Engineering & Mining Journal

JUN 2018

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Page 91 of 115

90 E&MJ • JUNE 2018 OPERATING STRATEGIES Lightning is a well-known and catastroph- ic risk, in which mining and other re- source industries have fi gured prominent- ly in recent accident statistics. This is not hard to understand considering surface mining is conducted by large numbers of people carrying on their normal workplace activities outdoors and often working in close proximity to plants and equipment that inherently exhibit a higher disposi- tion to being struck by lightning. Mine human resource and safety de- partments are required to develop and im- plement appropriate safe working proce- dures (SWP) across higher risk operations, in this case by outlining the required re- sponse to be undertaken by all personnel during thunderstorms. However, there will still be personnel that due to their normal activities, remoteness, and/or current sit- uation, may not have any timely access to any safe refuge whatsoever. Remote tented exploration and work camps are prime examples where person- nel can be mobilized to regions of higher lightning activity, and are provided with inadequate or no protection against local- ized lightning, nor will they have access to any nearby safe shelter. This is partly due to it being impracticable to construct appropriate lightning protection, ground- ing, and EPR controls, given the short term and transient nature of these camps, notwithstanding that helicopter access is often the only way in and out of these temporary camp sites. Grant Kirkby, an Australia-based spe- cialist in lightning safety and lightning risk mitigation, and an advocate for great- er awareness toward lightning risks, ad- dressed this topic in a recent online article. Known commercially as "Lightningman," he is the co-inventor of a portable safety mat used for minimizing lightning-strike risk to persons undertaking activities while outdoors with limited access to safe shelter. Kirkby noted that "it would be an in- teresting statistic" to determine just how many lightning fatality victims would still be alive today, had those victims received some prior notifi cation that dangerous conditions were developing, and that the risk of lightning was imminent. Although lightning-threat detection technologies have been around for many years, Kirkby said the vast majority of organizations still rely upon the use of cheap, and in some instances, ineffective lightning threat de- tection technologies that detect and alert to lightning strikes from a historic record and only after lightning has already struck. He explained that the most common lightning-threat detectors — handheld and portable — are very limited, as they cannot detect all types of lightning. In fact, they can only detect and then range Cloud to Ground (C-G) lightning strikes. They cannot detect Cloud to Cloud (C-C), or Intra Cloud (IC) lightning fl ashes, which are equally in- dicative that dangerous conditions exist, nor can they detect the developing conditions that lead to C-C, IC, and C-G lightning. He said a recent international stan- dard, IEC 62793-2016 (Protection Against Lightning: Thunderstorm Warn- ing Systems), offers a useful reference to those looking for guidance on matters involving lightning-threat detection. This standard applies to the use of the data obtained from thunderstorm warning sys- tems, and on atmospheric electric activity in order to establish preventive measures. IEC 62793 outlines and distinguish- es between four phases in the develop- ment and evolution of a thunderstorm and classifi es the various detection methodologies across the various storm phases, along with the type of discharges that can be measured. These phases include: • Phase 1: The electric fi eld rises - Initial stage. • Phase 2: Intra - Cloud (IC) and Cloud - Cloud (C-C) lightning - Growth phase. • Phase 3: Cloud - Cloud (C-C) and Cloud - Ground (C-G) lightning - Mature phase. • Phase 4: Number of lightning bolts de- creases - Dissipation Phase. The two most widely recognized and tested lightning-threat detection tech- nologies for the detection of thunder- storms include: • Electrostatic Class 1 detector – such as electrostatic sensors (Atstorm), and elec- tric fi eld mills (CS, Vaisala, and Boltek). • Electromagnetic Class 2 detector – such as "professional grade" Strike Guard and Vaisala lightning warning systems. (Note that online lightning locating services have not been included here, although these would come under the heading ÒClass 2 -Electromagnetic.Ó) In brief, Class 1 detectors detect storm activity during its whole life cycle (phases 1 to 4). Class 2 detectors detect C-C and C-G lightning (phases 2 to 4). Class 3 detectors detect only C-G lightning (phases 3 and 4), and Class 4 detectors detect C-G lightning (phase 3) but with limited performance. The majority of lightning-threat detec- tion used in higher-risk industries involve historical threat detection, whereby light- ning must fi rst strike to be detected and ranged. However, predictive threat warning is outlined under IEC 62793-2016; Class 1 electrostatic sensors can detect chang- es in the electric fi eld during the "Initial" stage (Phase 1). This electrostatic detec- tion technology can provide several minutes of advanced warning, well ahead of any fi rst lightning strike that may be detected by an IEC 62793-2016- Class 2 detector. Kirkby said Class 1 technology offers a true "predictive" nature to lightning- threat detection technology. This sensing Lightning Risk Mitigation: Going to the Mat for Miners As mining activities expand into more remote, lightning-intensive areas, producers should consider implementing technologies designed to minimize lightning-caused injuries and outages.

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