Publication No. 27
THE TRANSPORTATION, STORAGE, MIXING
AND HANDLING OF AMMONIUM NITRATE AND
ANFO.
CONTENTS
2.
INTRODUCTION
3.
AMMONIUM NITRATE
3.1
General
3.2
Quality of Product
3.3
Storage
3.4.
Transport
4.
FUELS
5.
MIXING AN, FO AND EMULSION
6.
CHARGING
7.
SAFETY AND FIRE PROTECTION
8.
ENVIRONMENTAL ISSUES
9.
SECURITY
2.
INTRODUCTION
The insensitivity of ammonium nitrate fuel oil mixtures, relatively low cost and good
blasting performance, have revolutionised the commercial explosives industry
throughout the world, allowing the practice of mixing ammonium nitrate with fuel oil
close to the location of use (on-site mixing) and as a cost effective blasting agent it has
established its credentials in almost every sphere.
However, the act of moving explosive manufacture away from the heavily regulated,
highly disciplined, atmosphere of explosives factories has created other problems.
The purpose of this Code of Good Practice is to ensure that the practices adopted with
Ammonium Nitrate and ANFO are of the highest possible standards.
It has been the habit in the past with these Codes of Good Practice to include
definitions of technical terms and phrases in the pre-amble.
The FEEM The “Glossary of Terms” included above for the European Explosives
Industry will act as a reference for all definitions.
3.
AMMONIUM NITRATE
3.1
GENERAL
Pure Ammonium Nitrate (NH4NO3) is a colourless, water-soluble, crystalline
substance with a melting point of 170oC. Decomposition starts at 210oC. Technical
grades may start to decompose at temperatures lower than 210oC because of
impurities.
The substance is classified as an oxidising agent Class 5.1(UN No. 1942).
As an oxidiser Ammonium Nitrate can support the burning of fuels relatively easily and
is used extensively to support the “fast” burning required in explosives. Decomposition
of Ammonium Nitrate takes place through several reactions. In the early stages
sublimation to ammonia and nitric acid dominates. At slightly higher temperatures, N20
is the main decomposition product. Above 260oC nitrous gases (NOX) are formed in
considerable amounts and these are toxic (See Section 9).
Ammonium Nitrate is used worldwide mainly as fertiliser. This is because of its unique
combination of nitrogen bound as nitrate and as an ammonium ion. The substance is
readily soluble in water and solubility is highly dependent on the temperature.
Ammonium Nitrate is manufactured by neutralising nitric acid with ammonia, resulting
in a solution with a high mass fraction of Ammonium Nitrate. This solution can be
delivered as hot solution as a raw material for slurry or emulsion explosives. Ammonium
Nitrate has at least five different crystal modifications existing at different temperature
intervals. The most interesting transition point is at 32oC. When the temperature for the
substance passes through this value, a volume change takes place in each particle
resulting in a breakdown to powder. In practice, this means an increased risk of caking.
3.2.
QUALITY OF PRODUCT
3.2.1 Ammonium Nitrate Form
The Product for explosives manufacturing can be delivered in different forms
depending on the type of explosives to be manufactured:
The most convenient form for the manufacture of the base emulsion or slurries is a
concentrated hot solution of Ammonium Nitrate. (See C.G.P. Emulsions).
However for storage, transport and cost reasons prills are often used to manufacture
the base emulsion. This base emulsion can then be mixed with more prills, or ANFO.
The most convenient form for the manufacture of dynamites or TNT sensitised
explosives, is a prilled or crystalised form which has been treated and/or coated with
an anti-caking agent.
Clearly it is important that any anti-caking agent which may be added does not
interfere with either the quality of the product or the manufacturing process of any
explosive.
In some instances the prills and the crystalline Ammonium Nitrate are crushed or
milled as part of the manufacturing process.
Ammonium Nitrate Fuel Oil Mixtures
Ammonium Nitrate in prill form is preferable for ANFO. However, the porosity,
density and strength of the prills may vary depending on the particular application.
