L-Class, M-Class and H-Class Dust Extraction Compared

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Dust class is not a quality rating and it is not an upgrade path — it is a legal specification set by the substance you are collecting. All three classes are defined by the same standard, EN 60335-2-69, and all three are tested across the complete machine rather than the filter alone. The difference between them is how much of the dust you collect goes back into the air you are standing in.

L-Class, M-Class and H-Class side by side

  L-Class M-Class H-Class
Hazard level Low Medium High
Minimum retention 99% 99.9% 99.995%
Dust returned to the air Up to 1 part in 100 Up to 1 part in 1,000 Up to 1 part in 20,000
Exposure limit band it covers Dust with a WEL above 1 mg/m³ Dust with a WEL of 0.1 mg/m³ or above Dust with a WEL below 0.1 mg/m³, plus carcinogens and pathogens
Typical filter grade fitted Standard cartridge or bag H13 HEPA H14 HEPA, sealed system
Construction dust — concrete, mortar, block Not compliant Minimum standard for general construction dust Where silica exposure is high — heritage stone and engineered stone
Wood dust — softwood, hardwood, MDF Not compliant for regulated species Minimum standard, hardwood included Where the COSHH assessment calls for it
Engineered stone and quartz worktops Not compliant Not compliant Required. HSE prohibits dry cutting — water suppression is the expected control.
Asbestos Not compliant Not compliant Mandatory under CAR 2012, Type H disposal, DOP-tested to BS 8520-3
Damp and mould Not compliant May be adequate for light, small-area cleaning — the risk assessment decides For significant remediation or heavy contamination
Healthcare Not compliant in any clinical area ICRA Type A and B Mandatory for ICRA Type C and D
Domestic and light commercial Correct specification Acceptable but not required Acceptable but not required
Machine requirements beyond filtration None specific Airflow warning when suction drops below the safe threshold Sealed, dust-free disposal and filter integrity certification
Regulation that bites None — outside COSHH scope COSHH 2002, CDM 2015, HSE EH40 CAR 2012, COSHH 2002 carcinogens, ICRA, BS 8520-3

Why the percentages matter more than they look

The gap between 99% and 99.9% reads like rounding. It is not. An L-Class machine passes ten times more fine dust back into the breathing zone than an M-Class machine, and an M-Class machine passes twenty times more than H-Class. On a sustained cutting or grinding operation that difference accumulates across a shift.

The fraction that escapes is also the worst fraction. Coarse dust is caught by any machine; what passes through is the finest, most respirable material — the particles small enough to reach deep lung tissue. A machine retaining 99% of asbestos-containing dust is returning one part in a hundred of those fibres to the operative. That is why substitution downwards is never acceptable on regulated work, however good the machine is in other respects.

Filter grade is not the same as machine class

This is the single most common specification error we see, and it matters on site. H13 and H14 are filter media ratings. L, M and H are whole-machine classifications, tested with the filter, bag, hose connections and motor exhaust all in place.

A machine can carry a high-grade HEPA filter and still leak at the seals, at the bag change or through the exhaust. HEPA on the box does not make a machine H-Class. That is precisely why the standard tests the assembled machine rather than the element inside it, and why an H-Class machine additionally has to demonstrate sealed disposal and filter integrity.

So there are two questions to ask, not one: what filter grade is fitted, and what class is the machine certified to. On regulated work the second question is the one that determines compliance — and the one an inspector will ask.

Translating between specifications

Different sectors ask this question in different words. A contractor asks for a class, a facilities manager asks for HEPA, a data centre references ISO 14644 and a cleanroom spec asks for ULPA. They are not all asking about the same thing, and the differences are where specifications go wrong.

I've been told I need a HEPA vacuum. Is that the same as H-Class?

No. HEPA describes the filter media — usually H13 or H14 — while H-Class describes the certification of the whole machine. A machine can be fitted with a HEPA filter and not be certified to any dust class at all.

If the requirement came from a method statement or a COSHH assessment for regulated work, what you actually need is the class. Ask for both: the class the machine is certified to, and the filter grade fitted.

Is H13 HEPA the same as H-Class?

No, and this is the pairing that causes the most confusion, because the letter H appears in both. H13 is a filter grade and it is the grade typically fitted to M-Class machines.

An H-Class machine uses H14 media and additionally has to demonstrate sealed, dust-free disposal and filter integrity. So “it has an H13 HEPA filter” is not evidence that a machine is H-Class — more often it indicates the opposite.

My specification says ISO 14644 Class 8. Which dust class is that?

ISO 14644 classifies the airborne particle count of a cleanroom or data hall. It does not classify vacuum cleaners, so it does not map directly onto L, M or H.

In practice, H13 is the minimum filter grade for routine cleaning in those environments, and H14 is required where the hardware OEM references Class 8 directly. Because the work is around live equipment, the sealed containment of an H-Class machine is usually the right specification rather than filter grade alone. ISO 14644-5 governs the cleaning operation itself.

What about ULPA — is that above H-Class?

ULPA is a higher filter grade than H14, but it is still a filter grade, and H is the top of the machine classification. There is no class above H-Class.

So a ULPA-filtered machine is still an H-Class machine — V-TUF's MIDI HSV is exactly that, ULPA15 media in an H-Class certified machine. The ULPA element buys you finer filtration within the same certification, not a higher one.

Where the class is set by risk assessment, not by a table

Two of the rows above deliberately do not give a single answer, because the regulation does not. For damp and mould, and for wood dust where a carcinogenic risk is identified, COSHH requires you to assess the extent of contamination and the exposure risk and then control accordingly. A small area of surface mould in a void and a heavily contaminated occupied property are not the same job and do not carry the same specification.

Where the assessment is borderline, specify upwards. The cost difference between M-Class and H-Class on one machine is far smaller than the cost of an HSE improvement notice, a stopped site or a health claim years later.

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