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Explosives Inspectorate | Bulletin | No.81 V 1 | 20 January 2023

Firing cables exceed maximum resistance

What happened?

Recent inspections have identified the use of firing cables that do not comply with the requirements prescribed in the Australian Standard.

How did it happen?

The resistance measured in the electric initiation systems exceed the limits prescribed in Australian Standard 2187.2, Appendix B, paragraph B7.

Key issues

Where firing cables exceed the maximum prescribed resistance per 100 metres, the output current from the exploder may be reduced between the exploder and the detonators.

A reduction in output current may cause detonators within the circuit to fail to initiate, or not function as intended.

Electric initiation systems require minimal electric current to successfully initiate all the detonators in the circuit. To achieve this, exploders should:

  • display their capacity, which is expressed in terms of (paragraph B5.4 of AS2187.2):
    • the maximum number of defined detonators; or
    • the maximum series of circuit resistance that can be fired by the exploder
  • meet the output currents prescribed in Paragraph B5.5.1 of Appendix B in AS2187.2.

Paragraph B7 of Appendix B in AS2187.2 prescribes:

“Firing cable for use with portable-type exploders, except sequential exploders, shall comply with AS/NZS 3191 and shall be of two-core flexible cord, thermoplastic insulated and sheathed. The cores shall be multi-stranded copper conductors having a minimum cross-sectional area and maximum resistance as follows:

  • (a) Heavy duty…………………………….. 2.0 mm2, not more than 2Ω/100m of cable.
  • (b) General duty…………………………… 1.0mm2, not more than 5Ω/100m of cable.

The cable shall be maintained in a sound condition, care being taken to avoid kinks, cuts and abrasions.”

Recommendations

  • When using an electric initiation system, ensure the firing cables adhere to the requirements of AS2187.2
  • Review routine maintenance of exploders to ensure compliance with paragraph B5.2 of AS2187.2
  • Review safety and security management systems, to ensure:
    • electric firing circuits are connected and tested in accordance with Appendix F1 of AS2187.2
    • workers are trained in electric initiation system
    • workers can identify incorrect firing cables and inadequate output currents of exploders for the number of detonators to be initiated
    • the procurement of firing cables and electric firing equipment meets the requirements of the AS2187.2.

References and further information

  1. Queensland Explosives Act 1999
  2. Queensland Explosives Regulation 2017
  3. Australian Standard 2187.2 – 2006
  4. AS/NZS 3191 - 2008

Authorised by Dr Snezana Bajic - Deputy Chief Inspector – Explosives

Contact: Shane Cooper, Senior Inspector Explosives , 07 3199 8023

Issued by Resources Safety & Health Queensland

Safety: This information is issued to promote safety through experience. It is not to be taken as a statement of law and must not be construed to waive or modify any legal obligation.