Combustible Dust and Hazardous Atmospheres: NFPA 660, ATEX Zones and Buyer Responsibilities

Dust extraction, pneumatic conveying, drying, and many process lines handle materials that can burn or explode when suspended in air: coal, grain, sugar, sulfur, wood, aluminium, and many chemicals and plastics. Solvent vapours and process gases add flammable-gas hazards. A blower in such a system is not just moving air, and the standards, zoning, and equipment rules that apply are a separate discipline. This guide explains the frameworks so buyers can specify correctly, and it states plainly what we do and do not supply.

Our Position

NextAir Systems does not currently manufacture ATEX-certified or AMCA 99 spark-resistant blowers. For a blower that would sit in a classified hazardous area, or handle a flammable gas, vapour, or combustible dust that requires such equipment, the blower should come from a specialist supplier. A standard blower is only appropriate where the blower and its motor sit outside any classified zone and the air handled is not explosive. The rest of this guide is here so that you can specify what you need from the right supplier, and check what you are offered.

Combustible Dust: The Standards Landscape

NFPA 660 is the consolidated combustible dust safety standard in the United States. It took effect in December 2024 and brought together several earlier commodity-specific dust standards, including NFPA 652, the general combustible dust standard, and others, into one document. It requires a dust hazard analysis (DHA) for facilities handling combustible dust. NFPA 68 (explosion protection by venting) and NFPA 69 (explosion prevention systems) remain separate standards.

These are US standards, but they are widely used as reference frameworks in many countries, and many consultants and insurers refer to them. Local regulations and the European ATEX framework also apply in their regions, so confirm which rules govern your project.

The Dust Hazard Analysis

A DHA identifies where combustible dust is present, how it could ignite and explode, and what protection is needed. The blower’s location is part of that analysis. Questions include whether the blower handles dust-laden air or clean air, whether dust can accumulate in or around the housing, whether the motor sits in a classified area, and what happens if the wheel touches the housing.

ATEX Zones for Dust

Under the ATEX framework, areas where combustible dust may form an explosive atmosphere are classified into zones according to how often the hazard is present.

Zone	Definition (typical)
Zone 20	Explosive dust atmosphere present continuously or for long periods
Zone 21	Likely to occur in normal operation
Zone 22	Not likely in normal operation, and brief if it occurs

Gas atmospheres use zones 0, 1, and 2 in the same way. Zoning is the plant operator’s responsibility, normally established through a hazardous-area study, and the equipment inside and outside the blower may be in different zones. Equipment for Group II surface industry is graded in categories 1, 2, and 3, with category 2 suitable for zones 1 and 21, and category 3 for zones 2 and 22.

Fans in Explosive Atmospheres: EN 14986

EN 14986 sets design requirements for fans intended for potentially explosive atmospheres. It covers Group II fans, gas categories 1, 2, and 3, and dust categories 2 and 3. It does not apply to Group I fans, which are those for underground mining, and it has limits on the conditions it assumes, including intake temperature and oxygen content. Fans for hazardous areas should carry marking that shows their group, category, gas or dust group, and temperature class, with documentation to support it.

Spark-Resistant Construction: AMCA 99

AMCA 99 describes three levels of spark-resistant construction. Type A requires non-ferrous material for the whole airstream, Type B a non-ferrous wheel and rub ring, and Type C construction so that a shift of the wheel or shaft cannot bring two ferrous parts into contact. For all types, bearings and electrical devices must be kept out of the airstream and the fan must be earthed. Spark-resistant construction reduces one ignition source. It is not the same as ATEX certification, and it does not protect against ignition from other causes or from catastrophic failure.

Where the Blower Sits Matters

Where a blower sits in the system changes its exposure. Some designs place the blower downstream of the collector, on the clean side, and some place it outside the building, so that the blower is not inside the dusty area, and these choices can affect how the blower’s location is classified. That is a design decision for the hazard study, and a clean-side position does not automatically remove the hazard, because dust can still reach the blower if the filter is damaged. Do not assume; take the decision from the DHA.

Protection Systems Are Separate

Explosion protection for a dust collection system usually includes venting or suppression on the collector, isolation devices in the ducts so that an explosion cannot propagate along them, and good housekeeping so dust does not accumulate. These are not blower features. The blower is one part of a system that has to be designed as a whole.

What to Ask a Specialist Supplier

1. Which group, category, and gas or dust group is the blower certified for?
2. What temperature class and maximum surface temperature?
3. What documentation comes with it: declaration of conformity, marking, and instructions?
4. Are the motor and any drive components suitable for the zone?
5. What construction features reduce ignition risk: materials, clearances, earthing, and bearing arrangement?
6. What conditions of use does the certification assume?

Where Our Range Fits

NextAir Systems manufactures centrifugal blowers up to 800 HP (about 597 kW) and up to 500 mm WC (about 4.9 kPa) static pressure for non-classified areas. If you tell us where the blower sits relative to your zone classification, we will tell you plainly whether a standard blower is suitable or whether you need a specialist supplier.

Tell Us Where the Blower Sits

Send your zone classification and the position of the blower, and we’ll tell you plainly whether a standard blower suits it. Contact us for a free quote.

Frequently Asked Questions