This section provides guidance on managing the risks of working with explosives, from planning and preparing, to blasting and disposing.

On this page

• 9.1 Requirements for explosives
• 9.2 Hazard management and emergency planning for explosives
• 9.3 Maintaining, transporting and storing explosives
• 9.4 Shotfiring: safe systems of work
• 9.5 Explosives selection criteria
• 9.6 Drilling, charging and blasting
• 9.7 Firing
• 9.8 Post-firing
• 9.9 Misfires
• 9.10 Minimising blast damage

9.1 Requirements for explosives

Safe and efficient blasting requires extractives operators and supervisors to understand and follow the correct procedures.

Risks to health and safety must be eliminated so far as is reasonably practicable. If elimination is not possible, risks must be minimised so far as is reasonably practicable. This includes having practices in place to prevent premature explosions and mishandling of explosives.

Operators must notify WorkSafe about planned blasting activity at least three working days before the first firing using this form Intended detonation and deflagration of class 1 substances for the extractives industry

The operator must make sure no person uses, handles or issues explosives unless they are a certified handler and hold a controlled substances licence.

The person in charge on the blast/site is the shotfirer. The shotfirer must be a certified handler and hold a controlled substances licence.

9.2 Hazard management and emergency planning for explosives

Principal hazard management plan

Any mining operation, A-grade quarrying operation or A-grade alluvial mining operation where explosives are used must have an explosives PHMP and an emergency management PCP. Sites where explosives are used must have an appointed manager qualified under the MOQO Regulations and Health and Safety at Work (Mining Operations and Quarrying Operations – Prescribed Competency Requirements for Certificates of Competence) Safe Work Instrument

Their certificate of competence may have extra or different requirements for using explosives.

A PHMP for explosives must contain the general requirements listed in Section 2.6 of these guidelines and Regulation 68 of the MOQO Regulations. It must also include the specific explosives PHMP requirements set out in Regulation 86 of the MOQO Regulations.

Emergency management PCP

The emergency management PCP must include the information set out in Regulation 105 of the MOQO Regulations. See also Section 3.0 of these guidelines.

Emergency response plans for explosives should be part of the site’s emergency management plans or PCP and should align with the Hazardous Substances Regulations.

Control measures for managing explosives at B-grade operations should be in the operation’s HSMS.

9.3 Maintaining, transporting and storing explosives

All equipment used for shotfiring should be checked before use and kept in a safe working condition.

Service the equipment regularly, based on how much it is used and the original equipment manufacturer’s (OEM) recommendations.

The explosives PHMP must cover how to inspect and report on the safety of equipment used to make, store, transport, and deliver explosives. It must also explain how to make unsafe equipment safe.

Transporting explosives

The PCBU in charge of transporting explosives must meet all the requirements listed in Part 8 and Part 9 of the Hazardous Substances Regulations.

These include, but are not limited to:

• making sure there is a certified handler personally controlling the transportation or the explosives are secured (see Regulation 9.48 of the Hazardous Substances Regulations for more information)
• meeting the vehicles requirements under Regulation 9.48 of the Hazardous Substances Regulations
• making sure there are sufficient fire extinguishers of the right type
• only carrying people who are needed for the job or an emergency – but if carrying more than 250kg of class 1.1, 1.2, 1.3 or 1.5 explosives, there must be at least two people in the vehicle
• making sure that the amount of explosives transported is within safe load limits
• maintaining separation distances and informing drivers of these both verbally and in writing
• making sure vehicles do not stop unless there is an accident, incident, emergency, need for urgent refuelling or another valid reason. If a vehicle does stop, the duration must be minimised. Explosives must be managed using an emergency response plan according to Part 5 of the Hazardous Substances Regulations.

Storage of explosives

Explosives must be stored according to Regulations 9.17 to 9.30 of the Hazardous Substances Regulations. The regulations cover:

• requirements for magazines
• segregation and separation distances
• emergencies.

Tracking explosives

Tracking means recording what happens to hazardous substances during their lifecycle – from manufacture or import, through distribution, to use and disposal. For more information, see Regulations 19.1 to 19.7 of the Hazardous Substances Regulations.

Security of explosives

Explosives must be secured at a hazardous substance location or designated use zone according to Regulations 9.18 to 9.21 of the Hazardous Substances Regulations.

They must be stored in containers that meet the requirements of Regulation 9.19 of the Hazardous Substances Regulations, unless under the personal control of a certified handler.

