OHS in Open-Pit Mines: Blasting and Slopes

The core document in mining safety

In an open pit, mining safety differs from OHS in a factory on one point: the workplace changes every day. The bench excavated yesterday is a new slope today, and yesterday's blasting area is today's truck road. That is why the Regulation on Occupational Health and Safety in Mining Workplaces of 19 September 2013 requires the risk assessment not as a one-off report but as a continuously updated health and safety document (HSD).

Under Art. 5 of the Regulation on OHS in Mining Workplaces, the employer:

• prepares the HSD before work begins at the workplace,
• shows in the document the identification of risks, including psychosocial risks, the measures to be taken and the instructions to be prepared, and the safe arrangement of the workplace and equipment,
• reviews the document, and revises it if necessary, when significant changes or additions are made, after a work accident and after incidents that had the potential to cause harm but did not.

If employees of more than one employer work on the same site, for example where haulage or drilling has been given to a subcontractor, each employer is responsible for the work under its own control; the employer responsible for the whole site coordinates the implementation of measures and writes the coordination method into its own HSD (Art. 5/4).

Annex 1 of the Regulation contains general provisions for all mining workplaces, and Annex 2 contains specific provisions for surface mining. The rules in this article are taken mainly from these two annexes.

Slope failure and bench safety

In open pits, the most serious accidents are caused by slope failure and rockfall from the bench face. Annex 2 sets the following rules:

• Work is planned taking into account the risk of landslide and collapse identified in the HSD. The angle and height of excavation faces and slopes suit the structure of the ground and the method used (1.1).
• Before every work period, slopes and excavation faces above the work area and haul roads are checked for falling soil and rock; measurements are taken where necessary (1.2).
• Bench faces, nearby roads and haul roads are continuously inspected for mass and block sliding and falling fragments. Until the danger is removed, nobody other than those assigned to that task is allowed to work (1.7).
• When work resumes after blasting, and after ground loosening caused by natural events such as frost, snow and rain, bench faces are cleaned by experienced workers by scaling off cracks from top to bottom (1.9).
• Undercutting bench toes and leaving them overhanging (reverse slope) is prohibited (1.10).

For pits where excavation and loading are done by hand, the Regulation also gives numerical limits (1.11):

In the same type of pit, bench height may not exceed 3 metres. For pits worked with excavators and loaders or using deep blast holes, the Regulation requires an open-pit operating instruction instead of a fixed value. This instruction covers bench height, bench width, slope angle according to the geological structure, blast hole depth and spacing, manoeuvring and loading rules for machines, and the measures to be taken during blasting (1.12). You can also find the general logic of collapse risk in excavation walls in our article on excavation and trench collapse measures.

Blasting safety

Section 6 of Annex 1 regulates the use of explosives in detail. The basic rules of blasting safety are:

1. Authorisation. Explosives and initiating materials are stored, transported and used only by shotfirers; the Regulation defines a shotfirer as a person holding a certificate of competence. No one other than a shotfirer may receive or fire explosives (Art. 4; Annex 1, 6.1–6.2).
2. Transport. Explosives are carried in special boxes; detonators and other explosives may not be kept in the same container. The quantity of explosives one person may carry may not exceed 10 kilograms. Receipts and consumption are recorded at the magazine (6.4–6.6).
3. Charging. Blast holes are charged by the shotfirer or by an experienced person under the shotfirer's supervision; tamping is done with non-conductive rods. In electric firing, the connections and the circuit are checked with a special measuring device before firing (6.7–6.9).
4. Perimeter security. Firing is not carried out without the necessary perimeter security in place (6.10). Warning signs, road closures and lookouts are part of this step.
5. Waiting time. After a blast, the area is not entered until at least 5 minutes have passed for electric firing or 1 hour for fuse firing, and until it has been examined by authorised persons and declared free of danger (6.11).
6. Misfires. If unexploded material is suspected, nobody enters until the area has been made safe; the remainder is fired, under the supervision of the responsible person, through a hole drilled parallel to the misfired hole at a distance of at least 30 centimetres (6.11).

The shotfirer certificate is one of the vocational training certificates required for hazardous and very hazardous work. For the requirement to employ certified workers, see our article on the vocational training certificate requirement and our vocational training page.

