Guidance note Safe distances when using explosives Information for employers and contractors about safe distances for general explosive blasting operations at sites other than mines and quarries, and setting up exclusion zones. March 2012 Background This guidance note has been revised and reissued following the Dangerous Goods (Explosives) Regulations 2011 (Explosives Regulations) coming into operation in June 2011. There has been a fatality and a number of incidents in recent years caused by fly rock thrown from explosive blasting operations. The Explosives Regulations require any person intending to fire blasting explosives (shotfirers) to take precautions to ensure that people (including workers and the public) near the blasting area are: at a safe distance, or provided with and use appropriate blasting shelters. For most general explosive blasting operations, such as trenching, pit or swimming pool excavation, ditching, draining or farm dam excavations, this means setting up a blast exclusion zone. Shotfirers must also: hold an appropriate WorkSafe Victoria licence for use of explosives develop a blast management plan (BMP) in accordance with the details in the incorporated Australian Standard AS 2187.2: Explosives Storage and use. Part 2: Use of explosives which requires details on exclusion zones prepare a safe work method statement (SWMS). This is required under the construction part of the Occupational Health and Safety Regulations 2007 for any task involving the use of explosives. If an exclusion zone of the required size cannot be established and controlled for the expected timeframe, another method of carrying out the task should be considered. For more information see AS 2187.2. This guidance note does not apply to blasting from a free (vertical) face which is common in quarrying. Table 1 - Small to to immediate intermediate blast hole blast diameter hole diameter using ANFO/emulsion using ANFO/emulsion blends (1.2g/cc) blends (1.2g/cc) Evacuation Minimum stemming length (m) distance (m) 51mm 76mm 89mm 102mm 114mm 127mm 140mm 152mm 165mm 100 1.4 2.3 2.9 3.7 4.3 4.9 5.6 6.3 7.0 150 1.1 1.9 2.3 2.9 3.5 4.0 4.5 5.1 5.7 200 0.9 1.6 2.0 2.5 3.0 3.4 3.9 4.4 4.9 250 0.8 1.4 1.8 2.2 2.6 3.0 3.4 3.9 4.3 300 0.8 1.3 1.6 2.0 2.4 2.7 3.1 3.5 3.9 350 0.7 1.2 1.5 1.6 2.2 2.5 2.8 3.2 3.6 400 0.7 1.1 1.4 1.7 2.0 2.3 2.6 3.0 3.3 450 0.6 1.1 1.3 1.6 1.9 2.2 2.5 2.8 3.1 500 0.6 1.0 1.2 1.5 1.7 2.0 2.3 2.6 2.9 550 0.6 1.0 1.2 1.4 1.7 1.9 2.2 2.5 2.8 600 0.6 0.9 1.1 1.4 1.6 1.8 2.1 2.3 2.6 650 0.5 0.9 1.1 1.3 1.5 1.7 2.0 2.2 2.5 700 0.5 0.8 1.0 1.2 1.4 1.7 1.9 2.1 2.4 750 0.5 0.8 1.0 1.2 1.4 1.6 1.8 2.1 2.3 800 0.4 0.7 0.9 1.1 1.3 1.4 1.7 2.0 2.2 Note shaded areas indicate increase risk of fly rock (stemming lengths less than 25 times the diameter of the hole) GUI0143/01/04.11 1
Calculating safe distances Fly rock is typically thrown from the collar of the blast hole. It can be controlled by correctly designing blasts, precise drilling, spacing and carefully loading the charge. A blast design needs to consider how deep the charge should be buried (known as stemming length or charge depth ) and the appropriate stemming material in the blast hole eg crushed rock (see page 3 for details). The major risk control on how far fly rock is likely to be thrown is the diameter of the drill hole and the stemming depth. The following factors also need to be considered when designing a blast: length of the charge - fly rock range is reduced for short charges only when the length of the charge is less than eight times the diameter of the hole if using bulk blasting explosives, risk increases when stemming lengths are less than 25 times the diameter of the blast hole risk increases when drilling and blasting in broken or weakened rock, particularly if one blast is badly loaded. Shotfirers should consult with the driller or examine drill logs before loading shots. Tables 1 and 2 help determine safety (evacuation) distances for setting up exclusion zones once the blast hole diameter and stemming length are known. Table 2 - Small to to immediate intermediate blast hole blast diameter hole diameter using ANFO using (0.8g/cc) ANFO (0.8g/cc) Evacuation Minimum