2. 18 BTI SUPPORT SHOTFIRER
Storage life
The storage life (shelf life) of an explosive is the manufacturers recommended time that
the explosive can be stored in normal magazine conditions (cool and dry). If conditions
are other than cool and dry, storage times can shorten dramatically particularly for
hydroscopic products such as prilled AN which may only last a few weeks in a very
humid, warm climate. The quoted storage life is conservative and will vary from supplier
to supplier but will generally lie within the following guidelines.
Product Maximum shelf life Effect of aging
ANFO 3 months Absorbs moisture, becomes
blocky and may break down
Packaged emulsion 2 years Emulsion crystallises.
Critical diameter may increase
beyond product diameter
Non-electric
detonators
12 months after
opening, 4 years in
unopened packages
Delay compositions age through
moisture absorption and oxidisation.
Delay times show increased scatter
Detonating cord 5 years Very little
Pentolite boosters 5 years Very little
Gassing agents Refer specific MSDS* Evaporation and crystallisation
Bulk Emulsion
Precursor
Refer specific MSDS* Product separation, crystallisation,
loss of viscosity
*The material safety data sheet (MSDS) will detail storage issues.
Temperature effects
AS2187.1 10.6.1 defines ‘hot’ material where the temperature is greater than 55 degrees
Celsius but less than 100 degrees Celsius. There are specific requirements for blasting in
hot ground and these must be followed. In particular specific recommendations must be
obtained from the manufacturer before loading any product into ‘hot’ ground.
It is not possible to make firm recommendations about safe exposure times for
explosives at various temperatures because of the wide range of operating conditions
and products available.
Emulsions are generally safe to use up to 100 degrees Celsius, but in most cases
the limiting factor will be the initiating system, which contains the most sensitive
components.
3. MODULE A5 19
For explosives inside blastholes at constant elevated temperatures, maximum safe
temperatures for exposure are summarised below:
Product Maximum temperature o
C
ANFO 100
Packaged emulsion 100
Non-electric detonators 70
PETN based detonating cord 70
Cast Pentolite boosters 70
Hot and reactive ground
Blast crew must always be aware of the potential for the presence of hot and reactive
ground. Where any of the the following are observed they must be immediately reported
to the shotfirer.
Reactive ground
• The presence of black sulphide bearing sediments
•
Sulphides within mineralised rock
•
Sulphides often appear as glittery or
shiny bands in the rock
•
Presence of white or yellow salts
on rock. This is an indication that
oxidation is taking place
•
Acidic conditions (generally resulting
from oxidation) as indicated by the
colour of run off water, usually yellow-red brown in colour
•
The spontaneous combustion of overburden or waste rock / ore either in dumps
or in the pit, especially as it is exposed to the air
•
The acrid smell of sulphur dioxide caused by the naturally occurring sulphide
oxidation reaction
•
The rock type occurring in the transition zone just below the limit of the oxidation
line (ie where light coloured bleached rock ends and darker coloured rocks begin)
Hot ground
• Steam rising from the blast hole
• Heat felt at the collar
• Melted dip rope
• Heat shimmer coming from hole
PROPERTIES OF EXPLOSIVES
Incandescent reactive ground in the 500
Orebody, Mount Isa Mines c.1960s.
(Mount Isa Mines, n.d.)
Sulphide mineral (pyrite) in bedded formation
4. MODULE A5 25
ANFO
In 1947 in Texas City USA two ships loaded with wax coated AN caught fire and subsequently
exploded. The investigation into the accident, which killed 576 persons, identified the liquid wax
‒ AN mixture as being responsible for the powerful explosion. This led to further investigations
into ANFO type mixtures.
Although any number of carbonaceous materials can be used with ammonium nitrate
(AN) to produce a satisfactory explosive distillate has been the fuel of choice since the
late 1950s. Distillate is an ideal fuel for mixing with AN to form explosives. It is readily
available, relatively inexpensive and easily blended with AN to produce a uniform mix,
commonly called ANFO (Ammonium Nitrate Fuel Oil).
ANFO is more sensitive and, therefore, more reliable than mixtures of AN and powdered
fuels. More volatile fuels (e.g. petrol, kerosene) give greater sensitivity but offer no
significant advantage in effective energy; they also exhibit lower flash points, thereby
introducing the risk of a vapour explosion during mixing and charging operations. For this
reason, legislation prohibits the use of liquid fuels with flash points lower than 61 0
C.
Mixing of ANFO
AN is usually mixed with distillate (diesel / FO) on site for use as an explosive. Correctly
proportioned and mixed ANFO can be charged most efficiently and rapidly by means of
Mobile Processing Units.