3.2.2 Porosity/Density:
For oxygen balance the oil content of ANFO should be 5.7%. It is desirable therefore
that the prill used is sufficiently porous to absorb readily at least this percentage. In
fact, an absorbency of >10% is preferable to prevent migration of the oil out of the
mixture over time. Such a migration leads to inconsistent mixtures and inefficient
blasting, and there will also be the likelihood of NOX fumes being generated in the
blast.
Porosity in excess of that required for absorbency of the oil will impart additional
sensitivity to the finished product if this is required. Prill size in the range 1-3mm will
allow greater loading density than if the prills are all of the same size. In certain
instances where the ANFO will not be kept in the borehole for long and a strong
primer is being used, a denser, less porous Ammonium Nitrate may be used. The
application will dictate the optimum porosity and density required for the efficiency of
the blast.
The general rule is that higher porosity/lower density prills result in larger areas of
contact between Ammonium Nitrate and fuel oil. This in turn increases the reactivity
of the product and decreases the critical diameter. Porosity and density can also effect
velocity of detonation and fume production.
3.2.3
Prill Friability
Prills should be strong enough to withstand the mechanical stresses of storage,
handling, transport, mixing and to some extent the impact of pneumatic loading.
However, in the case of pneumatic loading in mining/tunneling operations where the
drill holes are smaller it is desirable that the prill should break down to give maximum
loading density. This is also important where up-holes are being loaded; the crushed
prills must compact in the holes to prevent the ANFO falling out again.
3.2.4
Purity
Ammonium Nitrate is an oxidising agent and shall not contain more than 0.2% of
organic material, otherwise the product will be classified as an explosive according to
UN Recommendations for Transport of Dangerous Goods.
-
The chlorine content should be lower than 0.02% because of a risk of chemical
decomposition.
-
The pH shall not be lower than 4.5 measured in a 10% solution at 25oC. A lower
pH
means that the product can be unstable.
-
For operational purposes a pH range of 4.7 to 5.5 of a 10% solution is preferable.
Graphs published by permission of Norsk Hydro
3.3
3.3.1
STORAGE OF AMMONIUM NITRATE
General
Manufacturers of Ammonium Nitrate will supply advice to their customers of storage
requirements for Ammonium Nitrate and these should always be very carefully
observed. The following is a non-exhaustive list of good practice associated with the
storage of Ammonium Nitrate.
Ammonium Nitrate for use in explosives should be stored in a secure area.
It is common in some countries, provided the packaging gives adequate water
protection, to store Ammonium Nitrate in the open air. However, care must be taken
to observe that the material does not cycle through 32oC. See paragraph 4.3.10.
3.3.2
General Management
1. Arrangements should be in place for the store to be inspected at routine intervals.
2. The records should keep an accurate inventory of products stored and the contents
of the store at any time
3. Good product rotation should be practiced on a “first in-first out basis”.
4. All storage areas should be protected from entry of unauthorised persons.
5. Stores should be clearly labeled and comply with all the relevant National
Authority regulations.
6. Local and national regulations often apply to Ammonium Nitrate storage. These
should be checked and followed. Also national regulations derived from the
Directive 96/82/EC(Seveso II) should be checked.
3.3.3
Minimising Fire Risk
1.
Ammonium Nitrate should not be stored where it can be affected by any
source of heat or contaminated with any general combustible material.
2.
It is a good principle to store AN on its own. It is possible to store it with
other oxidisers. The practice of storing it with inert materials is possible,
but not recommended. Where Ammonium Nitrate is stored in the same
overall building with organic material, then a firewall must be placed
between the two.
3.
A “permit to work” system should be in operation on the site to ensure that
there is no unauthorised use of equipment such as acetylene burners or
welding equipment which might be a source of ignition.
4.
Prominent “No Smoking” signs must be displayed.
5.
No vehicle maintenance activities, or equipment repair activities, should
take place within the storage area of Ammonium Nitrate.
3.3.4
Good Housekeeping
1.
