1. INTRODUCTION
This Code of Practice has been written in line with the Industry Best Practice Guideline produced by the Group Environmental Engineers, submitted through the Chamber of Mines. The purpose of this code of practice is to ensure that the re-entry periods applied under differing occupational environmental conditions ensure that no persons are exposed to occupational health risks at Barberton Mines.
2. LEGAL STATUS OF CODE OF PRACTICE
2.1. In accordance with section 9(2) and (3) of the MHSA, Barberton Mines has prepared and implemented this Code of Practice for the safe operation of multi blasting accordance industry best practice guidance note issued by the Chief Inspector of Mines.
2.2. This COP sets out accepted good practices, the application of inferior practices without justification could be regarded as negligence.
2.3. The COP may be used in an accident investigation/inquiry to ascertain compliance and also to establish whether the COP is effective and fit for purpose.
2.4 All managerial instructions or recommended procedures and standards on prevention of flammable gas explosions are compliant with this COP and are reviewed to ensure compliance.
3. RELEVANT PROVISIONS OF THE MHSA
3.1 Barberton Mines has assessed the hazards and responded to the risks to health and safety, in terms of Section 11 of the MHSA, to which employees may be exposed while they are at work.
3.2 Barberton Mines has established and maintaining a system of occupational hygiene measurements and engage the part-time or full-time services of a person qualified in occupational hygiene techniques to measure levels of exposure to hazards at the mine, in terms of Section 12. (1) of the MHSA.
3.3 Every system of occupational hygiene measurements will be appropriate in terms of the hazards to which employees are, or may be, exposed and must provide information, which Barberton Mines can use to eliminate, control and minimise such health risks and hazards, in terms of Section 12. (2) of the MHSA.
3.4 Records are kept of all such measurements in order that it can be linked, as far as practicable, to an employee’s records of medical surveillance, in terms of Section 12. (3) of the MHSA.
3.5 Other relevant COPs and SOPs
Env-COP-21 Prevention Flammable gas explosions
Env-COP-26 Thermal Stress
Env-SOP-74 Lamp room
Env-COP-28 Lamp room
Env-SOP-55 Ventilation standard procedure
Env-COP-12 Airborne Pollutants
4. DEFINITIONS AND ACRONYMS
In order to differentiate between mining operations using multi-blasting and time blasting, these definitions will apply. It should be noted that in all three definitions cognizance must be taken of the occupational hygiene regulations, which requires that no persons must be exposed to airborne contaminants.
Time-blasting
Blasting operations taking place not more than once in any 24-hour cycle (as per paragraph 5.2).
Multi-blasting
Multiple blasting including shaft sinking operations, which could take place during any working shift. Such blasting may only take place where efficacious means of separating intake and return air e.g. a dedicated return airway is provided (as per paragraph 5.3).
Fixed-time multi-blasting
Blasting more than once per 24 hours, but not more than once per shift, for both stoping and development, taking cognisance of a re-entry period sufficient to clear all airways where persons are expected to work or travel (as per paragraph 5.4).
The re-entry period must be determined by a risk assessment and validated whenever key factors, that can have a significant effect on the re-entry conditions, change.
ACRONYMS
MHSA- Mine Health and Safety Act
RAW- Return Airway
L- L
W- With
H- Height
m/s- Meters per second
m³/s- Cubic meters per second
m³/s /m²- Cubic meters per second per square meter
FQ- Force Quantity
5. RE-ENTRY INTERVALS
In terms of Regulation 9.2(1) of the MHSA Barberton Mines will ensure that the occupational exposure to health hazards of employees is maintained below the limits set out in Schedule 22.9(a) and (b). The intervals which must expire before persons are allowed to re-enter the workings of your mine in which blasting has taken place, should be fixed as follows:
5.1 Nil re-entry interval
A re-entry interval need not be observed where persons are expected to work or travel if uncontaminated through ventilation has been established and is effective / operational.
