2026-09-21 · Équipe éditoriale KeXinMaterials
IEC 60079-31 / IEC 61241 Staub-Zone Explosionsschutz-Schutzkoffer B2B-Leitfaden
IEC 60079-31 (ersetzt IEC 61241) spezifiziert den Geräteschutz durch Gehäuse für brennbare Staubumgebungen. Drei Staubzonen (20, 21, 22) klassifizieren das Risiko nach Staubanwesenheitsdauer. Schutzkoffer für Staubzonen müssen Ex tb (Zuge-Koffer) oder Ex tc (Zuge-Koffer) tragen, mit IP6X-Schutz obligatorisch.
IEC 60079-31 vs IEC 61241 (Historical + Current)
IEC 61241 was the original dust-zone enclosure standard. Replaced by IEC 60079-31 in 2009. Some legacy references still use IEC 61241 designation.
IEC 61241 series: Original standard for dust-zone enclosures. Published in 2000-2005. Series includes IEC 61241-0 (general), -1 (DIP A/B, tD), -4 (pressurization).
IEC 60079-31: Replaced IEC 61241 in 2009 as part of harmonization with IEC 60079 series (gas atmospheres). Current edition 2022.
IEC 60079-0: General requirements for explosive atmospheres equipment. Always referenced by IEC 60079-31.
IEC 60079-31 scope: Equipment protection by enclosure "tb" (Zone 21) and "tc" (Zone 22) for use in combustible dust environments.
Why the change: IEC 60079 series unifies gas + dust explosion protection. Old IEC 61241 had parallel but separate marking system.
Legacy support: Equipment certified to IEC 61241 may still be used per most regulatory frameworks. New certifications use IEC 60079-31.
CENELEC: EN 60079-31 is the European equivalent. Used in EU ATEX 2014/34/EU certification.
B2B recommendation: Specify IEC 60079-31 (current) for new purchases. Accept IEC 61241 certification for legacy equipment continuity.
Dust Zone Classification Zone 20, 21, 22
Three dust zones classify risk by duration of combustible dust presence. Similar to gas zones 0, 1, 2 but different designation numbers.
Zone 20: Combustible dust cloud present continuously or for long periods (>= 1000 hours/year). Inside containers, ductwork, mills.
Zone 21: Combustible dust cloud likely during normal operation (10-1000 hours/year). Near dust handling equipment, filling stations, dust-laden air zones.
Zone 22: Combustible dust cloud not likely during normal operation, but short duration possible (<= 10 hours/year). Stockpiles, areas where dust may escape briefly.
Zone 20 -> protection level Da (very high). Zone 21 -> protection level Db (high). Zone 22 -> protection level Dc (enhanced).
Examples: Grain silo interior = Zone 20. Grain silo exterior near vent = Zone 21. Grain storage warehouse far from equipment = Zone 22.
Woodworking: Sawdust collection interior = Zone 20. Sawmill machine area = Zone 21. Lumber storage area = Zone 22.
Flour milling: Flour mill interior = Zone 20. Flour silo vent area = Zone 21. Loading dock for flour transport = Zone 22.
Pharmaceutical powder: Blender interior = Zone 20. Filling station = Zone 21. Staging area near filling = Zone 22.
B2B recommendation: Identify the dust zone where case will be used. Zone 22 cases (Ex tc) are simpler + cheaper. Zone 21 cases (Ex tb) are more rigorous. Zone 20 requires equipment inside the zone, not just cases.
Ex tb / Ex tc Marking for Protective Cases
Protective cases for dust zones carry Ex marking per IEC 60079-31. Two protection levels: tb (Zone 21) and tc (Zone 22).
Ex tb: Equipment protection by enclosure for Zone 21. Higher protection level. Case must prevent dust ingress even with regular contact + occasional impact.
Ex tc: Equipment protection by enclosure for Zone 22. Lower protection level. Case must prevent dust ingress under normal conditions.
Marking format: Ex tb IIIC T135°C Da or Ex tc IIIB T200°C Dc (example). Each component has meaning.
IIIC: Dust group. IIIA = combustible flyings (wood, paper). IIIB = non-conductive dust (grain, sugar, plastic). IIIC = conductive dust (metal powders, carbon).
T135°C: Maximum surface temperature. T135 = 135°C max surface temp (below dust ignition temp). T200 = 200°C. T450 = 450°C (special).
Da / Db / Dc: Equipment Protection Level (EPL). Da = Zone 20. Db = Zone 21. Dc = Zone 22.
Full marking example: "Ex tb IIIC T135°C Db" means Zone 21 case, dust group IIIC (conductive metal), max surface temp 135°C, EPL Db.