Mixing unit must be regularly calibrated. This is commonly done by disconnecting the oil
line and operating the mixer while catching the separate oil and AN. These can then be
weighed to check the % mix of each. Good mixing is needed as it is possible to have the
correct % of fuel overall but not consistent throughout the mixture.
Any machine used for mixing must be designed to avoid the possibility of frictional
heating and any bearings or gears must be protected from spillage of AN or ANFO.
A petrol engine must not be used for power-operated mixers. Approved electric –
powered motors can be used.
To provide an immediate visual indication of the distribution of distillate in the mix and
to distinguish between a mixed product and straight AN, it is standard practice to colour
the distillate with a vivid oil soluble dye before the distillate is added to the AN.
Mixing of AN and distillate constitutes manufacture of an explosive. For this reason, a
licence or permit to mix ANFO must be obtained from the appropriate statutory authority.
BULK EXPLOSIVES
5. 26 BTI SUPPORT SHOTFIRER
Maximum explosive energy is obtained with 5.8% by weight of distillate. The addition of
5.8% distillate to AN almost trebles the energy yield. With too much or too little distillate,
energy yield falls off. As one would expect, the VOD is also greatest at 5.8%.
The density of diesel is 0.83 kg per litre. If litres is used to calibrate the mixing of ANFO
(rather than weight) the correct proportion is 7 litres fuel oil to 100 kg AN.
ANFO (kg) AN (kg) Diesel (kg) Diesel (litres)
10.6 10 0.62 0.74
53.1 50 3.1 3.7
265 250 15 18.5
10 9.42 0.58 0.7
50 47.1 2.9 3.5
250 235.5 14.5 17.5
The advantage of having a uniform mix of AN and distillate is obvious. Even when the
correct amount of distillate is added unless it is evenly distributed explosives performance
will suffer. For example where 75 litres of distillate is added to one tonne of AN but half
receives 60 litres while the other half tonne receives only 15 litres, then the energy
generated by this tonne of ANFO will be about 23% lower than that from a completely
uniform mix.
The appearance of distinctly orange – coloured nitrogen dioxide fumes after an ANFO
blast may indicate too little distillate in at least some of the ANFO.
(However this is usually an indicator ANFO that has been attacked by blasthole water or
has been inadequately primed.)
Correct ratios for mixing small quantities of ANFO
Amonium Nitrate (kg) Diesel 5.8% (litres)
10 0.75
25 1.9
50 3.75
ANFO properties by weight % of FO
Mixing ratios for ANFO.
6. MODULE A5 31
Emulsion / AN blends – Doped Emulsion
Emulsion explosives may blended with AN prill and diesel to improve energy and reduce
cost. By blending varying proportions of AN and EP it is possible to manufacture a range of
products. Where emulsion is the major component, greater than 50%, they are called doped
emulsion explosives; where AN is the major component, they are called Heavy ANFOs.
Doped emulsion explosives
Doped Emulsion explosives consist of particles or
prills of ANFO or AN (dry phase) within an emulsion
matrix, the percentage of emulsion usually lying in
the 55 to 90% (weight basis) range. Provided the
emulsion phase content is maintained above about
45% (weight basis), there is sufficient emulsion to
completely cover the AN and the product is
considered waterproof.
The high proportion of emulsion gives doped
emulsion explosives excellent water resistance.
They are specifically designed for use in blastholes,
withstanding water and are often described as
“waterproof”. Doped Emulsion must be pumped into blastholes through flexible hoses
that deliver the product to blasthole toes, displacing the water upwards. It is normal for
emulsion explosives to be chemically “gassed” for
sensitivity and to produce a range of densities as required. A doped emulsion explosive
will compress under load and lose sensitivity with increasing column height. For this
reason the manufacturer’s guidelines for maximum depth and diameter must always
be observed.
As greater percentages of a dry phase are added to an emulsion, both the reaction rate
and detonation velocity decreases. The initial reaction proceeds through and takes place
within the emulsion matrix; the reaction in the (coarser) dry phase is initiated by the
emulsion’s reaction and extends over an appreciably longer period. Therefore, by adding
dry phase, the overall duration of the reaction is extended, thereby increasing heave
energy and muckpile looseness at the expense of strain wave (or shattering type) energy.
In relatively weak rocks, the presence of a dry phrase has the beneficial effect of reducing
energy losses associated with excessive fragmentation and plastic deformation close to
the charge.
