Elongated flexible detonating device

There is provided an elongated, flexible unitary detonating device of indeterminate length for detonating a selected explosive material within a bore hole. The detonating device includes, in combination, a detonating cord capable of detonating the selected explosive material when initiated while in direct contact with the selected explosive and a flexible energy absorbing layer formed around and carried by the detonating cord. The energy absorbing layer is formed from an energy absorbent material and has a radial thickness sufficient to preclude detonation of the selected explosive in direct contact with the energy absorbing layer when the detonating cord is initiated. In addition, an arrangement is provided for allowing stripping of the energy absorbing layer from the detonating cord at any selected position along the detonating cord to expose a portion of the detonating cord.

This invention relates to the art of detonating devices for explosives of 
the type placed in bore holes and more particularly to an improved 
elongated, flexible unitary detonating device for detonating from the 
bottom of a bore hole without using blasting caps or other highly 
sensitive explosives in the bore hole. 
The present invention relates to an elongated detonating device, similar in 
appearance to a detonating cord, which device is primarily used for bottom 
detonation of non-cap sensitive explosives, such as NCN and certain 
slurries, placed in a bore hole. The invention will be described with 
particular reference to this application; however, the invention has 
broader uses and may be employed for detonating certain cap sensitive 
explosives. 
BACKGROUND OF INVENTION 
In many explosive applications, a series of elongated, deep bore holes are 
provided in the material to be fragmented. Such bore holes are filled with 
an explosive material which is chosen on the basis of explosive 
characteristics and cost. In many instances, NCN and a variety of slurries 
are used as an explosive material because of their low cost. When these 
explosives are used, dynamite or cast primers are the commonly employed 
detonating devices. It has long been known that substantially more energy 
can be transmitted to the surrounding burden, if the explosive in the bore 
hole is detonated from a lower position. Consequently, substantial 
development work has been devoted to systems for detonating the explosive 
column at a lower position of a bore hole. The most widely used system for 
this purpose involves the use of an electric blasting cap. An electric 
blasting cap includes a housing having an explosive charge, which is 
capable of being detonated by an electrically heated resistance wire 
connected to two wires known as "leg wires" . The leg wires extend from 
the blasting cap to a remotely located source of electrical current. When 
using this type of detonating system, the electrical blasting cap can be 
positioned below the surface of the explosive column within a bore hole 
with the leg wires extending from the blasting cap, through the explosive 
column and to any remote position. A current source applied across the leg 
wires fires the blasting cap and detonates the explosive column. This type 
of electrical system has proven quite useful for lower detonation of bore 
holes; however, certain disadvantages have become apparent. In blasting 
locations, electrically operated equipment is often used for various 
non-blasting work. Many times ground cables must carry electrical current 
for operation of such equipment. In addition, certain equipment generates 
electrical current for use by the equipment itself. Since the blasting 
sites are exposed to atmospheric condition, it is possible to experience 
lightning and static electricity conditions. It has also been found that 
when a number of leg wires are connected for simultaneous detonation of 
several bore holes, these conductive wires can form receiving antennas 
which will generate electrical currents when exposed to electromagnetic 
energy sources, such as radio transmitting antennas. All of these sources 
of stray electricity present a potential for inadvertent detonation of 
electrically actuated blasting caps after the caps are placed into bore 
holes. To overcome the possibility of inadvertent detonation by stray 
electricity at a blasting site, expensive precautions are required. 
Because of the disadvantages of electrical blasting caps, it is somewhat 
common practice to detonate the upper portion of the explosive column in 
bore holes. In this manner, standard detonating cord can be used with a 
primer located at the upper portion of the explosive column. The 
disadvantages of electrical blasting caps are avoided; however, the 
additional explosive strength experienced with lower detonation of the 
explosive column is not obtained. To realize the benefit of lower 
detonation without using an electrical system, substantial effort has been 
devoted to development of a positive nonelectrical system for detonating 
explosive columns at a position deep in a bore hole. 
If a standard detonating cord, which does not present the basic 
disadvantages of an electrical system, is extended through an explosive 
column in a bore hole filled with NCN, slurry, dynamite or other explosive 
material, the explosive column is detonated from the top when the 
detonation wave in the cord reaches the explosive. This is due to the fact 
that the explosive wave of standard detonating cord is sufficiently strong 
to explode non-cap sensitive explosives in direct contact with the cord. 
For this reason, standard detonating cord can not be used for lower 
detonation of explosive columns in the confinement of bore holes. 