stemming length (m) distance (m) 51mm 76mm 89mm 102mm 114mm 127mm 140mm 152mm 165mm 100 1.2 2.0 2.5 3.1 3.7 4.2 4.8 5.4 6.0 150 0.9 1.6 2.0 2.5 3.0 3.4 3.9 4.4 4.9 200 0.8 1.4 1.7 2.1 2.5 2.9 3.3 3.7 4.2 250 0.7 1.2 1.5 1.9 2.2 2.6 2.9 3.3 3.7 300 0.7 1.1 1.4 1.7 2.0 2.3 2.6 3.0 3.3 350 0.6 1.0 1.2 1.5 1.8 2.1 2.4 2.7 3.0 400 0.6 1.0 1.2 1.4 1.7 1.9 2.2 2.5 2.8 450 0.5 0.9 1.1 1.3 1.6 1.8 2.1 2.3 2.6 500 0.5 0.9 1.0 1.3 1.5 1.7 1.9 2.2 2.5 550 0.5 0.8 1.0 1.2 1.4 1.6 1.8 2.1 2.3 600 0.5 0.8 0.9 1.1 1.3 1.5 1.7 2.0 2.2 650 0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 2.1 700 0.4 0.7 0.9 1.0 1.2 1.4 1.6 1.8 2.0 750 0.4 0.7 0.8 1.1 1.2 1.3 1.5 1.7 1.9 800 0.3 0.6 0.7 0.9 1.1 1.2 1.4 1.6 1.8 Note shaded areas indicate increase risk of fly rock (stemming lengths less than 25 times the diameter of the hole) Table 3 Stem lengths adjustment factors for short charges. Stem adjusted = F x Stemming Adjustment Factor, F, applied to minimum stemming length Charge length/diameter 2 3 4 5 6 8 For diameter < 100mm 0.78 0.86 0.91 0.95 0.97 1.00 For diameter >= 100mm 0.72 0.80 0.86 0.90 0.93 0.97 2
Tables for calculating evacuation distances Evacuation distances set out in Tables 1 and 2 are for bulk blasting explosives - ammonium nitrate and fuel oil (ANFO)/ emulsion blends with a charge density of 1.2g/cc (Table 1) and ANFO with a charge density of 0.8g/cc (Table 2) - with a charge length greater than eight times the blast hole diameter. The tables have a factor of safety of 150 per cent ie if the stemming length in every blast hole is equal to the appropriate value in the tables, fly rock should not be thrown more than two thirds of the corresponding evacuation distance. For example, if a charge density of 1.2g/cc is loaded into102mm diameter holes, and every hole has a stemming length of 2m, the evacuation distance should be 300m but fly rock should not be thrown more than 200m. Adjustments for small charges For blast hole diameters not listed in the tables, estimates of minimum stemming lengths can still be calculated for the required evacuation distances using these tables. When blasting ramps and thin seams, it is common for some blast holes in the pattern to contain charges of lengths shorter than eight times the blast hole diameter. The amount the minimum stemming length can be reduced (from the values contained in Tables 1 and 2) for short charges depends on the ratio of charge length to blast hole diameter. Table 3 shows adjustments to the minimum stemming lengths in Tables 1 and 2 for short charges of various charge length to blast hole diameter ratios, for both ANFO/emulsion blends and ANFO. For example, if a charge of 1.2g/cc is loaded into blast holes of 102mm diameter, and no hole in the blast pattern contains a charge longer than 400mm (ie Chg length/dia = 4), then the stemming length required for an evacuation distance of 300m (refer to Table 1) is 1.7m (0.86 x 2.0). Minimum distances for blasting boulders Packaged, low explosives should be used to crack boulders. High explosives with a high powder factor are likely to shatter a boulder and throw fly rock more than 300m. Ensure the blast hole is drilled to the correct depth and has adequate stemming when using packaged low explosives. If a high explosive has to be used, a powder factor of between 0.1 and 0.15 kg/m 3 is recommended, depending on the condition and type of rock. All boulders should be covered to reduce the risk of fly rock. Stemming materials Crushed, angular rock should be used for stemming materials in the blast holes to prevent rifling and fly rock. This material is safer than fine drill cuttings or odd sized and rounded rocks because it: interlocks wedges against the sides of blast holes to resist ejection displaces water and maintains frictional properties in wet blast holes. For effective distribution of the blast, the size of crushed rock should relate to the blast hole diameter (see Table 4). Protective covers Protective covers should only be used as an additional safety precaution for all general blasting operations regardless of stemming length to prevent fly rock damage to nearby facilities, structures or equipment. For larger blasts, more effective