Wiki — standards,
regulations and terminology

ACD

IEC classification for vacuum cleaners designed to collect combustible dust in areas without official ATEX zone classification. ACD vacuum cleaners are certified for internal Zone 20 (combustible dust inside the machine) but are not approved for external use in Zone 20, 21 or 22. ACD is not an ATEX approval and cannot replace a full ATEX certificate from a notified body. It is frequently confused with ATEX approval, and this is one of the most widespread misunderstandings in the market. The ACD solution is typically found on industrial vacuum cleaners used in pharma production sites, chemical process plants and 3D-printer rooms, where the production environment itself is not ATEX-classified but where the internal chamber of the vacuum cleaner can temporarily contain an explosive dust atmosphere.

AISI 316L

Austenitic stainless steel with low carbon content (L = Low Carbon) and molybdenum addition, giving high corrosion resistance to acids, bases and chloride-containing cleaning agents. Used as a standard material for collection containers, filter housings and external surfaces on industrial vacuum cleaners for pharma, chemicals, filling lines and combined ATEX/OEB environments. Withstands autoclaving at 121°C and 134°C without corrosion damage. AISI 304 is a cheaper alternative without molybdenum, typically used in non-corrosive environments.

Activated carbon — MRAC

An MRAC module (Middle Ring Activated Carbon) is a cylindrical activated-carbon charge placed between the collection tank and the motor head on certain Tiger-Vac ATEX vacuums — including the EXP1-10 (4W) RE HEPA (MRAC) in the II 2GD range. The carbon absorbs toxic and corrosive vapours in the work air before the HEPA section, protecting the HEPA media and reducing gas-phase emissions in the exhaust. The charge is selected according to the contaminant type and comes in four variants: Regular (212200B) — 3 mm bituminous activated carbon for general VOCs and light solvents. MERSORB (212200C) — sulphur-impregnated carbon that chemically binds mercury vapours (Hg). Used in dental clinics, laboratories, research facilities and mercury remediation. KOGC3 / KINA3 (212200K) — alkali-impregnated carbon that absorbs acid vapours and chlorides, including HCl, Cl₂, SO₂ and NO₃. Used in halogen chemistry, chlorine production and acid filling. A-3 (212200L) — acid-impregnated carbon that binds ammonia, arsine (AsH₃) and phosphine (PH₃). Used in semiconductor and LED manufacturing and in agricultural / fertiliser handling. Carbon service life depends on concentration and exposure time — routine VOC collection can run for months, while saturated mercury exposure can saturate MERSORB within weeks. Tiger-Vac recommends either downstream sampling or a scheduled replacement programme. The carbon is not field-regenerable and is disposed of as hazardous waste according to the absorbed substance class.

Antistatic

Property of a material (typically plastic or rubber) that allows it to dissipate static electricity to ground without short-circuiting. EN 60079-32-1 sets the guideline limit at no more than 10&sup9; Ω for a material to qualify as antistatic in an ATEX context. Antistatic hoses are mandatory on ATEX vacuum cleaners, where the grounding chain from nozzle to chassis bolt must be unbroken. Distinguished from electrically conductive material, which has resistance below 10&sup6; Ω.

ATEX

Collective term for the two EU directives regulating equipment (2014/34/EU) and the work environment (1999/92/EC) in explosive atmospheres. ATEX-certified equipment is designed and tested not to act as an ignition source under normal or foreseeable fault operation. The term covers both dust and gas environments and is the legal umbrella over all Zone 0/20, Zone 1/21 and Zone 2/22 classifications. The ATEX directives have existed since the 1990s, with the equipment directive revised in 2014. The first version of the workers directive was 1999/92/EC, implemented in Denmark via BEK 478/2003 in July 2003.

ATEX history in Denmark

The ATEX Workers Directive 1999/92/EC was implemented in Danish law through the Working Environment Authority's BEK no. 478 of 9 June 2003, taking effect on 1 July 2003. Before implementation, ATEX was neither a common term nor a commercial selling argument in Denmark, and few ATEX models existed on the Danish market — Particulair was an early actor in introducing the range to Danish customers. Tightened requirements followed through 2003–2010 with BEK 268/2010 from the Emergency Management Agency on zone classification. EN 17348:2022 (harmonised 2023–2024) marks the latest important step towards unambiguous product standards.

ATEX marking

The ATEX marking on a vacuum cleaner label states the equipment's complete explosion-protection specification on a single line. Example: II 2D Ex h tb IIIC T80°C Db. Reading: II = surface installation (not mining), 2 = category 2 (high safety, Zone 1 or 21), D = dust environment, Ex h = protection method (constructive, non-electrical), tb = electrical protection against dust (enclosure), IIIC = dust group (conductive dust — the strictest level), T80°C = maximum surface temperature, Db = Equipment Protection Level (typically Db for category 2D). The marking follows ATEX 2014/34/EU and EN ISO 80079-36/-37.

