Blasting is the most violent step in any opencast mine. In a few seconds, rock is thrown, the ground shakes and a shock wave runs through the air. When everything goes according to plan, nobody is hurt. When it does not, the consequences can reach well beyond the pit: to a worker in the wrong shelter, to a family living near the mine boundary or to an electric line crossing the lease.
This post explains the main causes of blasting accidents in opencast mines, the numbers one standard textbook gives for accidents between 1996 and 2011, and the precautions to take when lightning or a thunderstorm threatens a blast site. It is meant for students, supervisors and exam candidates, and it follows the points in the book closely, with extra explanation where it helps.
Please note: this article is for safety education and exam preparation. It is not a blasting manual. Every blast must follow the law, DGMS circulars and your mine's approved blasting procedures, carried out only by authorised, competent persons.
The six main causes at a glance
| No. | Cause | Typical result |
|---|---|---|
| 1 | Inadequate shelter and failures of warning | People injured or killed in the danger zone |
| 2 | Fly rock | Injury to workers and nearby residents, damage to machines and power lines |
| 3 | Ground vibration | Damage to houses, roads, railways and bridges, and to underground structures |
| 4 | Misfired holes | Accidents while drilling or while loading the muck |
| 5 | Lightning or storms | Premature blasting of charged holes |
| 6 | Blasting breaking into underground workings | Holes meeting old or live galleries during pillar cutting |
1. Inadequate shelter
This is the biggest cause the book lists. Before every blast, everyone in the danger zone must be in a proper shelter or outside the zone. The accidents happen when:
- People stay under vehicles or weak roofs. A truck, dumper, explosive van or drill is not a shelter, and neither is a weak roof of asbestos sheets, tiles or tin. Fly rock goes through them or hits the vehicle.
- The warning does not reach everyone. A power failure or a faulty siren means that some people in the danger zone never hear the signal.
- People misunderstand the "all clear" signal and leave the shelter too early, while a delayed blast or falling debris is still a risk.
- There are no sentries at vulnerable places, so outsiders walk into the danger zone through footpaths and lanes.
- Blasting is done without confirming that everybody has withdrawn. A final check, with a proper headcount, is the last line of defence.
The book reports that between 1996 and 2011, 60 accidents occurred due to these causes: 23 in coal mines and 37 in non-coal mines.
For coal mines, CMR 2017 requires the shotfirer to be sure that sufficient warning, by efficient signals or other means approved by the manager, has been given over the entire danger zone, which is a radius of 500 metres in opencast workings. That figure was tested in the WCL Mining Sirdar paper, which you can find in our WCL Mining Sirdar 2023 paper with the official answer key.
2. Fly rock
Fly rock is rock thrown beyond the intended area by the blast. It can hurt workers, or people in a nearby village, and damage machines and power lines. It is usually a sign that something in the blast design or execution was wrong: too little burden, a hole that was overcharged, poor stemming or a weak zone in the rock that the explosive energy escaped through. That is why fly rock control starts at the design stage, and why the danger zone and shelters must be planned on the assumption that fly rock can travel far.
3. Ground vibration
Every blast sends waves through the ground. Above a certain level they can damage houses in a nearby settlement, close-by roads, railways and bridges. Underground, vibration can damage dams, stopes and roofs. This is why blasts near habitations are monitored with vibration instruments, and why charge per delay is controlled. DGMS prescribes permissible vibration limits for different kinds of structures, so use the latest circular for the exact figures. For the basics of delay detonators, see our Blasting and Explosives MCQs.
4. Misfired holes
A misfire is a charge, or part of a charge, that has failed to explode. It stays in the muck or the bench as a hidden hazard. Accidents happen when:
- a driller drills into a hole that has already been charged and misfired, or very close to it, and
- a shovel or excavator loads muck that contains unexploded explosive.
The book reports 19 such accidents between 1996 and 2011: 3 in coal mines and 16 in non-coal mines. Misfires must always be handled under the approved procedure by competent persons, and nobody should start work near a misfire until it has been dealt with.
5. Lightning and thunderstorms
Lightning, or a storm that comes with lightning, can set off detonators or charged holes suddenly. The electrical energy induced in wires, in the ground or in a firing circuit can be enough to fire an electric detonator, which means a premature blast. This can injure or kill people who are charging holes at the time.
Precautions when lightning or a storm comes
- Do not handle detonators and explosives.
- Stop charging if holes are being charged.