9.4 Shotfiring: safe systems of work

You must make sure, so far as is reasonably practicable, to have safe systems of work in place that meet your obligations under HSWA, the Hazardous Substances Regulations, and the MOQO Regulations. Control measures for explosives use should include:

• protection against unintended initiation and how to deal with misfires
• hazard identification and checklist for clearing the blast zone before final connection
• a clear and concise procedure detailing the role of sentry guards at a site
• clearance distances and suitable shelter for all workers and people nearby throughout blasting activities
• face checks (before designing the drill plan and/or face profiling), installing suitable edge protection, and delineation of the blast zone from general operational activities
• storage, transport, and security of explosives (including magazine management if required)
• suitable blast warning signals (visible and audible), isolation barriers, and warning signs
• clear understanding of who should be in attendance throughout the blasting process.

Individual blast risk assessment

A formal risk assessment should be completed for each blast, to identify the hazards and control measures at each stage, including the extent of the blast exclusion zone during the firing sequence.

Before blasting, any risk assessment and control measures should be agreed to and approved by all the relevant parties involved in the blasting process.

See Table 9 for a list of factors to consider during the risk assessment.

Blast design

Blast designs will vary from site to site as different rock types require different explosives to be effective. The blast design should be tailored for each blast, in view of the conditions on the site. To be successful, evaluate the site-specific conditions for:

• the intended slope design and compliance with the mine plan
• geology – especially structure, hardness and other potential geological structures that may cause risk during blasting operations
• water conditions (perched aquifers, groundwater and surface water)
• vibration prediction
• angle of initiation
• blast pattern
• available free faces
• environmental consideration (dependant on the area of the blast technologies including face profiling, bore tracking and the use of electronic initiation systems may be required).

Once these conditions are defined, a controlled blast design can be developed that considers site-based risks.

The design should:

• make sure rock movement is contained in the declared blast exclusion zone, and includes any special precautions required to achieve this (for example, additional or false burden, use of blast mats)
• control ground vibration and air blast
• keep back-break to a minimum through optimised blast planning
• make sure the shape of the muck pile suits the loading equipment at the site
• make sure muck piles are created so that access for face scaling can be carried out
• minimise the risk of misfires
• enable the location of any misfired shots to be determined accurately
• include consideration as to the type of bulk explosive (ammonium nitrate fuel oil or emulsion) and initiating explosive (non-electric or electric detonators).

9.5 Explosives selection criteria

Ground conditions

Modern explosives used in extractives operations are typically safe when handled correctly. However, they can explode if exposed to excessive or prolonged friction, impact, shock or heat.

Potential hazards include:

• running pumps dry or dead heading them, when pumping from a mobile processing unit
• fires near process equipment or storage areas
• contamination from incompatible chemicals.

To manage these risks, assign a person to oversee the situation, typically the Mobile Processing Unit (MPU) operator.

Record all blastholes containing water to reduce the risk of misfires. For wet blastholes, use water-resistant explosives. For damp blastholes that need to sleep, use explosives with some water-resistant properties. Explosives containing high levels of emulsion are preferred to manage wet or damp holes because of their high-water resistance.

Use a clear system to identify and manage wet blastholes. For example, spray painting the depth of water next to the blasthole. You could also undertake dipping of the blastholes before charging. This helps operators or shotfirers identify holes needing dewatering or emulsion-based explosives.

Blasting in oxidising or reactive ground

Sulphide minerals and coal may oxidise rapidly when broken and exposed to air. If they are present in your operation, test to see if the ground is reactive.

The explosives to use and charging practices to adopt should be developed in consultation with explosive manufacturers and follow these precautions:

• Sheath ANFO explosives to inhibit exothermic reaction between the explosives and the blast material.
• Wash down all exposed surfaces in the blast vicinity to make sure there is no fuel available for a secondary explosion.
• Use the correct amount and type of stemming in all blastholes to prevent flame fronts developing at the blasthole collar.
• Use low explosive strength detonating cord that is not in contact with rocks or dust (to avoid detonating cord raising and igniting dust).
• Select the correct stemming for the conditions – usually a clay-rock stemming is preferred.

9.6 Drilling, charging and blasting

Drilling blastholes

Risks associated with the drilling of blastholes include residual explosives from previous blasts being encountered and initiated, and inaccurate drilled blastholes creating an unsafe situation during firing. Inaccurate drilling may be caused by the geology of the ground or operator skill levels.

Blast geometry and design is critical to create safe discharges and blast results.

Blasthole diameter, inclination and length should be adequately designed and recorded for the selected drill pattern. Correct drilling of blast designs will make sure hazards such as over break, fly rock, or air blast overpressure are significantly reduced.

A drillers log should be provided to the driller, and the operator should note any potential inconsistencies in the drill hole including interception of water (and at what depth), and the location of any cavities or caves.