5.2 General re-entry interval
Should blasting fumes however contaminate the air in any of the workings the general re-entry interval, as set out in the paragraph below, must be observed in those workings.
A general re-entry interval after the blast in all ventilation districts must be observed in terms of Regulation 9.2.1: “The employer must ensure that the occupational exposure to health hazards of employees is maintained below the limits set out in Schedule 22.9(2)(a) and (b)”. This re-entry interval has been determined after a detailed and recorded risk assessment and excludes the workings mentioned in paragraphs 5.1, 5.3 and 5.4.
5.3 multi-blast re-entry interval
In terms of Regulation 9.2.1 the employer must ensure that the occupational exposure to health hazards of employees is maintained below the limits set out in Schedule 22.9(2)(a) and (b).
A minimum 30-minute re-entry interval must be observed, and the following provisions must be made applicable to all multi-blast development ends or shafts being sunk:
5.3.1 Minimum air quantities required (relative to the air density at the working face)
5.3.1.1 The quantity of air forced shall be established through a risk assessment process to ensure that the air supplied is of a quality as set out in Schedule 22.9(2) (a) and (b) and should not be less than 0,25 m3/s for every square meter of face area, for all multi-blast development ends.
5.3.1.2 The quantity of air exhausted from the development end should be not less than twice more than the quantity of air supplied by the force column referred to in paragraph 5.3.1.1 above.
A minimum force exhaust ratio of 1:2 should be maintained at all times to ensure that no uncontrolled re-circulation takes place in the overlap section.
5.3.2 Ventilation arrangements
5.3.2.1 Horizontal development, inclines, declines and raises.
5.3.2.1.1 An exhaust-overlap system of ventilation should be used for every end being multi-blasted.
5.3.2.1.2 The intake of the exhaust column should be carried to a point not exceeding thirty (30) metres from the face.
5.3.2.1.3 The distance between the discharge of the force column and the advancing face must be such as to ensure that the ventilating air reaches the face and should not be more than twenty (20) metres from the face of the end after the blast.
5.3.2.1.4 The minimum overlap distance between the exhaust column intake and the force column intake points should be at least 10 metres and not exceeding 25 metres.
5.3.2.1.5 Fans in the exhaust column should be positioned in such a manner that the exhaust column remains under negative pressure, thus ensuring that no exhaust fumes leak back into the intake air flowing to the face.
a)To prevent open circuit exhaust fans from recirculating, sufficient through ventilation, at least 0.4 m3/s/m2 of through ventilation, should be provided at these fan sites at all times.
b)The exhaust fans in an exhaust-overlap system, which are the primary source of ventilation, should be interlocked with all other electrical appliances and equipment in the end being multi-blasted. This is to ensure that, in the event of the exhaust fans stopping, all other electrical appliances and equipment will also shut down.
c)No butterfly valves must be positioned in any exhaust column in development ends.
5.3.2.1.6. The force fan must be positioned only in the overlap section of the ventilation system.
5.3.2.1.7 An effective dust allaying mechanism must be operated during the blast and the re-entry period at a distance not exceeding 20m from the face.
5.3.2.1.8 If, at any stage, blasting fumes from the end being multi-blasted contaminates any working places in the vicinity, then multi-blasting must cease and conventional time blasting (as per paragraph 5.2) or fixed-time blasting (as per paragraph 5.4) must be followed until conditions have been rectified for multi-blasting. The ends so contaminated must also be on conventional time blasting.
5.3.2.1.9 The dust and fumes from blasting operations must be exhausted directly to surface via an established RAW and must not contaminate any place where persons may be required to work or travel.
5.3.2.1.10 The number of air changes, calculated on the volume of air between the face and the intake of the force column, required shall be determined through a risk assessment process to ensure that on re-entry after the blast the air in the development end is of a quality as set out in Schedule 22.9 (2) (a) and (b) and should not be less than 8 changes.
NB: For raises, winzes and declines the following will, in addition, apply:
a) The exhaust column intake must be situated in the crosscut; and
b) Ore passes must never be completely empty, to prevent re-circulation.