BLSD motor

Electronically commutated direct-current motor without brushes. Unlike traditional DC motors, which commutate mechanically through carbon brushes, the BLSD motor uses electronics to control current through the stator windings. The result is higher efficiency, longer service life and practically no spark formation — a critical advantage in ATEX contexts. BLSD motors are an option on several industrial vacuum cleaners from Tiger-Vac and are typically used on models that require an extra-high safety margin or that operate continuously.

Bypass motor

Universal motor that uses external, separate cooling air from the surroundings — not the working air through the vacuum cleaner. This means the motor can run continuously and under full load without risk of overheating, even when the working air is very hot or contaminated. The bypass motor is the standard choice on large ATEX vacuum cleaners where close placement to hot processes, long operating times and high airflow are critical. Distinguished from through-flow motors, which use the working air for cooling and are therefore more sensitive to heat and high duty cycles.

Combustible dust

Solid particles of micrometre size that, when sufficiently dispersed in air, can form an explosive atmosphere. Combustible dust includes organic powders (flour, sugar, starch, API), wood dust, coal dust and practically all metal powders. Even powders that look harmless can explode at high concentration: 15 g/m³ or more is typically explosible for organic powders. Characterisation is done via Pmax, Kst, MIE and MIT according to EN 14034 and EN 13821. The classification St 1, St 2 and St 3 based on Kst is the central basis for choosing the explosion-protection method.

Fire and explosion triangle

The model describing the three necessary conditions for a fire or explosion to occur: combustible material (dust or gas), oxygen source (typically atmospheric air) and ignition source (spark, heat, static electricity, friction). The explosion triangle is often extended to a pentagon that also requires: dispersed dust cloud and confinement. Removing just one condition prevents the explosion. Inerting (water or oil immersion) removes the oxygen; ATEX-approved equipment removes the ignition source; good handling and closed systems reduce dust clouds. The model is described in EN 1127-1.

CE marking

The manufacturer's own declaration that a product complies with all applicable EU directives and regulations. The CE mark is not a quality stamp but a legal statement that the manufacturer has carried out the required conformity assessment procedure. For ATEX vacuum cleaners this typically means simultaneous compliance with the ATEX Directive 2014/34/EU, the Machinery Directive 2006/42/EC, the Low Voltage Directive 2014/35/EU, the EMC Directive 2014/30/EU and the RoHS Directive 2011/65/EU. The manufacturer's EU Declaration of Conformity must list all applied standards.

Class II Group E

American classification under the National Electrical Code and NFPA 484 for areas with conductive metallic dust — including aluminium, magnesium and titanium. Class II denotes dust environments (versus Class I = gas), Group E denotes conductive metal powders. Class II Group E is the strictest dust classification in the USA and equipment used must demonstrate safety margins exceeding ordinary ATEX 2GD approval. Tiger-Vac PRS systems (Powder Recovery Systems) for 3D-print powders are certified to Class II Group E.

Cyclone pre-separator

Mechanical pre-separator that uses centrifugal force to separate the bulk of the collected material before the air reaches the filters. Effectively removes 95–98 % of the dust in the chamber and substantially extends filter life. Typically used on large dust collectors, on Powder Recovery Systems for 3D printing, and wherever larger quantities of dust need to be collected without constant filter changes. NFPA 484 explicitly requires cyclones in powder recovery systems not to have internal filter media (clause 11.2.4.4.1), precisely because the cyclone's centrifugal action must be the primary separation mechanism.

dKst

The maximum time-derivative of the explosion pressure inside a dust explosion, measured in bar/s. dKst is a supplementary value to Kst, expressing how fast pressure rises at the most critical instant during the explosion. Where Kst describes the overall reactivity, dKst describes the peak rate of pressure rise. Both values are measured in a 20-litre spherical test vessel per EN 14034-2 and are used together when dimensioning venting systems (EN 14491) and explosion-suppression systems.

EPL — Equipment Protection Level

EPL is the modern replacement for the old categories 1, 2 and 3 in the ATEX Directive. Da, Db and Dc are used for dust environments; Ga, Gb and Gc for gas environments. Da/Ga = highest safety level, required in Zone 0/20. Db/Gb = high safety, required in Zone 1/21. Dc/Gc = normal safety, required in Zone 2/22. The EPL system is internationally harmonised with IECEx and is used in modern ATEX marking. ACD vacuum cleaners are typically classified as EPL Dc internally.

ESD — Electrostatic Discharge

Sudden transfer of electric charge between two objects at different potentials. ESD typically occurs when insulating materials (plastic, rubber) are rubbed against each other or against metal parts — a process called the triboelectric effect. In ATEX contexts ESD is a critical ignition source, because even a weak spark (below 1 mJ) can ignite dust with low MIE. Protection is achieved by antistatic or conductive materials, grounding and equipotential bonding of all metal parts. EN 60079-32-1 and -32-2 are the central standards.

Ex d — Flameproof enclosure

Protection principle in which electrical components are placed in an enclosure designed to withstand an internal explosion without it propagating to the surrounding explosive atmosphere. The enclosure has special flame paths (narrow gaps between surfaces) that cool the exhaust gases below their ignition temperature. Typically used for motors and power electronics in Zone 1 gas environments. The dust-rated equivalent for dust is Ex tb.

