7.1. RECORDS
7.1.1. Authority to use Explosives
In the “Foreword” to AS 2187.2 it states “it is a fundamental requirement that persons are competent and authorized by their employer to handle and use explosives. Competence, with respect to handling and use of explosives, is recognized through compliance with relevant legislation and by having documentation confirming one or both of the following:
Current and valid shot firing ticket or licence applicable in the relevant State or Territory.
Currency with relevant competencies or qualification, attained through a national training package (i.e. endorsed by Australian National Training Authority).
Employers of persons who handle and use explosives also have responsibilities with regard to the safe and secure management of explosives by ensuring that systems are in place through legislation and their management plan (if required) to provide a safe place of work. From a security viewpoint, the presence and security of explosives on a worksite is the ultimate responsibility of the employer.”
Under section 64 of the Mining and Quarrying Safety and Health Regulation 2001, the appointment should be authorised by the site senior executive and recorded in the mine record. Note that a person is considered competent if:
1. That person holds a current shotfirer’s license under the Explosives Act 1999 that is applicable to the mine’s operations; or
2. The authorising person is satisfied the person has the competency accepted by the Advisory Council as qualifying the person to carry out the handling activity or has satisfactorily completed a competency based training program for carrying out the handling activity and is competent to carry it out.
For surface coalmines a shotfirer’s licence under the Explosives Act 1999, is required for the person in charge whilst others involved in storage, handling or use of explosives are required to be competent in accordance with the relevant competencies in MNC04, the National Coal Training Package.
7.1.2. Blast Design
Blasts should be planned and designed by persons qualified or deemed competent to ensure required blast results. A suitable blast design should be provided to the shot firer or produced by the shot firer before charging. The blast timing should be designed to ensure a suitable explosive weight per delay to minimise vibration and fly and produce the required blast results.
7.1.3. Blast Parameters
Blasting records including all key parameters such as hole specification, burden and spacing, quantities of explosives used, tie-in pattern and number of delays should be documented in a manner consistent with Appendix A of AS 2187.2.
7.1.4. Charging Over Shifts
Where charging is conducted over several shifts there needs to be a written procedure in place for communication between shifts. This should include communicating from one shift to another, information about charging and blasted locations, holes loaded and any unique hazards or unusual circumstances associated with the shot. There are many recorded incidents of persons driving both heavy equipment and other vehicles over unattended charged blastholes, both on surface and underground. There are many ways to control this hazard, but an exclusion barricade with signposting is usually effective.
7.2. SAFETY PRECAUTIONS
7.2.1. Safety Equipment
As required safety equipment is to be utilised whilst using explosives. The potential risks should be identified and suitable equipment selected for the procedure. This may include personal protective equipment such as fire retarding clothing, gloves, goggles and in some instances, anti-static footwear.
7.2.2. Handling of Explosives
Explosives are to be handled in a manner that prevents operations that could lead to ignition or initiation of explosives. Mishandling of explosives such as throwing of primers can result in ignition caused by impact with the ground.
7.2.3. Activities in Proximity
There should not be any activity undertaken within the proximity of the shot that could generate heat or sparks. This includes smoking, naked flames or operation of machinery. Unauthorised personnel and machinery not involved in the blasting operation needs to be removed a safe distance from the area (AS 2187.2).
7.2.4. Mobile Equipment on Non-electric Blast
Where mobile equipment is used on non-electric blasts there is a premature explosion hazard or misfire hazard due to running over of detonators. In addition a premature explosion hazard due to tensile (pulling) failure of signal tube resulting in “Snap, Slap and Shoot” phenomenon. Mobile vehicle access to the shot should be via clearly defined access routes and a spotter should be used to control vehicle movements in areas of restricted visibility.
7.2.5. Signage
Charging areas shall be clearly marked by appropriate warning signs. Where charged holes are to be left to sleep over night suitable warning signs and lighting is to be utilised. Approaching machinery and person needs to be able to clearly identify the charge area. If further warning is required an overnight guard can be utilised to direct persons and mobile equipment around the shot area.
