Preventing and Controlling Flyrock
Last Updated: 1/11/2018 11:48 a.m.
If you are involved in the world of mining or construction, blasting is inevitable. Whether you need to free mineral from rock, remove existing structures or otherwise reform the environment to achieve your goals, there are situations where the best, or the only solution, is blasting — which means explosives.
There are many hazards inherent in the use of explosives, not the least of which is flyrock. In fact, flyrock may be the greatest threat related to working with explosives, and it's something that those involved in the blasting situation may not realize. They may be primarily concerned about staying out of the blast radius and thereby avoiding being damaged by concussive force or ground vibrations, not realizing that flyrock may create a much greater danger. Why is flyrock so dangerous, and what is flyrock, exactly?
Image Courtesy of Halen
What Is Flyrock?
Flyrock is created when the force of an explosion projects rock fragments in varying directions that exceed the desired or expected distances from the blast face. Since the trajectory, size and speed of flyrock are difficult or impossible to anticipate, flyrock can create a tremendous danger for workers on your site. To fully understand flyrock, why it can be such a problem and how you can avoid flyrock-related injuries, it is first important to understand the causes of flyrock.
What Causes Flyrock?
So why does flyrock happen? Flyrock is generally a result of poor blast design or incorrect application of a good design. In addition, adverse rock conditions that lead to venting of pressurized blast-hole gasses can generate flyrock. Another common cause of flyrock can come from charging and firing mistakes, such as:
There are five main types of rock bursts:
- Flyrock Due to Design Error: Design errors that can result in flyrock include spacing holes too close together, using large blast holes for small benches, drilling deviations, variations in burden that cause an uneven blast face and inadequate burden.
- Flyrock Due to Adverse Rock Conditions: Rarely is a rock face perfect for blasting. Problems that can lead to excessive flyrock can include faults, cracks, discontinuities, weak planes, open fractures, open joints, mud seams and other rock deformities.
- Fault-slip burst: Fault-slip bursts are caused by the reduction of shear resistance and an increase in shear force across a fault line. Most fault-slip bursts occur in deep mines where the amount of stress acting on the fault is decreased due to nearby mining operations. Fault-slip bursts tend to release a large amount of seismic energy due to the fact that there is an instantaneous relaxation of the strain that was stored in the rock surrounding the slip or rupture.
- Flyrock Due to Charging and Firing Errors: Charging and firing errors that can cause flyrock include a concentration of free-flowing slurries at the bottom of holes, simultaneous firing, improperly sized stemming material, stemming columns that are too short and top initiations.
Understanding these causes of flyrock can make it much easier to take the necessary steps to minimize flyrock and flyrock damage on your site.
Why Is Flyrock So Dangerous?
Despite the fact that flyrock uses only about one percent of the explosive energy caused by the blast, it is responsible for up to 40 percent of injuries, as opposed to, for example, ground vibration. One can easily understand this when we think of flyrock as small projectiles fired with great force by exploding gasses. Essentially, the effect of flyrock is similar to spraying an area with bullets from a machine gun.
Complicating matters is the fact that separating pieces of rock from a rock face is the goal of blasting, whether it is actually to get at the minerals within the rock face or to get at what is behind it. Thus, blasters have every intention of creating this debris. However, the goal is to do it with controlled throw – knowing exactly where the pieces are going to go and making sure not to be in range of them.
Unfortunately, predicting the trajectory and amount of flyrock has proven to be a very inexact science. While steps can be taken to minimize flyrock and one can generate some reasonable predictions about rock throw, there are too many random elements to predict the trajectory, range and size of all explosive debris accurately.
This creates a massive problem for project managers because it is so crucial that they get these calculations right. Underestimating flyrock predictions can put people's lives and the company's property in danger while overestimating can impede the progress of the project. Studies to try to more accurately predict the impact of flyrock in various blasting situations have proven costly and not yielded highly satisfactory results.
While it is not currently possible to prevent the creation of flyrock itself, almost all flyrock injuries and fatalities, as well as flyrock damage to property, is avoidable when taking the proper precautions. Too often, people on mining or construction sites fail to anticipate the problems flyrock will cause, or they think of it as a ‘necessary evil' and hope for the best.
This kind of thinking can only lead to tragedy. Then there is the fact that some industries and situations that are not mining or construction related can also be prone to an unanticipated explosion, and the people in those situations often have no preparation or protection against flyrock whatsoever. Clearly, this is a problem people need to address.
The solution, then, in addition to being aware that flyrock will happen and that it will be dangerous, is to respond accordingly with these three steps:
- Take all the necessary precautions to minimize the damage flyrock can cause.
- Employ best practices to make the amount of created flyrock as small as possible.
- Have adequate protection products to shield people and property from unanticipated flyrock.