Ex e — Increased safety

Protection principle in which electrical equipment is built with extra-high safety margins so that neither normal operation nor foreseeable fault conditions can generate an ignition source. Typically used in terminal boxes, transformers and induction motors in Zone 1. Differs from Ex d by not containing the explosion but by preventing it from arising in the first place.

Ex h — Mechanical Ex

Protection principle for non-electrical equipment in explosive atmospheres. The construction is such that no ignition source can arise during normal operation — no moving parts that rub, no friction that creates sparks, no surfaces that get too hot. Defined in EN ISO 80079-36 and -37. Ex h has several sub-types: Ex h c (constructional safety), Ex h b (control of ignition source) and Ex h k (liquid immersion). Most passive ATEX accessories — hoses, couplings, nozzles — are certified to Ex h.

Ex i — Intrinsic safety

Protection principle in which electrical circuits are limited to such low energy that even in case of short-circuit or fault they cannot ignite an explosive atmosphere. Ex ia = highest safety level (safe even with two simultaneous faults), used in Zone 0/20. Ex ib = safe with one fault, used in Zone 1/21. Ex ic = safe during normal operation, used in Zone 2/22. Typically used for instrumentation and control electronics; less often for vacuum-cleaner motors that require higher power.

Ex m — Encapsulation

Protection principle in which the electrical components are completely encapsulated in a solid non-combustible material (typically epoxy or silicone), so that neither the explosive atmosphere can reach the components nor any potential ignition source inside the components can reach the explosive atmosphere. Typically used for small electronics, sensors and stationary passive components. Not used in vacuum-cleaner main motors.

Ex o — Oil immersion

Protection principle in which electrical components are placed in an oil bath that both cools the components and prevents the explosive atmosphere from reaching potential ignition sources. Extremely rarely used in modern equipment but found on older installations such as transformers and large contactors. Listed here purely for completeness — a modern ATEX vacuum cleaner does not use Ex o.

Ex p — Pressurization

Protection principle in which an enclosure is kept at slight overpressure with clean air or inert gas, so the explosive atmosphere cannot enter. Typically used for control cabinets, motors and control units. Requires a pressure monitoring and shutdown system that powers the equipment down if pressure drops. Rarely used on mobile vacuum cleaners but found on stationary installations in large ATEX plants.

Ex q — Powder filling

Protection principle in which an enclosure is filled with fine sand-like non-combustible powder (typically quartz sand) surrounding the electrical components. The powder prevents the formation of arcs in case of short circuit and prevents an ignition source from reaching the surrounding atmosphere. Typically used for transformers and power supplies. Rarely used on vacuum-cleaner equipment.

Ex t — Protection by enclosure

Protection principle for electrical equipment in dust environments. The equipment is built with an enclosure that prevents dust ingress and thereby ignition by electrical components inside the housing. Ex tb is used in Zone 21 (category 2D, EPL Db); Ex tc in Zone 22 (category 3D, EPL Dc). The corresponding variant for gas environments is Ex d (flameproof enclosure). Ex t is the dominant protection principle for electrical ATEX vacuum cleaners — the motor is placed inside a dust-tight enclosure that prevents external dust from reaching motor and electronics.

Explosion protection document (EPD)

The written documentation the employer must prepare under the ATEX Workers Directive 1999/92/EC and BEK 478/2003. Must contain the zone drawing, the risk assessment, documentation of the equipment placed in the classified zones, and an action plan for preventing and protecting against explosion. The EPD must be available during inspection by the Working Environment Authority and be updated whenever there is a substantial change in operating conditions. Note: EPD is also used as an abbreviation for Electrostatic Discharge — the context determines the meaning.

Filter class H13 / H14 / U15–17

Classification of the individual filter element under EN 1822-1, based on particle test efficiency at MPPS. H13 = 99.95 % efficiency at MPPS. H14 = 99.995 % — the most commonly chosen final stage on industrial vacuum cleaners for carcinogenic dust. U15 = 99.9995 %, U16 = 99.99995 %, U17 = 99.999995 %. ULPA classes U15 and above require scan testing of the finished filter (PAO/DOP method) to verify integrity. Distinct from system classes L/M/H, which assess the whole machine.

Filter class L / M / H

System classification describing the entire vacuum cleaner's ability to retain hazardous particles — not just the filter element itself. Class L = low hazard, up to 1 % filter penetration, for dust with MAK above 1 mg/m³. Class M = medium hazard, up to 0.1 % filter penetration, for dust with MAK above 0.1 mg/m³ (wood dust and similar). Class H = high hazard, up to 0.005 % filter penetration, required for carcinogens, fungal spores and asbestos. Important: the class applies to the whole system including hose, joints and container — not the filter medium alone.

Dust group IIIA / IIIB / IIIC

Classification of combustible dust under EN 60079-0. IIIA = combustible flyings (fibres, particles > 500 µm). IIIB = non-conductive dust (most organic powders such as flour and sugar). IIIC = conductive dust (metal powders such as aluminium, magnesium, copper). IIIC is the strictest dust group and requires the highest safety margin, because conductive dust can short-circuit electrical equipment and defeat ESD protection. ATEX vacuum cleaners marked IIIC can be used for all dust types in the three groups; IIIB-marked equipment cannot be used for conductive dust.

