October 14, 2013
Initiating safe, successful blast practices
Successful blasts do not come about by chance. They come about via careful planning, assessment, and management of risk, the knowledge and teamwork of all personnel involved and, importantly, what physically happens on the bench during loading and firing of the blast. Focusing on these items allows the achievement of safe and effective blasting in various scenarios.
Bench practices are the most readily observed of these items and are what most audits of drill and blast focus on. This auditing is essential but what is often missed in this process is the link between safe and effective bench practices and control of the blasts, as well as the effect on the economics of a blast, if not implemented well.
This is not new, but it is necessary to remember that implementation of blast practices on the bench influences heavily the successful outcome of the entire drill and blast process.
Maxam, an Australian company that specializes in the supply of explosives to the quarry industry, places great emphasis on bench practices because it recognizes that if they are not carried out to the required standard, risk will increase to unacceptable levels. Cutting corners on the bench will lead to problems and potential for serious incidents to occur or, at the very least, ineffective blast outcomes.
What are bench practices?
Bench practices are activities directly related to activities carried out on the actual blast. They are generally controlled or supervised by the shotfirer, but other personnel may control some pre-blast activities. These activities and their influence on blast outcomes include (but are not exclusive to):
Blast area preparation, including delineation and securing of the blast zone. If this is not carried out to the set standard, then security of the blast could be compromised. Standards of blast delineation need to be sufficient to separate any person or equipment from the blast activities. Load-and-haul adjacent to a blast area is possible, but they must never occur if it potentially impacts on the safety of the blast area. Water management is also an often-overlooked consideration in this category, and it can be required to prevent damage to explosive columns and/or blastholes. No successful open cut blast can occur when water is located on or flowing over a blast.
Blasthole management post-drilling. This includes collar consolidation (collars that are stable and do not collapse), depth measurement, water content and backfill. No blast will be successful if blastholes are not drilled in the correct location at the designed angle and to the right depth. Blastholes are often overdrilled to counter fallback. If fallback does not occur, then the blastholes need to be backfilled and if they contain water this backfill must be with aggregate, not drill cuttings. If this does not occur, then broken ground and overblasting, excessive powder factors and environmental concerns will result.
Vehicle movement. This must be controlled from once drilling is completed until firing of the blast. Vehicle movement on blasts before loading commences may result in loss of depth of blastholes or even entire blastholes.
Stemming distribution. This must be carried out before loading commences, and it must be carried out so it does not interfere with blasthole collars or mobile sensitizing units (MSU) access on the blast. This is a simple task that is often carried out to a less than required standard, causing MSU movement concerns, lost blastholes (covered or filled with stemming) and increased risk of injury due to excessive manual handling.
Distribution of explosive accessories. Careful placement of explosive accessories is fundamental. Boosters and down hole detonators must be placed so they are easily located and not lost in drill cuttings or down blastholes.
Priming of blastholes. Primers should be made up at the blasthole collar and placed in the blasthole at the required depth. If this is not carried out as required, adequate initiation energy may not be transferred to the explosive and/or misfires may occur.
Loading of blastholes. Loading, especially pumped explosive product, must be carried out as per manufacturers’ instructions. Top loading is not recommended due to potential density concerns, as well as dislocation of explosive columns. Hose retraction rates must be carefully monitored to ensure complete explosive columns free of water or mud are loaded. Primers must be within this explosive column and not “floating” due to poor loading technique.
Stemming of blastholes. This is a very important part of the process and, if carried out in a poor manner, will lead to energy loss, flyrock and environmental issues. It was an accepted industry practice to use inexperienced personnel to stem blastholes but this is becoming less likely due to the recognition that this has led to incidents in the past. Stemming is vital to confine explosion energy.
Surface connection. This requires the training of personnel in correct connection techniques recommended by the manufacturer. When personnel do not take care and ignore manufacturer recommended procedures, issues will arise. This is where human error can be an issue, and risk becomes unacceptable when misfires occur as a result.
Disciplined staff. The firing of the blast requires very good discipline from the shotfirer and blast controllers, otherwise unacceptable risk will occur.
Post-firing blast check. This is an often-overlooked bench practice that is vital in bringing to a close the bench activities. If the blast is not checked fully and misfires are not identified and handled, then risk is raised to site personnel excavating the blast. Access to the blast area post-blast by personnel and equipment must also be managed as blasts often alter access routes and barriers are often required.
The common challenges in bench practices vary and may depend on the site, geology, process used, and experience of the personnel and the shotfirer involved. Maxam uses uSafe, a safety management system, as a control of its activities on-site, as well as active risk management on the bench. Risk assessments are conducted before activities commence on a bench, in which risks are discussed and controls implemented. Safety is never compromised.
Shane Slaughter is the senior adviser for technical applications at Maxam Australia. This story originally appeared in the July 2013 issue of Quarry, the official journal of the Institute of Quarrying Australia, and is reproduced with permission.