7.2.6. Communication Devices
When using electric initiation, there is a possibility of the blasting circuit being energized by the electric field produced by radio transmitters, mobile telephones two ways, etc. Safe distances for electric detonators subject to radio frequency radiation can be determined from AS 2187.1 – Appendix I, however such devices should never be carried whilst holding or connecting electric explosives.
7.3. EXPLOSIVES SELECTION CRITERIA
7.3.1. Ground Conditions
When selecting a combination of explosives to be used for the ground conditions present, the objective is to ensure reliability and safety. Each blasthole that contains water should be carefully measured and recorded for specific treatment. To avoid the risk of a misfire wet blastholes should be charged with an explosive with the appropriate water resistant properties. Before using ANFO in damp blastholes the effect of water on the explosive column should be considered. If damp blastholes are required to sleep, an explosive with some water resistant properties is required. A clear identification system is required to ensure appropriate priming and charging of wet blastholes. For example spray painting the depth of water next to the hole.
7.3.2. Blasting in Hot Material
Hot material is a substance that exhibits a temperature between 55C and 100C. Explosives may detonate prematurely if exposed to high temperatures. Temperature measurements should be taken where hole temperatures are expected to exceed 55C.
It is not possible to recommend a safe exposure time for explosives at various temperatures, because of the wide range of products available and ground conditions encountered. There needs to be a written procedure for blasting in hot ground and guidance for this procedure should be sought from the explosives manufacturer and reference to AS 2187.2.
7.3.3. Blasting in Oxidizing / Reactive Ground
Both sulphide minerals and coal oxidise rapidly when broken and exposed to air. In operations where such minerals become dispersed as dusts, sparks or heat flash from blasting can initiate an explosion. The explosives to be used and the charging practices to be adopted should be developed in consultation with explosive manufacturers. There needs to be a written procedure for blasting in oxidising or reactive ground and guidance for this procedure should be sought from the explosives manufacturer and the following general precautions should be considered:
- Sheathing of ANFO explosives to inhibit exothermic reaction between the explosives and the material to be blasted.
- Wash down all exposed surfaces within the blast vicinity to make fuel unavailable for a secondary explosion.
- Use adequate stemming in all blastholes to inhibit the development of a flame front at the collar of a blasthole.
- Detonating cord is capable of raising and igniting a dust therefore low explosive strength detonating cord that is not in contact with rocks or dust should be used.
Selection of the correct stemming for such conditions is most important; usually a clay-cock stemming is preferred.
7.4. CHARGING OPERATIONS
7.4.1. Clearing and Measuring Blastholes
All blastholes should be checked prior to loading to ensure they are clear and drilled to the correct depth. Any blocked holes should be cleared with a charging pole or steel bar. All blastholes should have their depth measured and recorded immediately before charging. Short holes can lead to overcharging and digging problems, while overcharged blastholes can cause fly and airblast hazards.
7.4.2. Distribution of Pegs and Primers
The pegs should be positioned in a standardised pattern in relation to each hole so that when the hole is stemmed, the loader can work in a uniform manner. The peg needs to be securely placed in the drill cuttings so that down lines are not drawn into the hole. Explosive accessories should be distributed and placed along side the peg near the hole. They should not be placed in the drill cuttings or in a position where a vehicle could possibly run over a primer causing an unplanned explosion.
7.4.3. Priming
Primer cartridges should be handled carefully and the down line used to form the primer of suitable explosive strength (AS 2187.2). The primer should be located in the hole without using undue force and care taken to avoid the presence of extraneous matter between cartridges. The following general precautions should be taken whilst priming blastholes:
- Check explosives for damage.
- Any damaged explosive is to be disposed of appropriately and reported to the shotfirer (refer to Section 10).
- Down line securely tied to a peg to avoid primer being drawn into the hole (slumping).