Gas group IIA / IIB / IIC

Classification of flammable gas and vapour under EN 60079-0, based on MIE and MESG (Maximum Experimental Safe Gap). IIA = least hazardous gases (propane, butane, acetone). IIB = intermediate (ethylene, gaseous methanol). IIC = most hazardous (hydrogen, acetylene). Ex d or Ex e equipment marked IIC can be used for all three groups; IIB equipment cannot be used with IIC gases. In practice: fuel in the defence sector is typically IIA (jet fuel) or IIB (some petrol and alcohol blends).

Group I / II

First main classification of ATEX equipment. Group I = equipment for underground mining, where methane and coal dust may be present simultaneously. Group II = equipment for all other surface installations. Within Group II there is further sub-grouping: IIA, IIB and IIC for gas environments, and IIIA, IIIB and IIIC for dust environments. Practically all ATEX vacuum cleaners on the European market are Group II equipment.

Spark formation

Sudden electrical discharge or mechanically released glowing particle that can ignite an explosive atmosphere. Mechanical sparks arise from metal-on-metal friction, stones in the powder stream or broken steel wire in a motor. Electrical sparks arise at contact points, in brushed motors (universal motors), or when an isolated conductor short-circuits to ground. ATEX vacuum cleaners must be designed so that none of these spark sources can occur — hence the requirement for Ex h, Ex t or other Ex protection methods.

Harmonised standard

A European standard (EN/EN ISO/EN IEC) officially published in the Official Journal of the EU as the reference basis for documenting conformity with a specific directive. When a manufacturer applies a harmonised standard, conformity with the essential requirements of the directive is presumed. EN 17348 was harmonised under the ATEX Directive in March 2023 and under the Machinery Directive in August 2024 — the legal milestone that turned the standard from a technical recommendation into a practical reference for procurement and inspection.

HEPA filter

Filter class H13 and H14 per EN 1822-1, with minimum 99.95 % and 99.995 % efficiency at MPPS (Most Penetrating Particle Size, typically 0.1–0.3 µm). HEPA filters are made from glass-fibre material in a pleated construction that maximises surface area in a compact filter element. Used as the final stage on industrial vacuum cleaners for carcinogenic dust, lead-contaminated environments, pharma production, and anywhere returned air must be free of health-hazardous particles. H14 is the final stage typically required on shooting ranges and in ATEX vacuum cleaners for carcinogenic powders.

IECEx

International certification scheme for equipment in explosive atmospheres, run by the International Electrotechnical Commission. An IECEx certificate is recognised by all member countries and is typically the document used for export outside the EU. The ATEX Directive and the IECEx system are technically aligned on most points, but IECEx is a voluntary international recognition scheme, while ATEX is binding EU law. Many manufacturers hold both ATEX and IECEx certificates on the same product to simplify international projects.

Immersion separator

Construction type where the collected dust is led into a liquid bath in the collection tank and trapped on contact with the liquid (typically water or oil). Distinct from inerting by being a mechanical capture method; the liquid contributes to neutralising the dust, but the protection against ignition is also created constructively. Used on shooting ranges (gunpowder dust), in spray booths (overspray) and in ATEX applications where unburned or self-igniting dust may occur. Classified as WT (Wet Type Dust Collector) under EN 17348.

Inerting

Safety method that eliminates explosion risk by bringing the collected powder into direct contact with an inerting medium — water or oil — inside the collection tank. The principle is that explosive dust particles are immediately surrounded by a medium that blocks access to oxygen and prevents all electrical and mechanical ignition sources. Water immersion (wet mix) is suitable for most reactive metal powders but is insufficient for pyrophoric metals (aluminium, magnesium, titanium), which can react with water and release hydrogen gas. For these, oil inerting is required. Inerted vacuum cleaners are certified internally as Zone 20 (category 1D / EPL Da) and marked WT under EN 17348.

Internal Zone 20

Concept that classifies the explosion risk inside the vacuum cleaner's collection system — independently of the surrounding environment. Inside the tank and filter section, dust concentration can be high and continuously present, which is why the internal chamber in practice is always treated as Zone 20 (explosive atmosphere continuously present). EN 17348:2022 was the first standard to make this concept formally explicit. ACD vacuum cleaners are typically certified with internal Zone 20 but external non-ATEX, which is their defining characteristic.

Grounding (earthing)

Electrical connection between a metal part and the building's earth potential that prevents the build-up of static electricity. On an ATEX vacuum cleaner, the entire grounding chain from nozzle through hose, coupling, vacuum cleaner body and mains supply must be unbroken and verifiable. EN 60079-32-1 sets the guideline limit at no more than 10&sup6; Ω for a metal part to be considered safely grounded in most combustible-dust applications. Verification is done by measurement with a multimeter per EN 60079-32-2.

