Note: Descriptions are shown in the official language in which they were submitted.
CA 02606873 2007-10-15
PROTECTOR FOR DETONATOR, AND METHOD OF USE
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the priority right of prior United States patent
application 60/864,648 filed November 7, 2006 by applicants herein.
BACKGROUND TO THE INVENTION
Dangerous goods include liquid or solid substances, and articles containing
them, that have been classified according to internationally-agreed criteria,
and found
to be potentially dangerous (hamdous) during transportation and / or storage.
Most
countries base their legislative requirements for storage and transportation
of
dangerous goods on the "Recommendations on the transport of dangerous goods"
issued by the United Nations and the United Nations' prescribed testing codes
for
establishing the acceptability of various packaging and transportation
methods.
Dangerous goods are assigned to different Classes depending on their
predominant hazard, and on the basis of the specific chemical characteristics
posing
the risk. Such Classes include the following: class 1, explosives; class 2,
gases; class
3, flammable liquids; class 4, flammable solids; class 5, oxidizing materials
and
organic peroxides; class 6, toxic and infectious substances; class 7,
radioactive
materials; class 8, corrosives substances; and class 9, miscellaneous
(including
asbestos, dry ice, engines, etc.). Except for very small packages, all
packages and
containers, shipping containers, unit loads, tankers, etc. which hold
dangerous goods
for transport must carry the correct Class Label. This label shows the nature
of the
hazard by the colour and symbol, and the Class of the goods by numeral. The
Recommendations specify how storage areas are to be designed, constructed and
located to minimize risks. The Recommendations are designed to assist the
authorities
and other emergency services, and to ensure that they have enough information
to deal
with incidents.
According to the United Nations classification system, explosives are also
assigned compatibility group letters to facilitate their segregation during
transportation. The letters used range from A - S, except for the letters I,
M, 0, P, Q
1
CA 02606873 2007-10-15
and R. Also, they are sub-classified using the following sub-classes: 1.1 for
explosives with a mass explosion hazard; 1.2 for explosives with a severe
projection
hazard; 1.3 is for explosives with a fire, blast or projection hazard but not
a mass
explosion hazard; 1.4 stands for minor fire or projection hazard (includes
ammunition
and most consumer fireworks); 1.5 is for an insensitive substance with a mass
explosion hazard; and 1.6 for extremely insensitive articles. In the
explosives
industry, it is preferred to attempt to package some explosives such as
detonators in
such a way as to reduce their hazard classification from 1.1 to 1.4, so that
the
explosive substances as packed represent only a minor fire or projection
ha7ard. This
provides far greater levels of safety and allows for much cheaper
transportation costs.
In the case of detonator packaging, this certification relies on the fact that
they are
packed and designed so as to confine most of the effects of any accidental
explosion or
ignition within the package itself, and if there are multiple devices, one
detonator
exploding will not lead to mass detonation of the others in the package.
In order for detonators to be certified as 1.4, they must pass the UN Test
Series
6 external fire test (Bonfire test), which may include Tests 6(a), 6(b), 6(c),
and 6(d).
The packaging can have a significant influence on the explosive effects of
substances
and articles. The type of packaging can change the response of packed
explosives or
explosive articles in Test Series 6. One and the same explosive substance or
article can
therefore be assigned to different hazard groups, or even be rejected from
Class 1 for
transport depending upon the packaging used. The Bonfire test is performed on
packages of explosive substances or explosive articles, or unpackaged
explosive
articles, to determine whether there is a risk of mass explosion or a
potential hazard
from dangerous projectiles, radiant heat and/or violent burning or any other
dangerous
effects. Typically, a stack of test substances or articles is placed on a non-
combustible
surface (steel grate) above a lattice of dried wood soaked with diesel fuel or
equivalent
source. A wire basket or clamps may be used to hold the articles in place.
Sufficient
fuel is used to provide a 30-minute fire. Three aluminum witness plates, each
having a
surface area of 4m2 (2m x 2m), are placed away from the edge of the packages
at a
distance of four meters. The fire is ignited and the material is observed for:
2
CA 02606873 2007-10-15
a) Evidence of detonation, deflagration or explosion of the total contents;
b) Potentially hazardous fragmentation; and
c) Thermal effects (i.e. size of the fireball, etc.).
The results are used to determine whether a reaction from an explosive article
in its package, which was accidentally fired or initiated, would propagate to
other
articles or parts of the process. The package product is assigned a 1.4
certification if it
meets the following requirements:
1) no indentations of the witness plates are observed; and
2) no projection, thermal effect or blast effect is observed.