- Ensure that the tails of the down lines are neatly placed at the base of the peg so that they are secure and away from any vehicle movements.
- If a down line or primer is lost down the hole the shotfirer should be notified and the loss recorded and the hole reprimed.
- Never remove a jammed primer by applying excessive force. Multiple priming should be used if original primer cannot be removed.
7.4.4. Bulk Explosives
Care is required in the loading of free flowing granular explosives and pumpable explosives to avoid damage to down lines or allowing them to be pulled into the hole (AS 2187.2). The following general precautions should be taken whilst using bulk explosives:
- The shot should be loaded such that the holes furthermost from the access point are loaded first.
- Charging should be done as to prevent damage to the down lines and excessive spillage around the hole.
- The product should be regularly sampled for quality and density to avoid the possibility of desensitisation by compression (dead pressing).
- Where the truck empties during the charging of a particular hole, the hole should be suitably identified to ensure that the loading is completed prior to firing.
7.4.4.1. Mobile Manufacturing Vehicle
Where a mobile manufacturing unit is used to pump the explosive into the borehole, the vehicle is required to have the necessary specifications as outlined in AS 2187.2 and Section 5 (Transport of Explosives) of this Guidance Note. The following general precaution should be taken while using bulk explosives vehicles:
- A pre start check needs to be conducted to ensure that the vehicle is in sound condition and repair.
- All personnel operating the mobile manufacturing unit need to be competent to monitor any support equipment associated with the delivery of the explosives e.g. pump pressure gauges, emergency shut off.
- The mixing and delivery system needs to be conducted so that the operator either has full view of explosives delivery points, or has adequate communication with another operator who does have such a view.
- Mobile vehicle access to the shot should be via clearly defined access routes designated by the shotfirer and a spotter used to control vehicle movements in areas of restricted visibility.
- When working near the edge of the bench a risk assessment should be performed to ascertain what types of hazard controlling mechanisms will be needed. From these results, it is then possible to determine if a secure
harness system is needed to reduce the risk of falling.
- Before access to public roads, any explosive residue should be washed with water from pump hoses, explosive mixing receptacles etc.
7.4.4.2. Pneumatic Charging
Where pneumatic charging devices are used, they shall be effectively earthed. All charging hose are required to be semi-conductive and have a resistance of not less than 15000 ohms/m and not more than 2 mega ohms for its total length (AS 2187.2). Best practice for operation of a pneumatic charging is for antistatic footwear to be used and for the operators to remove their gloves and earth themselves before touching any electric detonator.
7.4.5. Sleep Time in Blastholes
Sleep time is defined as the time between charging and firing the shot. The sleep time of an explosive is important because explosive can often deteriorate under unfavourable conditions. Conditions such as heat, cold, humidity and water cause the explosive to deteriorate possibly causing failure of the explosives. Product
deterioration may result in a charge, or part of a charge, failing to explode or misfiring. Best practice is for explosives to be charged and fired at the earliest practicable time. In large shots, load-and-shoot firing eliminates a number of possible processes of deterioration. In the Coal Mining Safety and Health Regulation 2001, surface coal mining operations should include in their safety and health management system the stated allowable period for the explosives to remain in the ground before being detonated.
7.5. STEMMING
Care should be taken to ensure that the down line connected to the primer is not damaged during the placing of stemming material (AS 2187.2). The following general precautions should be taken whilst stemming blastholes:
- A check should be conducted to ensure that the hole has been loaded with explosives and that the collar length is correct.
- The tension on the down lines should be checked to determine whether the primers are in the product.
- Ensure that the stemming material is of a suitable quality and does not contain large fragments of rock that may cause damage to down lines.
- If loading with a front-end loader the operator should ensure that the bucket approaches the hole from the side opposite to the peg securing the initiating line (refer to section 7.5.2).
- Blastholes charged with gassed bulk explosives should be left unstemmed for the recommended time to allow for gas bubble expansion.