To provide lower detonation of explosive columns, certain modifications 
have been made in detonating cord. The first proposed modification of 
detonating cord has been the development of a low energy detonating cord, 
often known as LEDC, which includes a small continuous lead tube filled 
with standard high explosive material with an approximate distribution or 
load of 1-2 grains per linear foot. This compares with a standard 
distribution of 15-40 grains per linear foot for "economy" cord and over 
50 grains per linear foot for reinforced cord. By using this low explosive 
loading, in a flexible lead tube, sufficient detonating energy is created 
at a cut end of the tube for the purpose of initiating a blasting cap. As 
is known, a blasting cap is a standard component having a small primary, 
highly sensitive charge for converting a relatively small detonating 
force, such as created by a low energy cord, into a higher force for 
detonating a secondary charge. The secondary charge has sufficient bulk to 
detonate the explosive in a bore hole. This type of system requires a good 
physical contact between the lead tube and primary charge of the blasting 
cap. To assure a sound connection to the lead tube, the blasting cap is 
generally secured onto the detonating cord by a relatively expensive 
manufacturing operation performed at the manufacturer's plant. 
Consequently, the cap and cord must be purchased as a unit with the 
approximate length of cord being attached. If the cord length is not 
proper, it is not possible to splice the cord for changing its length. 
This caused difficulties in the field. This low energy type of system can 
be used for lower detonation if the proper connections are made at the 
initiating end and the blasting cap end. However, because of the 
sensitivity required to initiate this detonating cord, this system does 
not produce uniform results. If the blasting cap is not initiated after 
placed in a bore hole, it remains at the bottom of the bore hole in a 
dormant condition. As is well known, care must then be taken if the 
blasting cap is to be removed. Since the blastinc cap includes a very 
sensitive primary charge an inadvertent blow can detonate the cap and any 
explosive adjacent thereto. Because of the uncertainty of ignition, the 
possibility of leaving a dormant blasting cap in the bore hole, and the 
high expense of this type of system, this system has not proven the 
solution to the problems outlined above, although the low energy wave of 
the detonating cord does allow it to pass through certain explosive 
material to the lower portion of an explosive column in a bore hole. 
To overcome the disadvantage of requiring a demanding physical contact 
between the low energy detonating cord at both ends thereof and the cost 
contaminant thereto, a further type of lower energy detonating cord has 
been developed using the concept of a hollow plastic tube with the inner 
walls of the tube coated with a slight amount of high explosive material. 
This second type of low energy detonating cord is described in U.S. 
Letters Pat. No. 3,590,739. Approximately 0.5 to 2.4 grains per linear 
foot of explosive material is used on the inside surface of a hollow 
plastic tube for detonating purposes. By using this structure, it is 
possible to extend the hollow detonating cord through an explosive column 
to a lower portion of a bore hole; however, since relatively low energy is 
created by the small amount of high explosive within the cord, this system 
again requires a sensitive blasting cap in the bore hole itself. By 
requiring a blasting cap in the lower portion of the bore hole, as 
required in the first low energy type of detonating cord, a very sensitive 
primary charge is used in connection with a secondary primer charge. Thus, 
if detonation does not occur, expensive precautions are necessary to 
remove the blasting cap at the bottom of a bore hole. 
The two prior attempts to provide a blasting cord which can pass through 
the explosive charge of a bore hole for lower detonation thereof each have 
common disadvantages. They are both predicated upon the theory that a 
minute distribution or load of high explosive within the cord, less than 
about 4 grains per linear foot, is the proper procedure for preventing 
detonation of the charge as the cord is exploded through an explosive. The 
reduction of loading in the core of a blasting cord for reducing the 
probability of premature detonation in a bore hole causes substantial 
disadvantages. First, each low energy system requires a blasting cap in 
the bore hole. The low energy cord has insufficient usable energy for 
detonating a cast primer without a highly sensitive charge found in a 
blasting cap. Since these low energy cords use the concept of reduced 
available energy, detonation is less positive, especially in the variable 
ambient conditions within a bore hole. Another distinct disadvantage of 
low energy cord is the inherent inability to transmit a detonating wave to 
or from a standard detonating cord. Consequently, it is not practical to 
provide a standard detonating cord as a trunk line for direct connection 
to a low energy cord forming a down line of a bore hole. Thus, to initiate 
the low energy detonating cord, a strong positive initiating force must be 
exerted on the cord itself. This results in complications when multiple 
bore holes are to be shot simultaneously. In addition, low energy cords 
can not detonate from one cord to another. Thus, splicing of such cords is 
not practical. With all of the disadvantages inherent in using low energy 
detonating cord, relatively expensive blasting equipment is required and 
substantial expense is incurred by using such cord. Additional expenses 
are incurred to assure the safety of the site when an attempted detonation 
by low energy cord fails. 
