OHS in Quarries and Crushing and Screening Plants

Crushing and screening plant safety: see the plant as a line

Material blasted and loaded in a quarry is separated by size in the crushing and screening plant and turned into aggregate. A typical line runs as follows: feed hopper, primary crusher (usually a jaw crusher), belt conveyors, secondary crusher (impact or cone), screens and stockpiles. Crushing and screening plant safety requires treating every transfer point on this line as a separate risk area.

Quarries are mining workplaces; we covered quarry risks such as slopes, blasting and haul truck traffic in our article on OHS in open-pit mines. The Regulation on Occupational Health and Safety in Mining Workplaces requires a health and safety document for these workplaces; the crushing and screening plant should form a separate section of that document. This article focuses on the stage after the quarry, namely the plant's machinery.

Crusher safety: blockages and bridging

When a large block jams in the crusher mouth or material bridges in the hopper, production stops and the most dangerous moment begins: the urge to clear the blockage. In terms of crusher safety, the most serious accidents happen when a worker climbs down into the crusher mouth, climbs onto the feed hopper or tries to clear the blockage with a pry bar while the machine is running.

Basic rules around the crusher:

Feed area: Install a vehicle stop barrier at the hopper edge where the loader tips, and close the area around the hopper to pedestrians during feeding.
Flying rock: Do not leave the crusher mouth and discharge points open for viewing; if observation is needed, use a protected cabin or a camera.
Jaw plate and wear part changes: Heavy parts are moved with suitable lifting equipment. Lifting equipment and slings are subject to annual periodic inspection under Annex III of the Regulation on Work Equipment.
Mobile crushers: The area around tracked mobile crushers is closed off while they are being relocated; the operator using the remote control stays outside the movement zone.

Energy isolation during maintenance

Under Annex I, 2.13 of the Regulation on Health and Safety Conditions for the Use of Work Equipment, maintenance may only be carried out when the equipment is switched off, disconnected from its energy supply, all its movements have stopped and it is not running. Item 2.14 of the same annex requires the means of isolating energy sources to be clearly visible and identifiable.

In a crushing and screening plant, "isolating energy" means more than just switching off the breaker. The types of energy to be controlled are:

Electrical: The main isolator is locked and tagged; the "stop" button on the control panel is not enough.
Rotational inertia: The flywheels of crushers and screens keep turning for some time after the power is cut. Guards are not opened until it has been visually confirmed that motion has completely stopped.
Hydraulic and pneumatic: The setting systems of cone crushers and hydraulic accumulators may hold pressure; pressure is released according to the instructions.
Gravity and material: Material left in the hopper or crusher mouth may flow down; it is emptied or securely supported before work begins.
Trapped material: Rock jammed in a blocked crusher can move the rotor or jaw even when the power is off.

Every maintenance worker fits their own lock, and the equipment is not started until they have finished their work and removed their own lock. For step-by-step application, see our article on LOTO lockout tagout.

Screen maintenance: working at height on vibrating equipment

Screen maintenance is one of the most frequent yet least planned jobs in the plant. Worn screen wires and panels are replaced regularly and blinded apertures are cleaned. These jobs are often carried out at height, on narrow platforms and with heavy parts.

Fit the maintenance platforms around the screen with guardrails and fixed ladders; do not climb onto the screen body to work.
Do not clean blinded screen apertures while the screen is running. The screen body oscillates powerfully through its eccentric mechanism; a hand or arm can be trapped in seconds.
Move screen panels and wire frames with lifting equipment; for parts that are hard to lift by hand even with two people, the method should be decided in advance.
Do not run the screen until the pulley and belt guards have been refitted after maintenance. For types of guards, see our article on machine guards.

Belt conveyor risks

Belt conveyors are the longest moving equipment in a crushing and screening plant. The nip point between drum and belt can draw in an arm and the body. A significant share of accidents happen while shovelling spilt material from under a running belt or straightening a misaligned belt by hand.

In practice, these provisions translate into the following measures:

Fixed guards on head, tail and take-up drums, as well as at transfer points.
Pull-cord emergency stop switches accessible along the belt, with regular function tests.
Guarded crossover bridges for crossing the belt; jumping over or passing under the belt is prohibited.
Spilt material is cleaned up only after the belt has been stopped and locked out.
Correct tensioning and alignment to reduce belt drift; alignment adjustments are not made by hand on a running belt.