It is strongly recommended that the use of copper or copper alloys and zinc
should be forbidden because they will corrode severely in contact with
Ammonium Nitrate. According to some sources both copper and zinc can
sensitise Ammonium Nitrate and should be avoided for that reason.
2.
Floors should be made of non-combustible material without hollows where
molten Ammonium Nitrate could concentrate in the event of a fire.
3.
Normal good housekeeping practice is essential, including the disposal of
all rubbish (particularly inflammable rubbish such as broken pallets, paper
and all organic substances). Particular care should be paid to the avoidance
of oil and oil spills. Disposal of oily rags should be carefully undertaken.
4.
Buildings and constructions should be of non-combustible materials.
5.
Floors shall be easy to sweep and to clean with water.
6.
It should be noted that in the event of the necessity of using water to
extinguish fires in an Ammonium Nitrate store, there is a distinct risk of
damage to the environment as a result of Ammonium Nitrate contaminated
fire water being discharged into public waterways.
3.3.5
Storing Ammonium Nitrate in loose bulk.
1.
Ammonium Nitrate is a hygroscopic salt and unless properly treated cakes
readily on exposure to the atmosphere. Care should be taken to ensure that
any bulk Ammonium Nitrate stores are properly waterproof.
2.
Ammonium Nitrate may be stored indoors in bulk. The maximum amount
to be stored is generally controlled by local regulations and great care
should be taken to see that these are conformed to.
It is extremely important in this type of storage that the design of the
building and handling routines prevent organic material and other foreign
materials coming into contact or being mixed with the Ammonium Nitrate.
3.
Care should also be taken to avoid garaging any vehicle in the same
building as Ammonium Nitrate. Normally a firewall should separate
Ammonium Nitrate storage facilities and vehicles.
3.3.6
Bulk Storage in Silos
1.
Design of silos should be selected to minimise caking, using for example
flexible panels in the wall construction. Alternatively, a system of blowing
through dry air can be considered to prevent caking.
2.
loading.
Consideration can also be given to a vibrator feeding system for off-
3.
Silo walls should be a light colour to minimise overheating in summer.
3.3.7
Packaged Ammonium Nitrate
Packaged Ammonium Nitrate is normally delivered in bags or I.B.C.s containing 25kg
- 000 kg.
Again, storage conditions are usually subject to local regulations but some
fundamental principles have to be observed for the sake of good practice.
a)
There should be adequate space between each row of packaging to allow
for
inspection of the material.
b)
The packages should not be piled so high as to damage the packages of
the
lower units.
c)
3.3.8
There should be adequate space for the top of the package to the roof of
storage to allow for the operation of water sprinklers in the event of fire.
Separation from explosives activities.
Ammonium Nitrate should be stored separately from explosives, explosives
manufacturing and blasting operation. National Regulations generally exist for
separation distances for Ammonium Nitrate from explosives operations and storage.
These should be observed at all times.
3.3.9
Separation from Fuels (organic materials)
Ammonium Nitrate and fuels shall be stored in separate buildings or in separate
compartments of the same building with adequate fire protection separation. If stored
in the open the distance between the Ammonium Nitrate and fuel barrels should be
adequate to prevent cross-contamination.
3.3.10
Storage conditions
Ammonium Nitrate is readily soluble in water and has a crystal transition point of
32oC. Both of these properties have influence on suitable storage conditions.
However modern products treated with anti-caking characteristics resist moisture very
well.
For material which is not treated with anti-caking then a maximum of 60% relative
humidity is recommended.
It is desirable that the storage temperature should be kept below 32oC and it should be
noted that if the material is cycled through 32oC several times the prill structure will
break down. This change will inevitably damage the packaging material and the
porosity of the product.
3.3.11
Solidified Product
Solidified product can be broken into small pieces by mechanical means. Small bags
can be broken with manual tools or by hydraulic presplitters and then further treated in
conventional crushers.
DO NOT USE EXPLOSIVES TO BREAK DOWN SOLIDIFIED PRODUCT
as there is considerable risk that the Ammonium Nitrate will detonate.