SUMMARY OF INVENTION 
The disadvantages of prior attempts to provide a detonating cord which will 
detonate an explosive column within a bore hole at the lower position 
thereof are completely overcome by the present invention which relates to 
an elongated, flexible unitary detonating device of indeterminate length, 
which device has insufficient transverse energy to detonate an explosive 
column in a bore hole when the detonating device is extended through the 
bore hole to a lower position. The invention has sufficient strength to 
provide a positive detonation at the lower portion of the bore hole 
without requiring an intermediate energy increasing charge, such as found 
in conventional blasting caps. 
In accordance with the present invention, there is provided an improvement 
in a detonating cord having an outer surface and including a center core 
of particulate high explosive material, a tensile strength increasing 
layer surrounding the core and a moisture impervious layer surrounding the 
core. This improvement involves the use of an energy absorbing layer 
surrounding the outer surface of the detonating cord and releasably 
secured thereto. By utilizing an energy absorbing layer surrounding the 
outer surface of a detonating cord, it is possible to preclude detonation 
of an explosive column in a bore hole, even though the cord extends 
through the explosive to the bottom part of the bore hole. By releasably 
securing this energy absorbing layer onto the aforementioned outer surface 
of a detonating cord, it can be stripped at both the upper and lower ends 
so that a detonating wave may be initiated in the cord by either another 
standard detonating cord or other appropriate blasting machines. In the 
lower portion of the bore hole, exposure of the inner cord by stripping of 
the energy absorbing layer therefrom allows a substantial increase in the 
transversely transmittable energy usable for detonation. By this 
arrangement, lower detonation of a bore hole is made possible without the 
distinct disadvantages experienced when using low energy types of 
detonating cord having a grain load of less than about 4 grains per linear 
foot. 
In accordance with another aspect of the invention, there is provided an 
elongated, flexible unitary detonating device of indeterminate length for 
detonating a selected explosive material within a bore hole. The 
detonating device includes, in combination, a detonating cord capable of 
detonating the selected explosive material when initiated while in direct 
contact with the selected explosive; a flexible energy absorbing layer 
formed around and carried by the detonating cord, with the energy 
absorbing layer being formed from an energy absorbent material and having 
a radial thickness sufficient to preclude detonation of the selected 
explosive material when in direct contact with the energy absorbing layer 
while the detonating cord is initiated; and, means for allowing manual 
stripping of the energy absorbing layer from the detonating cord at any 
selected position along the detonating cord. 
In accordance with the preferred embodiment of the invention, the 
arrangement for allowing stripping of the energy absorbing layer from the 
internal detonating cord is a loosely woven yarn covering the outer 
surface of the detonating cord and covered by an extrusion of plastic 
which does not extend through the yarn and into fixed engagement with the 
surface of the detonating cord. With this arrangement, any section of the 
elongated element may be circumferentially cut and stripped to expose the 
internal detonating cord, which cord is sufficiently high in explosive 
force to detonate the explosive through which the cord extends. The 
loosely woven yarn provides a cushion between the outer surface of the 
inner detonating cord and the outer plastic extrusion over the layer of 
yarn. This cushion of compressible loosely woven yarn completely 
surrounding the inner detonating cord absorbs a certain amount of 
transversely transmittable energy, even though the yarn layer serves the 
primary function of a separating seam or joint between the energy 
absorbing layer and the inner cord. The outer plastic energy absorbing 
layer, which is relatively thick, coacts with the yarn to dampen and 
reduce the transmitted energy available when the inner detonating cord is 
initiated. 
In accordance with the invention, the inner detonating cord can have an 
explosive core with a longitudinal distribution of particulate high 
explosive material in the general range of 6-20 grains per linear foot. In 
practice, the explosive distribution is approximately 11-13 grains per 
linear foot. As can be seen, this type of cord, although it provides the 
bottom detonation characteristics, does not utilize the concept of reduced 
available energy, as previously used for lower detonation of bore holes. 
Thus, the present invention is a departure in kind from prior attempts to 
develop a nonelectrical cord which will extend through a column of 
explosive in a bore hole for bottom detonation. 
In accordance with another aspect of the invention, the above mentioned 
invention is connected to a standard cast primer in the lower portion of a 
bore hole by a unique connecting arrangement wherein the energy absorbing 
layer of the invention is stripped from the lower end of the detonating 
element and tied to a standard detonating cord which can be threaded 
upwardly through the explosive column and through secondary cast primers 
for successive upper detonation of the column after an initial lower 
detonation. The prior low energy detonating cords for bottom detonation 
could not be used for this purpose since they can not, by themselves, 
transmit a detonating wave to or from a standard cord. 
In addition, by using the present invention, a standard cord may be 
provided as a trunk line with the down lines formed from the invention. 