With respect to the transportation and storage of detonators, the relevant
criteria are generally accepted to be the UN 1.4 Code of testing. This
certification
relies upon the fact that when detonators are packed together for storage and
/ or
transportation, inadvertent initiation of one detonator will not lead to mass
detonation
of other detonators present. This is especially important for air
transportation since it
is the most restricted mode of shipping. For such transportation, the 1.4S
classification is required, the "S" being indicative that any hazardous
effects arising
from accidental functioning of the detonators in a package is confined within
the
package (unless the package has been degraded by fire, in which case all blast
or
projection effects are limited to the extent that they do not significantly
hinder or
prohibit fire fighting or other emergency response efforts in the immediate
vicinity of
the package).
Previously, packaging methods for the storage and transport of shelled
detonators have included the use of protectors on the detonators or specially
designed
transportation boxes. For example, International Patent Publication W095/19539
published July 20, 1995, discloses a protector for use in the transportation
and storage
of detonators, comprising a detonator holder which is open at one end for
insertion of
a detonator, and closed at the other end, and which radially encloses the base
charge of
said detonator, at least one detonator retaining means integral with the
detonator
holder, and a first wall which is radially spaced around the holder and
wherein the
holder and wall define a space. In use, the detonator retaining means holds
the
3
CA 02606873 2007-10-15
detonator within the holder such that a free volume is provided around the
base charge
of the detonator.
Another example is United States Patent 5,133,258 issued July 28, 1992,
which discloses a safe transportation holder and package for explosive devices
such as
blasting caps. Each cap is contained in an internal cavity in a holder, and
surrounded
by radially-spaced, elastomeric walls. The holders are arrayed in a container,
and
absorb the energy released by accidental detonation of one cap to prevent
sympathetic
detonation of others in the packages.
United States Patent 6,454,085 issued September 24, 2002 discloses a system
and method for packaging shaped charges for transportation. Each shaped charge
includes a housing and a liner having a high explosive disposed therebetween.
A jet
spoiler is positioned proximate the liner of each of the shaped charges to
prevent the
formation of a jet in the event of an inadvertent initiation of a shaped
charge. The
shaped charges are then oriented in first and second layers such that the jet
spoilers
positioned proximate the liners of the shaped charges in the first and second
layers
oppose one another. A shielding panel is disposed between the shaped charges
of the
first and second layers. The shaped charges including the jet spoilers and the
shielding
panel are placed within an expandable bag which is in turn enclosed within a
transportation container. The jet spoilers may be constructed of a suitably
dense
material such as wood, plastic, foam, rubber, plaster, cement and the like.
Ideally the
material would be one that is environmentally friendly for easy disposal,
lightweight
to facilitate shipping and handling and economical. For example, biodegradable
cardboard, balsa wood or compressed sawdust are suitable materials. The
expandable
bag is preferably made from a ballistic cloth, and the container may
preferably be a
corrugated cardboard box or a wood box.
United States Patent 6,629,597, issued October 7, 2003, discloses a system and
method for packaging shaped charges for transportation. Each shaped charge
includes
a housing and a liner having a high explosive disposed therebetween. A jet
spoiler is
positioned proximate the liner of each of the shaped charges to prevent the
formation
of a jet of shrapnel in the event of an inadvertent initiation of a shaped
charge. The jet
spoilers may be comprised of a metal or non-metal material. Wood, plastic,
rubber,
4
CA 02606873 2007-10-15
plaster, cement, cardboard, balsa wood, or compressed sawdust are disclosed as
particularly suitable attenuator materials for the jet spoilers. The shaped
charges are
then oriented in first and second layers such that the jet spoilers positioned
proximate
the liners of the shaped charges in the first and second layers are opposite
one another.
A shielding panel is disposed between the shaped charges of the first and
second
layers. The shaped charges, including the jet spoilers and the shielding
panel, are
placed within an expandable bag which is in turn enclosed within a
transportation
container.
As a further example, United States Patent 4,286,708 discloses a package
wherein the sympathetic or chain reaction detonation of stacked munitions is
prevented by confining any random explosion essentially to a single explosive
unit or
container. Frangible inhibitor plates are located between adjacent munitions,
such as
artillery shells, so as to isolate the adjacent explosive units from a
residual shock wave
or case fragment that would otherwise trigger sympathetic detonation. The
inhibitor
plates may be constructed as part of a container in which an artillery shell
may be
stored, or the plates may be separately inserted between any adjacent warhead
in any
conventional storage pallet or transporting configuration. The plates are
designed to
absorb only that amount of explosive energy required to prevent sympathetic
detonation, without requiring that the explosive forces be redirected away
from
adjacent shells, thus reducing the problem of redirected blast.
Other packaging methods involve wrapping a detonator in its down-hole wire,
and caging a box of detonators within its cardboard box. For example, Canadian
Patent application 2,118,528 discloses a non electric detonator assembly for
its safe
transport in bulk wherein a detonator is located substantially along the axis
of a coil of
initiation tubing, the initiation tubing being wound such that it may be
unwound by
drawing from the centre of the coil.
