CASE STUDY- A New Innovation in Lightning Safety for Higher Risk Workgroups.

  LightningMat (EPR) Safety Mat

ABSTRACT

Australian and international mining and resource sectors have a greater risk associated with the incidence of lightning injuring their workforce, inherently due to the large numbers of outdoor workers involved in these sectors, many of whom will be working in regions of higher “ground flash density” (GFD) and above average “thunder-day” (TD) activity.

Lightning and High Voltage (HV) electrical discharge events present as a significant risk injury hazard to humans, primarily via a risk mechanism known as “earth potential rise” (EPR).

In this paper lightning EPR in particular will be seen to be responsible for the vast majority of lightning injury statistics, yet up until this point there has had no suitable commercially available portable EPR control that has catered to this risk.

This paper outlines some particularly relevant aspects surrounding the EPR risk, and presents a new and innovative product development by which higher risk operations can now significantly deal with, and mitigate this EPR risk.

This new EPR mitigation control will be particularly useful to remote workgroups such as remote exploration camp workers, railway maintenance, and the like, who up until this point will have been precluded from any level of lightning risk mitigation, unlike their counterparts conducting activities at traditional mining and processing plant operations.

INTRODUCTION

Lightning is a well-known and catastrophic risk, to which the worldwide mining and resource sectors have figured disproportionately and prominently within the recent fatality and injury statistics. This is not hard to understand considering mining and resource activities are typified by large numbers of people carrying on their normal workplace activities whilst outdoors and often working in close proximity to large plant and equipment that inherently exhibits a higher disposition to being struck by lightning.

All reputable lightning safety researchers acknowledge that the vast majority of all lightning injury statistics had been outdoors when they sustained their injuries. Risks posed by lightning are generally considered to be low likelihood, however in any such event the resulting consequences are usually always severe and catastrophic.

HSEC departments are required to develop, and implement appropriate “safe working procedures” (SWP) across higher risk operations, by outlining the required response to be undertaken by all personnel during thunderstorms.

As such the provision of suitable safe shelter also forms an integral aspect of any SWP implementation, and operators should nominate lightning safe shelters, and apply placards, to ensure as far that as is practicable, all personnel are aware of safe refuge areas, and are never exposed to lightning risks during higher risk conditions.

However there will still be some personnel that due to their normal activities, remoteness, and/or current situation, may not have any timely access to any safe refuge whatsoever.

Such activities may typically include:

• ? tented exploration camps
• ? exploration drilling
• ? pipeline maintenance
• ? railway maintenance
• ? traffic signal maintenance
• ? electrical linesman
• ? environmental scientists
• ? geologists and surveyors
• ? fencing contractors
• ? outdoor workers

Defining the risk

Lightning is not an easily definable risk as are some other common threats, as it is impossible to predict where, when, or even if lightning will strike, where each and every lightning strike will be fundamentally unique, where it is impossible to predict whether the current magnitude of any particular lightning event will comprise of a few hundred amps, or several hundred thousand amps.

Soil resistivity will also have a dramatic effect on the EPR developed, as when lightning current strikes the earth, the local soil being highly resistive results in a large EPR, roughly proportional to current (I) x resistance (R).

                                           Figure 1: EPR Hot Zone of electrification.

In the instance where a large magnitude lightning current was injected in soil exhibiting a high resistivity, the resulting EPR can be exponentially magnified, resulting in much larger areas of ground electrification, which we refer to throughout this paper as the EPR “hot zone”.

This area of hot zone electrification is very non-specific, making risk determinations as to what might be considered safe and unsafe ground even more difficult, although it is highly probable that any person situated within this EPR hot zone is highly likely to be severely injured or even killed.

A recently lightning strike at the “2016 Rock Am Ring” music festival in Germany saw over 80 people seriously injured as a result of lightning EPR. Interestingly 12 months earlier at the same festival, the “2015 Rock Am Ring” there was a similar lightning EPR incident, where over 30 persons were also injured. Lightning EPR can affect large areas.