Where the dry phase is totally enveloped by highly reactive emulsion, its reaction
commences with great vigour and proceeds to completion more easily and efficiently
than in the case of ANFO where prills are surrounded essentially by air. Therefore, it
seems reasonable to believe that the actual energy produced from an emulsion / dry
phase blend is appreciable greater than that for ANFO. This is perhaps the most
important factor to explain the observation that such products perform better than their
theoretical energies suggest.
BULK EXPLOSIVES
7. 32 BTI SUPPORT SHOTFIRER
The importance of fragmentation seems to have been over emphasised at the expense
of muckpile looseness. Whilst fragmentation is usually the most influential feature of a
muckpile, looseness has a very considerable effect on the ease, speed and cost of
digging and hauling. The desired amount of muckpile looseness depends very largely
on the explosives heave energy. By adding a dry phase to an emulsion, the heave energy
and, hence, muckpile looseness are increased. The inclusion of up to 40% dry phase
has the beneficial effect of increasing muckpile looseness usually without detracting from
effective fragmentation.
8. MODULE A5 41
Non-electric detonators
The development of shock tubing in the early 1970’s revolutionised initiation system design.
Thirty years later the majority of surface and underground blasting is still based on this
product. It is only the development of simple and reliable electronic initiation systems that are
now starting to challenge the dominance of shock tube systems.
Usage
Non-electric detonators are widely used as in-hole delay downlines to initiate cast and
packaged primers in blastholes.
Other applications include providing a delay in a detonating cord trunkline, hookup
in a surface ‘daisy chain’ network to provide hole by hole initiation in surface blasts and
initiating detonating cord.
Construction
Non-electric detonators typically consist of a length of shock tubing with one end sealed
and the other crimped into a detonator. Variations to the base unit include the addition
of plastic connector blocks and different spooling and coiling configurations. In the next
sections we look at the shock tube and detonator construction.
Shock tube
Shock (or signal) tubing is the basis of all non-electric initiation
systems. Shock tubing consists of a 3 mm outer diameter
plastic tube with a 1 mm hollow core. The core is lined with
a coating of reactive powder (HMX and Aluminium) at around
16 grams per kilometre.
INITIATION SYSTEMS
9. 42 BTI SUPPORT SHOTFIRER
Functioning
Shock tube
When the tubing functions the shock wave travelling in front of the reaction lifts the
powder from the walls of the tube. The reaction then progresses through the tube in
the form of a ‘dust explosion’ unlike detonating cord which ‘detonates’.
The velocity of detonation of tubing is only 2000 metres per second compared to
9100 m/sec for HMX explosive.
Hazards and failure modes
Shock tube sensitivity
Shock tubing is relatively insensitive to accidental initiation from impact and heat
although there have been regular occurrences of initiation by the ‘snap, slap and
shoot’ mechanism.
This occurs when machinery becomes entangled in shock tube and when moved
stretches and snaps it. Initiation is possible and around one incident per annum is
reported from somewhere around the world. The consequences of an accidental initiation
of a downline when there are persons and equipment in the vicinity is often catastrophic.
Shock tubing is relatively insensitive to accidental initiation from radio frequency (RF)
energy, static and stray currents. Tests with static discharges over 10 kV have failed to
initiate tubing. However shock tube is not immune to initiation from direct lightning strike
and normal evacuation procedures in the event of electrical storm must be followed.
Failure modes
Shock tube may also fail when exposed to the oil phase of explosives for extended
periods of time. Standard tubing should last for at least two weeks sleeping in a blasthole.
For longer periods most manufacturers produce a ‘heavy duty’ tubing. This is formulated
from a plastic more resistant to oil penetration. High temperatures reduce the amount of
time to unit failures occur.
Shock tubing will also fail should a small quantity of moisture enter the tubing.
To prevent this the end seal should never be removed.
10. MODULE A5 71
Geotechnical assessment
When assessing a work area for risk rock slope stability must be assessed on a continual
basis. Blasted faces exposed to weather and mining activity may deteriorate further
during the mining cycle meaning that what was safe last week may not be now.
Rock slope stability is dependent on many factors, the key ones for blast crew are:
1. Characteristics of the rock mass
2. Geometry of the exposure
3. Common failure mechanisms
These will be briefly identified in the following sections.
Characteristics of the rock mass
Rock masses vary enormously in strength and structure. At one extreme there is
completely intact rock masses with no joints
At the other there is highly jointed weak rock with weathered and slippery joints.
These rock masses will behave very differently when exposed by mining activity.
