Blast Hole Liner

Designed to provide quick, hassle free lining of blast holes on the go.

Blast Hole Liners are securely packaged in convenient size packs which can be easily transported on site. Dispensing of liners down blast holes takes place speedily and effectively.

• Durable polyethylene material is abrasion resistant and watertight.
• Unique packaging method allows for efficient insertion of liner into blast hole without the risk of tangling or twisting.
• Liner unravels to take the form of the blast hole as it fills with emulsion.
• Prevents loss of emulsion into cracks and voids.
• Eliminates the need for costly adjustments to emulsion formulations in wet holes.
• Can be used with emulsion and ANFO.
• Allows for consistency of charge volume in blast hole.
• Improves productivity and ensures overall improvement in effectiveness of blasting.

Safe Working Procedure for Inserting the Blast Hole Liner

1. Select correct size liner for hole diameter.
2. Using scoop provided, fill tail compartment with dirt / soil / gravel.
3. When filled, pull cable tie closed securely.
4. Using spike on side of scoop, pierce corner of top end of bag.
5. Extract approximately 600mm of sleeve from open end of bag.
6. Hold firmly on to sleeve.
7. Drop bag down hole whilst holding firmly on to end of sleeve.
8. Fold end of sleeve and feed through hole in lid.
9. Place lid securely over open hole.

The Blast Hole Liner Site Test Trail

Please see the below extract from a site test trial report conducted in Zambia recently:

Today we trialled the blast hole 165mm sleeves in west 12. It was set in the manner of a time trial, to see if the mine would save time with our new easy to use packaging. At the same time we were looking for any other advantages it would bring. The trial was done using 36 holes on the old product and 36 holes of the Penhine Blast Hole Liner new product. The results were as follows:

The few advantages that were noticeable:

1. The Penhine Blast Hole Liner bag has a separate compartment for the weight, so if it does get damaged on the way down, emulsion will not escape when pumped.
2. There was less twisting in the plastic, should allow for easier placement of the booster.
3. The packaging is advantageous, as the labour does not need to carry a large roll to each hole.
4. Less fatigue as a result of the above. Also no strain on the persons back.(which the gents were complaining about).
5. A much faster placement time.

Step by Step Procedure for Inserting the Blast Hole Liner

Contact Clayton Hitchcock 

It is not uncommon to find unfired explosive in the muck pile after the blast. It is often concluded that the misfire probably resulted from a cut off or a missed hole and the incident is forgotten, until it reoccurs.

Originally a “misfire” meant that an explosive charge did not fire. “Cut off” is a general term used to either describe a cutting of the initiator leads, before it has a chance to energize, or cutting off the powder column by shifting rock beds. Missed holes are those where the initiator was not connected into the firing circuit.

Unfortunately, today whenever any amount of explosive is found after the shot, it is normally concluded that some type of cut off occurred and that the cut off was the reason for the unshot explosive. The blaster is normally confident that all initiators were connected into the circuit, therefore, a missed hole was considered unlikely. Although shifting beds can cause cut offs to powder columns and initiators in very seamy rock, where bed movement or movement through seams can easily occur, operators often blame cut offs as the problem for misfires in monolithic granite, limestone, or sandstone formation. How can this physically happen?

Misfires and cut offs have been blamed for many problems that result from improper behavior of a blasthole. Misfires or cut offs have become generic terms meaning something did not go as planned and either no explosive detonation or partial detonation occurred.

During the past few years, it has been generally recognized that there are many problems on blasts, which cause explosives not to detonate or partially detonate, releasing only a fraction of the potential energy. High air blast levels and high vibration does not mean efficient energy release, in fact, it can mean just the opposite. On some blasts, 30% to 50% of the holes did not detonated properly. This is not a rare occurrence. On many operations, each and every blast produces these types of statistics. Today there are diagnostic tools available, which have proven conclusively that these problems are occurring.

What is tragic is that our general acceptance of “misfires and cut offs” have lead many operators to the conclusion that misfires and cut offs are acts of God, which are normally geologically dependent and that they may not happen on the next shot; therefore, it probably isn’t worth the time and effort to figure out what went wrong. The truth of the matter is that once the problem is found and corrected the additional energy saved is available for fragmentation. Fragmentation can then vastly improve with no need of additional explosives or if 1 the fragmentation was satisfactory, the amount of explosives can be reduced. In either case, it can mean a saving for the operator and greater safety for all involved.

Causes of Malfunctioning Blastholes

It is necessary to change our definitions in blasting and refer only to those holes that did not shoot as misfires, and those that never received the detonation signal to fire as missed holes. In other cases, where blastholes did not function as intended and released little useful – energy, they should be called malfunctioning blastholes. Malfunctioning holes result from many different causes. The causes can be broken down into the following four general classes:

1. Insufficient energy release.
2. Initiator error or incompatibility.
3. Poor execution of the blasting plan.
4. Unusual local geology.

These four factors have a significant effect on the performance of the explosive in the blasthole and the amount of energy released into the surrounding rock. Examination of these four causes will show how they effect the energy release, breakage, violence and create unpleasant environmental effects.

