1. INTRODUCTIONThe likelihood of a premature detonation resulting from radio-frequency (RF) radiation is extremely remote. Nevertheless ahazard exists when given the correct combination ofcircumstances.

2. ENERGY INPUT INTO BLAST CIRCUIT2.1 If electric detonators are in a string RF radiation field,

unshielded leg wires and connecting wire —within a circuit(whether connected to a blasting machine or not) or shortcircuited or alternatively with open ends—will act as anantenna similar to that on a radio or TV set. This antennawill absorb RF energy from the transmitter RF field and theelectric current produced in the leg wires will flow into thedetonator.

2.2 In certain cases depending on the strength of the RF fieldand the antenna configuration formed by the leg wireand connecting wire circuit and its orientation, sufficientRF energy may be induced in the wires to fire one ormore detonators.

2.3 Electric detonators may also be initiated by direct contactwith a transmitting antenna or some metallic structurebehaving as an unintended antenna.

3. SOURCES OF RF ENERGYPossible sources include the following:3.1 Fixed and mobile radio and television transmitters3.2 Radar transmitters3.3 Geophysical survey equipment3.4 Mobile phonesWith the exception of 3.3 the above sources may be airborne,and possible RF hazards from low-flying aircraft should beconsidered.

4. DETONATORS IN TRANSITWhen electric detonators are wound in figure-of-eight coils assupplied by the manufacturer, they are safe in any field strengthlikely to be encountered.

5. RADIO RECEIVERSThere is no hazard when a radio is in the receiving mode.However, in order to prevent accidental transmission, it is advisablefor the operator to be positioned at a safe distance from the blastarea. (See 9.1)

6. ASSESSMENT OF HAZARDIn order to ascertain whether a potential hazard exists at aparticular distance, the power output of the transmitter inquestion together with its operating frequency must be known.Calculations may then be carried out and/or reference made to BC6657:1991 Prevention of inadvertent initiation of electro-explosivedevices by radio-frequency radiation.

7. RF RADIATION ABOVE SAFE LEVELIn the even to the calculated RF radiation being above the safelevel, the source must be removed. If this is not possible electricdetonators must not be used in the blasting operation.

8. RF RADIATION WITHIN SAFE LEVEL8.1 If the RF radiation is within a safe level, the following

precautions should be taken:

8.1.1 A detonator or its leg wires should not be allowedto come into contact with any radio antenna or feederline at any time.8.1.2 The leg wires should not be unwound until thedetonator is required for use.8.1.3 When loading in a borehole the leg wires should beunwound to a minimum extent sufficient for making up theprimer and then unwound further only when the primer isinserted in the borehole.8.1.4 For use outside the borehole the detonator legwires should be unwound to a minimum extent forpreparing the charge and unwound further only when thefiring circuits to be connected.8.1.5 Excess leg wire and/or connecting wire should bekept as close together and as near to the ground as theshot firing circuit allows in order to minimise any looparea.8.1.6 The use of a twin core firing cable in goodcondition considerably reduces the risk of radiointerference. The cable should also be kept at groundlevel with the ends of the cable short circuited at the firingpoint.8.1.7 All wires in the shot firing circuit should be keptinsulated from the ground. Special joint insulatorssupplied by Irish Industrial Explosives Ltd. arerecommended.

9. RECOMMENDATIONS9.1 Portable walkie-talkie equipment, mobile telephones

and vehicle transmitters should not be operated closer than 100m from the blast site.

9.2 For stronger transmitters the following distances aresuggested:

Transmitter Safe distancestrength from(KW) transmitter (m)Up to 1 3001–10 200010–100 4000100–1000 10000These figures are not intended to suggest that blastingshould not be undertaken within these distances but toindicate that a hazard might exist. An expert surveyshould be obtained before planning the blastingoperation.

10. CLARIFICATIONClarification and advice on any of the above points is availablefrom Irish Industrial Explosives Ltd.

REFERENCES1. British Standard Guide to Prevention of Inadvertent

Initiation of Electro-Explosive Devices by Radio-FrequencyRadiation. BS 6657:1991. Published by British StandardsInstitution.

2. Blasting Practice. 4th Edition. Published by NobelExplosives Company Limited.

3. Radio Frequency Energy. Safety Library Publication No.20of Institute of Makers of Explosives.

IRISH INDUSTRIAL EXPLOSIVES LTD PRODUCT INFORMATION + TECHNICAL DATA

RADIO-FREQUENCYDETONATION

The information and recommendations are given without warranty,expressed or implied, statutory or otherwise, and no liability shall beaccepted for the consequence of any reliance placed thereon. Recipients should make their own tests to determine the suitability ofproducts for their particular purposes.

NOTE: If in any doubt concerning the correct use of theabove products contact Irish Industrial Explosives Ltd.IMPORTANT: If considering destruction of surplusproducts in the field please refer to Recommendedmethods for the destruction of Explosives and Accessories.

IRISHINDUSTRIALEXPLOSIVESLTD87/89 WATERLOO ROADDUBLIN 4 TEL: 016685193FAX: 016685248

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