BLAST PREPARATION
11. 72 BTI SUPPORT SHOTFIRER
Geometry of the exposure
The exposure geometry in relation to stability is defined by three key parameters:
Height
The higher the exposure the more load on the toe and the more likely that failures will
occur on existing planes of weakness. Moreover failures on high faces generally involve
more rock moving faster.
Angle
The steeper the face the more likely a failure.
Steep faces are more prone to all failure mechanisms including ravelling, sliding
and toppling.
12. MODULE A5 81
Validate drill pattern
After checking for risk the next step is to validate the drill pattern. The objective here is to
confirm that the drill design has been properly executed and that holes are in the correct
position and properly identified.
An accurate drill plan is required for reference. The plan should be scaled and show all
holes, hole ID’s and relevant local features to enable the blast crew to locate themselves.
Drill pattern detail.
Where a drill monitoring system has been used the drill plan should be based on this data.
Plans that show redrills and true positions are a more reliable check of the as-built.
Redrills should be shown on the plan and identified on the ground.
Drilled holes are to be checked against the provided drill plans. As a minimum the end
hole in each row should be identified and confirmed.
Where holes are missing these should be recorded on the drill plans.
BLAST PREPARATION
13. MODULE A5 123
Preparation
When blastholes are being primed and loaded, ensure security of the blast area.
Minimise other work in the area and allow no other work to be done within a safe distance
of charged holes.
Working with load standards
Each site should develop a general load standard to communicate to shotfirers the site
requirements of the blast design and the allowable tolerances. Load standards, typically
expressed in a site data
sheet, will reflect site
equipment, available
products and design
standards and should
define design parameters
and details such as
backfill requirements,
stemming tolerances
and product selection
criteria.
An example of a load
standard is shown adjacent.
Load standards provide general information in regards to a site or an area or bench on a
site. They are an appropriate means of managing loading where there is little variation in
the blast designs and the bench height and faces are relatively constant.
A limitation with using load standards / site data sheets as the design communication to
the shotfirer is that changes to bench geometry may not be picked up and may lead to
poor blast performance and increased risks.
The diagram below (taken from an actual flyrock incident) demonstrates the problem
with using a site data sheet without consideration of actual / changing bench conditions.
Owing to situations like this many operations choose to go to the next level and
implement load sheets to manage blasting on a daily basis.
LOADING
14. 124 BTI SUPPORT SHOTFIRER
Working with load sheets
Load sheets are produced on a shot-by-shot basis and provide detailed information for
each hole in the pattern.
Whilst the use of load sheets provides a higher level of control it requires a drill and blast
office to develop the sheets from survey and mine plans and process the drill and dip data
to calculate the design hole loading.
Even with accurate load sheets, the individual load heights must be controlled by the
shotfirer owing to variations in column rise due to holes drilled by worn bits and variation
in explosives density from design.
Whilst load sheets cannot be used without shotfirer supervision they still provide the best
level of control. Accurate blasthole depths and water levels are key to designing loads for
individual holes, particularly on sites where multiple products are used.
An example of a load
sheet identifying the
key parts is shown to
the right.
Whilst the blast design
and load sheets will
provide sufficient
information to correctly
load holes that are
correct to design it is
up to the shotfirer in
charge to determine
when holes are
sufficiently‘out-of-spec’
to justify a change in
explosive loading or stemming.
“On-bench” decisions on loading typically involve holes where burden or bench conditions
present potential overcharging and generation of flyrock or environmental excursions. Any
change from either a load standard or a load sheet specification should be recorded for
later reference.
Example:
A 150 mm hole has a design load of 17.7 kg/m at density 1.0.
A 15 m hole with 5 m stemming would therefore have a design load of 177 kg.
However if the bit is worn to 142mm the hole will load at 15.8 kg/m.
The column loaded is then 177 / 15.8 = 11.2 m and the resulting stemming
height is 3.8 m.
This may be insufficient to contain the explosives resulting in rifling and
potential flyrock.