The following standards and procedures should be in place:

• The drilling site should be prepared and drill holes marked before drilling.
• Drilling should not be carried out on any face or bench until it is examined for misfires and suitably treated. For more information see Section 9.9.
• The driller should record every drill hole including date, time, length, inclination, and position relative to a fixed point or benchmark.
• The driller should record any unusual events during the drilling (for example cavities, soft rock, or an inability to drill designated holes).
• When positioning the drill rig or while drilling near the edge of the bench, the drill rig should be positioned so the operator always has a clear view of the edge and far enough away to prevent the drill rig toppling over the edge. Consider using delineators or cones to mark the end of the bench. Provide edge protection for workers working near the edge of the face.
• Do not drill in a hole if any part is too close to a hole with explosives (this distance should be set by a risk assessment with expert technical advice).
• If face profiling and boring tracking holes for accuracy, provide the driller with results to assist them with ongoing accuracy of drilling.
• When drilling near the bench edge, the drill rig’s driver access side should face away from the edge.

Charging operations

CLEANING AND MEASURING BLASTHOLES

Check blastholes before loading to make sure they are clear and drilled to the correct depth.

Any blocked blastholes should be cleared, and short blastholes redrilled where possible. To prevent blocked blastholes, protect the hole’s collar (for example, using caps or cones).

Short blastholes can cause increased toe being left, creating digging issues.

Overcharging can increase risk, for example, flyrock, air blast, and increased vibration.

DISTRIBUTION OF INITIATION EXPLOSIVES

Initiation explosives should be placed near the blasthole collar, so they are not in the way of the loading and stemming process.

It is also important that boosters or detonators cannot be accidentally knocked into blastholes or lost in drill cuttings.

If these situations are likely, secure the initiation explosives near the blasthole collar.

PLACING INITIATION EXPLOSIVES IN BLASTHOLES

Use compatible boosters and downhole detonators to form the primer according to the manufacturer’s recommendations.

Once assembled, locate the primer down the blasthole without excessive force and take care to avoid unnecessary material build-up between the primer and explosives column.

Take the following precautions:

• Check explosives for damage.
• Report any damaged explosive to the certified handler to dispose of appropriately.
• Secure lines to avoid primer being drawn into the hole (slumping).
• Place the tails of the downline neatly at the collar of the blasthole so they are secure and away from any vehicle movements. Tie them to a rock or stick to keep things tidy and reduce the risk of operators tripping over the downhole leads.
• If a downline or primer is lost down the blasthole, notify the shotfirer, record the loss and reprime the blasthole.
• Never use excessive force to remove a jammed primer. If the original primer cannot be removed, use extra priming.

LOADING EXPLOSIVES

When loading explosives, avoid damaging down lines or pulling the down line into the hole. Take the following precautions:

• Load the shot so the holes furthest from the access point are loaded first.
• Charge the shot in a way that prevents damage to the down line and excessive spillage around the hole.
• Regularly sample the product for quality and density to avoid possible desensitisation by compression (dead pressing).
• When the truck empties during charging of a particular hole, identify any partially filled holes and make sure they are fully loaded before firing.
• Liaise with the contractor about which holes to load and in what order.

MOBILE PROCESSING UNITS (MPUs)

Take the following precautions while using MPUs:

• Do a pre-start check to make sure the vehicle is in sound condition and repair.
• Make sure all workers operating the MPU are competent.
• Make sure MPUs are electrically earthed during mixing and transfer operations to dissipate static charges. This may include electrical continuity through the piping system on the vehicle and fitting tyres that can conduct static charges.
• The operator should have full view of explosive delivery points or be in reliable communication with another operator who has a full view.
• Make sure vehicle access to the shot is near a clearly defined access route designated by the shotfirer.
• In areas of restricted visibility, use a spotter to control vehicle movements.
• When working near the edge of the bench, identify hazards and appropriate fall protection.
• Before accessing public roads, wash explosive residue should be washed with water from pump hoses, explosive mixing receptacles, and so on.

PNEUMATIC CHARGING

Pneumatic charging devices should be properly earthed. Operators should wear antistatic footwear, remove their gloves, and earth themselves before touching electric detonators.

PREVENTION OF FLY ROCK

Preventing fly rock is important. The main causes of fly rock are:

• The explosives column is brought too high up the blasthole. Check that the stemming height matches the blast design.
• The rise of explosives has not been checked. Bulk explosive has filled into a cavity, fissure, joint voids or cracks, all of which may reduce the burden and cause over charging.
• Blastholes have deviated when drilled and are closer together, causing a portion of the shot being over charged.
• The drill angle on an inclined blasthole reduces the burden at the bottom of the hole causing overcharging.
• A section of rock has fallen out of the face after profiling, causing an unidentified reduced burden and overcharging.
• Poor delay sequences cause too much time between adjacent holes reducing burdens during blasting and leading to fly rock.
• The amount of explosives placed in the blasthole is not suitable for the rock type leading to overcharging.
• A geological anomaly creates a band of weaker rock in front of a charged blasthole, which can cause overcharging. These anomalies are hard to spot because the surface rock looks the same as expected. The drilling could be into competent rock with a band of weaker rock located between the blasthole and the free face.
• Rock around the collar may be fragmented by blasting the previous working bench.