Grounding resistance

The measured electrical resistance from a metal part through the entire grounding chain to the building's earth potential. Guideline limits per EN 60079-32-1: below 10&sup6; Ω for conductive material (safety against ESD ignition in most applications), below 10&sup8;–10&sup9; Ω for antistatic material (safety against dangerous build-up). Resistance is measured with a multimeter or a specialised grounding tester. Measurement must be performed under typical operating conditions — with the hose mounted, the coupling assessed and contact surfaces cleaned.

Combined zone

Area where both an explosive gas atmosphere and an explosive dust atmosphere can occur simultaneously. Marked with combined codes: 3GD = Zone 2 (gas) + Zone 22 (dust); 2GD = Zone 1 + Zone 21; 1GD = Zone 0 + Zone 20. Combined zones require equipment that meets both zones' requirements simultaneously — typically a factor 2–3 more expensive, and found on specialised ATEX vacuum cleaners for pharma, chemicals and additive manufacturing. Particulair Ex-Vac Hub markets combined solutions as a separate category (atex-kombi).

Conductive dust

Dust with electrical conductivity, primarily metal powders (aluminium, magnesium, copper, iron, zinc) but also certain carbon-based powders such as coke dust and graphite. Conductive dust is a particular challenge in ATEX contexts because it can short-circuit electrical equipment and defeat ESD protection by creating unintended conductive paths. Classified as dust group IIIC under EN 60079-0 — the strictest dust group, requiring the highest safety margin. NFPA 484 uses the parallel classification Class II Group E.

Gunpowder dust

Solid residues of unburned propellant and primer compound from ammunition. Accumulates on shooting ranges in the firing hall, at the bullet trap, on shelves and in ventilation ducts. Gunpowder dust is both explosive and combustible: ignition can occur from about 170 °C upwards, and even a layer of 1 mm thickness can explode. The hazardous airborne concentration is from around 15 g/m³. Static electricity or a small spark is enough to trigger fire or explosion. Cleaning requires an ATEX Zone 21-certified vacuum cleaner with liquid bath/inerting, HEPA H14 as the final stage and a complete ESD and grounding chain.

Kst

Characteristic parameter for the violence of dust explosions, measured in bar·m/s in a 20-litre spherical test vessel per EN 14034-2. Kst expresses the nominal rate of pressure rise normalised to one cubic metre of volume. Classification: St 1 = Kst 1–200 (mild explosion, e.g. flour and sugar), St 2 = 200–300 (strong, e.g. some plastic powders), St 3 = > 300 (very strong, e.g. aluminium powder). The Kst value is used in the dimensioning of venting systems (EN 14491) and explosion-suppression systems.

BLV / BOELV (lead in blood and air)

Binding EU exposure limit values for occupational lead exposure, tightened with effect from 2024 (Directive 2024/869 under CMRD). BOELV = 0.03 mg/m³ lead in air over an 8-hour working day. BLV = 15 µg/dL lead in blood (with a transitional limit of 30 µg/dL until 31 December 2028). For many European shooting ranges, measured values lie 20–30 times above the new airborne limits, which is one of the core reasons the sector is under significant pressure to upgrade. Cleaning requires an H14-filtered vacuum cleaner and closed collection method.

LEL / UEL

Explosion limits for gas or vapour in air. LEL (Lower Explosive Limit) is the lowest gas/air concentration that can be ignited; below this value the mixture is too 'lean'. UEL (Upper Explosive Limit) is the highest; above this value the mixture is too 'rich' and cannot be ignited. Example: jet fuel JP-8 has LEL around 0.7 vol% and UEL around 5.0 vol% vapour in air. ATEX zone classification is based on whether and how often concentrations can fall between LEL and UEL. For dust, the parallel parameter is MEC (Minimum Explosible Concentration), typically 15–500 g/m³.

MEC — Minimum Explosible Concentration

The lowest dust/air concentration that can be ignited into a dust explosion, measured in grams per cubic metre of air. Determined per EN 14034-3 in a 20-litre spherical test vessel. Typical MEC for organic powders is 15–60 g/m³; for certain metal powders only 30–125 g/m³. By comparison: 60 g/m³ corresponds to only about 0.03 teaspoons of dust per litre of air — typically not visible to the naked eye. Used in assessing explosion risk inside vacuum cleaners and dust collectors.

MIE — Minimum Ignition Energy

The lowest energy that can ignite a dust/air mixture or gas/air mixture, measured in millijoules (mJ). Determined for dust per EN 13821 and is one of the central parameters for classifying combustible dust and selecting the explosion protection method. MIE < 3 mJ = electrostatic discharges can ignite — ESD protection and equipotential bonding are critical. MIE < 1 mJ = practically all electrical and friction-based ignition sources can ignite — ATEX-approved equipment is strictly required. MIE < 0.1 mJ = inerting is typically the only safe solution.