Quarry dust and noise

Dust is generated at every point of crushing, screening and where material drops from one belt onto another. Quarry dust may contain crystalline silica depending on the type of rock; limestone does not produce the same dust as granite or quartzite. That is why dust measurement should cover not only the amount of dust but also the crystalline silica content of the respirable dust; details are in our articles on dust measurement and respirable dust and crystalline silica dust.

Source	Dust	Noise	Priority measure
Primary crusher mouth	High	High	Water spraying, operator in an enclosed cabin
Transfer points	High	Medium	Enclosed chutes, water misting
Screens	High	High	Enclosed screen, noise barrier, remote monitoring
Stockpiles and roads	Medium	Low	Watering roads, reducing drop height
Control room	Depends on cabin	Depends on cabin	Filtered ventilation, door and window sealing

On a quarry noise map, the highest sources are usually the crushers and screens. Under the Noise Regulation, hearing protection must be made available above 80 dB(A), its use is mandatory above 85 dB(A), and the 87 dB(A) limit value, taking into account the attenuation of the protector, may never be exceeded. Where 85 dB(A) is exceeded, hearing tests are mandatory. We covered the health effects of noise in our article on noise-induced hearing loss.

Workers in dusty jobs have chest X-rays taken in line with the ILO standard, at a frequency set by the workplace physician. For pneumoconiosis to be recognised as an occupational disease, at least three years of exposure is required; changes detected early buy time to reduce exposure. We plan dust and noise measurements with authorised laboratories and feed the results into the risk assessment.

Training, lone working and supervision

Crushing and screening plants are often run by a small number of workers, over a large area and at a point far from the quarry face. The operator in the control room may not be able to see the maintenance worker in the field. Three matters therefore need separate planning:

Communication: A radio or similar communication system should be set up between a maintenance worker working alone in the field and the control room, and the worker should be required to report their status at set intervals.
Pre-start warning: An audible and visual warning should be given before the line is restarted, and the operator should make sure nobody is left in the field. The lockout system does not replace this warning; it complements it.
Training: Induction training is given for at least two hours, face to face and hands-on. In basic training, the section on risks specific to the job and workplace is delivered face to face in hazardous and very hazardous workplaces. In this section, the instructions for blockages, screen changes and belt cleaning should be explained in the field, at the equipment itself.

For the risks faced by plant operators during loading and feeding, see our article on construction machinery operators.

Checklist for the plant

Draw up a diagram of the line; number every crusher, screen, belt and transfer point.
Mark the energy isolation points and lock locations for each piece of equipment on the diagram.
Prepare separate written instructions for blockages, screen changes and belt cleaning.
Record the test dates of pull-cord switches and emergency stop buttons.
Check that water spray systems remain operational and protected against freezing in the winter months.
Track the periodic inspection dates of conveyors, lifting equipment and construction machinery with the OHS calendar; you can schedule the inspections through our periodic inspection service.

For quarries and aggregate plants in Bursa and the surrounding provinces, we apply this list to each plant's own line through our OHS specialist and risk assessment services. Our approach to the construction and building materials sector is on our construction page.

Frequently Asked Questions

What should be done when the crusher is blocked?

Feeding is stopped, the crusher is switched off and its energy is locked out. Large blocks are broken with a hydraulic breaker from a protected platform. Nobody enters the crusher or stands on the hopper material.

Is an emergency stop required on belt conveyors?

Yes. The Mining OHS Regulation requires conveyors to be fitted with a device allowing them to be stopped at any point. In practice, this is achieved with pull-cord switches accessible along the belt, and the switches are tested regularly.

What should be checked in dust measurement at a quarry?

Personal sampling should look at the amount of respirable dust and the crystalline silica content of that dust. Since the silica content varies with the rock, the total dust value alone can be misleading.

What is the most common mistake in screen maintenance?

Trying to clear blinded screen apertures or straighten a misaligned belt by hand while the equipment is running. These jobs should be done only after the energy has been isolated and locked out and all motion has completely stopped.