Understanding the geology is key when developing blast design. Before charging the blastholes, it is important to double-check this information. Following the blast design carefully helps make sure the blast goes smoothly and safely. If conditions change, you may need to adjust how the explosives are distributed.

Shotfirers should:

• frequently check the rise of explosives in the blasthole
• visually check the alignment (azimuth) and inclination of every blasthole and compare them with the design
• carefully consider any deviations
• consider re-profiling if a rock falls or a slip has occurred after the initial profile was done
• include a written delay sequence schedule in the blast specification so excessive delay periods can be easily identified
• check the powder factor for the rock type to calculate the quantity of explosives (compare with previous successful blasts if needed)
• examine other site faces for evidence of joint voids or cracks
• consult with the driller and check the drillers log for evidence of geological anomalies (for example, voids, clay seams, cavities, fissures, joint voids, cracks or weaker rock)
• consider increasing the top stemming where rock around the collar is fragmented by blasting the previous working bench.

SLEEP TIME IN BLASTHOLES

Sleep time of an explosive matters because explosives can deteriorate when exposed to heat, cold, humidity, and water and could cause failure of the explosives. Product deterioration may result in a charge, or part of a charge, failing to explode or misfiring. Explosives should be charged and fired as soon as possible.

When a blast is being slept, complete a full risk assessment, including site management and blasting personnel. If the risk assessment shows blast guards are needed, they should be assigned, briefed, and stay in position until the blast is fired.

CHARGING DURING SHIFT CHANGES

When charging is being done during shift changes, make sure a written procedure is in place for communication between the shifts. Share information about charging and blasted locations, holes loaded, and any unique hazards or unusual circumstances associated with the shot.

PPE

You must identify hazards that may arise when charging and firing explosive, and you should provide and wear personal protective equipment (PPE). Safety Data Sheets for the products being used will outline PPE requirements. These may include gloves, goggles, and sometimes, anti-static clothing.

ACTIVITIES IN PROXIMITY

Avoid any activity being done near the shot that could generate heat, sparks, or an impact or pressure shock that could cause an explosion or fire. This includes smoking, naked flames or operation of machinery. Unauthorised workers and machinery not involved in the blasting operation should be removed a safe distance from the area.

VEHICLES ON NON-ELECTRIC BLAST

If vehicles are used at non-electric blasts, there is a risk of a premature explosion or misfire if they run over detonators or damage the signal tube. Use a clearly defined access route for vehicle access to the shot. Where there is restricted visibility, use a spotter to control vehicle movements.

SIGNAGE

Charging areas should be clearly marked by appropriate warning signs and comply with Regulations 2.5 to 2.10 of the Hazardous Substances Regulations.

Where charged blastholes will be left to sleep overnight, suitable barricades, warning signs and lighting should be used. Approaching vehicles and people need to be able to clearly identify the charge area. If further warning is required, an overnight guard can be used to direct people and vehicles around the shot area.

COMMUNICATION DEVICES

When using electric initiation, the blasting circuit can be energised by the electric field produced by radio transmitters, mobile telephones, two-way radios, vape pens, and so on.

Such devices should never be carried while holding or connecting electric explosives.

Safe distances for electronic detonators subject to radio frequency should be determined.

Stemming

Avoid damaging the down line connected to the primer when placing stemming material. Take the following precautions:

• Make sure the hole is loaded with explosives, and the collar length is correct.
• Check the tension on the down lines to make sure the primers are in the product.
• Check the stemming material is a suitable quality and does not contain large fragments of rock that may cause damage to down lines.
• Approach the hole from the side opposite to the marker securing the initiating line if loading with mobile plant.
• Leave blastholes charged with gassed bulk explosives un-stemmed for the recommended time to allow for expanded gas bubbles. The shotfirer will check holes for gassing of product, then advise workers when and where to start stemming.
• Stem all loaded blastholes before the end of the shift. If this is not possible, consider blocking the blasthole with a gasbag or covering it with drill cuttings.

TAMPING RODS

Use only wooden or other non-metallic rods when tamping to prevent an explosion from shock, friction, or impact. Make sure the lead wires, detonating cord, or signal tube connected to the primer are not damaged during the tamping process. A primer should never be tamped because impact could cause it to explode.

