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Blasting 

 
Authors: Maurie Phifer (Montana Tech) and Priyadarshi Hem (Norman B. Keevil Institute of Mining Engineering - University of British Columbia)

Revised: March 2012

Summary

This review is an overview of the use of blasting in the mining industry. Topics covered include blasting consultants and suppliers of blasting equipment, some legal requirements for blasting, different blast design techniques, blasting contractors, and websites that offer additional information on blasting.

Introduction

Blasting is an essential part of the mining cycle. In virtually all forms of mining, rock is broken by drilling and blasting the rock. Blasting technology is the process of fracturing material by the use of a calculated amount of explosive so that a predetermined volume of material is broken. From the earliest days of blasting with black powder, there have been steady developments in explosives, detonating and delaying techniques and in the understanding of the mechanics of rock breakage by explosives. Good blast design and execution are essential to successful mining operations. Improper or poor practices in blasting can have a severely negative impact on the economics of a mine. The use of excessive explosives at a mine site can result in damages to the rock structures and cause unwanted caving and large increases in support costs.

Blasting is used in both open pit and underground mining operations. While traditional blasting utilized black powder and dynamite, there are many different types of explosives used today. Common explosives used in industry now are ANFO (ammonium nitrate/fuel oil), slurries, and emulsions. Many factors are taken into account when determining what type of blast design or explosive will be used. Rock type, density, and strength are all important factors, as well as fracture condition of the rock, and water conditions.

Blasting is one of the more hazardous aspects of mining. As reported on the website of the National Institute for Occupational Safety and Health:

Copied by permission from the

Between 1978 and 2000, 106 miners were killed and 1,050 were injured by explosives and breaking agents. In 2001, there were 7 blasting-related injuries and fatalities in the mining industry, compared to 140 in 1978. For the past two decades, most explosives-related injuries and fatalities in surface mines occurred when workers were struck by rock, either because they were too close to the blast or rock was thrown much farther than expected. The second leading cause was blasts that shoot prematurely. In underground mines, most explosive-related fatalities were caused by miners being too close to the blast, followed by explosive fumes poisoning, misfires, and premature blasts. Misfires lead to injuries and fatalities as miners try to shoot explosives that failed to detonate in the original blast. Premature blasts occur without warning while blasters are near the explosive-loaded boreholes; the explosive may be initiated by lightning, the impact of explosives being dropped down a dry borehole, or careless handling of the initiating system (blasting caps).


BLASTING IN SURFACE MINES

Most rocks require blasting prior to excavation in surface mines. Usually four types of explosives are used in surface mining: slurries, dry mixes, emulsions and the hybrid heavy ANFO. Selection of explosives depends on many factors, which primarily includes critical diameter, hydrostatic pressure, temperature, minimum primer weight, density weight strength, bulk strength, gap sensitivity, water resistance, loading procedures, coupling or decoupled properties, shelf life, reliability for bulk operations and overall drilling and blasting economics.

Blasting Practices in Mines, a paper by P. Sharma provide a quick overview on blast design and pattern in surface mines. Here are two pictures which I have taken from his paper:

Bench Blast Pattern in Quarry / Open Pit, from

Bench Blast Pattern in Quarry / Open Pit



Blastholes / Initiation patterns for shots fired to an open face, from

Blastholes / Initiation patterns for shots fired to an open face


BLASTING IN UNDERGROUND MINES

Most of the mining methods underground uses blasting as the primary method of rock excavation.
Underground Blasting provides a good overview for a wide variety underground blast designs. A typical arrangement for blasting in VCR methods of mining is shown below:
Arrangement of VCR Blasting

CONTROLLED BLASTING

Controlled blasting is a technique of blasting for the purpose to reduce the amount of overbreak and to control the ground vibrations. Following are the different types of controlled blasting techniques:

Pre-Splitting - this is an old but highly recognized technique with the purpose to form a fracture plane beyond which the radial cracks from blasting cannot travel. Other methods include Trim (Cushion) Blasting, Smooth blasting (contour or perimeter blasting) for underground mines and muffle blasting as a solution to prevent fly-rock from damaging human habitants and structures.


SECONDARY BLASTING

As stated in Webref,
"Irrespective of the method of primary blasting employed, it may be necessary to reblast a proportion of the rock on the quarry floor so as to reduce it to a size suitable for handling by the excavators and crushers available. Two methods of secondary blasting of rock are available. The first, called the plaster or mudcap method, is to fire a charge of explosive placed on the rock and covered with clay, the shock of the detonating explosive breaking the block. The second technique, known as pop-shooting, is to drill a hole into the block and fire a small charge in this hole, which is usually stemmed with quarry fines."