This is made possible by stripping the releasable energy absorbing layer 
from a selected upper portion of the invention and then intimately 
connecting this stripped portion with a standard detonating cord trunk 
line. The standard detonating cord will initiate the invention, which 
forms the down line to each bore hole. 
The primary object of the present invention is the provision of an 
elongated, flexible detonating device, which device can extend through an 
explosive column in a bore hole for lower detonation of the column. 
Another object of the present invention is the provision of an elongated, 
flexible detonating device, which device can extend through an explosive 
column in a bore hole for lower detonation of a column, without using a 
blasting cap at the point of detonation. 
Still a further object of the present invention is the provision of an 
elongated, flexible detonating device, which device can extend through an 
explosive column in a bore hole for lower detonation of a column without 
requiring a high sensitivity primary charge for detonating a secondary 
primer charge preparatory to detonation of the column. 
Another object of the present invention is the provision of an elongated, 
flexible detonating device, as defined above, which device does not depend 
primarily upon the use of small core loading for its ability to fire 
through a portion of an explosive column in a bore hole without detonating 
the column. 
Yet another object of the present invention is the provision of a 
detonating device as defined above, which device can transmit a detonating 
wave to and from a standard detonating cord. 
Yet another object of the present invention is the provision of a flexible 
detonating device as defined above, which device includes an outer layer 
of an energy absorbing material formed as a unit onto an inner detonating 
cord, but selectively releasable from the cord.

PREFERRED EMBODIMENT OF THE INVENTION 
Referring now to the drawings wherein the showings are for the purpose of 
illustrating a preferred embodiment of the invention only, and not for the 
purpose of limiting same, FIG. 1 shows an elongated, flexible unitary 
detonating device or element A constructed in accordance with the present 
invention which element can be wrapped, tied and otherwise used in the 
same manner as a standard detonating cord. Detonating element A includes 
an indeterminate length which can be cut to provide two longitudinally 
spaced ends 10, 12, one of which can be connected to a standard initiating 
device and the other to a primer or other element to be detonated. In 
accordance with the invention, detonating element A includes an inner 
detonating cord 20 having an outer surface 22 and constructed in 
accordance with somewhat standard practice in the detonating cord art. 
Cord 20 is used for transmitting a detonating wave by high explosive 
particles, as in a standard detonating cord. Surrounding surface 22 of 
detonating cord 20 there is provided an energy absorbing layer, or sheath, 
30 which functions to reduce the transverse transmitted energy caused 
during initiation of detonating cord 20, so that detonating element A can 
extend through a column of explosive material, such as NCN and/or slurry, 
without detonating the same. 
Referring now more particularly to the somewhat standard inner detonating 
cord 20, this cord is constructed in accordance with normal manufacturing 
techniques such as those described in U.S. Pat. No. 3,726,216, which is 
incorporated by reference herein. The detonating cord 20, in the preferred 
embodiment of the invention, differs from the cord specifically disclosed 
in this prior patent in certain respects. For instance, detonating cord 20 
has an explosive distribution or grain load in the general range of 6-20 
grains per linear foot, whereas the disclosed detonating cord in the prior 
patent has a grain load generally in excess of 15 grains per linear foot. 
In addition, with the lesser explosive distribution or grain loading, 
particles of explosive material, as will be explained later, are smaller 
in the present invention than in this prior patent. The outer textile 
wrapping of thread coated with a wax for tying purposes shown in the prior 
patent is omitted in the preferred embodiment of the present invention. It 
is appreciated that such a wrapping could be incorporated in the invention 
without departing from the intended scope. 
Inner detonating cord 20 of the present invention includes the centrally 
located explosive core 40 formed around a feed assisting thread or string 
42 which enhances gravity feeding of the high explosive particulate 
material forming core 40. In practice, core 40 is formed from small 
particles of pentaerythritoltetranitrate (PETN), 
cyclotrimethylenetrinitramine (RDX), cyclotetramethylenetetranitramine 
(HMX), tetryl, ditrinitroethylurea, trineitrotoluene (TNT) and mixtures 
thereof. In the preferred embodiment of the present invention, Class II 
Trojan (PETN) is used. This material has a grain size which allows a 
majority amount by weight of the PETN particles to pass through a 325 
United States Standard screen. Indeed, this material actually allows most 
of the PETN particles to pass through this relatively small screen to 
enhance the wave propagation characteristics of core 40 after initiation. 
The particle size of the PETN in the preferred embodiment is applicable 
for grain loading of approximately 6-12 grains per linear foot. If higher 
loading is used in detonating cord 20, a correspondingly larger PETN grain 
size could be used with an increase in the ease of feeding the particles 
into the core. As explained in the prior patent, the PETN particles are 
first dried and then treated with an appropriate flowing or anti-static 
agent and an anti-wicking agent which are well known in the art. These 
agents facilitate easier gravity feed of the small particles around thread 
or string 42 and into core 40 during the formation of detonating cord 20, 
in accordance with standard practice and with standard detonating cord 
manufacturing equipment. 