STEMMING HOPPERS

If mobile plant is used to carry a hopper to load stemming into charged blastholes, the mobile plant should have good visibility (use a spotter). Take care not to damage down lines on charged blastholes. Complete stemming as soon as possible.

Initiation

Consider the following when connecting shots using non-electric, detonating cord, or electric initiated systems:

• Workers carrying out the hook-up should be trained, competent, and follow a tie up plan.
• After connecting the shot, check to confirm it is correct. The shotfirer in charge of the blast is ultimately responsible for the hook-up and should personally check the connections before firing.
• You must make sure that the system for firing the explosive is not readied to the point that only one final action needs to be taken to fire the charge, until all safety requirements have been done, including clearing the blast area.
• If a thunderstorm develops, the person in charge should assess its proximity and decide whether to continue activities. If it approaches, stop handling or preparing the explosives and evacuate everyone in line with Regulation 9.29(3) the Hazardous Substances Regulations.
• Where a shot is not going to be fired, the shotfirer should disconnect the control row before evacuating, if safe to do so.

NON-ELECTRIC FIRING

A procedure should be in place to provide a safe hook-up of non-electric explosives. Connections and detonating cord charge weight (grams of explosives per metre) should follow the manufacturer’s instructions.

ELECTRIC FIRING

Below are some things to consider when doing any electric firing:

• Electric detonators are susceptible to accidental initiation by sources of stray electricity. To reduce the risk of accidental ignition, 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.
• Stop all surface charging operations if an electrical storm is imminent. Use lightning detector devices to track storms and lightning strikes, to see if surface charging operations should be stopped. Select an appropriate detector for the type of charging operation and follow the manufacturer’s instructions.
• Keep detonators clear of the ground until charging starts.
• Never hold an electronic delay detonator while it is being tested or programmed.
• Do not use plastic liners in blastholes unless they are permanently conductive.

CIRCUIT TESTERS

Before connecting the firing circuit, check the detonating circuit and firing circuit for continuity. It is possible an explosion might occur when testing. Therefore, put appropriate control measures in place, including clearing the blasting area and choosing a safe location for testing. The shotfirer should make sure the circuit tester is maintained in correct working order.

SHOTFIRING CABLE

When using a shotfiring cable to initiate a blast, the shotfirer should make sure the cable is properly protected and insulated for the blasting conditions. Take precautions to prevent the cable contacting electrical installations, metal objects, or anything that could damage the insulating cover.

Keep the cable short-circuited at each end during the charging operation and at the power end while the leads from the detonators are being connected. The short-circuit at the power end should not be opened for connection to the source power until the blasting area is clear of people. As soon as the blast has been fired the short-circuit should be re-established by physical disconnection from the exploder.

EXPLODERS

Only exploders capable of storing or generating the electrical energy required to reliably initiate electric detonators should be used. They should be carefully handled and regularly tested to ensure reliable performance.

9.7 Firing

Blast exclusion zone

The shotfirer, certified handler, and site operator should set the blast exclusion zone and the location of guards by doing a risk assessment that considers any technical concerns or known hazards in the shot.

The PCBU with management or control of a hazardous substance location must comply with Regulations 9.27 and 9.30 of the Hazardous Substances Regulations.

Warning procedures

The PCBU in charge of the detonation must make sure anyone not specifically authorised by the certified handler to be in the designated area is kept out, using these methods:

• Information must be displayed that:
  • warns a substance is being detonated, and entry is prohibited
  • is visible from all points 5m outside the perimeter of the designated use zone
  • should meet the level of comprehensibility and clarity required for signage in Part 2 of Regulations 2.5 to 2.10 of the Hazardous Substances Regulation.
• Make a visual check of the zone immediately before firing to confirm all people not directly involved are excluded.
• One minute before firing, sound a distinctive warning that is loud enough to be heard throughout the zone and 5m beyond, by someone with normal hearing.

External parties

If necessary, give external parties warning before conducting blasts. External parties may include adjoining properties, residences or the general public.

Withdrawal of people and machinery

Before firing the shot, people in the vicinity of the blast area must be warned and moved to a safe area outside the blast exclusion zone. They should not return until the ‘all clear’ signal is given. It is critical that everyone involved in the blast can reach a predetermined safe position before firing.

Machinery in the blast exclusion zone should be moved, where possible, to a safe location to make sure machines are not damaged by flyrock.

Do a visual check of the blast exclusion zone before firing.

Signage

Information must be displayed to warn people there will be a blast and entry is prohibited. Signs must be clearly visible and written so people can clearly understand them.