5.3.3 Shaft sinking
5.3.4 The bank area must be kept clear of blasting fumes and the shaft must remain down casting, in the bank area, at all times.
5.3.4.1 The force column delivery must at least be to the bottom deck of the stage during blasting.
5.3.5 Compliance testing Shafts
5.3.5.1 Workplace environmental conditions on re-entry must be of a quality as set out in Schedule 22.9(2)(a) and (b).
5.3.5.2 Gravimetric dust measurement results on re-entry with a Tyndall meter or similar dust-measuring instrument must be less than an AQI of 1,0 taken over a 2-minute period, using previously determined hazardous pollutant values.
5.3.6 Blasting initiation
Blasting initiation must be conducted electrically.
5.4 Fixed-time multi-blast re-entry interval
For blasting more than once in 24 hours, but not more than once per shift, a minimum re-entry interval will be determined after a detailed and recorded risk assessment with the following provisions made applicable to all fixed-time multi-blast development ends or stopes:
5.4.1 Minimum air quantities required (relative to the air density at the working face)
5.4.1.1 The quantity of air forced shall be established through a risk assessment process to ensure that the air supplied is of a quality as set out in Schedule 22.9 (2) (a) and (b) and should not be less than 0, 15 m3/s for every square meter of face area, for all multi-blast development ends.
5.4.1.2 The minimum stope face velocity averaged across the height of the stope should be determined through a risk assessment process to ensure that the quality of air is such that it meets the requirements as laid down in Schedule 22.9 (2) (a) and (b) and should not be less than 0.25 m/s. This should vary when determining the desired re-entry interval.
5.4.1.3 The number of air changes, calculated on the volume of air between the face and the intake of the force column, required shall be determined through a risk assessment process to ensure that on re-entry after the blast the air in the development end is of a quality as set out in Schedule 22.9 (2) (a) and (b) and should not be less than 8 air changes. The risk assessment must take into account all areas that maybe contaminated by the blast including “back pressure”.
5.4.2 Compliance testing Fixed-time multi-blast
5.4.2.1 Workplace environmental conditions on re-entry must be of a quality as set out in Schedule 22.9(2)(a) and (b).
5.4.2.2 Dust measurement results on re-entry, with a Tyndall meter (direct electronic dust monitor) or similar dust- measuring instrument, must be less than an AQI of 1,0 taken over a 2-minute period, using previously determined hazardous pollutant values.
5.6 Blasting initiation
Blasting initiation must be conducted electrically.
6. RISK ASSESSMENT
6.1 Aspects to be addressed
The risk assessment must, at least, cover the following;
6.1.1 A risk-assessment must be conducted and recorded on the specific operation.
6.1.2 Appropriate exposure measurements and environmental engineering controls must be put in place to comply with legal occupational hygiene requirements.
6.1.3 Hazards to be taken into account when conducting a risk assessment should include, but not limited to, the following:
- Noxious fumes from blasting;
- Dust created by blasting;
- Flammable gas;
- Thermal environment; and Diesel particle emission
6.2 Waiting Place
6.2.1 Blasting must be carried out from a place of safety demarcated by the manager. This position must be sign posted as “Waiting Place” and also act as a contraband control point, where applicable.
6.2.2 The blasting times must be recorded, and the re-entry interval must be specified and posted on the waiting place signboard and other relevant conspicuous places.
6.3 Miscellaneous
6.3.1 Continuously operating flammable gas measuring instruments must be used at all drilling sites (inclusive of cover/diamond/prospect drilling sites).
6.3.2 All calculations must be done and verified by the person engaged in terms of section 12.1 of the MHSA.
6.3.3 Your attention is also drawn to the MHSA Regulations published in the Government Gazette No. 23583, dated 2 July 2002. The following regulations must be noted: 9.1(3), 9.1(4) and 9.2(1).
6.3.4 All persons concerned must be made fully conversant with the terms of this guidance note, copies of which must be readily available to them.
