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Blasting: Assistants, Labourers & Security Guards

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The document outlines safety procedures and methodology for conducting blasting operations.

Employees must undergo safety training and use proper PPE. Blast areas must be cleared and monitored for vibrations and noise.

The type and amount of explosives used depends on factors like the distance from structures, season, and size of drill holes.

EXCAVATOR HIRE

DOC
MS/EH012
NO.
10/02/2016 Blasting
REV 0

METHOD STATEMENT

SPECIFICATION: D.O.M, PB Blasting


ACTIVITY: Removal of Rock by Blasting
MATERIALS: Explogel explosive cartridges and / or Anfex
PLANT: Drill rigs, Compressors and Two way radios
PERSONNEL: Blasting Engineer, PRO, Safety Officer, Blasters, and Drillers,
Assistants, Labourers & Security Guards.

Contents

1. Purpose
2. Reference Documents
3. ECOHS
4. Methodology
5.1 Introduction
5.2 Explosive Selection

5.3 Drill and Blast Pattern


5.4 Control Plans
5.5 Ground Vibration
5.6 Fly rock control
5.7 Fire control Plan
5.8 Noise control

5. Conclusion

1. Purpose
The purpose of this Method Statement is to ensure satisfactory and safe blasts within contract
requirement and mines legislation.

2. Reference Documents.
 Project Specifications
 Department of Mines legislation.

3. ECOHS
 Ensure that all employees undergo safety, security and site inductions and medical
examinations where required.
 Ensure that safety talks are held on daily basis.
 Brief all the employees of the major risks associated with the works.
 Conduct pre-task risk assessment every time prior to starting work.
 Ensure that the blasters and drillers are experienced and/or licensed.
 Ensure that the explosives vehicle is in good condition and licensed to carry explosives.

Method Statement MS/EH 012 Rev: 0 Blasting


EXCAVATOR HIRE

 The explosives and accessories shall only be handled and used by people with valid
blasting licenses.
 The blasting design to be done by the Blasting Engineer who is a blasting license holder
and/or a Professional Engineer.
 Where the explosives are stored on site, the magazines shall be set up in accordance with
the legal standards governing explosives and shall be licensed.
 No blasting shall be done without approved blast design.
 Ensure that the area surrounding the blast is cleared of people and animals by physically
patrolling the area prior to blasting.
 The employees and surrounding people to be educated about blasting and the blasting
siren so that they are aware of the blasting operations.

 Ensure that employees wear the appropriate PPE at all times.

4. Methodology
4.1 Introduction

Blasting is one of the high risk activities in this project in its nature due to use of explosives
which could be very harmful if not properly handled and/or used. The major risk associated with
rock blasting is damage to structures and general safety of people and animals during blasting.
Blasting shall therefore, be carried out only with prior consent of the Engineer. Prior to any
blasting activity, the contractor and the Engineer shall conduct a survey of private properties
surrounding the site, in the presence of the owners, for defects and all the noted defects shall
be recorded and documented for future reference. Where blasting is required in close proximity
of existing structures and buildings to the blast area, the need to reduce or minimise the effect
of ground vibrations resulting from the blast will have to be considered.  These vibrations shall
be measured using a calibration vibrometer, to measure the peak particle velocity (PPV) in
mm/s.  This would be achieved by drilling small charge holes and increasing the number of
delays, i.e. it depends on mass of explosives per delay.  Should a delay per hole be used for
example, the ppv readings would be negligible resulting in little or no ground vibrations being
transferred to the adjoining structures.

4.2 Explosives Selection

For bulk blasting far from existing properties during the dry season, Anfex will be used with 6
g/m detonating cord and 25 x 200 cartridges explosives as primer. During the rainy season, an
equivalent charge of bigger 65 x 560 cartridges will be used. Within 300m of private houses,
500/ 25 ms hand masters shall be used to replace the detonating cord and 65 x 560 cartridges
used instead of Anfex.
For small diameter drill holes, 25 x 200 cartridge size will be used, with cord and 25 ms relays
placed accordingly, depending on the distance of the blast from the nearest damageable
structure.
All blasts will be initiated electronically using Instantaneous Electronic detonator, to avoid the
waiting/burning period - hence greater risk of inadvertent entry - when using nonelectric
initiation methods such as the safety fuse.