LOAD SHEET
Shot NR-3204- West Toe Super-Slurry density 1.25
Location Centre pit - Bench 26 Column ANFO @ 0.8
Date 22/11/2009 Hole diameter (mm) 165
Design Stemming (m) 4
Hole ID Dipped Target Backfill Water Toe Column Toe Column Comments
A26 24.7 25.5 3 150 250 160 240
A27 26.4 25.5 4 200 200 400 Fully wet
A28 26.2 25.5 3 150 250 160 240
A29 26.8 25.5 1.3 3 150 250 170 230
A30 24.5 25.5 5 200 200 230 170
A31 24.1 25.5 5 200 200 230 170
A32 23.7 26 5 200 200 220 180
A33 24.6 26 6 250 150 270 130
A34 25.4 26 6 250 200 260 190
A35 24.3 26 4 200 200 Blocked at 5m
A36 25.7 26 4 200 200 220 180
A37 26.1 26 5 200 200 210 190
B1 23.5 24.5 2 150 200 180 170
B2 23.7 24.5 100 250 110 240
B3 26.3 24.5 1.8 100 250 130 220
B4 26.7 24.5 2.2 100 250 130 220
B5 25.7 24.5 1.2 100 250 140 210
B6 24.1 24.5 100 250 130 220
B7 25.0 24.5 100 250 120 230
B8 25.9 24.5 1.4 2 150 250 180 180 Inc stem to 6m weak collar
B9 26.5 24.5 2.0 3 150 250 180 220
B10 23.7 24.5 3 150 200 160 190
B11 27.2 24.5 2.7 3 150 250 160 240
B12 25.4 25 4 200 200 220 180
B13 24.5 25 4 200 200 210 190
B14 24.3 25 4 200 200 240 160
Design Charge (kg) Actual Charge (kg)
15. MODULE A5 151
Using a “reel off” LIL kit
A “reel off” LIL kit provides a spool of shock tube with splices and end caps to allow
more flexible use and user control of tube consumption, commonly with remote firing
systems. Part spools may be retained for later use. A surface detonator unit is used as
the initiating detonator.
Be aware that any ingress of water or dirt into an open signal tube may result in shutdowns.
Use a reel off, field assembly, LIL system only where shutdowns can be tolerated.
A typical application is illustrated above; note the use of a reel off LIL to the initiating
point. To ensure that the splices do not become separated, it is good practice to
double the tubes and tie a loose overhand knot. Again the last connection should be
at the initiation point.
HOOK-UP
16. 192 BTI SUPPORT SHOTFIRER
Types of explosives
Explosives are classified in a number of different ways.
For example a shotfirer might refer to cast boosters as
HE or High Explosives whereas these will be
“Composite Molecular Explosives” to the chemist and
‘Class 1.1D’ to the shipper.
For the purpose of storing explosives it is the Class of
explosive that defines compatibility. All explosives are
Class 1. This is denoted by the ‘1’ at the bottom of
the orange diamond as shown here.
The Class is then further defined by the Hazard Division and the Compatibility Group,
these being the number and letter after the 1 on the diamond shown.
Hazard Divisions
1.1
those ‘substances and articles which have a mass explosion hazard’
i.e. if any part detonates the entire load is likely to detonate.
1.4
means that there is no significant hazard in that a part may detonate
but this will not set off the remainder of the load.
1.5
comprises substances which may explode but are so insensitive there
is little probability of initiation or transition from burning to detonation.
After the Hazard Division, the letter denotes the Compatibility Group. This tells us what
explosives can be stored and transported with which other explosives.
The two main Compatibility Groups are D, for secondary explosives and B for articles
containing primary explosives.
As a support shotfirer you will generally only deal with Compatibility Group D and
Group B explosives.
Group D
(secondary explosives) contains articles such as boosters, detonating cord,
packaged explosives, shaped charges and ANFO.
Group B
(Primary explosives) contains articles with a primary explosive such as
detonators (both in-hole and surface) and detonating relay connectors.
The golden rule for storage and transport is:
Never mix Compatibility Group D and Group B products together.
17. MODULE A5 193
CLASSIFICATION and STORAGE of EXPLOSIVES
In summary the classes of explosives you will likely come across as a support shotfirer
are as follows:
Class General description Examples
1.1D Secondary explosives with a mass
explosion hazard.
Boosters, packaged explosives,
ANFO.
1.1B Primary explosives with a mass
explosion hazard.
MS detonators, Millisecond
connectors.
1.4B Primary explosives with no mass
explosion hazard.
Some detonators packed with
protective sleeves around the
base charge
1.4S Article packed such that the
packaging contains any hazardous
effect from accidental functioning
Shot shell primers for lead in line
starters
1.5D Very insensitive substances which
have a mass explosion hazard
Some emulsions, slurries and
watergels.
The class of a particular explosive is shown on the:
• Technical Data Sheet (TDS) available from the manufacturer.
• Material Safety Data Sheet (MSDS) also from the manufacturer.
•
The Australian Explosives Code (AEC) lists all explosives, their properties
and the classification.
• The orange diamond printed on the box or other packaging.
More information on the various classifications, hazard
divisions and compatibility groups is provided in the
Australian Explosives Code (AEC) particularly to
Appendix 2 on pages 127–183.