Lightning Risk Mechanism Statistics

Despite a common belief that “direct strikes” account for the majority of injury and fatality statistics, the most common lightning injury risk mechanisms involve “Step’ and “Touch” potential injuries, caused through “contact” and “ground” currents that are attributed to EPR.

In terms of actual injury and death statistics, US based researchers have conducted some of the more detailed studies and have collated the best databases, hence US data will be represented here. This data would also be fairly representative of Australian statistics, given our similar rates of GFD and TD, but would substantially underestimate the proportion of incidents that would occur in higher lightning areas such as Asia, Africa, and Central America.

The US lightning fatality and injury statistics taken over a 6.5 year period have been obtained from an article published by well-known researcher “Dr Mary Ann Cooper within www.emedecine/medscape.com, which is a highly regarded online medical website (https://emedicine.medscape.com/article/770642-overview).

The results are summarized below in Table 1.

Table 1: Lightning injury data for the USA from 2007 to the present. The probability value is based on a total population of 300 million. (2014) has only partial data.

Additionally Mills et al (2009) had also published the mean lighting death and injury data rates for Canada for the period 1986 to 2005. This data is shown in Table 2.

Table 2: Mean annual lightning injury data for Canada from 1986 to 2005. The probability value is based on a total population of 35 million.

Similar tables for the Australian statistics aren’t readily available, although we understand that the corresponding mean numbers for Australian lightning fatality and injury statistics will be up to 10 deaths, and over 100 injuries per annum. For an Australian population of 22 million people, the probability is roughly 3.4 x 10-6.

Cooper and Holle (2008) have collaborated on various extensive and detailed studies of the North American lightning related injuries and deaths, and had found that around 50% of all lightning injury/ fatality statistics were attributed to ground current EPR as the single largest risk factor.

Additionally they found that 15-25% of injuries had been attributed through contact/ touch potential exposure, which incidentally is also an EPR related mechanism. Hence, 65-75% of all lightning injuries are EPR related, in which case the mitigation of lightning EPR is absolutely essential for reducing lightning fatality and injuries to persons.

                    Figure 2: Injury mechanism breakdown (Courtesy Cooper and Holle)

Mandated EPR Regulations

EPR is a recognized primary risk within all electrical regulatory requirements worldwide and is mandated for application within all High Voltage (HV) electrical switchyards and substations, and any other facilities where HV switching operations are undertaken.

In Australia AS/NZS 3000, AS/NZS2067, AS/NZS4871.1, AS/NZS2081, ENA EG0 and ENA EG1, all describe the maximum acceptable step and touch potential voltages, where a voltage/time relationship is outlined to determine the permissible limits of any prospective fault current that may be attributed through EPR.

Traditionally EPR controls are comprised of large earth grids that are constructed in-situ using large cross sectional area copper conductors that are then formed and bonded into a large direct buried mesh that extends across the total extent of the switchyard. All transformers, HV switchgear, metallic equipment frames, lightning masts and any metallic objects that are located within the confines of, (and including the perimeter fence) are all required to be equipotentially bonded to this buried earth grid.

Earth resistance must not exceed specified limits, where additionally “step” and “touch” voltages must be calculated to be within the maximum permissible limits. Additionally a thick layer of high resistance rock aggregate is then applied to the surface layer, to help reduce the magnitude of any EPR that electrical workers may be exposed to whilst performing their duties.

So whilst EPR controls are mandated for use in all HV applications, up until this point there has been no commercially available or cost effective EPR control that could be easily applied to other higher risk EPR applications, for example lightning. This is despite the known and ongoing statistics involving some higher risk activities, workgroups, and recreational campers within tents, which had resulted due to close proximity lightning, strikes, and which could have been reduced through the use of a portable EPR control.

Remote tented exploration and work camps are prime examples where personnel can be mobilized to regions of higher lightning activity, whereby personnel are provided with no adequate protection against localized lightning, nor will they have access to any nearby safe shelter. This is partly due to it being impracticable to construct appropriate lightning protection, grounding, 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.