Audible warning device

An audible warning device must be used to indicate a blast is going to take place. The device must make a sound that stands out from any other warning or operational signals on site. It must be loud enough to hear throughout the blast zone and at least 5m beyond.

Radio signal

If radios are used for warning signals, everyone on site should clearly understand what they mean.

If the site uses more than one radio channel, choose one channel to always use for blasting. The warning signal should also be broadcast on all other channels used in the blast area.

Preventing access to the blast exclusion zone

Place adequate roadblocks and guards at any road or access point into the blast exclusion zone during the firing, and keep them there until the shotfirer gives the all clear.

Blast monitoring

When blasting near buildings or structures, monitor ground vibration and air-blast overpressure to record the blast details.

The shotfirer must make sure the firing is monitored.

9.8 Post-firing

Post-firing inspection

The certified handler should inspect the area after the blast. Before entering the blast area, wait long enough for dust and fumes to clear. Going in too soon can cause illness from breathing in toxic gases and fumes. Dust and fumes can also make it hard to see, causing accidents like collisions, falls, trips or missing unstable rocks.

Where a blast is initiated by electric detonators, disconnect the firing cable from the exploder immediately after firing, and before the post-firing inspection. Short-circuit the ends of the firing cable together, and remove the key from the exploder.

The purpose of a post-firing inspection is to confirm conditions in the blast area are safe to restart the work. In particular, the shotfirer should look for evidence of unstable ground, misfires, and burning explosives.

UNSTABLE GROUND

Blasting can cause vibrations, concussion and ground stress changes that may loosen rock around walls - even those far from the blast site. Blasts can also create voids under the blast area, especially in places with underground workings, limestone, or soft ground. Areas stable before a blast might become unsafe or even collapse after blasting, particularly with large blasts. Falls of ground are a serious safety risk for workers nearby.

When inspecting after a blast, approach the area carefully and avoid the toe and crest of the face. If possible, inspect the blast muck-pile from a bench below or to the side.

MISFIRES OR BURNING EXPLOSIVES

If explosives misfire or burn, there is a serious risk of additional detonations, which can cause blast damage and flying rock. Misfired explosives can be hard to spot, and accidental detonation in a confined space can lead to fatal or serious injuries.

During the post-blast inspection and all mucking operations, carefully check for any signs of misfired detonators or detonating cords. If a misfire is found, you must make sure no person approaches the misfired charge for:

• 10 minutes for electrically fired charges
• 60 minutes for charges fired by a fuse.

Do not give the all clear and keep all guards, barricades and signs in place. The certified handler should notify the quarry or mine manager right away.

Only after the post-firing inspection is complete and the area confirmed as safe, should the all clear be given and barricades, cautionary signs and guards removed.

For more information on misfires, see Section 9.9.

Prevention and management of post-firing fumes

Blasting can release toxic gases like nitrogen oxides, ammonia, nitric acid, carbon monoxide, and carbon dioxide into the air in large amounts. These gases are known as blast fumes, and even low levels can be a serious health risk. Nitrogen dioxide is visible as a reddish-brown colour; the others are not visible.

Safety management systems should include the different control phases for blast fumes such as:

• prevention: how to prevent or minimise blast fumes
• management of fumes: where blast fumes extend beyond the blast exclusion zone
• management of an exposure: for when people are exposed to blast fumes.

Mining and quarrying operations should include control measures in their explosives PHMP and emergency management PCP.

PREVENTION

Wet ground is closely linked to the production of excessive blast fumes. Other factors that can cause blast fumes include:

• incorrect fuel to oxygen ratio
• product pre-compression
• insufficient priming
• acidic soils
• presence of pyrite
• product formulation.

Blast fumes can be reduced by:

• selecting the right explosive for the conditions
• dewatering holes before loading
• keeping sleep times to the minimum time recommended by the manufacturer.

Understanding and applying meteorology (such as weather conditions, wind speed, direction and stability classes) and gas cloud distributions help calculate how long a blast gas plume will take to reach areas of interest. For example, a ‘smoko’ hut, workshop, office or house. Buildings should not be used as shelters unless assessed by competent persons as safe havens. This knowledge also helps determine how far the gas plume will spread and how the gas concentration will change with distance.

Anyone developing prevention and emergency management plans should understand the gas toxicology and the exposure standards of a gas, such as nitrogen dioxide, especially for high concentrations over short periods.

MANAGEMENT OF FUMES

Before a gas plume occurs, it is important to have a system for managing a potential incident including evacuations. The system should include information about wind speed, wind direction and the location of the safe assembly point. Communication systems should be in place and already tested.

MANAGEMENT OF AN EXPOSURE

Exposure to nitrogen dioxide can cause delayed health effects that may be life-threatening, even if the person initially seems unaffected. For this reason, anyone exposed to nitrogen dioxide should get medical help immediately and stay under observation as advised by their doctor. As a precaution, they may need to be monitored for up to 12 hours.