In accordance with somewhat standard practice, core 40 is supported by a 
carrier or tube 50 formed from longitudinally wrapped fibrous material, 
such as Crepe paper. Carrier or tube 50 provides a means for forming core 
40 into a continuous flexible column which allows propagation of a 
detonating wave therethrough. Although Crepe paper having a width of 
approximately 1/4 inch and thickness of approximately 0.002-.005 inches 
is employed in the preferred embodiment, other appropriate supporting 
material could be used, such as plastic or fiberglass tape or ribbon. 
Disposed around the carrier 50 is a textile layer 52 which is used for 
increasing the tensile strength of detonating cord 20. This fibrous or 
textile layer 52 may include ten strands of thread wrapped around carrier 
50. These strands can be formed from continuous lengths of various fibrous 
materials such as cotton, rayon, jute and the like. In practice these 
strands have about 1500 filaments and a weight in the range of from about 
1,100 to about 2,200 Denier. To further increase the tensile strength of 
detonating cord 20, it is possible to wrap, in an opposite direction, a 
second layer of textile material over the first layer 52, although this is 
not illustrated in the preferred embodiment of the invention. Around 
tensile strength increasing layer 52, there is provided a moisture barrier 
60 formed from 8 mils of polyethylene extruded around textile layer 52 and 
forming a moisture impervious barrier preventing moisture from 
contaminating the PETN of core 40. Of course, other extrudable materials, 
both plastic and elastomeric, could be used to provide the moisture 
barrier for core 40. Although polyethylene is used in the preferred 
embodiment, polyvinylchloride and polyethylene terethphalate or the like 
is also appropriate as a barrier. In accordance with normal practice, 
barrier 60 is extruded around core 40, although it is possible to use a 
ribbon or tape wrapped around fibrous layer 52 to provide this barrier. As 
so far described, barrier 60 defines the outer surface 22 of detonating 
cord 20. 
Although the high explosive material in core 40 may have a grain load or 
explosive distribution in the general range of 6-20 grains per linear 
foot, in the preferred embodiment of the invention, the grain load is 
about 11-13 grains per linear foot. In the example to be provided later, 
the grain loading is 11.8 grains per linear foot. As can be seen, 
generally the grain loading of detonating cord 20 is below grain loading 
of a standard detonating cord and above the grain loading of low energy 
detonating cord. There may be a slight amount of overlap between the lower 
loading for economy cord and the upper limit of the preferred loading of 
the present invention. When the present invention approaches a loading of 
15-20 grains per linear foot the energy absorbing layer 30 becomes 
relatively large. This reduces the economy of the invention and creates a 
relatively large channel through the explosive column. For these reasons, 
the upper practical limit of the invention may be approximately 20 grains 
per linear foot; however, higher loading is possible without departing 
from the invention if the remaining criteria are observed. The lower limit 
of grain loading is substantially above the previous low energy detonating 
cord. As will become apparent, cord 20 functions, for initiation and 
detonation purposes, as a standard cord. With loading less than about 6 
grains per linear foot, special boosters and equipment, not contemplated 
by this invention, would be required. Indeed, loading below about 6 grains 
per linear foot would preclude needed initiation by a standard cord. 
As so far explained, detonating cord 20 is constructed in accordance with 
well known detonating cord technology. In the manufacture of detonating 
cord, often surface 22 is provided with a thin thread wrapped around the 
surface and coated with a wax. This thread is used to facilitate tying of 
the detonating cord which is easier when a waxed thread coating is used. 
Although this thread coating could be used in the present invention, it is 
not contemplated in the preferred embodiment. 
The cord 20, which is constructed in accordance with standard practice, 
includes a sufficient high explosive grain loading to guarantee detonation 
of a standard 40-50 grain detonating cord when the cord is intimately 
associated with outer surface 22 by a knot or other cord connecting 
arrangement. Since cord in some instances may have a grain load as low as 
15 grains per linear foot, the loading of core 40 may be increased to 
initiate to or from this low load cord; however, generally core 40 is 
loaded to initiate to or from a 40-50 grain cord. In practice, it has been 
found that a grain loading of 11-13 grains per linear foot will detonate a 
40-50 grain detonating cord when a 8 mil barrier 60 is used for the cord 
20. With this loading of the high explosive particles, cord 20 would have 
sufficient transverse detonating energy to detonate an explosive in a bore 
hole, such as a blasting agent or slurry. Consequently, cord 20 by itself 
can not be used for bottom detonation of explosive columns in bore holes. 