Mining haul truck and earthmoving machinery traffic

In an open pit, trucks, excavators, loaders and drilling rigs share the same narrow area. Annex 2 requires at least one working road on each bench, benches and haul roads to be built strong enough for the vehicles used and to be maintained, and safety berms of sufficient height at places where machines could fall, such as dump areas and bench edges (1.4–1.6). Annex II of the Work Equipment Regulation also requires traffic rules and speed limits in areas where mobile work equipment operates, and requires unauthorised people to be kept out of these areas.

Most mining haul truck accidents happen in blind spots, while reversing and at the dump edge. Put the following into written rules on site:

• Separate pedestrian and vehicle routes; mark unavoidable pedestrian crossings.
• Use a banksman at reversing and dumping points; the banksman must not stand in a blind spot.
• Set the loading sequence between truck and loader and the rule that the driver stays in the cab.
• Lower the speed limit for road surfaces and ramp gradients in wet weather.
• Have earthmoving machinery and lifting equipment periodically inspected every year; operators must hold valid certificates.

For equipment inspection intervals, see our article on periodic inspection intervals for work equipment.

Dust, noise and health surveillance

Dust generated by drilling, blasting, crushing and loading may contain crystalline silica depending on the rock type. The mining regulation requires the Ministry's dust control legislation to be taken into account against the harmful effects of dust (Annex 1, 5.3.2). Dust collectors or wet drilling on drilling rigs, watering roads, water sprays at crusher and screen outlets and filtered ventilation in machine cabs are the basic measures. Workers exposed to dust have chest X-rays taken in accordance with the ILO classification, at a frequency set by the workplace physician; details are in our article on the Dust Control Regulation. We plan dust and noise measurements with authorised laboratories and enter the results in the HSD.

Supervision, instructions and emergencies

• Every workplace has a competent person with sufficient skills and expertise on duty for as long as work continues (Annex 1, 1.2). Work is carried out under the supervision and control of these persons; if the HSD deems it necessary, work areas are checked at least once every shift (1.3.1).
• Appropriate supervision is provided for lone workers (1.1.4).
• Written instructions are prepared on the transport and storage of explosives and the safe use of work equipment; the instructions also cover how to act in an emergency (1.6).
• The drill schedule in mining workplaces is stricter than in other workplaces: Art. 13/2 of the Regulation on Emergencies leaves mining workplaces to the Mining OHS Regulation; this regulation requires drills to be held at least every six months, footage to be recorded and minutes drawn up, and emergency plans to be renewed every six months (Art. 5/1; Annex 1, 15).
• Search, rescue and evacuation training is documented and renewed every six months. Whether a rescue station is set up at surface mines is decided according to the characteristics of the workplace and the drills, and is written into the HSD (Annex 1, 14.1 and 14.4).

The hazard class determines the specialist's certificate class and the frequency of medical examinations and training; in very hazardous workplaces a Class A specialist is appointed. Do not forget to check the class of your activity code.

There are stone, marble and aggregate quarries and mining sites in Bursa and the surrounding provinces; the Mermerciler OIZ (organised industrial zone) in Mustafakemalpaşa shows the place of natural stone in the region's industry. For planning notes for these areas, see our Mustafakemalpaşa, Kütahya and Balıkesir pages; for site inspections and the HSD, see our OHS specialist and risk assessment services.

Frequently Asked Questions

What is prepared instead of a risk assessment in an open pit?

Under Art. 5 of the Mining OHS Regulation, a health and safety document (HSD) is prepared. The document contains the risk assessment, the measures to be taken and the necessary instructions; it is prepared before work begins and reviewed after changes, accidents and incidents that did not cause harm.

Are there numerical limits for slope angle and bench height?

In pits where excavation and loading are done by hand, bench height may not exceed 3 metres, and the slope angle may not exceed 60 degrees on sound ground, 45 degrees on loose and weathered ground and 30 degrees on slippery and wet ground. In mechanised pits these values are set in the open-pit operating instruction.

When can the area be entered after blasting?

Wait at least 5 minutes for electric firing and 1 hour for fuse firing, and nobody may enter until the area has been examined by authorised persons and declared free of danger. Cracks are then scaled off the bench face.

Who may use explosives?

Only a shotfirer; the Regulation defines a shotfirer as a person holding a certificate of competence. Blast holes are charged by the shotfirer or by an experienced person under the shotfirer's supervision and responsibility; detonator connections and firing are carried out by the shotfirer personally.