- All loaded holes should be stemmed prior to the end of the shift. In cases where this is not possible consideration should be given to blocking the hole with a gasbag or covering it with drill cuttings.
7.5.1. Tamping Rods
Only wooden or other non-metallic rods are to be used when tamping to prevent the possibility of an explosion from shock, friction or impact. Take care and ensure that the safety fuse, lead wires, detonating cord or signal tube connected to the primer are not damaged during the tamping process (AS 2187.2). Note: A primer should never be tamped due to the risk of explosion caused by impact.
7.5.2. Front-End Loaders
Where loaders are used for the loading of stemming into charged holes the vehicle is required to have the necessary modifications for operation within the vicinity of an explosive area (AS 2187.1). Stemming should be completed as soon as possible and care should be taken to ensure that down lines are not accidentally run over or caught up in the loader (snap, slap, shoot phenomenon). A spotter should be used to control vehicle movements in areas of restricted visibility.
7.6. INITIATION
The following procedures should be considered as hazard controls whilst tying up of shots using non-electric, detonating cord or electric initiated systems:
- Initiation tie-in should not commence until all operating equipment has completed operations in that section of the blast area and the section to be tiedin has been clearly isolated and defined.
- Personnel carrying out the tie-up should have a tie-up plan.
- The tie-in should be conducted in a planned methodical and approved manner.
- After tying up the shot, the tie-up should be checked to confirm that it is correct. The shotfirer is ultimately responsible for the tie-in and is obligated to personally check the tie-in before firing.
- In the event of a possible electrical storm developing during the tie-in the person in charge has to assess the immediacy of the storm and decide to fire or disconnect the control row and clear the blast area. Note: High-energy discharges of electricity are capable of detonating various forms of nonelectric signal tube.
7.6.1. Non-Electric Firing
A procedure should be in place that provides a safe system of hook-up of non-electric explosives. Connections and detonating cord charge weight (grams of explosives per metre) should be in accordance with manufacturers instructions (AS 2187.1).
7.6.2. Electric Firing
Electric detonators are susceptible to accidental initiation by sources of stray extraneous electricity (AS 2187.2). To reduce the risk of accidental ignition the following controls need to be addressed and maintained:
- Keep wire ends, connectors and fittings, shorted (twisted) until immediately prior to use.
- Do not use electric detonators near power lines or other potential sources of electric current.
- Cease all surface charging operations if an electrical storm is imminent.
Portable lightning detector devices can be used to track storms and lightning strikes giving greater determination of whether surface charging operations should be ceased e.g. Boltek LD-250 Lightning Detector.
- Keep detonators clear of the ground until charging commences.
- Never hold an electronic delay detonator while it is being tested or programmed.
- Do not use plastic liners in blastholes unless they are genuinely and permanently conductive.
7.6.2.1. Exploders
Only exploders suited to the task should be selected by the shotfirer. Exploder’s are preferably stored in a clean dry place and the shotfirer is required to ensure that exploders are maintained in correct working order (AS 2187.2).
7.6.2.2. Circuit Testers
Before connecting the firing circuit, the detonating circuit and firing circuit shall be checked to ensure continuity of the circuit. It should be assumed that when testing an explosion might occur and appropriate precautions are required to clear the blasting area and choose a safe location for testing. The shotfirer is responsible to ensure that the circuit tester used is maintained in correct working order (AS 2187.2).
7.6.2.3. Electric Firing Circuits
Where a shot firing cable is used to initiate a blast, the person who uses the cable should ensure the cable is adequately protected and insulated for the conditions under which the blasting is to be carried out. Adequate precautions are essential to prevent the cable from coming into contact with electrical installations, metal object and areas where possible damage can be caused to the insulating cover.
The cable is to be kept short-circuited at each end during the charging operation and at the power end while the leads from the detonators are being connected to each other or to the firing cables. The short circuit at the power end should not be opened for connection to the source power until all persons have been withdrawn from the blasting area. As soon as the blast has been fired the short circuit has to be reestablished by physical disconnection from the exploder.