measures should be used to control risk. The common forms of protective covers are blasting mats or 2m of clean, stone-free fill. The following precautions should be taken when using blasting mats: cover the rock with a layer of sand or sandbags, at least in the area of the blast hole collar, to protect the mat from damage only the blast holes that can be adequately covered by blasting mats should be fired at the one time do not place rock or debris on top of mats, as these may become missiles if firing blast holes in sequence, only use short delay detonators (millisecond type). Long delays (due to half second delay detonators or safety fuse wiring) may lift the mats off the remaining unfired blast holes do not use mats made from wire rope or steel rings near overhead power lines use care when laying mats to prevent damage to connecting wires or detonating cord trunklines. Planning an exclusion zone Once evacuation distances have been calculated, a plan can be prepared for the exclusion zone showing the following features: site location (map reference) and direction of north outline for exclusion zone and distance from the blast outline of roads inside and going outside the zone location and legend for all site features eg houses, pipes location of all above and below ground utilities location of any protected works, public places and vulnerable facilities location of the area/object to be blasted, the firing point and any shelter location of sentries 3
location of the explosives storage areas location of first aid/first aider/first aid vehicle location of the vehicle car park and the equipment parking area. Assigning roles to key personnel Table 5 shows typical responsibilities for key people operating an exclusion zone: Table 4 - Crushed rock size for blast hole diameters Blast hole diameter (mm) Crushed rock sizing (mm) 50-130 6-13 130-200 13-20 Table 5 - Examples of tasks and responsibilities for key people Shotfirer Sentries Overall responsibility for the conduct of the blasting operation including the establishment, maintenance and disestablishment of the exclusion zone. Briefing and positioning sentries. Collecting sentries during disestablishment. Ensures the removal of all mobile plant/dangerous goods/explosives/vehicles to an area outside the exclusion zone. Supervises the removal of any fly rock or debris on roads or other areas. Ensure no entry into the exclusion zone. Provide information to the shotfirer of any suspicious activity/trespassers near the exclusion zone. Liaise with the members of the public about the exclusion zone and any inconvenience caused by the operation. Liaise with the emergency services and the shotfirer about any matter raised (ie ambulance access). Maintain communication with the shotfirer on the allocated frequency. Responsibilities of others at the site First aider Supervisor Drillers Contractors Workers Provision of first aid as required. Removal of drilling equipment from the exclusion zone. Ensure that all persons at the site, including contractors and their workers, follow the shotfirer and supervisor s instructions on the requirements of the exclusion zone. Follow instructions of the shotfirer and supervisor on the requirements of the exclusion zone. Establishment of the exclusion zone Written procedures should be provided for establishing the exclusion zone. Procedures should include: briefings for all persons working on site about the operation of the exclusion zone eg waiting areas/approximate timings/warning sirens/signals contact details for all contractors associated with blasting operations including drillers, suppliers, traffic management, waste removal and plant operations identification of the sentry points checks to ensure sentries have personal protective equipment, communication equipment (ie portable radio and mobile phones as back up) and other appropriate sentry equipment before being posted posting sentries, briefings for them at their location and ensuring copies of the briefing are at each control point. testing of communications between the firing point/ shotfirer and the sentries a list of all areas to be cleared such as houses, roadside rest areas, toilets, under bridges etc and a schedule for checking them before firing putting control measures in place, such as barriers and signage, to prevent access into cleared areas once sentries are in position, clearance checks (by the shotfirer/supervisor) of all areas in the zone, including checks that barriers are in place and warning signs positioned final notification by the supervisor to the shotfirer that the exclusion zone is established and the site is secure warning procedures before firing are according to the shotfirer s requirements. 4