Another method used for packaging explosive devices such as detonators is
one inspired by the military industry. It involves the use of a cardboard tube
having a
clay plug or equivalent thereof at one end. Such equivalents to a clay plug
may
include, but are not limited to, a plug comprising wood, compressed sawdust,
cement,
granulated sand, plaster, dry wall materials, and other materials. The device
is
5
CA 02606873 2012-09-13
- 6 -
enclosed in the tube, with its explosive end at or near the clay plug end. The
plug acts, at
least in certain circumstances, as a jet spoiler to absorb shrapnel from an
explosion, and the
tube functions as a flame retardant. The tube is preferably made of cardboard
because this
material is not too dense, inexpensive and environmentally benign. Examples of
this
packaging method can be found in United States Patent Applications published
as
2005/0150781 and 2006/0108237 on July 14, 2005 and May 25, 2006 respectively.
US
2005/0150781 discloses a detonator protector including a housing fitted with
an end cap at
one end and a plug at the other end. US 2006/0108237 discloses a tubing
assembly having
opposed ends and a thick wall of relatively low-density fibrous material, and
having an
impact absorbing element positioned at each end of the tube.
Although numerous methods for the storage and transport of dangerous goods
have
been developed, there remains a continuing need to develop improved methods to
increase
security and safety of dangerous goods, and in particular explosive devices
such as
detonators. Moreover, there remains a continuing need to develop packaging
methods for
storage and transportation of detonators, with improved protection against
inadvertent
mass initiation of other detonators within a package.
SUMMARY OF THE INVENTION
According to the present invention there is provided an assembly comprising:
(a) a detonator comprising a detonator shell having an explosive end, and a
base charge of explosive material at the explosive end;
(b) a detonator protector comprising a recess for receiving and
covering at least
the explosive end of the detonator shell to contain shrapnel and/or explosive
energy
derived from the detonator in the event of inadvertent actuation of the base
charge, said
detonator protector being dimensioned such that it covers less than one-third
of a length of
the detonator shell from the explosive end, thereby to allow the explosive
material of said
base charge to deflagrate in the event of inadvertent actuation of the
detonator and/or
exposure of the assembly to the heat of a fire;
wherein the detonator and detonator protector are held together by a friction
fit
when at least the explosive end of the detonator shell is received in the
recess and covered
by the detonator protector, said detonator protector being made of a resilient
material and
being resiliently deformable to facilitate receipt of the at least the
explosive end of the
CA 02606873 2012-09-13
- 7 -
detonator shell in the recess and to facilitate tight fitting and gripping of
the detonator
protector on the at least the explosive end of the detonator shell to keep the
detonator
protector in place during transportation or storage of the assembly, or
inadvertent actuation
of the detonator.
Further according to the present invention there is provided a method of
protecting
a detonator from emitting shrapnel and/or explosive energy during
transportation and/or
storage, the method comprising the step of:
applying to an explosive end of the detonator a detonator protector comprising
a
recess for receiving and covering at least the explosive end of the detonator
shell to contain
shrapnel and/or explosive energy derived from the detonator in the event of
inadvertent
actuation of the base charge, said detonator protector being dimensioned such
that it covers
less than one-third of a length of the detonator shell from the explosive end,
thereby to
allow the explosive material of said base charge to deflagrate in the event of
inadvertent
actuation of the detonator and/or exposure of the assembly to the heat of a
fire;
wherein the detonator and/or detonator protector are held together by a
friction fit
when at least the explosive end of the detonator shell is received in the
recess and covered
by the detonator protector, said detonator protector being made of a resilient
material and
being resiliently deformable to facilitate receipt of the at least the
explosive end of the
detonator shell in the recess and to facilitate tight fitting and gripping of
the detonator
protector on the at least the explosive end of the detonator shell to keep the
detonator
protector in place during transportation or storage of the assembly or
inadvertent actuation
of the detonator.
Still further according to the present invention there is provided a method of
packaging a plurality of detonators, comprising placing a plurality of
detonator assemblies
according to the invention into a container.
In one embodiment, the step of placing comprises: disposing each detonator
assembly within the container according to an alternating pattern, wherein
when one
detonator assembly has its protected explosive end facing one side of the
container, each
adjacent detonator assembly has its protected explosive end facing a side
opposite said one
side thereby to form a row of alternately disposed detonator assemblies.