MIT — Minimum Ignition Temperature

The lowest surface temperature that can ignite a dust/air mixture or a dust layer, measured in degrees Celsius. Typically determined in two variants: MIT-cloud for dust in cloud form and MIT-layer for a 5 mm thick dust layer (T 5mm). The MIT value is decisive for selecting the T-class on ATEX equipment; the maximum surface temperature of the equipment must be at least 75 °C below MIT-cloud and at least MIT-layer minus 75 °C. Example: gunpowder dust has MIT-cloud around 320–370 °C; T80°C-marked equipment therefore has a margin.

MOC / LOC — Minimum Oxygen Concentration

The lowest oxygen concentration that can support an explosion. Below this value, a dust or gas/air mixture cannot be ignited regardless of concentration or ignition source. Measured per EN 14034-4 (dust) and is the technical basis for inerting methods. Typical MOC for organic powders is 8–12 vol% O₂; for the most reactive metal powders as low as 4–7 vol%. Inerting with nitrogen or CO₂ reduces oxygen content below the MOC limit and eliminates the explosion risk.

MPPS

The particle size that passes most easily through a HEPA or ULPA filter, typically 0.1–0.3 µm. Filters are most effective on larger particles (impaction, interception) and on very small particles (diffusion); MPPS is the band in between where both mechanisms are weakest. Filter classes per EN 1822-1 (H13, H14, U15–17) are all based on efficiency measured at MPPS — it is the strictest assessment. H14 = 99.995 % efficiency at MPPS.

Notified Body

Independent body designated by an EU member state to perform the mandatory conformity assessments under the ATEX Directive 2014/34/EU. For equipment in categories 1 and 2, a notified body must be involved in type examination and ongoing production control. For category 3, the manufacturer may declare conformity alone. Examples of European notified bodies for ATEX vacuum cleaners: TUEV (Germany), Bureau Veritas (France), Eurofins (DK), CESI (Italy). Notified body numbers can be looked up in the NANDO database at the European Commission.

Oil inerting

Inerting method where the collected metal powder is led into an oil chamber in the collection tank and completely surrounded by inerting oil. The oil prevents any contact between the powder and atmospheric oxygen and thereby eliminates the risk of ignition. Unlike water immersion, oil does not react chemically with pyrophoric metals such as aluminium and magnesium, and no hydrogen gas is generated. Oil inerting is the internationally recognised standard method for vacuum collection of self-igniting and pyrophoric metal powders in additive manufacturing. Typically classified as category 1/2D (Zone 20 internal, Zone 21 external) and certified to ATEX 2014/34/EU and IECEx.

Equipotential bonding

Electrical connection between all metallic parts in an installation, keeping them at the same electrical potential. Distinct from grounding by not necessarily being connected to earth potential — equipotential bonding only ensures that no part of the system can reach a different potential than the rest. In practice, equipotential bonding and grounding are two sides of the same principle: all metal parts are connected both to each other and to ground. Missing equipotential bonding is one of the most frequent ignition sources in ATEX accidents, because an isolated metal component can charge up and give off a spark on contact with a grounded component.

Pmax

The maximum pressure a dust explosion can generate in a closed vessel, measured in bar (typically bar(g) overpressure). Determined in a 20-litre spherical test vessel per EN 14034-1. For organic powders, Pmax typically ranges 7–10 bar; for some metal powders up to 12–13 bar. Pmax is used in the dimensioning of all explosion-protection measures: pressure-rated vessel construction, venting systems (EN 14491), explosion-suppression systems and isolation devices. Sealed ATEX vacuum cleaners must withstand the internal Pmax without rupture.

Pneumatic vacuum cleaner

Vacuum cleaner driven by compressed air instead of an electric motor. No electrical components are present in the machine itself, which eliminates all electrical ignition sources — a critical advantage in the strictest ATEX zones. Pneumatic vacuum cleaners can run uninterrupted 24/7 without risk of motor overheating and are the typical choice on filling lines, chemical process plants, and anywhere compressed air is available and continuous operation is required. Tiger-Vac SS-20 and ATEX-10A are examples. Trade-off: pneumatic machines require 800–2,500 l/min of compressed air and are noisy.

Powder Bed Fusion / Additive manufacturing

Collective term for additive manufacturing methods that use an energy source — laser or electron beam — to melt or sinter layers of powder material on a powder bed. Selective Laser Sintering (SLS) is used for plastic powders; Selective Laser Melting (SLM) and Direct Metal Laser Sintering (DMLS) for metal powders. After each print job, large quantities of unused powder remain in the printer chamber and powder bed. Powder residues are typically classified as combustible and — for metal powders — also as conductive and potentially reactive. Safe collection requires ATEX-certified machines and often a PRS system.

PRS — Powder Recovery System

Integrated system for collecting and recycling unused powder from powder bed fusion printers (SLS, SLM, DMLS, EBM). A PRS system combines an industrial vacuum cleaner with a high-efficiency cyclone pre-separator that separates up to 98 % of the powder before it reaches the filters and collects it cleanly in a separate removable stainless-steel tank. The tank can then be coupled to sieving equipment and the powder returned to the print process. Particularly relevant for metallic powders, since these are expensive and recycling is economically critical. ATEX-certified PRS systems are typically marked II 2GD or II 1/3D and comply with NFPA 484.