Solidified material in big bags or in piles may need more sophisticated equipment in
the form of tractors and shovels, and specialist advice from the Ammonium Nitrate
manufacturers should be obtained.
3.3.12
Vehicles in an Ammonium Nitrate Store
It is recommended that any vehicle used in an Ammonium Nitrate store is battery or
diesel powered. Petrol and LPG powered vehicles are specifically to be excluded.
Also any vehicle used in a building with bulk unpackaged Ammonium Nitrate should
be fitted with an effective spark arrester to its engine exhaust.
The vehicles should be checked carefully for any fuel, lubricating or hydraulic oil
leaks as these can become mixed with Ammonium Nitrate on the floor and form
substances which could be flammable or explosive.
3.4
TRANSPORT OF AMMONIUM NITRATE
Ammonium Nitrate is classified as oxidising agent (UN Class 5.1), so all transport on
public roads is regulated in ADR. Corresponding regulations are in place for transport
by rail and boat. There can be additional legislation too, especially for security
reasons.
It should be noted that if Ammonium Nitrate contains more than 0.2% organic
material it is considered as UN Class 1 explosive and must be treated accordingly.
Refer to UN Recommendations for Transport of Dangerous Goods (Orange Book).
4.
FUELS
By far the most common type of fuel added to Ammonium Nitrate is diesel or gas oil
although other fuels are used in some circumstances.
The most common of these include:
Mineral oils
Aluminium powders
Carbon powders
4.1
4.1.1.
DIESEL OIL
Quality
The quality of the oil used for ANFO manufacturing may vary and is not critical as
long as the flash point is significantly higher than the process or ambient temperature.
It is recommended that the flash point should be more than 55oC .
4.1.2
Storage
Diesel or gas oils should be stored in designated areas away from oxidising materials,
heat and open flames. The tanks should be kept closed and the tanks must be bunded.
Smoking should be prohibited in the area of storage.
The storage of diesel oil and gas oil is well regulated in every State and close
consideration must be given to National Regulations.
4.1.3
Toxicity
Gas oil/diesel oil is an irritant to the eyes and may cause dermatitis on prolonged or
repeated contact. The skin may be seriously affected by prolonged exposure
especially when clothing is also oil contaminated.
Aspirations of the liquid into the lungs following ingestion is highly hazardous.
Appropriate measures must be taken to prevent skin or face contact and protective
clothing should be worn, and regularly changed.
4.2
ALUMINIUM POWDER
Aluminium powder may also be added to ANFO and it should be noted that it is a
hazardous material classed as “flammable solid” and in the United Nations
Recommendations for Transport of Dangerous Goods is Class 4.
4.2.1
Storage
Aluminium powders should be stored separately from other products and in a dry
location and it should be noted that under certain circumstances these powders can
react violently with water.
4.2.2
Toxicity
The acute toxicity and irritant effects of aluminium powder are low, but it should be
noted that chronic exposure to aluminium dust can result in fibrogenic effects possibly
severe on the lungs.
4.2.3
Dust
It should be noted that in certain circumstances the presence of Aluminium dust can
lead to explosions. Care should be taken to avoid the creation of dusty atmospheres.
4.3
OTHER FUELS
When other fuels are used, the suppliers’ recommendation must be followed and
National Regulations adhered to at all times.
If a fuel oil other than diesel is used then care should be taken that the flash point is
greater than 55oC.
With respect to storage, the fundamental rule is to ensure that it is kept separately from
the Ammonium Nitrate and that cross-contamination should not be a risk.
5.
MIXING AMMONIUM NITRATE AND FUEL OIL AND
EMULSIONS
5.1
PERCENTAGE OF FUEL OIL
In the production of ANFO, it is important to add sufficient fuel to the Ammonium
Nitrate prills in order to achieve a mixture which is close to oxygen balance. For fuel
oil, i.e. diesel or gas oil, oxygen balance is achieved by the addition of 5.5 - 5.7% (by
weight) of oil, depending on the elemental composition of the Fuel Oil.
