A blocked crusher is a stopped machine with rock balanced above or inside the chamber. What makes clearing dangerous is not the task itself — breaking a rock — but the fact that nobody knows what is holding the load, or what will happen once it is freed. Serious crusher accidents often happen at that moment: outside production, during an intervention everyone thought would be short.
This article describes the hazards specific to clearing, compares the methods used on site and proposes a procedure built on one simple principle: nobody enters the chamber or stands under a suspended load to clear a blockage. It does not replace your site's procedure or the lockout requirements of your jurisdiction.
Why clearing is dangerous
Bridging. Two or three rocks wedged against each other above the opening form an arch that can hold tonnes of material. Remove the rock that holds it and the whole load drops at once, sometimes with the person working on it.
Stored energy. A stopped crusher is not necessarily de-energized: a pressurized hydraulic system, flywheels that can turn, a jaw or mantle bearing on a jammed rock, a loaded upstream conveyor, a feeder that can restart. Every source must be identified and neutralized.
Falling rock. In a hopper or above a gyratory, material built up on the walls can come loose during the work.
The space. A crusher chamber or a hopper is hard to get into and out of: dust, poor visibility, access by ladder or harness. Depending on its configuration, it can meet the definition of a confined space, with the requirements that follow.
Improvisation. Clearing is an irregular task, often under production pressure. That is when a tool meant for something else gets used — a crane hook, a loader bucket — or a lockout step is skipped "for five minutes".
The methods, compared
| Method | Where people are | Limits |
|---|---|---|
| Bar, lever, hand hammer | At the edge of or inside the chamber | Direct exposure to bridging, falling rock and dust; wear on the liners |
| Crane hook or bucket | On the ground, guiding close by | Suspended load over the opening; crane rarely available right away; uncontrolled forces on the machine |
| Excavator with a hydraulic breaker | In the excavator cab, near the opening | Mobilizing and positioning the machine; access to the opening often limited; see fixed boom vs excavator-mounted breaker |
| Fixed unblocking boom (breaker on a hydraulic boom) | In a protected control station, outside the zone | Investment; must be sized for the crusher geometry |
| The machine's own hydraulics (tramp release, setting opened) | At the control station | Handles the bottom of the chamber, not a bridge at the opening |
What the last two methods share is that they take people out of the danger zone. That is the purpose of a permanently installed unblocking boom: always available, able to reach the whole opening, and controlled remotely, with a camera if visibility requires. What changes from one crusher type to another — jaw, gyratory, impact — is detailed in unblocking booms by crusher type.
A procedure that keeps people out of the chamber
This is the outline we find at sites where clearing is done without incident. It is adapted to each installation and fits into the existing lockout procedure.
- Stop the feed upstream — feeder, conveyor, truck dumping — so the situation does not get worse during the intervention.
- Assess from a safe point: type of blockage (bridging rock at the opening, tramp metal at the setting, packed material), hopper condition, visibility. Cameras and lighting help do this without getting close.
- Choose the method for the type of blockage: the machine's hydraulics for the bottom of the chamber, the unblocking boom for the opening, and only as a last resort a method that exposes people — with a specific risk assessment.
- Lock out what must be locked out: the energy sources of the crusher and the feed are isolated under the site procedure before any intervention that places a person or a machine in the zone. A remotely controlled boom is operated under its own procedure, agreed at commissioning.
- Clear progressively, starting from the top of the load, never undermining the rock that holds the bridge from below.
- Check before restarting: chamber clear, tools removed, people out of the zone, safety devices restored; then restart in the normal sequence.
- Record the event: duration, likely cause, method. That record is what makes it possible to reduce blockage frequency and put a cost on it — see what a crusher blockage really costs.
Reducing the number of blockages
The best intervention is the one you do not have to make. The levers are well known: a crusher sized for the real block size, a scalping grizzly or a breaker upstream for oversize, steady feed, tramp metal detection, and measuring the frequency and duration of blockages to know where to act.
Going further
Sizing, supplying, installing and commissioning an unblocking boom — with its operating procedure and operator training — are described on the IC Boom System page. To put a figure on your situation, use the crusher downtime cost calculator. For a specific crusher, tell us about the machine and the type of blockage.
Frequently asked questions
Can someone enter a stopped crusher to clear a rock? Only under the site procedure, after locking out every energy source and assessing the risk of bridging and falling rock. Where possible, a remotely controlled method avoids entering at all.
Why is a crane hook not a good method? It puts a suspended load over the opening, applies uncontrolled forces to the machine and depends on the crane being available — which pushes people to improvise.
Does an unblocking boom replace lockout? No. It allows work without people in the zone, under its own operating procedure; any intervention that places a person in the chamber remains subject to lockout.
Hicham Marouazi, ing., PMP
Engineer and project manager (PMP) at Induscoat Solutions. Over 16 years of experience on mining, energy and petrochemical sites in Canada and internationally — selecting, installing and commissioning industrial equipment.