Pyrophoric

Property of certain substances — particularly fine metal powders — that allows them to ignite spontaneously on contact with air, moisture or frictional heat, without an external ignition source. The most important pyrophoric materials are aluminium and aluminium alloys, magnesium, nano-sized titanium and certain nickel-based superalloys. Pyrophoricity is particle-size-dependent and is amplified strongly at very fine particle sizes. For pyrophoric powders, conventional ATEX dry vacuuming is insufficient, and water immersion can be dangerous (aluminium and magnesium react with water and release hydrogen gas). Oil inerting is the only safe collection method.

Risk assessment

Systematic assessment of where and how often an explosive atmosphere can occur in a workplace and which ignition sources may be present. The risk assessment is the formal basis for zone classification and for selecting ATEX equipment of the appropriate category. Must be performed under the ATEX Workers Directive 1999/92/EC (in Denmark via BEK 478/2003) and documented in the explosion protection document. Must be updated whenever there is a substantial change in operating conditions.

Dust class L / M / H

Used as a synonym for filter class L, M and H per EN 60335-2-69. Describes the entire vacuum cleaner's ability to retain hazardous particles — not the filter element alone. L = low-hazard dust, up to 1 % penetration. M = medium-hazard dust, up to 0.1 % penetration. H = high-hazard dust (carcinogens, fungal spores, asbestos), up to 0.005 % penetration. ACD vacuum cleaners are typically class H, but a class H marking is not the same as ACD approval — the two certificates address different aspects of the same machine.

SDS — Safety Data Sheet

Legally required document that accompanies hazardous chemical substances and mixtures on the European market. Contains 16 sections with information on identification, hazard classification, first aid, fire and explosion data, handling, exposure control and disposal. Section 9 (physical and chemical properties) and section 10 (stability and reactivity) are decisive for assessing whether a substance should be treated as combustible or explosive. Section 14 contains transport information. The SDS is the practical contact point between the CLP classification and the choice of collection equipment.

Side-channel blower

Type of air-moving equipment that generates a constant, high airflow with moderate negative pressure. Distinct from turbine motors (high vacuum, low flow) and bypass motors (medium of both). Side-channel blowers are typically used in industrial vacuum cleaners for continuous operation with large air volume — for example on filling lines and on large dust collectors.

St 1 / St 2 / St 3

Classification of combustible dust by its explosion constant Kst (measured in bar·m/s). St 1 = Kst 1–200 (mild explosion, e.g. flour, sugar, starch, many APIs). St 2 = 200–300 (strong explosion, e.g. some plastic powders, finer-grained powders). St 3 = > 300 (very strong explosion, e.g. aluminium powder, magnesium powder). The St class is the central basis for choosing the explosion-protection method: at St 3, explosion suppression or full inerting is required. ATEX vacuum cleaners must be dimensioned for the dust's actual St class.

Static electricity

Electrical charge that builds up on an isolated or poorly grounded surface, typically through friction between two different materials (triboelectric effect). Static electricity is one of the most frequent ignition sources in dust explosions: a human body can build up 10–15 kV by walking across a carpet, and filling a powder into a plastic bag can generate even higher voltages. ATEX protection against static electricity relies on antistatic or conductive materials, grounding and equipotential bonding. EN 60079-32-1 and -32-2 are the central standards.

T-class — Maximum surface temperature

The ATEX marking entry stating the highest surface temperature the equipment can reach during normal operation or foreseeable fault conditions. For gas environments, classes T1 (450 °C max.), T2 (300 °C), T3 (200 °C), T4 (135 °C), T5 (100 °C), T6 (85 °C) are used. For dust environments the actual maximum temperature is given directly in °C, e.g. T80°C or T125°C. The T-class must be at least 75 °C below MIT-cloud and at least MIT-layer minus 75 °C for the dust in the application.

Take-home lead

Contamination with lead particles transported from the workplace to the home via clothing, shoes, hair and equipment. A well-known phenomenon at shooting ranges, where lead dust from ammunition can follow shooters home and be released indoors through inhalation or hand contact. The risk is particularly high for children: there is no known safe lower threshold for blood lead in children, and even low levels are linked to lasting cognitive and behavioural damage. NIOSH (USA) and European occupational-health authorities recommend changing clothes, dedicated work shoes and dedicated laundering — combined with an H14-filtered vacuum cleaner on the range itself to minimise the source.

TEFC motor

Electric motor with a fully sealed housing that prevents ingress of dust and moisture, cooled by an external fan mounted on the motor shaft. TEFC motors are robust industrial motors with IP protection class typically IP54–IP65 and are suited to environments with dust, moisture and aggressive atmospheres. In an ATEX context, TEFC motors are used in vacuum machines with inerting — for example the Delfin MTL INERT and DM2 INERT series — where a bypass motor cannot be used due to continuous duty and heat loading. TEFC is NEVER bypass and NEVER BLSD — the three motor types are practically mutually exclusive.