Difference Ex tb vs Ex tc: Ex tb requires impact test (5 J on enclosure, dust must not enter). Ex tc has lower mechanical requirement.
Both require IP6X ingress protection (dust-tight). Difference is mechanical impact + thermal testing.
B2B recommendation: For grain / flour / sugar / wood industry: Zone 21 (Ex tb) with dust group IIIB (or IIIC if metal dust). For pharmaceutical / general industry: Zone 22 (Ex tc) often sufficient.
Dust Ignition-Proof Case Construction
Dust ignition-proof cases have specific construction requirements: IP6X ingress, dust-resistant gaskets, anti-static surface, restricted surface temperature.
IP6X (dust-tight): IEC 60529 IP6X test. 8 hours in circulating talcum powder chamber. No dust ingress allowed.
Gasket material: Silicone rubber + PTFE preferred for dust resistance. EPDM also acceptable. Avoid natural rubber (degrades with dust).
Gasket compression: 25-35% compression for dust-tight seal. Compression too high damages gasket. Compression too low allows dust ingress.
Cable entries: Ex-certified cable glands required. Brass cable glands with EPDM grommet for dust zones.
Anti-static surface: For conductive dust (IIIC), case exterior must be anti-static OR marked with warning. Plastic cases need conductive coating.
Surface temperature: Maximum surface temperature below dust cloud ignition temp. For most organic dusts, T135°C safe. For metal dusts, T200°C or higher.
Pressure relief: Cases for Zone 21 may include pressure relief valve to release internal pressure buildup from heating/cooling cycles.
Latches: Multiple-point latching for uniform gasket compression. Stainless steel preferred for dust environments.
Material: Stainless steel, aluminum (anodized), or anti-static polymer. Avoid bare metal that could generate sparks from friction.
B2B specification example: "Ex tb IIIC T135°C Db" + "IP6X" + "anti-static polymer shell" + "silicone gasket" + "stainless steel latches"
Dust Zone Case Testing + B2B Workflow
Testing for Ex tb / Ex tc certification follows IEC 60079-31. Test sequence + cost + duration + B2B procurement workflow.
IEC 60079-31 test sequence: (1) Drop test (1.5m onto concrete for portable cases). (2) Impact test (5J for tb, 4J for tc on case). (3) IP6X dust chamber (8 hours). (4) Surface temperature test (full load + ambient). (5) Thermal endurance (heat/cold cycling).
IP6X dust test: Case loaded with dummy equipment + closed. Placed in dust chamber with circulating talcum powder. 8 hours. Opened - no dust inside permitted.
Surface temperature test: Case powered with internal heat load simulating worst-case. Surface temperature measured at hottest points. Must be below T-class specified.
Certification cost: Ex tb certification EUR 15,000-40,000 per case model. Ex tc EUR 8,000-25,000. Add IP6X test EUR 3,000-5,000.
Certification duration: 8-16 weeks including lab booking + testing + report + ATEX Notified Body certificate.
Notified Body: EU ATEX requires Notified Body (e.g., TUV, DEKRA, UL) certification for Ex tb/tc. Not self-certified.
US/Canada equivalent: NEC Class II (US) + CEC Class II (Canada). Different but equivalent to IEC dust zones.
B2B procurement workflow: (1) Identify zone 21 or 22 use environment. (2) Specify Ex marking + IP6X + dust group + temp class. (3) Verify ATEX Notified Body certificate + IEC 60079-31 test report. (4) Confirm case construction matches spec (gasket, latches, cable entries).
B2B recommendation: For grain / flour / wood / pharmaceutical / chemical industries handling combustible dust, specify Ex tb IIIC T135°C Db (Zone 21, metal dust, 135°C max surface temp) + IP6X + ATEX Notified Body certificate.
Points clés
- IEC 60079-31 (aktuell) ersetzte IEC 61241 (Legacy) im Jahr 2009 für Staubzonengehäuse.
- Drei Staubzonen: Zone 20 (kontinuierlich, 1000+ Std/Jahr), Zone 21 (Normalbetrieb, 10-1000 Std/Jahr), Zone 22 (kurze Dauer, <=10 Std/Jahr).
- Ex tb für Zone 21 (höherer Schutz) vs Ex tc für Zone 22 (niedrigerer Schutz). Beide erfordern IP6X-Eintrittsschutz.
- Staubgruppen: IIIA (Späne), IIIB (nichtleitender Staub), IIIC (leitfähiger Metallstaub). Oberflächentemperatur muss unter Staubentzündungstemperatur liegen.
- B2B-Empfehlung: Für Getreide/Mehl/Holz/Pharma-Industrien, die brennbaren Staub handhaben, Ex tb IIIC T135°C Db + IP6X + ATEX-Benannte-Stelle-Zertifikat zwingend erforderlich.
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