Any deviation from oxygen balance decreases the available energy output of the
explosive and increases the amount of toxic gases produced on detonation. The
mixing process should be designed to keep deviations from oxygen balance to a
minimum.
Ideally the finished product should be checked on a regular basis for Fuel Oil content.
5.2
QUALITY OF MIXING
It is important to ensure that any process chosen to mix Ammonium Nitrate and Fuel
Oil to produce ANFO is capable of mixing the ingredients to the required tolerances.
It is also a requirement that the process disperses the Fuel Oil evenly throughout the
product. Uneven dispersion of Fuel Oil will yield more noxious gases on detonation
than in a homogeneously mixed product. Finally, the mixing process should not
produce excess amounts of fines by crushing or damaging the prills.
In order to verify even dispersion of Fuel Oil it is considered good practice to use a
colorant. This gives a visible check on the completeness of the mix.
5.3
POROSITY OF AMMONIUM NITRATE AND FUEL ABSORPTION
The Ammonium Nitrate prills should have sufficient porosity to absorb all of the Fuel
Oil which is added. In addition the prills should be capable of holding the Fuel Oil
without appreciable liquid separation, for extended storage periods where required.
ANFO is an explosive and is classed according to UN Recommendations for the
Transport of Hazardous Goods as either 1.1(UN No. 0082) or 1.5 (UN No. 331) and
will have to be transported and stored accordingly.
5.4
SPILLAGE
All spillages of Ammonium Nitrate, Fuel Oil or ANFO should be contained, and steps
taken to avoid or minimise contamination of any watercourse. Spillages of ANFO
should be collected in a suitable receptacle for disposal in a proper manner, e.g. either
burning in an approved manner, or by detonation in a borehole.(See Code of Good
Practice - Disposal of Waste Explosive)
5.5
MIXING METHODS
a) Equipment
All electrical equipment must be designed and maintained to the appropriate standard
for mixing explosives.
The mixing of ANFO can and should be achieved by means of equipment with low
energy input into the process. In common with other explosives mixing processes,
equipment should be designed to avoid the possibility of entrapment of foreign objects
in moving machinery by providing screens and filters for the ingredients and allowing
adequate clearances between moving parts.
The design of the mixing equipment should be such that the possibility of explosive
remaining in corners and crevices is minimal, and inspection ports should be provided
for cleaning and decontamination.
Because of the corrosive nature of Ammonium Nitrate, care should be taken in the
choice of materials of construction for equipment designed to mix Ammonium Nitrate
and Fuel Oil. The solvent properties of Fuel Oil (e.g. for grease), should also be taken
into consideration.
ANFO mixers and hoses should be constructed to avoid the build up of static potential
and the various components of the mixer should be earthed. Suitable materials of
construction include stainless steel and aluminium.
A regular and thorough maintenance programme should be instituted to check
equipment used for mixing and loading ANFO to minimise the possibility of failure
causing a potentially hazardous situation. Regular checks on any earthing system and
the arrangements to avoid static build up should also be made.
b) Underground mixing
Because of the hazards associated with post detonation gases, ANFO for use
underground should be manufactured to a high standard to minimise the amounts of
carbon monoxide and nitrogen oxides evolved.
It is not usual to mix and store large amounts of ANFO underground, because of the
hazards associated with explosives and explosives plants in a confined situation. It is
therefore preferred that ANFO for use underground be mixed on surface.
In small diameter holes underground it is common practice to load ANFO
pneumatically through a hose, which is a practical way of filling such holes, and
which increases its loading density and velocity of detonation.
c) Surface Mixing
It is common practice in some countries for Ammonium Nitrate to be mixed by hand
with Fuel Oil using a hand implement such as a nylon or wooden shovel. This
practice is not recommended by FEEM. ANFO should only be mixed by suitable
equipment ensuring the appropriate quality of mix. (See paragraph 8.1)
Whatever method is used for mixing and loading ANFO near the point of use, records
of the quantities of Ammonium Nitrate and Fuel Oil used, and the amount of explosive
mixed should be kept. Facilities should be available for the storage of material that is
excess to immediate requirements.