Triboelectric effect

Physical phenomenon where two materials exchange electrical charges on contact or through friction, becoming oppositely charged when separated. The triboelectric effect is the cause of practically all static electricity in industrial powder handling processes: powder runs through a sack, funnel or hose, and friction generates an electrical charge that can discharge as a spark on near-contact with a grounded component. Countermeasures: conductive or antistatic materials, grounding and equipotential bonding.

ULPA filter

Filter class U15, U16 and U17 per EN 1822-1, with higher efficiency than HEPA: 99.9995 %, 99.99995 % and 99.999995 % at MPPS. ULPA filters require scan testing (PAO/DOP method) at manufacture to verify integrity — the oil thread test allowed for H13 and H14 is not acceptable for U15 and above. ULPA stages are typically used in laboratory vacuum cleaners and pharma vacuum cleaners for the most potent APIs, and in specialised ATEX vacuum cleaners where the absolute highest filtration is required.

VOC — Volatile organic compounds

Organic chemicals with high vapour pressure at room temperature, which therefore evaporate easily into air. Includes many solvents (acetone, ethanol, isopropanol), bonding agents in adhesives and coating products, and propellants in spray cans. In ATEX contexts, VOCs are relevant because many are flammable and can form explosive vapour/air mixtures at even low concentrations. An activated carbon filter is the only effective method for removing VOCs from the airflow in a vacuum cleaner; particle filters alone do not capture them.

Water immersion (wet mix)

Inerting method where the collected powder is mixed with water in the collection tank. The water surrounds the powder, blocks access to oxygen and prevents all electrical and mechanical ignition sources. Suitable for most reactive metal powders and is the primary inerting method in most pharma and chemical applications. Important exception: water immersion must NOT be used for pyrophoric metals (aluminium, magnesium, titanium), which react with water and release hydrogen gas — for these, oil inerting is required. Water-immersion vacuum cleaners are typically marked WT (Wet Type) per EN 17348.

WT — Wet Type Dust Collector

Marking code under EN 17348:2022 for vacuum cleaners and dust collectors that use a liquid bath (water or oil) as the inerting medium. The WT category covers both water immersion and oil inerting and distinguishes these machines from conventional dry vacuum cleaners. WT-marked equipment is typically certified with internal Zone 20 (category 1D / EPL Da) and is used for pyrophoric powders, gunpowder dust and other reactive or self-igniting substances.

Zone 0 (gas)

Area where an explosive gas atmosphere is present continuously or for long periods. Typical examples: inside tanks for volatile liquids, inside process piping and open tank hatches. ATEX-marked equipment in Zone 0 must be category 1G (EPL Ga) — the highest safety level. Rarely relevant for vacuum cleaners, which are typically used outside the most critical gas zones, but occurs in specialised fuel and chemical applications.

Zone 1 (gas)

Area where an explosive gas atmosphere is likely to occur under normal operation. Typical examples: around the filling ports of fuel tanks, around pump stations and spray booths. ATEX-marked equipment in Zone 1 must be at least category 2G (EPL Gb). Tiger-Vac explosion-protected vacuum cleaners for fuel handling in the defence sector are typically certified for Zone 1.

Zone 2 (gas)

Area where an explosive gas atmosphere is not likely to occur during normal operation and, if it does, only for short periods. Typical examples: outer zones around spray booths, ventilated rooms with weak vapour sources. ATEX-marked equipment in Zone 2 must be at least category 3G (EPL Gc). The most common gas zone in industrial applications.

Zone 20 (dust)

Area where an explosive dust cloud is present continuously, for long periods or frequently. Annex A of EN 60079-10-2 indicates: > 1,000 hours per year. In practice, Zone 20 is rare in open work areas but is common inside sealed vessels, silos, filter housings and vacuum-cleaner tanks (internal Zone 20). ATEX-marked equipment in Zone 20 must be category 1D (EPL Da). ACD vacuum cleaners are certified with internal Zone 20.

Zone 21 (dust)

Area where an explosive dust cloud is likely to occur under normal operation. Annex A of EN 60079-10-2 indicates: 10–1,000 hours per year. Typical examples: around filling ports, during powder filling, around conveyor belts. ATEX-marked equipment in Zone 21 must be at least category 2D (EPL Db). Most large ATEX vacuum cleaners in pharma and chemical environments are certified for Zone 21.

Zone 22 (dust)

Area where an explosive dust cloud is not likely to occur during normal operation and, if it does, only for short periods. Annex A of EN 60079-10-2 indicates: < 10 hours per year. Typically covers areas with accumulated settled dust and peripheral zones at filling. ATEX-marked equipment in Zone 22 must be at least category 3D (EPL Dc). The most common dust zone in industrial applications and the typical level for many Tiger-Vac, Delfin and Depureco ATEX models.

Zone drawing / zone map

Drawing or plan that visually documents the boundaries of all ATEX-classified areas at a site, marking each zone's type (0, 1, 2 for gas; 20, 21, 22 for dust) and extent. The zone drawing is part of the explosion protection document and is a legal requirement under the ATEX Workers Directive 1999/92/EC. The physical marking on the plant itself must match the drawing and is regulated in Denmark by BEK 268/2010.