Combustible Dust Management SWMS (Food Processing)

Combustible dust management is a critical safety discipline in flour milling, grain handling, sugar refining, milk powder production, and broader food manufacturing where finely divided organic solids generate explosive atmospheres. Under WHS Regulation 2025 Part 4.1, any workplace where combustible dust may form a hazardous atmosphere must classify zones, control ignition sources, and document risk controls before work commences. Dust deflagrations have caused multiple fatal incidents across Australian food processing facilities, with secondary explosions amplified by accumulated dust on rafters, cable trays, and equipment housings. This Safe Work Method Statement addresses Zone 20/21/22 classification per AS/NZS 60079.10.2, electrical equipment selection, bonding and earthing, the 3mm housekeeping trigger, extraction system performance, and emergency response to deflagration events. A SWMS is mandatory because the work involves hazardous chemicals under section 291 of the WHS Regulation and exposes workers to fire, explosion, and asphyxiation risks requiring documented, consulted, and signed-on controls.

Hazards identified

7 hazards covered, sorted by priority.

Control measures

Hierarchy-of-controls order: elimination → substitution → isolation → engineering → administrative → PPE.

1. 1Elimination — Redesign process to wet milling or slurry transfer where product specification permits, eliminating dust cloud formation at source per AS/NZS 60079.10.2 risk hierarchy.
2. 2Elimination — Remove all unnecessary horizontal surfaces, ledges, and cable trays above process equipment to prevent dust accumulation that fuels secondary explosions.
3. 3Substitution — Replace pneumatic conveying with enclosed mechanical screw or drag conveyors to reduce airborne dust generation and Zone 20 footprint within the facility.
4. 4Substitution — Use pelletised or agglomerated feedstock instead of fine powder where formulation allows, raising minimum ignition energy above realistic ignition source levels.
5. 5Engineering — Install explosion venting, suppression, or isolation systems on silos, mills, and dust collectors compliant with AS 4745 and verified by competent explosion protection engineer.
6. 6Engineering — Specify Ex tD or Ex tb IIIC electrical equipment in Zone 20/21/22 areas, bond all conductive surfaces to earth with resistance below 10 ohms verified annually.
7. 7Administrative — Implement housekeeping schedule triggering immediate cleanup when dust depth reaches 3mm on any surface, documented in shift logbook and audited weekly by supervisor.
8. 8Administrative — Require hot work permit signed by site manager with dust cleardown, atmospheric testing, and fire watch for sixty minutes post-work in all classified zones.
9. 9PPE — Issue flame-resistant cotton or Nomex coveralls compliant with AS/NZS 4824, antistatic safety footwear per AS 2210.3, and conductive wristbands when handling fine powders.
10. 10PPE — Provide P2 respirators per AS/NZS 1716 for housekeeping tasks and full-face air-purifying respirators during dust collector filter changeouts and confined entry into silos.

Applicable Codes of Practice

High-Risk Construction Work triggered

Worked example

At a regional flour mill scheduled to replace bearings on the No. 3 roller mill, the maintenance supervisor opens the Combustible Dust Management SWMS at the 6:30am pre-start toolbox with the fitter, electrician, and contract welder. Working through the hazard register, the team identifies that the task crosses a Zone 21 boundary and requires hot work for bracket modification. The supervisor walks the crew through the control hierarchy: first confirming the mill is isolated and purged, then verifying dust depth on the platform — a quick measurement shows 4mm accumulation on the gearbox housing, exceeding the 3mm trigger. Work is paused while the cleaning team vacuums the area using an Ex-rated industrial vacuum, and the supervisor records the intervention on the SWMS amendment page. The hot work permit is then signed, atmospheric testing confirms dust concentration below 10% of minimum explosive concentration, and the fire watch is briefed for the sixty-minute post-work observation. Each worker signs the SWMS sign-on register acknowledging the antistatic footwear and FR coverall requirement. Mid-task, the fitter notices the bonding strap on the adjacent conveyor has corroded; he stops work, calls the supervisor, and the SWMS is amended on-site to add bonding continuity verification before resumption. The document functions as a live control reference, not a filed certificate, demonstrating the consultation and adaptive control required under WHS Regulation 2025.

Related legislation

• WHS Act 2011 (model)
• WHS Regulation 2025
• AS/NZS 3000 — Electrical installations

Frequently asked questions