Furthermore, the step of placing comprises placing more than one row of
detonator
assemblies into the container, with explosive ends of at least one pair of
adjacent detonator
CA 02606873 2012-09-13
- 7A -
assemblies from adjacent rows facing generally into the package in aligned
opposition, and
disposed explosive end to explosive end, said at least one pair of adjacent
detonator
assemblies from adjacent rows being protected by a detonator protector
comprising two
recesses for simultaneously receiving each explosive end of said pair, to hold
the
Any of the aforementioned steps of placing may further comprise placing
multiple
rows of detonator assemblies into the container, stacked one on top of
another. Optionally,
the adjacent stacked rows of detonator assemblies are separated by a flame-
retardant
material.
Yet still further according to the present invention there is provided a
package
comprising plural detonator assemblies in a container, wherein each detonator
assembly is
according to the invention and/or wherein the package is foinied by the method
of
packaging according to the invention.
The detonator protector used in the invention may further comprise a second
recess
for receiving at least an explosive end of said second detonator. The first
mentioned
detonator and a second detonator in the second recess may be in an opposing,
aligned
orientation, with their respective explosive ends separated by a portion of
the detonator
protector. In embodiments said portion of the detonator protector between the
opposing
BRIEF DESCRIPTION OF THE DRAWINGS
Various embodiments of detonator assemblies, methods and packages according to
the invention will now be described by way of example only, with reference to
the
accompanying drawings, in which:
Figure la is a sectional view of an assembly of the present invention.
Figure lb is a perspective view of the assembly shown in Figure la.
Figure 2 is a sectional view of a preferred double-protecting device of the
present
invention.
Figure 3a is a sectional view of a preferred alternate packaging.
Figure 3b is a sectional view of another preferred alternate packaging.
=
CA 02606873 2007-10-15
Figure 3c is a sectional view of another preferred alternate packaging
Figure 3d is a sectional view of another preferred packaging
Figure 3e is a side, perspective view of stacked rows of assemblies
DEFINITIONS:
Base charge: refers to any discrete portion of explosive material in the
proximity of
other components of the detonator and associated with those components in a
manner
that allows the explosive material to actuate upon receipt of appropriate
signals from
the other components. The base charge may be retained within the main casing
of a
detonator, or alternatively may be located nearby the main casing of a
detonator. The
base charge may be used to deliver output power to an external explosives
charge to
initiate the external explosives charge.
Blasting machine: any device that is capable of being in signal communication
with
electronic detonators, for example to send ARM, DISARM, and FIRE signals to
the
detonators, and / or to program the detonators with delay times and / or
firing codes.
The blasting machine may also be capable of receiving information such as
delay
times or firing codes from the detonators directly, or this may be achieved
via an
intermediate device to collect detonator information and transfer the
information to the
blasting machine.
Central command station: refers to any device that transmits signals via radio-
transmission or by direct connection, to one or more blasting machines. The
transmitted signals may be encoded, or encrypted. Typically, the central
blasting
station permits radio communication with multiple blasting machines from a
location
remote from the blast site.
Explosive end: refers to a portion of a detonator where a base charge is
located within
the detonator, generally at an end opposite an end of a detonator that
receives a signal
transmission line or other means for receiving signals from an external
source.
Actuation of the base charge upon receipt by the detonator of a command signal
to
FIRE, optionally following count-down of a delay time, causes a release of
explosive
8
CA 02606873 2012-09-13
- 9 -
energy at or about the explosive end. As discussed herein, the base charge may
also be
accidentally or inadvertently actuated when a physical shock or unwanted
electrical current
is applied to the detonator, for example during transportation and storage.
Preferably: identifies preferred features of the invention. Unless otherwise
specified, the term preferably refers to preferred features of the broadest
embodiments of
the invention, as defined for example by the independent claims, and other
embodiments
disclosed herein.
Flame retardant/flame retardant additive: refers to any substance, material,
or
composition that exhibits at least some degree of flame retardant properties.
In selected
embodiments, such a flame retardant may help impart fire resistance to a
protector as
disclosed herein. In selected embodiments, little or no flame retardant
additive may be
required. In other embodiments, such as those relating to paper and polymer-
based
protectors, fire retardant materials such as those described, for example, in
"Fire Retardant
Materials", by Dennis Price and A. Richard Horrocks, CRC, Woodhead Publishing
Limited, Feb 2001 may be utilized. Such families of flame retardant materials
may include
but are not limited to halogen-based compounds (eg: brominated compounds such
as
PBDE, and PBB), phosphorus based compounds (eg: ammonium phosphate), borates,
metal hydroxides (eg: aluminum hydroxide) and other hydrated inorganic
additives (eg:
plaster). Flame retardant materials can also be added to the silicone rubber
to improve its
heat resistant properties, such as those available from the Dow Chemical
Company and
other suppliers. Numerous silicone rubber compositions that include flame
retardant
additives are known in the art. United States Patents 4,310,444 issued January
12, 1982,
4,366,278 issued December 28, 1982, and 4,678,827 issued July 7, 1987, are
just a few
examples of references disclosing such compositions and flame retardant
additives.