Insufficient Energy Release

Inefficient energy release can occur from many causes. Field mixed explosives such as ANFO and ANFO – emulsion blends, which are bulk loaded, can have a highly variable energy – release depending on the mixture. The bulk mixed explosives need to be near oxygen balanced to produce maximum energy. The fuel oil content needed is inversely proportional to the amount of emulsion used in the mixture. For ANFO alone, the most efficient fuel oil content is 5.7% by weight. It is common to find ANFO with fuel oil content varying between 3% and 10%. A 3% fuel oil content rather than 5.7% produces an energy loss of at minimum 20%.

The behavior of the explosive during detonation in the blasthole is controlled both by the local environment in the blasthole and the effect of outside influences from the adjacent blastholes. A loss of confinement can be caused by holes shooting out of sequence, and” is but one example of an outside influence from an adjacent blasthole. Many factors can cause non-ideal detonations. Blastholes are normally fired on delays and all do not fire simultaneously. Adjacent holes “feel” the effect of high stress levels created by the stress wave passing the blasthole from other holes firing earlier. Depending on the type of explosive and the local environmental condition, the high stress levels, in some cases, can cause precompression or dead pressing of the main charge. Precompression can cause some explosives to fire inefficiently and release a small fraction of their available energy. In other circumstances, high stress levels can cause propagation from deck to deck or even from hole to hole within the pattern. In the case of propagation, blastholes fire out of sequence and will override initiator delays.

It must also be recognized that when blasts are designed we expect explosive products to release a specified amount of energy. The energy level of products, lot to lot, can vary, and in a some instances explosives release only a small fraction of their rated energy. Extended storage of the explosive after manufacturing can drastically change its characteristics and have significant effects on its response to local environmental conditions.

Initiators Error or Incompatibility

Selection of the proper initiator is critical to proper blasting performance. Too often, blasters are more concerned with price per unit and number of periods and do not pay sufficient attention to the actual firing time in milliseconds and the conditions of intended use. The improper selection of initiators can cause; destruction of initiators in adjacent charges, intended to fire on a later delay; and detrimental effects on the powder column. Initiators firing at the wrong time can cause breakage problems, as well as detonation problems for explosives in adjacent holes.

Initiators are placed in the blasthole to transfer the detonation signal from one hole to another at a precise time. In normal blasting operations, blastholes do not fire instantaneously; therefore, both the initiator and the explosive are subject to high pressure stress waves from adjacent holes. Whenever blastholes are used in close proximity to one another, initiators can be damaged or destroyed from the firing of adjacent holes. This destruction may cause the initiator to fire improperly or may cause the initiator to totally misfire. This phenomena is commonly called the water hammer effect. Operators must realize that some initiators will better withstand the effects of water hammer than others, and that in some applications this is a major concern when purchasing Initiators.

Improper use of detonating cord downlines can cause as much as a 50% loss of energy in the powder column. In other applications, the cord has been found to cause the explosive to prematurely bum, releasing little energy. When explosives are prematurely initiated by detonating cord downlines, the cord acts as an inefficient primer. The charge may deflagrate or go into a low order detonation. Either case will cause a significant energy loss.

The selection of initiators simply for sequencing holes is a common error. The precise number of milliseconds of time between initiator periods is extremely important in rock breakage. Initiator firing times are not precise and some initiators have large errors, both in nominal firing times and in the deviation from cap to cap, or what is called cap scatter. In order for blastholes to properly function the design of the pattern must consider both the true (nominal) firing time and cap scatter. If this is not done, holes commonly fire out of sequence. Methods exist to design patterns which will function properly in spite of the initiator inaccuracy. Poor timing is a common occurrence which causes holes to malfunction. As an example, if holes fire either out of sequence or without the proper time window from one hole to another, fractures will not necessarily move in the directions planned, instead the cracks can extend into adjacent holes. Figure 1 shows what can happen if holes fire out of sequence. Delay number 4 has fired before number 3. If adjacent holes suffer a loss of confinement or a disruption in the powder column, some of the explosive may burn, and some, depending on the degree of disruption, may not detonate. Having improper drill spacings and burdens can also cause cracks to move in the wrong directions.

Execution of the Blasting Plan

The operator has a significant influence on whether or not blastholes will function properly, and whether they will release their full energy. Poor drilling procedures such as; closely spaced holes, can subject neighboring holes to high stress levels, and can cause problems with the explosive, such as dead pressing, propagation, and non-ideal detonation. Therefore, the pattern design, pattern execution and the blasthole drilling are extremely important for proper results. The manner in which the blaster loads the holes also has an effect on performance. For example, insufficient stemming between decks within a hole, invites propagation from deck to deck. Bridging of bulk explosives or cartridge hangup can also lead to loss of energy or unexploded explosive within the blasthole.

When misfires occur in the field and one examines the cause of the misfire, it is sometimes found that the blasthole initiator was never tied into the circuit, and a missed hole was the problem. Care during hookup, to insure that all initiators are tied in, is extremely important. Another factor, which has caused serious problems in blasting, is the improper hookup of initiators. Many initiation systems used today require that the initiators be hooked together into a particular series to provide the proper detonation path from hole to hole. If the initiators are hooked into the series in improper order, holes will fire out of sequence.