In accordance with the present invention, cord 20 is provided with an 
outer energy absorbing layer 30 releasably secured to surface 22. Energy 
absorbing layer 30 has sufficient energy absorbing characteristics, based 
upon the required loading of core 40, the material of layer 30 and the 
thickness of the layer 30, to prevent detonation of an explosive charge 
through which element A extends. This energy absorbing layer will be 
modified according to the core loading required to obtain positive 
initiation and detonation for a particular application. If initiation is 
to be by a low loaded cord, core 40 will have a higher loading and layer 
30 will have a high energy absorbing capability. A variety of energy 
absorbing layers could be provided for meeting this requirement. In a like 
manner, a variety of arrangements can be used for allowing selective 
removal of the energy absorbing layer from certain portions of element A 
to initiate the element and, when necessary, to detonate a cast primer or 
other detonating device in the bottom of a bore hole. 
In accordance with the preferred embodiment of the invention, the energy 
absorbing layer 30 is formed from a heavier layer of plastic material 
which is the same as the plastic material forming barrier 60. This heavier 
layer is extruded around detonating cord 20 with a thickness of 35-45 
mils. In practice, the nominal thickness is approximately 42 mils. To 
allow stripping of the energy absorbing layer from selected areas of 
element A, there is provided a layer of fibrous material 70, which layer 
is formed from rayon, cotton or other yarn. The primary function of layer 
70 is to prevent tight adhesion between energy absorbing layer 70 and 
surface 22. In practice, a loosely woven rayon yarn designated 20/2 is 
used to create a separating seam 80 between the energy absorbing material 
and surface 22. This rayon yarn is formed from a number of short naps 
twisted together in two strands so as to create a loosely woven fiber 
layer 70 which is wrapped around surface 22 and does not fixedly adhere 
thereto. Layer 72 forms the primary energy absorbing structure of layer 30 
and is extruded around the wrapped yarn layer 70. The plastic in layer 72 
does not extend through the yarn layer and into adhesion with layer or 
barrier 60. Since the yarn forming layer 70 is loosely woven with numerous 
twisted short naps, this layer has an energy absorbing characteristic of 
its own. This is a secondary function of layer 70. The space between 
plastic layers 60, 72 which is filled by yarn layer 70 has voids that 
dissipate energy attempting to be transmitted through this space. In some 
instances, it would be possible to provide between layers 60, 72 a yarn or 
thread similar to that provided in fibrous layer 52. This would prevent 
adhesion between plastic layers 60, 72; however, would be more expensive 
and would provide less additional energy absorption. The preferred 
embodiment includes the loosely woven type of yarn for its added energy 
absorbing characteristics. In addition, since this yarn sticks to neither 
layer 60 nor layer 72, the loosely woven yarn provides a convenient means 
for releasing outer energy absorbing plastic layer 72 from cord 20. This 
construction of element A is schematically shown in FIG. 2. 
To remove energy absorbing layer 30, and more particularly the heavier 
plastic tubular extrusion 72, from cord 20 it is only necessary to 
manually cut layer 72 circumferentially as indicated by cut 90 in FIG. 3. 
This cut may be only partially through layer 72 and partially around the 
circumference of layer 30. After a cut around about 3/4 of layer 30 is 
made, element A can be flexed at the cut to break away plastic layer 72. 
Thereafter, the layer may be slipped from the end of element A, as shown 
in FIG. 3. This leaves only the fibrous strands in layer 70 surrounding an 
exposed portion of cord 20. These strands may then be cut away or unwoven 
from surface 22 and pulled away from the surface so that cord 20 may be 
tied to a trunk line or other initiating system. Cut 90 is generally made 
approximately 6-12 inches from an end of element A so that the exposed 
portion of cord 20 is sufficiently long to form a connection. 
FIG. 4 illustrates the releasing characteristic between layer 72 and 
barrier 60 at seam 80. In practice, an axial release is used instead of 
the illustrated circumferential release which would be possible by making 
a longitudinal cut and a circumferential cut. A view similar to FIG. 4 
illustrating a modification of the preferred embodiment of the present 
invention is shown in FIG. 5 wherein elongated flexible element A' 
includes an inner detonating cord 20' which differs from cord 20 by 
including an elastomeric barrier 100 instead of a plastic barrier 60, as 
used in the preferred embodiment. This elastomeric barrier could be tar, 
asphalt or other similar water impervious material coated or extruded 
around carrier 50. Except for this change in detonating cord 20, element 
A' is substantially the same as the preferred embodiment of the invention. 