Further flame retardant additives that are known in the art may be used with a
protector as
disclosed herein. A skilled artisan may select a flame retardant additive that
is suitable for
use with a protector material or composition.
CA 02606873 2012-09-13
-10 -
Protector: refers to a device for use in the present invention as described
herein that
substantially covers an explosive end of a detonator, and optionally
additional portions of a
detonator, and helps to prevent movement away from the explosive end of
shrapnel and/or
explosive energy upon actuation of a base charge located at or near the
explosive end. The
term "protector" may, at least in selected embodiments, be interchangeable
with the term
"cap".
Shrapnel: refers to any fragments or debris thrown out by any exploding
object,
more particularly from an explosive end of a detonator upon actuation of a
base charge
located at or near the explosive end.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention provides, at least in preferred embodiments, for
protected
detonator assemblies, methods for the storage and transport of detonators, and
packages of
protected detonator assemblies, preferably to achieve 1.4 packaging
requirements in
accordance with UN Recommendations. A protector or "cap" is used to cover at
least the
explosive end of a detonator shell while the rest of the detonator may be left
at least
substantially uncovered by the cap. Preferably, the protective cap is made of
material
resistant to high temperature and flame, which means having the property to at
least
substantially maintain its shape and cohesion upon actuation of a nearby base
charge, or
exposure to high temperatures or flames. The cap comprises a resiliently
deformable
material, for reasons that will become apparent below. For example, any
polymers,
plastics, elastomers, vinyls, rubbers, having that property can be used. (An
agent that is
not merely fireproof, but which calcines upon burning or concretes upon
heating, may be
less suitable for this invention since it may provide less protection for the
detonator when
burnt.) In preferred embodiments, the material also has a certain degree of
malleability
and/or elasticity to fit on the explosive end and stay in place. Preferably,
the material used
is a cross-linked polymer, and more preferably silicone rubber. In other
embodiments, the
CA 02606873 2012-09-13
- 11 -
protector may comprise less resilient materials such as Ceramifiable polymer,
resins and
plasters, or wood-derived products. In a most preferred embodiment, the
material further
comprises a flame retardant additive.
The present invention has been developed by virtue of multiple discoveries by
the
inventors, which in combination provide optimal results to achieve the
advantages outlined
above. One discovery relates to the need for maintaining a sufficient mass of
explosive
energy-absorbing material generally or immediately adjacent the explosive end
of a
detonator. The inventors have discovered that a mass, specifically located
adjacent the
explosive end of the detonator, helps to impede the acceleration of shrapnel
derived from
the explosive end upon actuation of the base charge, and thus limits the final
velocity and
the inertia of the shrapnel. In this way, the protector contains the shrapnel
created when
the detonator explodes. This is achieved by designing the detonator protector
in such a
way that a portion of its mass is located at the axial end of the explosive
end, preferably in
direct contact with the detonator, so that it effectively "catches" the
shrapnel when the base
charge is actuated.
The detonator protector comprises a resiliently deformable material that is
able to
foini a tight fit around the explosive end of the detonator. Resiliently
deformable materials
are particularly advantageous, since they may better assist in deceleration of
shrapnel
material being ejected or emanating from the explosive end, thereby reducing
the inertia of
the shrapnel. Moreover, the preferred tight fit of the detonator protector, by
virtue of the
resilient deformability of the detonator protector material, results in a
tightly sealed
interface leaving little or no gap between the detonator protector and the
explosive end. In
this way, any shrapnel will have neither time nor space to accelerate prior to
encountering
the detonator protector, further contributing to the advantages of the device.
Moreover, a
tight fit reduces the possibility of the protector being removed from the
detonator before,
during, or after actuation of the base charge, so that its protective function
is maintained.
CA 02606873 2012-09-13
- 12 -
The protectors herein are not, however, limited to those that stay in place
only by
interference or friction fit. A protector may be held on an explosive end of a
detonator by
any means, including for example, screw-thread fitting, snap-fitting, or any
other form of
suitable engagement, assisted by friction fitting such as that provided by the
use of resilient
materials.
