RISK MATRIX

Frequency - Likelihood

1

2

3

4

5

Severity - Consequence

1

1

3

6

10

15

2

2

5

9

14

19

3

4

8

13

18

22

LOW

4

7

12

17

21

24

MEDIUM

5

11

16

20

23

25

HIGH

FREQUENCY-LIKELIHOOD

SEVERITY-CONSEQUENCE

Frequency Level

Description

Frequency of Events

Severity Level

Impact

Health & Safety

Blasting result & outcome

Loss/Damage

5

Almost certain (occurs often) Expected to happen

Occurs on very blast

5

Catastrophic / Critical

Multiple   Injuries

Misfired blast

Work on dangerous ground

Frozen ground

Re blast & repair cost

Production interruption

Penalties

>R 1.0Mil

4

Likely (known to occur) May easily happen

Occurs Once a week

4

Severe/ Major

Single Fatality / Permanent disabilities.

Uneven broken ground removal

Risky work environment

Poor fragmentation.

High loading cost.

Slow production.

Secondary blasting

R.0.8 – 1.0 Mil

3

Possible (known to occur occasionally) May Happen

Occurs Once a month

3

Major/ Moderate

Reportable injury. or noise induced hearing loss.

Property damage

Flyrock

Property damage

Financial loss

R 0.5- 0.8Mil

2

Unlikely (has occurred somewhere) May happen sometimes

Occurs Once a quarter

2

Moderate / Minor

Lost time injury / Health effect with reversible impairment

1

Rare (could happen but unlikely)                                  

Occurs Once a year

1

Minor/Low

Medical treatment case / Slight health effect with no impairment

Step or

Event

Potential Hazard

(A source of or exposure to danger)

Potential Risk

Consequence

Likelihood

Real risk rating  

Existing / current control

Consequence

Likelihood

 Residual risk rating

Critical Task (PTO)

ü

Responsible Person

Stemming of blast holes

Stemming  holes in a pool of water.

Fly rock,

Blow-out & out of hole detonation

Harmful explosives gasses ejection –

Gassing

Poor blast result.

3

4

18

Stemming supervision

Minimum stemming length – 0.8 x burden

Twine all holes when charging up

 Stemming type ;

    -Aggregate (10% of hole dia.)

3

1

4

Blaster 

Blasting assistant

Stemming a hole filled with water

Slow stemming process –

 Using charging stick vigorously  to contain stemming material within water creates;

- Ineffective containment of explosives ;

- Riffling effect of wet tamping

- Out of hole detonation

- Damages to accessories & misfires

- Flyrock

- Excessive airblast effect.

- Ineffective blast result

3

4

18

Stemming Supervision

Twine all holes when charging up

Method 1

When water can not be extracted sufficiently

Use only 10% Aggregate – 0.8 x burden minimum stemming.

Method  2

Extract water from the stemming area.

 Minimum stemming type and length;

   - Drill chippings   – 0.9 x Burden

   - 10% Aggregate – 0.6 x Burden

3

1

4

Blaster

Blasting assistant

Inadequate Stemming material

Fly rock,

 Airblast effect

Poor blast result

3

4

18

Stemming Supervision

 When drill chippings are too fine, the stemming length must be increased to at least 1.2 x Burden.

Only dry stemming material must be used.

Consolidate the stemming lightly with a charging stick as not to damage the accessories

3

1

4

Responsible person.

Blaster 

Overcharged holes

Fly rock, Blow-out & harmful explosives gasses ejection –

Poor blast result.

Excessive gassing

4

4

21

Stemming supervision.

Twine all holes to required height of explosives and stemming depth.

Extract excess  water in the hole.

Extract the excess emulsion to required depth. Place excess in a hole to be charged.

Stem as needed

4

1

7

Blaster

Blasting assistant

Stemming Wet Holes

  1. Ensure that the stemming material is suited to the stemming length to achieve the required result
  2. Water in the stemming area will affect the effectiveness of a consolidated stemming
  3. Bottom charge all water-filled holes. This will result in water on top of the charge
  4. Remove the water and explosives gunk in the stemming length with a water extractor before stemming the hole. The hole will be dry and the stemming can affectively be consolidated.
  5. 10% aggregate is normally used when;
  • holes are situated in a pool of water
  • to ensure the optimum fragmentation in very hard rock
  • a short stemming is needed i.e., hard rock in collar area that may create slabbing.
  • no flyrock is allowed in restricted areas

Drill chippings (not fine sand) can be used effectively in dry holes as indicated below

General Stemming Chart ‐ Flyrock effect

Hole diameter

x Burden

Dry hole graded aggregate

Graded aggregate in water

Dry hole drill chippings

Drill chippings in water

Result ‐ Flyrock effect

10 x Dia

0.4 x B

Moderate

High

High

Excessive

15 x Dia

0.6 x B

Little

Moderate

Moderate

High

20 x Dia

0.8 x B

Little or none

Little

Little

High

25 x Dia

1.0 x B

None

Little/none

Little/none

Moderate

30 x Dia

1.2 x B

None

None

None

Little

35 x Dia

1.5 x B

None

None

None

None

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