Federation of EuropeanExplosives Manufacturers
BLASTING PRACTICE
TECHNICAL BULLETIN No. 1
PREVENTION
OF PREMATURE INITIATION
CONTENTS
GENERAL REMARKS
- ELECTRIC DETONATORS
- SPECIFIC PRECAUTIONS TO PREVENT PREMATURE INITIATION WITH ELECTRIC DETONATORS
- NON-ELECTRIC INITIATION SYSTEMS
4. Electronic Detonator Initiation Systems EDIS
The TECHNICAL BULLETIN N° 3 has been published by the FEEM Blasting Working Group
in March 2002
FEEM is affiliated to CEFIC (European Chemical Industry Council)
Route1, Avenue F Van Nieuwenhuyse 4 – B1160 Bruxelles
TECHNICAL BULLETIN N°3
PREVENTION OF PREMATURE INITIATION
GENERAL REMARKS
In spite of the fact that considerable advancements have been made in initiating systems it is important that all detonators are handled with great care.
Initiation systems are divided into two main groups:
- Electric Systems
- Non-electric Systems
Handling of all types of detonators should always be done in accordance with the manufacturer's instructions and it should never be forgotten that all detonators are subject to accidental initiation by impact, heat, and friction.
All handling of explosives should cease whenever electric storms are threatened.
Rough handling should be avoided at all times
Note:- Surface detonators including connectors should be protected at all times from impact, heat and friction.
1. ELECTRIC DETONATORS
Possible causes of accidental electrical initiation of detonators include the following:
1.1Premature Connection to the Shot Exploder
In order to avoid accidental initiation by improper connection of the shot exploder during the charging operation and while connecting the round, the ends of the firing lines, at the point where the shot exploder will be connected, must be short circuited and remain in this condition until all the personnel have retired to the place of safety. Only then, may the circuit be opened for electrical testing, and thereafter connected to the shot exploder. Furthermore, the exploder must be under the control of the shot-firer, who will have the means for operating the exploder in his possession at all times.
1.2During Circuit Testing
In order to prevent electrical initiation while testing the circuit, the equipment used must be fit for purpose, approved according to national regulations and properly maintained. Repairs to this equipment must only be carried out by authorised workshops.
1.3 Stray Current
The term stray current refers to all uncontrolled electricity, which could pass through a detonator while it is being used.
This electricity can be generated by any one of the following:
-Electrical Storms
-Static electricity
-Electrical Power Lines
-Current leakage
-RF Transmitters
-Galvanic currents.
1.3.1Electrical Storms
Clearly, if there were a lightning strike on the blast site or in the vicinity of the blast site, it is very probable that an initiation of the electric detonators would occur.
But it should also be noted that discharges some kilometres away could be dangerous for blasting in both surface and underground operations.
1.3.2Static Electricity
Most electric detonators have some sort of protective systems built in at the manufacturing stage. However, when static electricity is known to be a severe problem such as in dry or dusty conditions, then particular care should be taken by operators to prevent an accidental discharge to a circuit. Such precautions can include for example wearing conducting footwear by shot firing operators.
1.3.3Electrical Power Lines
Electrical power lines can be a hazard when they are located close to a blast site for a number of reasons:
a)Leaks to ground as result of faulty or inadequate insulation
b)Induced current. The total included area of the firing circuit loop should be as small as possible.
c)Accidental direct contact
1.3.4 RF Transmitters
Radio frequency systems of communication, such as radio transmitters, television, radio telephones, mobile phones, radar systems, etc. emit energy by means of their antennae. This energy can be captured by a blasting circuit, that is to say, the blasting circuit or an individual detonator can act as an antenna and receive energy.
1.3.5Galvanic currents
Some metallic mines can produce this type of current, due to the minerals acting as batteries.
Also in underwater blasting the barges can act in the same way.
2.SPECIFIC PRECAUTIONS TO PREVENT PREMATURE INITIATION WITH ELECTRIC DETONATORS
In the case of electric blasting, before commencing with the charging of the shotholes, suitable precautions must be taken to prevent stray currents getting to the firing point at the work place
When there is a risk of premature initiation caused by any electrical hazard use an alternative, safer form of blast initiation.
2.1Neither the primers nor the explosives to be loaded may be taken to the working place if there are electrical storms in the area.
2.2 The shot firer must control the use of portable radio transmission equipment including mobile telephones in the vicinity of the blast site. In general, special attention must be paid to television repeater stations, radar stations, power transmission lines, electrified rail systems, and any other items that could produce a similar effect.
2.3Shot firing cables should have suitable insulation and be tested for continuity before use. Good maintenance of shot firing cables is essential.
The bared ends of the shot firing cable should be shunted until required for use.
2.4Great care must be taken in order to prevent the firing lines from being in the proximity of batteries or any other power source and electrical conductors, as well as from touching rails, piping or any other metallic items in general.
2.5Until the moment of firing, the firing line must remain disconnected from the shot exploder and in short circuit. The firing handle of the shot exploder must be in the possession of the shotfirer or the person responsible for the blast at all times.
3.NON-ELECTRIC INITIATION SYSTEMS
In the correspondence dealing with the approval of other initiation systems, other than rounds initiated by safety fuse and rounds initiated electrically, mention will be, specifically, made of the general safety regulations which will be applicable and those specific to each particular system.
3.1Shock Tube Initiation Systems
Premature initiation of shock tube detonators may occur in the shock tube due to a phenomenon known as Snap, Slap and Shoot. The process involves stretching the shock tube to breaking point so that it snaps. The built up elastic energy in the tube will recoil the tube in a high velocity whiplash action. Under the right condition this can accelerate the tip to such velocities that if impacting towards a hard surface accidental initiation can occur. Snap, Slap and Shoot incidents are very rare and only a small number have been recorded around the world. However, the consequences of such incidents can be very serious if a detonator fires. Therefore, treat shock tube with the same degree of respect as other explosives and the following precautions should be considered: -
3.1.1(Dealing with misfires.) No attempt should be made to retrieve a non-electric detonator by pulling the shock tube.
3.1.2 No vehicle should ever drive over the shock tube of the initiating system.
3.1.3 Always lead shock tubes to the hole in a direct line and keep excess tube tidy
3.1.4 Never pull, stretch, kink or put tension on a shock tube such that the tube could be caused to break or otherwise malfunction.
3.1.5 Situations that could result in signal tube becoming caught or entangled in machinery or vehicles must be avoided.
3.2Detonating cord
Detonating cord contains a core of explosive, usually PETN, and premature initiation can therefore be induced by heat, friction or impact.
Detonating cord is often cut to a length required for the specific job and it is the cutting process which can lead to a risk of premature initiation. The following points should be considered when cutting detonating cord.
3.2.1Use a clean sharp knife and cut the cord with a single stroke.
3.2.2 If required cut on a wooden block.
3.2.3 Never use a sawing action to cut the cord.
3.2.4Never use side cutters (e.g. pliers) or similar tools which can crush the cord. (Special cord cutting tools may be available from your supplier).
3.2.5When the cord has been cut take care not to spill any of the core explosive onto dirty or abrasive surfaces.
3.3 Safety Fuse
Safety fuse contains a core of blackpowder and the same precautions as for detonating cord should be followed
4.Electronic Detonator Initiation Systems EDIS
EDIS of various brands are new products and no general precautions can yet be issued. Normally these systems are less sensitive to stray currents, electrical storms, RF fields etc. but the user must follow each manufacturer’s advice. Generally, the same precautions as for electric detonators should be observed.
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