Another important discovery by the inventors relates to the need for the
protector,
at least in preferred embodiments, to allow the detonator (to which it is
attached) to burn or
"cook off' in as full and complete a manner as possible, in the event of
inadvertent
detonator actuation. Indeed, failure of detonators to "cook off' sufficiently
during a
standard UN Test Series 6 external fire test (Bonfire test), can result in an
unacceptable
quantity of unburned explosive material remaining within the detonators after
the test is
complete. The inventors have discovered that by protecting principally the
explosive end
of the detonator, whilst leaving other portions of the detonator at least
substantially
unprotected by protector materials, improved detonator "cook-off' is
achievable, even
when the protectors of the invention remain attached to detonators during the
testing
procedures. In this way, the portions of the detonator shell not covered by a
protector
permit the heat of a test fire to be conducted more efficiently to the
explosive material in
the base charge at the explosive end of the detonator, thereby allowing it to
burn or cook
off more rapidly and/or efficiently. A more rapid cook-off also helps to
reduce burning or
other consuming of the protector material by the fire, so that a sufficient
mass of the
protector can be retained at the explosive end, for sufficient time for the
protector to
provide the required protective function. Preferably, the protector is
designed to stretch
onto and to fit tightly upon the explosive end of the detonator, so that it
can maintain its
position and its protective function throughout all the packaging, storing,
and transporting
procedures. This may be facilitated by selecting an appropriate material as
discussed
above.
CA 02606873 2012-09-13
- 13 -
When packaging multiple detonators, it is preferred to favour alternate "head-
to-
tail" orientation of adjacent detonators in the package. This helps to
maintain at least a
limited distance between the percussion-actuation ends of adjacent detonators
within the
package. With this arrangement there is a reduced possibility that inadvertent
actuation of
the base charge of one detonator may be directed to cause actuation of the
base charge of a
second detonator. Therefore, propagation to further detonators is less
unlikely. The
present invention therefore further provides for a method of packaging
multiple detonators
by protecting each detonator with the protector of the invention, and
positioning each
detonator in an alternating pattern, the explosive end of a first detonator
facing one side of
the package as the explosive end of its adjacent protected detonator is facing
the opposite
side of the package and so on, thereby to folin a row of alternately oriented
detonators. If
required, multiple rows of alternately oriented detonators may be stacked so
that the
detonators within one row are oriented in an opposite, alternating manner to
detonators in a
row stacked immediately above or below. Multiple rows may also be present in a
single
layer of detonators. Most preferably, any space in between adjacent protected
detonators
in a row, and in between adjacent rows or stacked rows, may be filled with an
energy-
absorbing and/or isolating material. Such isolating material may comprise any
suitable
material including but not limited to paper products, resins, plastics and
foams. Any kind
of packaging material, suitable for transport and storage of detonators, may
be used,
preferably having a capacity to absorb explosive energy, as well as flame
retard properties.
Such materials may also be used to surround protected, stacked arrays of
detonators, once
packaged.
Copper alloy shelled detonators are known in the art to be more shock
resistant
than aluminum detonators. They are also known to project shrapnel at a longer
distance
and with a greater energy. Such shrapnel may be more penetrating, due in part
to the fact
that copper is a denser metal than aluminum. Copper has the property to have
superior
electrical and thermal conductivity than aluminum, and well as superior shock
resistance.
CA 02606873 2012-09-13
- 14 -
For those reasons, there is a trend in the explosive industry to favor copper
detonators over
aluminum ones. Preferably, the present invention permits safe packaging and
transport of
copper-shelled detonators in compliance with UN 1.4 standards.
Subject to the requirement for the detonator protectors used in the present
invention
to be made of a resilient material and to be resiliently deformable, they may
be comprised
of any metal or non-metal material. Silicone rubber, wood, plastic, rubber,
plaster, cement,
cardboard, balsa wood, resin, or compressed sawdust are a few examples of
suitable
attenuator materials for the protectors. Silicone rubber and plaster have been
demonstrated
to exhibit particularly preferred properties. The testing by the inventors has
enabled
silicone detonator protectors to pass at least UN Test Series 6(d) testing to
date, and
corresponding plaster detonator protectors have passed 6(a), 6(c), and (6d)
testing to date.
Silicone rubber also represents a preferred material due to its resiliently
deformable
properties, that are particularly suited to tight securing of the protector
onto the percussion-
actuation end of a detonator. Plaster and silicone rubber, as well as other
materials listed
therein, are generally non-toxic and thus may present little environmental
concern if
discarded or otherwise not recovered from a blast site.
Certain exemplary embodiments thus provide for an assembly comprising:
(a) a detonator comprising a detonator shell having an explosive
end, and a
base charge of explosive material at the explosive end;
(b) a detonator protector comprising a recess for receiving and covering at
least
the explosive end of the detonator shell to contain shrapnel and/or explosive
energy
derived from the detonator in the event of inadvertent actuation of the base
charge, said
detonator protector being dimensioned such that it covers less than one-third
of a length of
the detonator shell from the explosive end, thereby to allow the explosive
material of said
base charge to deflagrate in the event of inadvertent actuation of the
detonator and/or
exposure of the assembly to the heat of a fire;
CA 02606873 2012-09-13
- 15 -
wherein the detonator and detonator protector are held together by a friction
fit
when at least the explosive end of the detonator shell is received in the
recess and covered
by the detonator protector, said detonator protector being made of a resilient
material and
being resiliently deformable to facilitate receipt of the at least the
explosive end of the
detonator shell in the recess and to facilitate tight fitting and gripping of
the detonator
protector on the at least the explosive end of the detonator shell to keep the
detonator
protector in place during transportation or storage of the assembly, or
inadvertent actuation
of the detonator.