A further modification is illustrated in FIG. 6 wherein an elongated 
flexible detonating element A' is provided with an inner detonating cord 
20 corresponding to the detonating cord of the preferred embodiment. The 
outer energy absorbing plastic layer 72 of the preferred embodiment is 
replaced by an elastomeric energy absorbing layer 110. This layer has 
sufficient thickness to perform the function attributed to energy 
absorbing layer 72 of the preferred embodiment. A further modification of 
the preferred embodiment is illustrated in FIG. 7. In this modification, 
an inner detonating cord 20 is formed in accordance with the preferred 
embodiment of the invention. The outer plastic energy absorbing layer 72 
is releasably secured to surface 22 of cord 20 by a releasing material 120 
which may be a plastic having a dissimilar melt index from plastic of 
layers 60, 72. Other materials could be provided between the energy 
absorbing layer 72 and barrier 60. Indeed, it is possible that the two 
plastic materials forming the energy absorbing layer 72 and barrier 60 
could be so dissimilar that they would not adhere. When this type of 
structure is used, the space between layers 60, 72 is not filled by a 
fibrous layer. Thus, it may be difficult to slip the severed portion of 
the energy absorbing layer from the end of the detonating element. In that 
instance, a longitudinal cut may be used or required to sever the energy 
absorbing layer from the inner detonating cord. It is apparent that 
various modifications are possible in the preferred embodiment of the 
invention without departing from the intended spirit and scope of the 
invention. For instance, various energy absorbing layers, releasing 
arrangements and detonating cords can be used to obtain the desired 
results of the invention. In all instances, the flexible elongated 
detonating element is a unitary structure which can be wrapped on a reel 
and transported to a blasting site in accordance with standard 
transportation procedures for detonating cord. Thus, the two element 
structure is a unitary structure until the stripping process is performed. 
FIG. 8 illustrates a connection between the detonating element A and a 
standard cast primer 130. In this illustrated arrangement, the lower 
portion of element A is stripped to expose inner detonating cord 20. This 
cord is then molded into the cast primer 130 for subsequent use in the 
bottom of the bore hole in a manner to be explained later. 
FIG. 9 shows another aspect of the invention wherein an improved connection 
is provided between detonating element A and a standard cast primer 140 
having the usual axial bores 142, 144. Element A is stripped at portion 
150 to expose inner cord 20, which is connected to a standard 50 grain 
detonating cord 152 by an appropriate knot 154 or other connecting 
arrangement. Standard detonating cord 152 extends upwardly through bore 
144 for a purpose to be explained later. When detonating element A is 
initiated, it may have sufficient transverse energy to detonate primer 
140. If detonation does not occur, then the exposed detonating cord will 
positively detonate the higher energy standard detonating cord 152 for 
positive detonation of primer 140 and any additional primers located along 
cord 152. 
Referring now to FIG. 10, cast primer 130 shown in FIG. 8 is positioned at 
the bottom of a bore hole 160 filled with a column 162 of explosive 
material, such as NCN, TNT, slurry, etc. The column and bore hole have a 
lowermost end 164 and an uppermost end 166. Cast primer 130 is positioned 
adjacent lowermost end 164 and element A extends through the explosive 
column 162 to an upper blasting device 170 adjacent the uppermost end 166 
of the bore hole. The blasting device is only representative and element A 
may be initiated by a trunk line, an electric initiator or other 
appropriate device. Before element A can be initiated, the upper portion 
has the energy absorbing layer 30 stripped. In this manner, positive 
initiation to the inner detonating cord 20 is possible. Upon initiation of 
element A, a lower detonation 180 occurs adjacent lowermost end 164 of 
bore hole 160. 
As shown in FIG. 11, the blasting device 170 of FIG. 10 may be a standard 
trunk line 190 extending over bore hole 160. Element A forms the down line 
from the trunk line. A connector 192, including diametrically opposite 
openings 194 and flexible lips 200, 202, is used to connect a bight 210 of 
cord 20 with the trunk line. This can be done by extending one end of 
element A through connector 192 and then forming bight 210 around trunk 
line 190. The free end of element A is then threaded through the connector 
and the connector is shifted upwardly to engage trunk line 190 and 
resiliently hold detonating cord 20 in tight, intimate wave transmitting 
contact with the trunk line. In this manner, the standard trunk line can 
be used to detonate a down line formed in accordance with the preferred 
embodiment of the present invention. 
Referring now to FIG. 12, a system utilizing the present invention is 
illustrated. In this system, the cast primer 140, as shown in FIG. 9 is 
positioned at the lowermost end 164 of bore hole 160. An initiating or 
blasting device 170 can be used for bottom detonation of cast primer 140. 