5.6
HEAVY ANFO
Ammonium Nitrate or ANFO can be mixed with base emulsion in ratios of 20% to
50% of emulsion to form “heavy ANFO”.
This is normally mixed and delivered by augering. The process of packing and storing
heavy ANFO should follow the same routines as for ANFO.
The product has a limited waterproofness and should not be used in holes with flowing
water.
The oxygen balance is important and with the capability of most “heavy ANFO”
mixing equipment to vary ratios of the components easily, the quality of the final
product must be carefully monitored.
5.7
FIRE PROTECTION
Mixing buildings and equipment should, where possible, be constructed of nonflammable materials. Electrical equipment should comply with a suitable standard.
Where ANFO is mixed in large quantities it is recommended that a suitable sprinkler
system is installed which can be activated both automatically by a fire and by the
operator on leaving the building in an emergency.
Suitable fire extinguishers should be kept on mixer/placer units for fighting electrical
or oil fires..
In common with other types of explosives, it should be made clear to all involved
that fires involving explosives should not be fought. (See Code of Good Practice “
Design of Buildings”).
5.8
ENVIRONMENT ISSUES
The ingredients of ANFO are harmful to aquatic life and drinking water, so care
should be taken to avoid spillage into ponds, rivers or streams etc. It is not acceptable
to dispose of spillages or excess quantities of ANFO by means of dissolution in water
where there is a risk of the ingredients entering a watercourse. (See Code of Good
Practice – “Nitrates in Ground Water.”)
Arrangements should be made for environmentally acceptable methods for disposal of
any contaminated water (e.g. the waste water can be re-cycled).
5.9
CLEANING CONTAMINATION
On cessation of operations mixing and loading equipment should be cleaned of
Ammonium Nitrate, Fuel Oil and ANFO. Loose material should be collected in
suitable receptacles for disposal. Cleaning for maintenance work should be rigorous,
and can be achieved with water with a suitable detergent.
5.10
SAFETY
Whilst ANFO is relatively insensitive to accidental detonation, it should be impressed
upon those involved in its manufacture and use that it is an explosive and should
therefore be treated as such.
When mixing and loading (especially blow loading) ANFO, suitable protective
clothing and eye protection should be provided and worn at all times.
5.11
SECURITY
ANFO should be stored in secure magazines, and a record kept of all movements.
6.
CHARGING
6.1
POURING
ANFO can be charged simply by pouring it into dry vertical boreholes. The borehole
diameter should not be less than 50mm to ensure propagation of the detonation
through the whole column. It should be observed that the charge density will be less
than 850 kg/m3
If there is water standing in the borehole, the water should be removed before
charging. If this is not done the borehole must be charged with packaged or water
resistant product to at least above the water level.
Dewatering can be performed either by pumping it out by special dewatering trucks or
blowing with compressed air. The first method needs quite expensive equipment,
while the second normally results in wet personnel!
In boreholes with flowing water ANFO should not be used.
6.2
PNEUMATIC CHARGING
There are many different brands of pneumatic chargers on the market. They transport
the ANFO through a loading hose into the borehole. It is good practice to withdraw
the hose as the hole is loaded keeping it 20 - 40 cm from the surface of the charged
explosive. The ANFO is transported at high speed through the hose and there is a
possibility of building up electrostatic charges due to friction. Therefore the hose
should be conductive or other arrangements should be made to prevent static build up..
The design and properties of the charger and the hose must be approved by the
appropriate authority in each country.
The pneumatic charger can be used for horizontal boreholes and for charging up holes.
As it is possible to obtain higher charge densities (up to 1000 kg/m3) pneumatic
chargers sometimes are used for boreholes downward to increase the charge density.
In practice pneumatically charged bore holes tend to have a lower critical diameter and
it is found possible to use ANFO in holes down to 35mm diameter.