Safety data sheets for all products being used should be readily available to everyone involved in the blasting process.

9.9 Misfires

Shotfiring notifiable events include:

• any incident in which any part of an explosive charge, after initiation, fails to completely detonate (misfires)
• any unplanned or premature ignition of a shot
• any accident where a person suffers injury or dies as a result of shotfiring
• any accident where material is projected beyond the declared danger zone, or otherwise exposes any person to danger during blasting operations.

Your site should have a written procedure providing a safe system of entry and inspection for misfires and their treatment, including the methods used to detect a misfire.

Mining operations, A-grade quarrying operations and A-grade alluvial mining operations must have procedures in their explosives PHMP to find, recover, and detonate misfired explosives. Keep records for all misfired explosives.

The PCBU who directs the carrying out of the detonation or deflagration of an explosive must make sure any misfired charge is identified.

Determination of misfires

Methods used to determine if a misfire has happened are based on many factors, including appropriate training, standard operating procedures, and guidance from standards (for example AS 2187.2-2006 Explosives – Storage and Use).

There are certain events that indicate a misfire has happened, including:

• when any part of an explosive charge fails to completely detonate after initiation
• if using safety fuse, the number of shots counted is less than the number of holes fired or a disagreement on the count of shots fired
• if damaged safety fuse, detonating cord, lead wires or unfired signal tube is exposed in a hole that has been fired
• evidence of cut-offs, butts, or remaining portions of blastholes (for example boulders with drill holes) suspected of containing explosives
• holes that have slumped between charging and firing, due to dispersion of the explosive from water ingress or through joints and fissures
• if during the normal excavation of the blasted ground, uninitiated explosives are found or the load out mobile plant encounters poor ‘diggability’ of the blasted ground
• uninitiated product found in the processing of material.

A careful examination of the debris for explosives should be done and, if present disposed of safely (see ‘disposal of surplus and defective explosives and packaging’ later in this section for more information).

Misfire treatment

If you find a misfire, do not attempt to drill into the charged blasthole. Instead, do a hazard identification and risk assessment to decide on a safe way to handle it.

Be aware that a misfire among multiple charges can cause excessive rock scatter when fired, because the successful shots have relieved the overburden. In such cases, make sure adequate extra cover is used.

REMOVAL OF STEMMING AND RE-PRIMING

Where a blasthole has completely misfired, the stemming may be removed by either applying water under pressure or by compressed air and water through a length of antistatic hose (such as FRAS). No metal fitting should be in the hole.

If water under pressure (or water and air pressure) is not available, the stemming may be ‘sludged’ out using water and a wooden or other approved implement. Do not use just compressed air.

When the stemming has been removed a fresh priming cartridge may be inserted and the blasthole again stemmed and fired. An artificial burden or cover should be placed around and over the hole to prevent fly rock.

If a misfired blasthole contains ANFO (an explosive material consisting of ammonium nitrate and fuel oil) or emulsion-based product, it may be ‘sludged’ out down to the primer using the same procedure to remove stemming. The slurry explosive washed out should be treated as deteriorated explosives and dealt with as detailed in Section 11.2. The blasthole should then be re-primed and fired to explode the original primer. Do not remove a primed charge from the blasthole.

RELIEVING BLASTHOLE MISFIRE TREATMENT

If it is not possible to explode a misfire by re-firing, a relieving blasthole should be drilled parallel to the original blasthole then charged and exploded as follows:

• Mark the misfired blasthole clearly or block it by inserting a wooden plug.
• If the misfired blasthole is 50mm or less in diameter and less than 3m in length, do not drill the relieving blasthole closer than 600mm to the nearest point of the misfired hole.
• If the misfired blasthole is larger or longer than 50mm and 3m respectively, increase the distance between the misfired blasthole and the relieving blasthole so the misfired charge is not drilled into.
• If an electric detonator is involved, first short-circuit the detonator wires, then tie to a permanent object to recover the detonator after a relieving blasthole has been fired.

All explosives recovered from misfired blastholes should be collected and disposed of as detailed in the section under ‘disposal of surplus and defective explosives and packaging’.

SHATTERED GROUND

If the ground around the misfire is shattered, do not use the relieving blasthole method. In this case the ground around the misfire should be carefully cleared until the explosives are uncovered. Do this cautiously by following the wires or fuses down to the charge, and removing the last few inches of cover by hand.