Precautions to Take
Because flyrock can be so dangerous, it's important to exercise care when blasting. Precautions that can limit your exposure to flyrock damage include:
- Parking all vehicles and equipment a safe distance from the blasting area whenever possible
- Staying behind a blast shield or blast mats for flyrock protection during blasting
- Making sure everyone has evacuated the blast area before proceeding
- Always following the supervisor's instructions
- Scrupulously guarding the access roads to the blast area and otherwise maintaining good blast site control
Blasting Best Practices
You can greatly control flyrock by using proper blast practices. These practices can include avoiding secondary blasting of boulders, making sure fuses are long enough to avoid overcharging, clearing loose stones from the blast site and clearing water from the blast holes. To avoid burden-related flyrock problems, it's important that bore holes not be angled, shallow or overloaded. Other flyrock control best practices include:
- Make sure the holes are properly collared relative to the inclination of the face. Undercharging the front row holes will not protect you from flyrock, as you will get flyrock out of the vertical catering of the holes at the rear.
- Make sure the stemming length is greater than the hole burden. Be sure to use a quality stemming material to avoid explosive gasses venting through the stemming column prematurely. Choose crushed angular rock over fine drill cuttings for stemming material.
- Make sure when connecting delay devices in the holes that you double-check the initiation sequence so you do not initiate the blast holes out of sequence.
- Try to keep your face length-to-width ratio between three and four to minimize flyrock.
Using Blast Mats for Flyrock Protection
Starting a mining or construction job without having blast shields or blast mats for preventing flyrock damage could be a catastrophic error. Flyrock is inevitable, but sustaining injury or property damage due to flyrock is not.
The safety that proper flyrock protection can bring far outweighs any cost. And flyrock protection isn't just for mining and construction operations, although blasting mats are a must at any mining or construction site. They can also be useful in chemical laboratories, manufacturing plants or anywhere there is a possible unexpected explosion risk.
Your Number One Source for Flyrock Protection Products
TM International, LLC, a leader in explosive flyrock protection, offers Mazzella blasting mats for preventing flyrock. Mazzella is one of the most trusted and most popular names in blasting mat manufacturing. They have been producing explosive debris protection for over 100 years, since the development of the legendary New York City subway system necessitated the invention of the wire rope blasting mat.
If you've ever used the New York City subway system, you know it's an impressive maze of underground tunnels that snakes through virtually the entire city and the outer boroughs. Creating such a feat of human engineering required those on the project to do a lot of blasting to excavate those tunnels. This blasting not only presented a danger to the workmen, but also potentially to the houses and people living and walking on the streets above.
Civilian casualties resulting from making the subway happen would have been unacceptable, so a new, more effective solution was needed. It came in the form of a steel wire rope mesh that was lightweight enough to move around the subway system, but strong enough to block any debris from hurting innocent bystanders.
The solution was so effective that it has endured for over a century, and we wouldn't choose any other type of product for the blast mats we sell. Until they come up with a better idea than these steel wire blast mats — which we don't see happening anytime soon — that's what we'll provide.
Advantages to Purchasing Blast Mats for Flyrock Protection from TM International, LLC
These mats are economical, environmentally friendly and recyclable. You won't use them once and have to buy whole new mats for each blasting scenario. Naturally, providing your people and surroundings with the greatest level of protection is paramount, but if you're in charge of a project, you always need to keep your eye on the bottom line.
TM International, LLC helps you do that, with efficient, highly cost-effective solutions for preventing flyrock damage. In addition to the fact that you won't pay twice, you will also find that they are easier to transport to your site because more of our mats fit in each shipment. These steel cable mats weigh only 16.5 pounds per square foot. Also, they are faster to install and remove, and they can be used in any blast environment as well.
Unlike rubber blast mats, these steel cable blast mats are fireproof, so you won't lose your mat to fire, a common occurrence around blasting sites. They also vent gasses, so you have more control.
Additionally, if you are working a green construction site, using rubber blast mats to protect you is counter to your mission. Steel wire blast mats are not only more efficient, but they are also much more in line with a green vision for building. These blast mats can stand any explosive substance and work with any detonation device, so you can really use them in any project whatsoever.
Contact TM International, LLC and Protect Your Blast Sites Today
It is highly unlikely that the problem of flyrock is going away anytime soon. While there are some continuing efforts to understand how flyrock comes about and how to prevent it most effectively, the science of completely predicting the outcome of an explosion and preventing any unanticipated debris is still far, far off. There will be a need for high-quality blast mats to protect workers and property at blast sites for a long time.
TM International, LLC is passionate about making every worksite that includes blasting safer, and we do that every day by providing easy, efficient, highly-effective debris protection solutions to our customers. We don't want anyone anywhere in the world to suffer an unnecessary injury due to flyrock.
If you're interested in giving your worksite maximum protection, reducing the chances of equipment damage, injury and liability, while saving money and helping the environment, you'll want blast mats for flyrock protection from TMI International, LLC. We can't wait to help make your mining site, construction site or facility a safer place to be for you and the people you work with. We ship our mats anywhere in the world in a 20-foot container. For a price quote on any of our products or to learn more, contact us today.