Comparison of explosives

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For discussion purposes, the vast number of explosives in current commercial use, can be categorized into 4 groups. These are ANFO based explosives, slurries, emulsions, and accessories (including boosters, detonating cords and detonators).

Contents

ANFO Based

ANFO based explosives are the backbone of the explosives industry. Ammonium nitrate mixed with 5.5 % by weight fuel oil produces a very economical and effective explosive. Many compounds may be added to ANFO. Aluminum may be added to increase the bulk strength, perlite or other inert ingredients may be added to reduce the bulk strength for improved wall control, and the density of the prills may be increased to increase the bulk strength and marginally improve the water resistance. The main drawback of ANFO is it's lack of water resistance.


Anfo Explosive Property Table

PROPERTY
ANFO
Borehole Size
Up to 1.5"
Borehole Size
2" to 4"
Borehole Size
6" to 8.5"
Density Blown 0.95 g/cc Poured 0.84 g/cc Poured 0.84 g/cc
Velocity of Detonation 3300 M/sec 3200 M/sec 4200 M/sec
Detonation Pressure 2600 KPA 2100 KPA 3900 KPA
Borehole Pressure 1300 KPA 1050 KPA 1850 KPA
Bulk Strength 1.12 1.0 1.0
Wt. Strength 1.0 1.0 1.0
Water Resistance None None None
Sensitivity Detonator Booster Booster
Storage 6 Months 6 Months 6 Months
Gas Volume Produced 954 l/kg. 954 l/kg. 954 l/kg.
Cost Factor (W.R.T. ANFO)


- By Weight


- By Volume

1.0


1.2

1.0


1.2

1.0


1.0


Slurries

A slurry is a mixture of nitrates such as ammonium nitrate and sodium nitrate, and fuel oil.


Slurries are made water resistant through the use of gums, waxes, and cross-linking agents. The variety of possible slurry formulations is almost infinite, and may be custom formulated for a specific job. The list of possible fuel sensitizers is especially long, although carbonaceous fuels, aluminum, and amine nitrates are the most common. Some slurries are dependent on entrapped air for their sensitivity, with cap- sensitive slurries dependant to a lesser extent.


Watergels and Slurries Explosive Properties Table

PROPERTY WATERGELS / SLURRIES
Borehole Size Up to 1.5" Borehole Size 2" to 4" Borehole Size 6" to 8.5"
Density 1.2 g/cc 1.25 g/cc 1.4 g/cc
Velocity of Detonation 4200 M/sec 4500 M/sec 4600 M/ sec
Detonation Pressure 5500 KPA 6500 KPA 8400 KPA
Borehole Pressure 2800 KPA 3200 KPA 4200 KPA
Bulk Strength 1.4 1.7 1.7
Wt. Strength 0.9 1.0 1.0
Water Resistance Excellent Excellent Excellent
Sensitivity Detonator Booster Booster
Storage One Year 6 Months One Year
Gas Volume Produced 560 l/kg. 700 l/kg. 960 l/kg.
Cost Factor (W.R.T. ANFO)


-By Weight


-By Volume

6.4


9.7

2.7


5.0

2.6


4.5

Emulsions

Emulsions share most of the same properties as slurries. The main difference is the mixture of the explosive components. Emulsions are prepared in the form of water-in-oil emulsions. The internal phase is composed of a solution of oxidizer salts suspended as microscopically fine droplets, which are surrounded by a continuous fuel phase. The emulsion thus formed is stabilized against liquid separation by an emulsifying agent.


As the components of an emulsion explosive are microscopic in size and the oxidizer and fuels are so intimately mixed, emulsions have a very high VOD and the resulting chemical reaction or detonation releases essentially all of the stored energy.



Emulsions Explosives Properties Table

PROPERTY
EMULSIONS
Borehole Size Up to 1.5" Borehole Size 2" to 4" Borehole Size 6" to 8.5"
Density 1.14 g/cc 1.2 g/cc 1.25 g/cc
Velocity of Detonation 5000 M/sec. 5000 M/sec. 5000 M/sec.
Detonation Pressure 7700 KPA 7500 KPA 6600 KPA
Borehole Pressure 3850 KPA 3750 KPA 3300 KPA
Bulk Strength 1.27 1.2 1.26
Wt. Strength 0.88 0.82 0.87
Water Resistance Excellent Excellent Excellent
Sensitivity Detonator Booster Booster
Storage One Year 3 Months 3 Months
Gas Volume Produced 786 l/kg. 786 l/kg. 786 l/kg.
Cost Factor (W.R.T. ANFO)


-By Weight


-By Volume

2.9


4.3

2.9


4.3

2.9


4.3


Accessories


Primers and Boosters

A primer is a unit of cap-sensitive explosive used to initiate other explosives or blasting agents. A primer contains a detonator. A booster is often cap sensitive, but does not contain a detonator. Although various products are used as primers and boosters, high strength ammonium gelatin, pentolite and TNT are the most commonly used materials, due to their high VOD and detonation pressures.


Detonating Cords

Detonating cords vary in the amount of the explosive contained in the core of the cord and the number and types of textile coverings for the core load. The core load is measured in grams per foot of PETN (pentaerythritol tetranitrate). The prime function of a detonating cord is to initiate detonators, boosters or explosive.


Detonators

Detonators currently in use can be divided into two categories, electric instantaneous and non-electric delay detonators. The instantaneous electric detonators are the most simple in design and are used almost exclusively to initiate either a single shot as in secondary blasting or to initiate a multiple delayed period blast.


The delay detonators employ a pyrotechnic or burning delay element in their construction to achieve the delayed effect. Various compounds are used to achieve the desired burning time for both the long period and short period detonators.


The important thing to remember regarding the delay times of caps is they achieve their delay by the use of this burning element. Prolonged storage, changes in relative humidity and temperature will effect this burning time. Although the accuracy of these delay elements has and is consistently improving, there will always be a scatter in the actual firing time of the detonator relative to its nominal or design firing time. The interval between delay periods was originally designed to reduce the probability of a higher numbered period cap, initiating before a lower period. Currently 90% of all caps will likely initiate within -3 to + 8% of their nominal firing times. Although these figures will vary somewhat with each manufacturer, the above numbers are a general guide and more specific numbers may be obtained from the supplier.

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