Method Statement MS/EH 012 Rev: 0 Blasting


EXCAVATOR HIRE

4.3 Drill and Blast Pattern

Ideally excavation by the hydraulic excavator would be completed and the rock exposed, and
the rock levels shall be taken and used to compute the depth and/or volume of rock to be
blasted. This information shall be used to design the blast and the drilling patterns. Generally in
excavations less than 1.5m depth, the drilling burden and spacing will be in the order of 500mm
x 500mm to ensure good fragmentation, hence greater excavation productivity.
Originally, the initial burden and spacing at powder factor 1 shall be used. However, there is
some scope for blast parameter optimization after trial blasting and monitoring of the excavation
productivities on site. If drilling will be through the overburden, drill penetration and output data
will be also be used for ‘fine tuning’ the drill and blast pattern, assuming of course, that
geological conditions will remain constant throughout the project servitude.
Besides the topography and geology, the drill and blast pattern shall also be adjusted to
compensate for nearby structures and services to achieve the desired explosives energy ratio to
break the rock without causing any structural damage to these.

4.4 Control Plans.

All blast scheduling is pre planned, submitted and approved by the Engineer.
No blasting shall be done outside the day time hours

4.5 Ground Vibration

When blasting is to be done in the built up area, the most important variable for managing
blast – induced damage to houses is the explosive charge mass per unit delay. When used
properly to control the mass of explosives firing at any one time, these milliseconds delays can
eliminate possible damages to neighbouring property. On this project 2 types of relays will be
available: the 25 ms surface relay with detonating cord for blasting where there are no existing
buildings. And the in – built 25 ms surface / 500 ms down hole shock tubes for really sensitive
blasting in the built up areas due to its more accurate timing, can reduce ground vibrations by
up to 20%. The threshold PPV value of 30 mm/s, is normally specified for build up areas and
this is ‘generous’ by all accounts.
The resulting ground vibrations from a blast can be measured using a properly calibrated vibro
-meter which measures the peak particle velocity (PPV) of the ground through which a blast
induced energy wave passes through. Accordingly, for each blast a ppv reading and distance
from point of measurement shall be recorded in the blast report form and duly signed.

4.6 Fly rock Control Plan

A balanced blast design incorporating a stemming length of 20% of the charge depth shall be
used. Additional covering the blast with gravel up to 1.2 x charge depth shall effectively
eliminate this problem.
The levels shall be taken to determine the depth the rock to calculate the required cover and
stemming heights for the different rock profiles encountered.
Stemming material shall be of good quality graded stone in the size range to be specified by
the blasting Engineer, for the blast hole diameter of 32 mm.

Method Statement MS/EH 012 Rev: 0 Blasting


EXCAVATOR HIRE

In order to counter act secondary blasts, the blast charge shall be suitably covered using
materials not containing sharp rocks or shrouds, having the potential to cause uncontrolled
damage.

4.7 Fire Control Plan

After the re-entry period for each blast has elapsed, typically 5 minutes, the blaster shall
inspect the area for any indication of fire or fire hazard. Drilling and blasting occur when the
area has been bush cleared; therefore there will be minimum dry vegetation left to increase
the fire hazard. By design, explosives vaporize, as opposed to smouldering, at the instant of
detonation minimizing fire risk. As a precautionary measure, the blaster shall pick up any
plastic shock tubing left from the initiation system for later burning and also ensure that the
initiating detonator is placed on clean ground – within a minimum of 2 m radius.

4.8 Noise Control Plan

Since all blasts will be covered for fly rock, this precaution will automatically take care of any
resulting noise levels. Detonating cord used as indicator for complete detonation, commonly
referred to as “policemen” on site, shall be secured to a stick and buried on the cover to
dampen noise levels. No noise threshold has been specified in the contract and noise is
unlikely to be an issue of concern.

5. Conclusion

In conclusion, we shall follow the safety regulations as contained in the Explosives


Regulations of Botswana and the Contract Blasting specifications, in addition to our own
Code of Conduct for Blasting Operations to ensure an incident free blasting contract.
We shall maintain a blasting quality control programme on site to manage the following
critical variables: drilling accuracy, blast design parameters – burden, spacing, blast hole
charge loading, stemming, firing sequencing /timing, ground vibrations and fly rock. Our aim
remains to ‘get the required levels right first time’ without compromising any safety rules.

6. Documentation

All the pre blast records of photographs and reports shall be documented and submitted to
the Engineer for record
All the blasting designs shall be compiled and documented
The PPV readings for all blasts shall be recorded and documented
The post blast records of photographs and reports shall be documented and submitted to
the Engineer

Method Statement MS/EH 012 Rev: 0 Blasting

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