As discussed above, such a detonator assembly may exhibit the desired
attributes of
excellent containment of shrapnel and/or explosive energy in the event of
inadvertent
actuation of the detonator, combined with rapid and/or efficient cook-off of
the explosive
material of the base charge.
Preferably, the detonator protector is made of a material having a resilience
to
maintain its shape and cohesion upon exposure to a high temperature, a flame,
or upon
actuation of a base charge located in said explosive end. In particularly
preferred
embodiments the material may be selected from any cross-linked polymer or
silicone
rubber, and may optionally further comprise any flame retardant as an
additive. Such
substances and additives are well known in the art. Silicone-based materials
are
particularly preferred, since they provide excellent cohesion, flame-
retardancy, and
resiliently deformable properties. In further exemplary embodiments, the
protector may
comprise a polymer that in the event of exposure to fire is capable of
conversion to a
ceramic-type material. Such polymers are known in the art such as those
manufactured
and/or utilized in Pyrolex0 Ceramifiable0 cables manufactured by Olex Cables
of
Tottenham, Victoria, Australia,
Regardless of the particular material, the detonator protector is comprised of
a
resiliently deformable material to facilitate placement or securing of the
protector onto the
explosive end of the detonator, and to help achieve a tight fit and secure
grip by the
CA 02606873 2012-09-13
- 16 -
detonator protector on the explosive end, thereby to keep the protector in
place during
transportation, storage, or detonator actuation. Furthermore, dimensioning of
the detonator
protector is such that it covers less than one-third of a length of the
detonator from the
explosive end. As discussed above, by leaving most of the detonator shell
exposed, this
improves the speed or efficiency of cook-off the detonators for example by
virtue of
improved heat conductance to the base charge. This helps to reduce the
possibility of
explosive materials remaining in the detonator following inadvertent actuation
thereof.
In selected embodiments, a detonator assembly of the invention may comprise
more than one detonator associated with a detonator protector. For example,
the assembly
may comprise two detonators each with their explosive ends contained within
each of two
recesses in a detonator protector. In preferred embodiments, such a protector
may be
configured so that insertion of the explosive ends of both detonators causes
the detonators
to attain an opposing, aligned orientation, with their respective explosive
ends separated by
a portion of the detonator protector. The portion of the detonator protector
between
opposing explosive ends of the detonators may be perforatable by shrapnel and
or
explosive energy emitted upon inadvertent actuation of one of the detonators,
such that
said inadvertent actuation causes cook-off of a base charge in the other of
said detonators,
said detonator protector substantially containing shrapnel from one or both of
said
detonators. In other related embodiments, the protector may not include any
material
between the opposing ends of the detonators, so that the protector is
effectively in the form
of a tube of material, with each open end of the tube being dimensioned to
receive an
explosive end of a detonator.
Still further exemplary embodiments pertain to methods of protecting a
detonator
from emitting shrapnel and/or explosive energy during transportation and/or
storage. Such
methods may comprise the step of: applying to an explosive end of the
detonator, a
detonator protector to form a detonator assembly as described herein.
CA 02606873 2012-09-13
- 17 -
Still further exemplary embodiments pertain to methods of packaging a
plurality of
detonators each comprising a detonator shell and an explosive end comprising a
base
charge. Such methods comprise the step of: placing a plurality of detonator
assemblies as
described herein into a container. Preferably, the step of placing comprises:
disposing each
protected detonator within a container according to an alternating pattern,
wherein when a
protected detonator has its protected explosive end facing one side of the
package, each
adjacent detonator assembly has its protected, explosive end facing a side
opposite said
one side thereby to form a row of alternately disposed protected detonators.
The step of
placing may additionally or alternatively involve placing more than one row of
detonators
into the container, with explosive ends of at least one pair of adjacent
detonators from
adjacent rows facing generally into the package in aligned opposition, and
disposed
explosive end to explosive end, each pair of detonators protected by a
detonator protector
comprising two recesses for simultaneously receiving each explosive end of
said pair, to
hold the detonators in said aligned opposition, with their respective
explosive ends
separated by a portion of said detonator protector. The step of placing may
also comprise
placing multiple rows of protected detonators into the container, stacked one
on top of
another, wherein adjacent rows of protected detonators and/or multiple rows of
protected
detonators stacked one on top of another, are preferably separated by a flame-
retardant
material.
