops below that threshold
  • Filter to 99.99 per cent — retaining the captured dust rather than exhausting it back into the workspace
  • Use a sealable bag for safe disposal — so dust is not released when the vacuum is emptied

For most silica-generating tasks on a construction site — cutting concrete, grinding mortar, drilling masonry — M-Class is the minimum standard required.

H-Class: maximum protection for the highest-risk tasks

H-Class (High hazard) meets all M-Class requirements and goes further. It is designed for the most hazardous and carcinogenic dusts — including engineered stone, which can contain up to 95 per cent crystalline silica.

The key differences from M-Class:

  • Filtration to 99.995 per cent — capturing finer particles that M-Class may not retain
  • Designed for carcinogenic and toxic dusts where maximum operator protection is required
  • Higher filtration means more frequent filter maintenance — factor this into your maintenance schedule

Which applies to your site?

The task determines the requirement. If your site involves cutting concrete, brick, stone or mortar: M-Class as a minimum. If your site involves engineered stone, silica-heavy materials or any task generating dust that is classified as carcinogenic: H-Class.

Where uncertainty exists — or where you are running multiple task types — the safest approach is to review what you are currently using against the classification requirements and close any gaps before they become an inspection finding.

A practical note on compliance

Having the right equipment is only part of the picture. HSE inspectors will also want to see evidence that it is being used correctly, maintained to schedule and that workers understand why. Specification, training and records together constitute a defensible position. Equipment alone does not.

If you are unsure which standard applies to the tasks on your site, or whether your current equipment meets it, speak to one of our advisors. We will give you a straight answer.