NON-EXPLOSIVES ROCK BREAKING

Non-explosives are used in areas very closed to sensitive structures. These are mostly used in construction industry for breaking oversize rocks, concrete etc. Rockfrac and Dexpan produce expansion chemicals which are used to break rocks. Most of these are used in limestone and sandstone quarrying. Expansion chemicals require huge amount of drilling.

NonexTM and Magnum BusterTM are another two types of non-explosives which uses non-detonating chemicals to break rocks.

Arrangement of VCR Blasting

Before and after NonexTM breaking


There are also hydraulic rock splitters that can be used where blasting is not permitted, or where it is not suitable. STM Construction Equipment is one of the companies that does this type of rock breaking. Also take a look at this video.




BLASTING INSTITUTIONS

Here are some journals and institutions that specialize in blasting:

(1) Journal of Explosives Engineering issued by the International Society of Explosive Engineers.

(2) Institute of Explosive Engineers. This site is mainly for explosives engineers in the UK, but also in other countries. They have lots of news about blasting and demolition, although a lot of it is for their members only. The institute's membership consists of engineers, scientists, logisticians, academics and legislators in disciplines such as excavation, quarrying, construction, demolition, and tunneling.

(3) Office of Surface Mining (OSM) Appalachian Regional Office offers an excellent Blasting Download page with a comprehensive list of U.S. Rules, Regulations, Research and Resources. The site also includes many reports, such as OSM reports, State reports, and US Bureau of Mines reports, as well as training aids, presentations and movies.


LEGAL

Before you blast you generally need a state Blaster's License. For example, California regulations state:

In order to obtain a Blaster's License, the applicant shall pass a written or an oral qualifying examination given at such times and places as determined by the Division. The examination shall include questions related to the license classification requested. Field tests may also be required as deemed necessary to determine the candidate's qualifications to perform the duties of a blaster. Every person requesting a Blaster's License shall:
(a) Be at least 21 years of age.
(b) Be able to understand and give understandable orders.
(c) Furnish satisfactory proof that he is proficient in the use and handling of explosive materials; the equipment and protective devices necessary for blasting operations; the safety precautions necessary in conducting blasting operations or furnish proof that he has had at least 3 years experience at blasting as an assistant to a person having a valid Blaster's License in various phases of the use and handling of explosives.
(d) Be of such moral character and physical condition that would not interfere with the proper performance of his duties and have the ability to direct and/or conduct blasting operations.

Help from a school is valuable; see http://www.cloc.com and http://www.alphaexplosives.com/safety-training.html

In Canada, each province has its own regulations regarding requirements for a blaster's permit. In each of the provinces, someone looking to obtain a permit must write a blasting exam and be knowledgeable about all health and safety requirements. In BC, the Worksafe BC site lists the certification requirements and examinations, as well as providing a link to the Ministry of Energy and Mines site that specifically deals with blasting permits for mine sites. This review does not cover each province or states license requirements but suffice to say that throughout North America, a permit is required before any blasting may done.


BOOKS

One of the best books available that covers open pit blasting principles and techniques is William Hustruid's, "Blasting principles for Open Pit Mining".

Then there is The Blasting Primer by Jim Ludwiczak. The author is a professional geologist, a certified and licensed blaster, and a blasting instructor. Visit his company's website, Blasting & Mining Consultants, Inc if you cannot get the answer from his book.


SOME BLAST DESIGNS

Bench blasting is a common blast technique most often used for open pit mines. By definition, bench blasting is blasting in a vertical or sub-vertical hole or a row of holes towards a free vertical surface. More than one row of holes can be blasted in the same round. A time delay in the detonation between the rows creates new free surfaces for each row.

One type of bench blast design is short-hole blasting which is usually limited to drilling rounds of 1.2 m to 5.0m length and hole diameters of up to 43 mm. Cut and fill and room and pillar underground mining methods commonly employ short-hole blasting. Both ANFO and water gels can be used for this type of blasting. Holes are generally drilled in a square pattern.

Longhole bench blasting is similar to bench blasting in open pits, using long holes drilled downward either parallel to each other or in slight rings to cover the stope area. Initiation of the blast is with a booster down the hole.

Ring drilling and blasting is done from a series of sub level drill drifts developed in the ore body. The drill pattern is designed to cover off the extent of the ore in the stope. This type of blasting will cause the ore to swell by 30%, and this must be allowed for when blasting otherwise the blast may freeze.

Crater or VCR blasting was developed by INCO in the mid-1970's for primary stoping, pillar recovery and raising. This type of blasting is made possible by using much larger diameter holes underground. Accuracy of drilling is essential for this type of blasting.

