Grain Silo Combustible Dust & Hot Work SWMS

Grain silo combustible dust and hot work covers entry into a grain silo or bin and any hot work in or around it. It is high risk construction work under the NSW WHS Regulation 2025 because entry to a silo is work in a confined space and in a contaminated or flammable atmosphere (s291), so a SWMS is mandatory under s299 and a confined space entry permit is required under Part 4.3. The silo concentrates several lethal hazards in one space. Flowing or bridged grain can engulf and suffocate a worker in seconds — grain behaves like quicksand and a person sinks faster than they can be pulled out. The stored grain depletes oxygen and can generate toxic gases, and fumigation leaves residual phosphine, a gas that is both acutely toxic and flammable. Over all of this hangs a combustible grain-dust explosion risk: fine grain dust suspended in air is explosive, and any hot work — welding, cutting, grinding — or even a spark can ignite it, turning the silo into a bomb. The SWMS therefore controls entry by permit, eliminates or strictly controls hot work, manages the flammable and toxic atmosphere, and prevents engulfment by isolating all flow and never entering grain that can bury a worker. Confined space entry is to AS 2865, and SafeWork NSW is the regulator. Hot work and confined-space entry are not allowed to coincide unless the explosive atmosphere has been positively eliminated.

Hazards identified

7 hazards covered, sorted by priority.

Control measures

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

1. 1Elimination — Carry out inspection and cleaning from outside the silo using poles, vibration or remote methods so no entry into grain is required
2. 2Substitution — Substitute cold-cutting and mechanical fastening for hot work in and around the silo, removing the ignition source
3. 3Engineering — Isolation and lockout of all fill, discharge and conveying systems so grain cannot flow while a worker is inside
4. 4Engineering — Mechanical ventilation and continuous multi-gas monitoring (oxygen, phosphine, combustible dust) throughout entry
5. 5Engineering — Dust suppression and removal before any permitted hot work, with the atmosphere proven non-explosive
6. 6Administrative — Confined space entry permit and a separate hot-work permit that cannot both be open at once unless the explosive atmosphere is eliminated
7. 7Administrative — No entry onto, into or below bridged or flowing grain; a fall-arrest and retrieval system for any permitted entry
8. 8Administrative — Trained standby attendant and a rescue plan that does not require a second person to enter the grain
9. 9PPE — Air-supplied or appropriate respiratory protection for phosphine and dust, with a full-body harness and retrieval line
10. 10PPE — Eye protection, gloves and intrinsically safe equipment in the flammable atmosphere

Applicable Codes of Practice

High-Risk Construction Work triggered

Worked example

At 7:00 am a maintenance team from Harvest Storage Services is tasked to repair a cracked weld on the inside wall of a steel grain silo. The supervisor first confirms the silo was fumigated two weeks earlier, so phosphine is on the monitoring list. All fill and discharge augers are isolated and locked out before anything else — the grain must not move. The atmosphere is tested through the hatch: oxygen is low and a trace of phosphine reads, so forced ventilation runs and the team waits until oxygen recovers and phosphine clears, with the multi-gas monitor staying live inside. Because the repair needs welding, the dust is vacuumed and the atmosphere re-proven non-explosive before any hot-work permit is opened — and the confined-space and hot-work permits are sequenced so the explosive risk is gone before the torch is lit. The entrant wears a harness on a retrieval line, never standing on bridged grain, while a trained attendant holds the permit at the hatch with a non-entry rescue rigged. The weld is done, the torch is shut down and the area re-monitored before the entrant exits and the permits are closed.

Related legislation

• WHS Act 2011 (model)
• WHS Regulation 2025
• Confined Spaces Code of Practice
• AS 2865 Confined spaces

Frequently asked questions