In accordance with the illustrated system, a plurality of axially spaced 
secondary primers 220 are positioned in the bore hole. Standard detonating 
cord 152 is threaded through the spaced secondary primers for further 
detonation of explosive 162 in bore hole 160. In practice, the secondary 
cast primers have a lesser weight than the basic cast primer 140 in the 
lower portion of the bore hole. Initiation of element A detonates 
explosive column 162 in a manner clearly apparent by the drawings. A 
similar arrangement for using the structure shown in FIG. 9 in a decking 
arrangement is illustrated in FIG. 13. The secondary cast primers 220 are 
located in axially spaced explosive charges 162a separated by dirt 
portions 230. Initiation of element A by device 170 fires the explosive 
charges 162a separately from the bottom of the bore hole to the top 
thereof. 
EXAMPLE AND TESTING 
As an example of the present invention, the following energy absorbing 
detonating device has been produced: 
______________________________________ 
Element Process lbs/1000 ft 
______________________________________ 
(a) Center String Fed longitudinally 
to assist in feed- 
ing PETN 0.024 
(b) PETN (11.8 Fed around center 
grains/ft) supporting string 
1.68 
Class II 
Trojan* 
(c) 1/4 inch Crepe Wrapped around said 
paper PETN core for support- 
0.003 inches ing core 0.254 
(d) 10 strands of Spun around paper 
1650 Denier tube for tensile 
Rayon Thread with 
strength 2.040 
1500 filaments 
each. 
(e) Inner Plastic Extruded around 
Water Impervious 
Rayon threads to 
layer (8 mils) protect core from 
(Polyethylene) moisture 1.180 
(Standard Manufacturing Steps to this condition) 
(f) Overspin of Spun around inner 
20/2 rayon yarn 
plastic layer. 
Covers inner plas- 
tic layer to form 
releasable contact 
with inner plastic 
layer 0.893 
(g) Outer Plastic Extruded over 
layer (42 mils) 
loosely woven 
(Polyethylene) rayon yarn 11.27 
Enerby Absorbing 
layer. 
TOTAL 17.34 
______________________________________ 
*Class II Trojan PETN is a fine grain PETN wherein a majority of the 
material passes through a 325 United States Standard screen. 
Elongated detonating devices, constructed in accordance with the above 
example, were initiated while extending in a confined column of ANFO 
without detonating the column. Also, a length of the detonating element 
was twisted three times longitudinally around a length of standard 40 
grain/ft detonating cord which was then placed in a 2 inch diameter, 5 
feet length of pipe. The pipe was filled with sand and the detonating 
element was initiated. In these tests, the 40 grain/ft detonating cord was 
not detonated by the device having the energy absorbing layer in place. To 
further test the detonating capabilities of the detonating device with the 
energy absorbing layer in place, the device was spliced to a 50 grain/ft 
standard detonating cord. In five tests, only twice was the 50 grain cord 
initiated. Consequently, the detonating element was shown, by these tests, 
to be a relatively ineffective initiator or detonator for a blasting agent 
or standard detonating cord when the energy absorbing layer or layers 
remained intact around the inner detonating cord. 
The outer energy absorbing layer or layers were then stripped from the ends 
of the detonating element constructed in accordance with the above 
example. The element was spliced with a standard 50 grain/ft detonating 
cord with the exposed inner plastic layer in contact with the cord. In ten 
successive tests, initiation of the invention caused initiation of the 50 
grain cord. This indicates an increased detonating characteristic for the 
stripped portion of a detonating device constructed in accordance with the 
example. In addition, the detonating device was placed in a cast primer of 
standard PETN, composition B, etc. construction. The initiation of the 
device was sufficient to detonate the primer without requiring any 
intermediate charge, such as needed in prior non-electric detonating 
systems which can detonate in the lower portion of a bore hole. 
The present invention was tested in 14 bore holes 70 feet deep filled with 
ANFO. An elongated element constructed in accordance with the invention 
extended through the ANFO to a lower one pound cast primer. The upper 
portion of the elongated detonating device was stripped for initiation and 
initiated by a trunk line of 30 grain/ft standard detonating cord. Each of 
the bore holes was detonated from the bottom, indicating that the 
detonating wave through the invention propagated through the ANFO to the 
lower cast primer without predetonation at the upper portions of the 
explosive column. The lower primer had no high energy charge required by 
other detonating elements allegedly capable of detonating a bore hole 
charge from a location adjacent the bottom of the bore hole. 
Attempts to initiate the detonation element constructed in accordance with 
the above example without removing the energy absorbing outer layer or 
layers have proven inconsistent and generally ineffective. It has been 
found that the energy absorbing layer or layers used to allow bottom 
detonation must be removed to obtain consistent initiation by standard 
detonating cord and other common initiating devices.