- Secure the charged holes. The detonating fuse, detonator wires or detonator lead of the charged holes are placed at the mouth of the hole and covered with wood or stone.
- Move everyone away from the holes and out of the danger zone immediately.
- Park the explosive van separately, away from the mine and the magazine.
- If the firing circuit was already prepared before the storm arrived, the textbook advice is to move everybody quickly to a safe place and fire the blast immediately.
Notes: the last point is the book's advice for a specific situation. Always follow your mine's approved procedure and the latest DGMS instructions, because the decision to fire or not to fire in stormy weather must be made by the competent person in charge, with the manager's guidelines in mind. Also remember that many mines use non-electric (shock tube) or electronic initiation, which are less sensitive to lightning-induced electrical energy than conventional electric detonators. They reduce the risk but do not remove the need for precautions.
6. Blasting breaking into underground workings
When an opencast mine cuts through pillars of old or live underground workings, blast holes can break into the underground galleries. This can lead to loss of explosive, uncontrolled blast energy underground and danger to anyone working below. Accurate plans of the underground workings, marked on the opencast plan, and careful hole depth control are essential in such situations.
What the numbers tell us
| Cause (1996 to 2011) | Coal mines | Non-coal mines | Total |
|---|---|---|---|
| Inadequate shelter and related failures | 23 | 37 | 60 |
| Misfired holes | 3 | 16 | 19 |
Two things stand out. In both categories, non-coal mines had more accidents (about 62 percent of shelter-related accidents and about 84 percent of misfire accidents). And the human factors, such as where people stand, whether the warning works and whether everyone is accounted for, outnumber purely technical failures. Both are controllable.
A practical pre-blast checklist for supervisors
- Shelters: strong, properly located, big enough for the people who will use them, and not under weak roofs or beside vehicles.
- Danger zone: clearly defined, with sentries at every approach, including footpaths and lanes.
- Warning system: siren and signals tested, with a backup if the power fails.
- Headcount: a final check that everyone has withdrawn, before the blast.
- Signals: everyone trained to understand the "all clear", and nobody leaves the shelter before it.
- Weather: a clear rule on what to do if lightning or a storm approaches.
- Fly rock and vibration: blast design checked, with protection for people, machines, power lines and nearby structures.
- Misfires: a defined procedure, a competent person in charge and strict control of drilling and loading near suspected misfires.
- Underground workings: up-to-date plans and hole depth control where pillars are cut by opencast.
Test yourself: 8 quick MCQs
- A. Inadequate shelter in the danger zone
- B. Fly rock
- C. Misfired holes
- D. Using too much water in drilling
Show Answer
- A. It is not a proper shelter and offers no protection from fly rock
- B. Trucks are noisy
- C. It wastes time
- D. Trucks may run out of fuel
Show Answer
- A. Charge faster to finish before the storm
- B. Charging should be stopped and explosives and detonators should not be handled
- C. Ignore the storm
- D. Move the explosive van to the blast site
Show Answer
- A. Loss of explosives
- B. Increase in coal quality
- C. Damage to nearby houses, roads, railways and bridges
- D. Cooling of the mine
Show Answer
- A. A charge that fails to explode as intended
- B. A very strong blast
- C. Dust blown by wind
- D. A shot fired at the wrong time on purpose
Show Answer
- A. To save fuel
- B. To keep it clean
- C. To make loading easier
- D. To reduce the risk if lightning strikes
Show Answer
- A. Nothing, it is safe
- B. They get a bonus
- C. They may be hit by fly rock or a delayed blast
- D. The blast is cancelled
Show Answer
- A. To count the dumpers
- B. To stop outsiders from entering the danger zone
- C. To check the weather
- D. To hand out tools
Show Answer
Frequently asked questions
What is the biggest cause of blasting accidents in opencast mines?
According to the book's data, inadequate shelter and related failures in the danger zone, with 60 accidents between 1996 and 2011.
What is fly rock?
Rock thrown beyond the intended blast area, which can injure people and damage machines and power lines.
Why is lightning dangerous at a blast site?
The electrical energy can fire detonators or charged holes unexpectedly, which causes a premature blast.
Why are misfires dangerous?
Unexploded explosive may be hit by a drill or picked up by a shovel with the muck.
Where can I read more?
Browse our blasting and explosives and mine safety articles.
Disclaimer: this article is a summary of points from a standard textbook chapter, with added explanation, for education and exam preparation. It is not legal or technical advice, and the accident figures are as reported in the book. Always follow current regulations and your mine's approved procedures.
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