Dust suppression at the primary crusher and dump hopper

If a visitor saw only one dust cloud on a mine or a quarry, it would be the one at the primary crushing station: a truck of several tens of tonnes backs up, tips its body, and a wall of dust rises from the hopper for a few seconds — then the crusher does the rest. It is the most visible emission point, the most intermittent, and the one where respirable crystalline silica is produced first.

Yet the primary station is not one point: it is four, with different geometries and rhythms. Treating them as one — "a cannon over the hopper" — leaves the other three untouched.

Point 1 — Truck (or loader) dumping

When the body tips, the load falls several metres into a hopper that is often already half full. The air displaced by the falling mass is driven upward, loaded with the fines that were in the body and those stripped at impact. The event lasts as long as the dump, then stops: a brief, intense emission, repeated with every truck.

What suits it. A misting curtain over the hopper opening, aimed so that the droplet cloud meets the expelled air — or one or more fog cannons pointed at the hopper. In both cases, on-demand triggering is essential: by truck detection (loop, radar, beam), by the tipping signal, or by a dust monitor. A system that mists continuously wastes water, wets the ore for nothing and freezes in winter. A wall or wind screens around the hopper reduce the wind that would carry the cloud away. Capture is rarely the right answer here: the volume of air displaced by a truck body is too large and too brief for extraction.

Point 2 — The crusher opening

Between the hopper and the crusher, material travels down an apron feeder or falls directly into the opening of a gyratory. There, crushing itself produces fines, and the chamber's motion — gyrating mantle, swinging jaw — pumps dust-laden air upward. The emission is continuous as long as the crusher runs.

What suits it. Partial enclosure — a hood or walls around the opening, as far as access for unblocking and maintenance allows — and dry fog or fine misting inside that enclosed volume. Dry fog has the advantage of adding no moisture to the ore heading for the secondary and the screen; misting is fine if a little water does no harm. Nozzles go around the perimeter of the opening, aimed inward, not above the opening where they would sit in the path of the rocks.

This is where the unblocking boom comes in. On a gyratory or a large jaw, the hydraulic boom sweeps the opening to break oversize and clear blockages; hood, spray bars and enclosures must sit outside its reach and its rest positions, and the fog must not reduce camera or operator visibility during unblocking. The two systems are designed together — see the IC Boom System page and what a blockage really costs.

Point 3 — The feeder and scalping grizzly

At many stations, an apron feeder and a grizzly or vibrating scalper separate the fines ahead of the crusher. The vibrating scalper is an emitter in itself — it shakes dry fines in the open air — and its discharge to the undersize conveyor is a transfer point like any other.

What suits it. A hood over the scalper with dry fog inside, or capture if the building is enclosed; at the discharge, the same rules as a transfer point: shaped chute, skirtboards, settling zone.

Point 4 — The crusher discharge

Under the crusher, the product falls into a surge pocket or onto a discharge conveyor. The drop is often large, the product is fresh — full of new fines — and the space is enclosed (gallery, tunnel): dust accumulates there and stays.

What suits it. Dry fog in the discharge pocket and at the conveyor loading point, which are enclosed by nature; capture if the gallery is a regular workplace. The idlers and the motor of the discharge conveyor are the first equipment to suffer from untreated dust here.

Rules common to all four points

Trigger, don't drench. At the primary, emissions are intermittent (trucks) or tied to the crusher running. A controller that drives the misting on those signals divides water consumption and avoids soaked ore.

Measure the moisture added. The secondary screen and, in a cement plant, the dryer are the first to suffer from excessive spraying. The choice between dry fog and spray depends on it: see dry fog vs water spray.

Plan for winter. A primary station is often outdoors or semi-open. Traced and insulated lines, heated nozzle enclosures, automatic drain-down on stop, water fed from a heated room, dried compressed air for dry fog: without these, the system is out of service from December to March — precisely when frozen ore produces the most fines during unblocking.

Leave access. The primary station is where blockages, wear-part changes and boom interventions happen. Removable bars and hoods, nozzles protected from falling rock, enclosures clear of lifting zones.

And compliance?

At the primary, the inspector's question is not "can you see dust?" but "what is the workers' exposure?". The station operator, the driver at the hopper and the unblocking crew are the positions to sample. Permissible exposure values for respirable crystalline silica are set by the CNESST in Quebec, the Ontario Ministry of Labour and OSHA in the United States; the suppression system is the means, the measurement is the proof. A before-and-after survey at commissioning documents what the system changed.

Going further

Surveying the four points, choosing one technology per point, coordinating with the unblocking boom and designing for winter are part of our Dust suppression systems page; supply and installation fit into a shutdown window with our installation service. For a specific station, tell us the crusher, the tonnage and how trucks dump.

Frequently asked questions

Is a fog cannon enough for the primary station? It treats the truck dumping — and only that. The crusher opening, the scalper and the discharge are continuous emissions in more or less enclosed volumes, which call for dry fog or capture.

Does dry fog interfere with unblocking? It must not: nozzles sit outside the boom's reach and the fog can be cut automatically during an intervention, to keep camera and operator visibility. It is a matter of designing the two systems together.

Can the primary run without water? Inside an enclosed building, a well-sized capture system can treat the opening, the scalper and the discharge. Truck dumping remains the point where on-demand misting is the most realistic answer.