6.3
CARTRIDGED ANFO
Provided the AN used is appropriate ANFO can also be cartridged in large diameter
(50 mm) plastic film or plastic tube cartridges. However it should be noted that the
capability of transmission of the detonation from one cartridge to another is impaired
as a result.
The advantage of cartridging ANFO is to be able to use it in water, however, there is a
loss of loading density and a consequent reduction in bulk strength
7.
SAFETY AND FIRE PROTECTION
7.1
GENERAL
It is the duty of the owners/operators of the Ammonium Nitrate storage facility to
ensure that emergency procedures are in place to cope with major fires in Ammonium
Nitrate stores.
Further, it is the duty of the owners/operators to ensure that all personnel who are
involved with the store or who work in close proximity to the store are thoroughly and
properly trained in those emergency procedures. The following is a non-exhaustive
list of the considerations which should be covered in such an emergency procedure
instruction.
7.2
1.
Provision of fire-fighting equipment including water supply, static
tanks or fire hydrants.
2.
Provision of chemical extinguishers for fires on equipment where
Ammonium Nitrate is not directly involved.
3.
The provision of sprinkler equipment.
4.
The provision of water cannons.
TRAINING
Correct procedures for storage and handling.
Correct procedures for fire fighting.
Correct use of safety equipment.
7.3
EVACUATION SYSTEM
Large Ammonium Nitrate fires should not be fought. The procedure should be to
evacuate the area to an appropriate distance based on the assumption that the product
will detonate.
7.4
LIAISON WITH POLICE AND FIRE BRIGADE
It should be remembered that the police and fire brigades are not always familiar with
the properties of Ammonium Nitrate and a liaison should be established with both the
police and the fire brigades well in advance of any incident so that the emergency
procedures can be identified and executed by properly informed personnel. This is
particularly important when storing large quantities of Ammonium Nitrate and
reference should be made to National Regulations.
8.
ENVIRONMENTAL ISSUES
8.1
STORAGE OF AMMONIUM NITRATE AND ANFO
Ammonium Nitrate is a hygroscopic salt and is readily dissolved in water. Care must
be taken to ensure that any Ammonium Nitrate solutions are not carelessly discharged
into public waterways.
In general, it is considered good practice to keep Ammonium Nitrate and ANFO
stores as dry and as clean as possible.
Whenever Ammonium Nitrate is converted into solution it is recommended that the
solution tanks should be bunded in order to prevent Ammonium Nitrate solutions
being accidentally discharged.
8.2
CHOICE OF FUEL OIL
Consideration may be given to the choice of oils in order to minimise the possibility of
damage to the Aquatic Environment.
8.3
TOXIC FUMES
Thermal decomposition of Ammonium Nitrate can lead to the release of oxides of
nitrogen.
Too little oil in the ANFO mix can lead to NOX fumes which are particularly toxic
and the effects of their inhalation may lead to pulmonary oedema (fluid on the lungs).
However, if the Ammonium Nitrate and fuel oil are oxygen balanced and the
boreholes are properly primed the amount of toxic after-detonation gases should be
equal to or less than those from conventional cartridged explosives.
On the other hand, in the event of excess fuel the resultant gases will contain CO
which is not only highly toxic, but is also undetectable by nose or eyes.
If ANFO is carelessly loaded into wet boreholes, some of the Ammonium Nitrate can
dissolve with a consequent failure to detonate, and an unbalanced product. It is for
these reasons that the recommendation that ANFO be used only in dry holes, is made.
8.4
CHARGING OPERATIONS
During charging with ANFO there is a clear risk of spillage round the mouth of the
borehole. Good housekeeping should be practised to keep the ANFO spillage to a
minimum. Systems should be in place for the removal of any spilled ANFO.
(See Code of Good Practice “Use of Explosives on Ground and Surface
Water”)
9.
SECURITY
Although ANFO is a relatively insensitive product, which lends itself to on-site
mixing it is a class 1 product and all the appropriate security measures relating to such
a product should be observed.