For the purposes of still further clarification of the invention, specific
preferred
embodiments of the invention will now be described with reference to the
appended
drawings, which are in no way intended to be limiting. Figure la illustrates a
detonator
assembly of the invention, which comprises a detonator protector 1 shown in
section,
which generally covers the explosive end 2 (comprising a base charge) of the
detonator 3
by way of recess 6 in detonator protector 1, leaving the rest of the detonator
uncovered 4.
The Figure also illustrates that a portion la of the mass of the protector is
located in an
axial position or otherwise adjacent the explosive end of the detonator to
"catch" or
CA 02606873 2012-09-13
- 18 -
otherwise contain shrapnel from actuation of the base charge. Figure lb
illustrates the
assembly shown in Figure la, in perspective view.
It should be noted that although the protector illustrated in Figure la (and
the
following figures) is generally rectangular in section, the protector may have
any shape or
size, providing that it is adapted for catching or otherwise containing
shrapnel and fitting
securely upon the detonator. Also for purpose of clarity, the figures may
illustrate a gap
between the protector and the detonator surfaces. However, this is merely for
illustrating
the components present and is in no way intended to be limiting. Any such gap
may be
small or absent, as long as the functions of the detonator protector are
maintained.
Figure 2 illustrates a "double" protector 5 of the invention in section, which
is
designed to protect two detonators at the same time. Detonator protector 5 has
two
recesses 6a and 6b at opposite ends to cover explosive ends of two different
detonators. It
may be noted that part 11 between the explosive ends of the detonators as
represented in
Figure 2 is in no way intended to be limiting. This part can be absent, thin
or otherwise
perforatable by shrapnel and/or explosive energy derived from a detonator
being protected
by the protector, thereby to cause the second detonator to at least
substantially cook off in
the event the first one accidentally explodes.
Figure 3 illustrates a package of detonator assemblies generated according to
an
embodiment of a packaging method of the present invention. Figures 3a and 3b
illustrate a
plurality of detonators oriented according to an alternating pattern. Each
detonator 3 is
protected by a detonator protector 1 (each shown in section). Each detonator
assembly is
disposed according to an alternating pattern from adjacent detonator
assemblies in a row of
detonator assemblies. In Figure 3a, the first detonator assembly 30 has its
protected end 7
facing side 8 of package 20, the adjacent detonator assembly 31 has its
protected end 7
facing the opposite side 9 of package 20, the third detonator assembly 32 has
its protected
end facing side 8. This pattern may be repeated to generate several rows of
detonator
assemblies in the package.
CA 02606873 2012-09-13
- 19 -
Another option for an alternate packaging is illustrated in Figure 3b. The
first
detonator assembly 30 has its protected end 7 facing generally into package
20, so that its
uncovered part 4 is facing the side 9 of the package. The adjacent detonator
assembly 32
also has its protected end 7 facing generally into the package but with its
uncovered part 4
facing opposite side 8.
Figure 3c illustrates an alternative packaging arrangement wherein pairs of
detonators 3 are side¨by-side, but the pairs of detonator assemblies are also
packaged in an
alternating pattern. When two detonators of a pair have their explosive ends 2
facing
generally into the package in alignment, disposed explosive end 2 to explosive
end 2, the two
detonators can be protected by a double protector 5 shown in Figure 2. The
other pair
adjacent detonator assemblies each have their protected ends 7 facing sides 8
and 9 of the
package according to an alternating pattern.
Figure 3d shows a package comprising pairs of detonator assemblies 3 each
being
disposed explosive end 2 to explosive end 2 and protected by a double cap 5 as
shown in
Figure 2.
Figure 3e illustrates how rows of detonator assemblies may be stacked within a
container, one row on top of another, so that each row has opposite
orientation of detonator
assemblies compared to a row immediately thereabove or therebelow, i.e. the
first detonator
assembly 3A of a row 20 is in an opposite position compared to the first
detonator 3B of row
21 beneath row 20, and that the first detonator assembly 3C of row 22 is in
the same
orientation as detonator assembly 3A. For convenience and ease of
illustration, only the first
detonator assemblies 3A, 3B, and 3C are shown in rows 20, 21, and 22.
Additional
detonator assemblies may be present in each row in alternating orientation as
previously
discussed.
While the invention has been described with reference to particular preferred
embodiments thereof, it will be apparent to those skilled in the art upon a
reading and
CA 02606873 2012-09-13
- 20 -
understanding of the foregoing that numerous detonator protectors,
corresponding
detonator/protector assemblies, and methods for transportation and storage of
detonators,
other than the specific embodiments illustrated are attainable, which
nonetheless lie within
the spirit and scope of the present invention, It is intended to include all
such methods,
systems, and equivalents therefore within the scope of the appended claims.