PRE-DRILLING PRECAUTIONS

No blasthole should be drilled in any face or bench until it is thoroughly cleaned and washed down within a radius of 1m from the intended hole. Examine any cut-offs or sub-drill blastholes to make sure they do not contain explosives, then plug sub-drill blastholes with a wooden plug. If examination reveals explosives, the cut-offs or sub-drill blastholes should be primed and fired and the pre-drilling precautions above taken again.

Misfire workers

If a misfired charge is identified, the certified handler must make sure no-one approaches for 10 minutes for an electrically fired charge. For a charge fired by a fuse increase the time to 60 minutes.

The certified handler must then safely dispose of the malfunctioning charge according to the Hazardous Substances (Disposal) Notice 2017.

The certified handler may have an experienced person to assist. All other people must be kept well clear of the area.

The PCBU must make sure the requirements of Regulation 9.28(3) of the Hazardous Substances Regulations are maintained until safe disposal by the certified handler is completed. This includes displaying information, sounding warnings and visual checks.

LOADING OUT A MISFIRE

Before retrieving misfired material, a written hazard identification and risk assessment should be completed by competent people. This assessment should consider the site shotfiring procedures and focus on key areas like:

• the excavator may need to have extra protection for the operator. This depends on the properties of the material involved
• using CCTV or other suitable means of isolation to observe the muck pile during the loading operation, so the mobile plant operator can be alerted to the presence of suspect material
• how blastholes involved in the misfire can be located in the muck pile. Survey equipment may be used which can define the hazardous area more accurately
• flags, bunting, or warning notices may be needed to mark the areas identified.

While the mobile plant operator recovers explosive material, accidental initiation can occur by:

• the mobile plant’s bucket striking the explosive material during excavating, and rock falling and striking the explosive material
• mobile plant running over the explosive material
• movement of rock in the bucket when transporting
• tipping the rock out of the bucket at the search site.

All explosive materials are sensitive, some more than others. Heat, pressure and friction can initiate the explosives or detonators, especially if they are damaged.

When misfired charges are found, the PCBU who directs detonation or deflagration of the explosive must safely dispose of them.

Records

Blasting records including all key parameters such as hole specification, burden and spacing, quantities of explosive used, tie-in pattern and number of delays should be documented and records kept.

Reporting requirements

The certified handler should report all misfires to the PCBU.

Misfires and other explosive incidents must be reported to WorkSafe in accordance with Schedule 5 of the MOQO Regulations.

Disposal of surplus and defective explosives and packaging

The disposal of explosives is considered an inherently hazardous task. There have been a number of fatalities and serious injuries where people have attempted to dispose of explosives themselves. Disposal of explosives should only be done by fully trained, competent people with specialist experience in this field.

EXPLOSIVES NO LONGER REQUIRED

Explosives that are no longer needed should be returned to the supplier. If they cannot be returned disposal must be done according to the Hazardous Substances (Disposal) Notice 2017. Do not throw away, bury or flush explosives.

EXPLOSIVES FOUND WHILE LOADING

Treat any suspected explosives found while excavating as live. Shut the area down, set up a prohibited zone and put control systems in place - including informing the site manager.

DETERIORATED AND DEFECTIVE EXPLOSIVES

The Government provides a free collection service for the disposal of deteriorated and defective explosives which is conducted by Civilian Ammunition Inspectors and the New Zealand Defence Force.

To arrange for the collection and disposal of deteriorated or defective explosives contact your local Police station in the first instance (do not dial 111).

Deteriorated and defective explosives include:

• explosives with an expired shelf life
• explosives recovered through a misfire procedure
• damaged explosives.

Explosives packaging

Before disposal, check empty explosive packaging to make sure no explosive remains hidden or lodged in any packaging.

Clearly mark labels so there is no uncertainty of the packaging contents.

Disposal of empty explosive cases

Disposal of empty explosives cases hazardous to the environment must comply with Regulation 10 of the Hazardous Substances (Disposal) Notice 2017.

If burning empty cases after a blast, take them away from the blast site to a secure place. Check no explosive remains hidden or lodged in the case and remove any residual content, then burn them under controlled conditions. Clear and secure the site during burning. Check the area after burning to make sure there is nothing left of the cases.

9.10 Minimising blast damage

Inappropriate blasting practices can result in substantial damage to the rock mass in the interim and final slopes. The consequences of poor blasting practices include:

• loose rock on slope faces and batter crests
• over-break in the face causing over-steepening of the slope, leading to further instability depending on the level of stability allowed in the original design
• sub-grade damage that can destroy safety benches, leading to reduced effectiveness of retaining loose rock falling from above
• a cumulative reduction in the strength of rock mass where the slope is developed. In particular, reduced shear strength of the structural defects.

Set up standardised drilling and blasting practices, using proven and recognised blast design procedures that suit the ground conditions at the site.