There are many different types of blast design and this review does not attempt to cover them all. Along with the importance of selecting the proper blast design other important factors that influence blast results are:

  • properties of explosives being used
  • the initiation systems,
  • the distribution of the explosive in the blast,
  • rock structure,
  • the overall geometry

COURSES

The EduMine course on blasting is one of the most comprehensive treatments of the theory of blasting that is currently available online. If you want to know how the gel moves into the pores spaces and then generates gas pushing the rock out of the way during the explosion, this is the course for you. This course provides "a review of blasting theory and blasting products, and emphasizes the design, assessment and optimization of blasting practices. The course focuses on drilling and blasting as it is applied in surface mines and quarries. Design methodology for safe and efficient blasting is provided. Monitoring and assessment to improve blast performance and reduce blast vibrations are discussed and examples of optimization programs are provided to illustrate the process.""

SUPPLIERS

The best pictures on the web of equipment to transport, store, and load blasting supplies is from AAMCOR LLC in Utah and they smell and sound like the rugged place it is.

In South Africa there is African Explosives Limited (AEL). They are also "well established in East, West, Central and Southern Africa, with production facilities and offices in Ghana, Mali, Nigeria, Tanzania, Ethiopia, Zambia, Zimbabwe and Botswana." AEL provides a wide range of products ranging from explosives, and initiating systems to blasting accessories and industrial products. AEL has developed the S200Eco range of emulsion - an Ammonium Nitrate/Calcium Nitrate (AN/CN) formulation, which they state is more environmentally friendly than other products available, and will help companies reduce their carbon footprint.

Dyno Nobel detonator

The Dyno Nobel website is the world's leading commercial explosives company with over 5,200 employees in 36 countries, research and technology facilities on four continents and sales of over US$ 1.2 billion per year. Dyno Nobel claims to have developed every major explosives innovation starting with the Safety Fuse in 1831. Other blasting advances include the development of slurry and water based explosives, and emulsion technology.

ORICA Mining Services maintains one of the best sites about blasting I have come across. If you need to blast or are simply interested in the technology, I can do no more than urge you to go to their sites. It will reward you.

CONSULTANTS

Here are a couple of the big companies that offer blasting services:

Orica Mining Services is the world's leading supplier of commercial explosives and blasting systems. They offer a number of what they call "Blast Based Services". The most recent and advanced services they offer are the Electronic Blasting Systems: i-kon, Uni tronic, and eDev. These systems are all about greater accuracy and flexibility, significant productivity gains, greater security and more safety features.

DMC Mining Services One of their specialities is mine shaft sinking. Here's what they say on their website: "DMC's expertise in mine shaft sinking is based on more than 100 years of combined manpower experience. During this time DMC has continuously worked to develop technical improvements, the most significant of which is the patented Long Round Jumbo technology which involves a process for blasting 5 metre long shaft benches and which has materially increased the speed at which shafts can be sunk."

Here is the rest of the InfoMine list of blasting consultants:

CONTRACTORS

There is sure to be somebody near you willing to be your blasting contractor. In South Africa, Rhino Blasting Contractors promises to do everything from swimming pools to mines.

In Western Canada, Westrail Construction Ltd. has been providing drill and blast services for over 30 years to some of the largest drilling and blasting projects in Canada. Some of the mines that Westrail has been employed at include Gibralter Mines, Endako Mines, Rabbit Lake Mine, and Green Hills Operation. Westrail works closely with northern communities in training and employing local people and services whenever possible.

SOFTWARE

WipFrag Granulometry Analysis Software (Photo: WipWare Inc.) Master Blaster is an inventory and blast management software system that dramatically improves documentation accuracy, minimizes paperwork, and allows for rapid search and retrieval of inventory and blast documentation. This innovative web-based software product enables blasters, support staff, and managers to have secure access to the most up-to-date information regarding customers, inventory, billing, seismograph and other blast data from anywhere in the world via the Internet.

Your staff accesses Master Blaster via a user name and password from their laptops or from the host system (internal server). A secure login page directs blasters to the appropriate data entry forms and directs managers, executives and support staff to the appropriate content management and report areas of the Master Blaster system.

WipWare Inc. supplies WipFrag. Here is their description of it: "Blast models, formulas, expected results, we all know that this approach to predicting blast results is useless without the tool to quantify what really matters; fragmentation. Our technologies root deep in the explosives industry, we understand the steps required to improve blast fragmentation, and the infinite number of variables which effect the results. Our technology empowers you with the tools you need to collect historical data, establish a statistical baseline and track subtle changes throughout the optimization process so you can make decisions based on fact, instead of theory."

Soft-Blast is a software system for blast design, analysis, and management. This software can be utilized for "surface, underground, or tunnel blasting applications, explosives supply, consultation, contracting and education". The software is available in packages or as stand-alone modules. Some of the applications of this software include extended blast and/or timing analysis, and a program to analyse digital images acquired in the field and determine the size distribution of your fragmented rock at any stage in the comminution process.

VIDEOS

Blowing 1 Million Tonnes of Iron-Ore (Discover Channel)

Surface Mine Blast

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