Emergency services and other authorities All necessary agencies (police, fire authority and air traffic control) should be notified about the blasting operation and the exclusion zone and contact details made available to the shotfirer and key personnel. Discussions with emergency services and other authorities should cover: timings and procedures for notification notification for fire or explosion or incident to appropriate authorities (WorkSafe Victoria and fire authority) procedures for safe passage of emergency vehicles such as police, fire and ambulance in and out of the exclusion zone. In the case of trespassers being detected in the exclusion zone: the sentry reports to the shotfirer and awaits further instructions the shotfirer stops blast operations police are called if trespassers will not leave the exclusion zone. Delays and misfires In poor weather, the loading of the shot may need to be delayed until it is safe to resume. If the shot has to remain loaded overnight: the shotfirer should ensure the firing circuit is safe the exclusion zone has to be secured eg barriers and warning signs relieving sentries may be required throughout the night sentries are provided with appropriate communications equipment and contact details for key personnel in case of trespassers or emergencies. Where the exclusion zone has been disestablished, the procedure for re-establishing the zone should be re-started with all steps to be completed. The BMP must include a procedure for dealing with misfires. Disestablishment of the exclusion zone The exclusion zone needs to be maintained until the site has been cleared and is ready to be returned to normal conditions. Clearance of all areas, including public places and toilets, involves the supervisor: advising the shotfirer of any fly rock or debris on roads or other areas and removing it identifying fumes in underground areas collecting all blasting equipment advising the shotfirer that the area has been cleared. People involved in the blasting operation and sentries should remain at their control point until advised by the shotfirer that the area is clear. The shotfirer should collect all sentries from their control points once the area is disestablished. Further information Contact the WorkSafe Victoria Advisory Service on 1800 136 089 or go to worksafe.vic.gov.au Australian Standards Australian Standard AS 2187.2: Explosives Storage and Use Part 2: Use of Explosives standards.com.au The tables and other information in the document have been adapted from: Flyrock Range & Fragment Size Prediction. Cameron K. McKenzie, Blastechnology Australia. Published in the International Society of Explosives Engineers 2009G Volume 2 Selection of Stemming Length. A presentation by Cameron K. McKenzie, Blastechnology, Australia, cameron@blastechnology.com Note: This guidance material has been prepared using the best information available to the Victorian WorkCover Authority and should be used for general use only. Any information about legislative obligations or responsibilities included in this material is only applicable to the circumstances described in the material. You should always check the legislation referred to in this material and make your own judgement about what action you may need to take to ensure you have complied with the law. Accordingly, the Victorian WorkCover Authority cannot be held responsible and extends no warranties as to the suitability of the information for your specific circumstances; or actions taken by third parties as a result of information contained in the guidance material. WorkSafe Victoria is a trading name of the Victorian WorkCover Authority. 5