LightningMat EPR Safety Mat

Back in 2010, this author in collaboration with leading Australian Lightning researcher “Dr Franco D’Alessandro”, looked to investigate innovation in this area of personnel lightning safety, and lightning risk mitigation.

Amongst many other lightning safety projects, EPR risk mitigation was a key area of focus, to which it was decided that if some lightweight and highly “portable” EPR control could be developed, this would prove an important risk innovation for reducing the greater % of overall lightning risk to the aforementioned higher risk workgroups.

Five years on, we have now commercialized and patented an innovative and highly portable EPR risk mitigation control, the LightningMat “EPR Safety Mat” which has been developed primarily for ease of portability, and to provide a cost effective and simple means for mitigating EPR hazards to remote personnel via a unique three (3) layer flexible mat design, comprising of:

1. ? A central, electrically‐conductive mesh layer that rapidly equalizes electrical potential developed across the mat.
2. ? An upper insulating layer that insulates personnel /and assets from the electrically conductive central layer.
3. ? A lower electrically‐conductive layer that protects the central layer, and provides electrical continuity to the central layer.

                           Figure 2: LightningMat EPR Safety Mat cross sectional view

This three (3) layer mat arrangement provides a method and apparatus for mitigating EPR hazards arising from nearby “cloud‐to‐ground” (C-G) lightning discharges, and other electrical phenomena involving large fault currents being injected into the ground.

                    Figure 3: LightningMat EPR Safety Mat - isometric cutaway view

The LightningMat works by redistributing the surface voltage profile associated with EPR, so as to reduce differential potential gradients across the mats structure.

Any persons situated upon the LightningMat during an EPR event, should then be equipotential with the mat, such that they should not be exposed to significantly differing and dangerous voltage gradients resulting from the EPR.

The LightningMat concept is very simple. Think of a bird perched upon a HV powerline completely unaffected by its direct contact with the High Voltage wire, that is until such time as the bird comes into contact with another phase wire, or an earthed object, at which point the differential voltage will then flow across the differential contact points, and the bird "will cease to exist".

Key practical features of the LightningMat have been considered whereby all of the layers are sufficiently flexible so as to enable the LightningMat to be simply rolled and unrolled as may be required, making it suitable for use in temporary, semi-permanent, or even use in permanent applications. Individual LightningMat’s can also be joined together, so as to make a larger LightningMat, as some applications may require.

The LightningMat will prove invaluable to remote field personnel working exposed to the elements, and who may have limited or no access to appropriate safe shelter during the period of a lightning threat.

Additionally, LightningMat will provide safer working environments to those personnel working in contact with, or in close proximity to long conductive elements (including railway lines, guy wires, long conductors, pipelines, and fences).

Attaching the optional "bonding kit" to these long conducting elements, brings the LightningMat to the same electrical potential as the long conducting element, thereby equalizing dangerous voltage differentials.

And whilst the LightningMat can be used without an electrical bond to nearby touchable objects (since it redistributes the surface voltage profile), enhanced performance and voltage reduction is achieved wherever an electrical bond is used.

Whilst LightningMat does not cater to, nor does it remove the risk posed through direct strike, (statistics highlight as around 3-5% of all lightning injuries), although LightningMat does cater to the 55-75% of lightning injury statistics that up until now, have had no commercially available risk mitigation control.

TESTING

The following testing has been carried out:

• CDEGS computer modelling.
• Compliance to IEC 61111:2009 –Electrical Insulating Matting.
•  Verification of the function of the LightningMat EPR Safety Mat via a full‐  scale current injection testing in the field. (Lightning Protection International)
•  Independent review and validation of the testing methodology applied to EPR safety mat.  (Power Quality Research Centre - University of Wollongong, Australia)

(All reports are available upon request)

REFERENCES

• ? Lightning Protection International. EPR Safety Mat- Statistics on Lightning & Power-related Injuries 2014
• ? Cawley, J.C. & Homce, G.T, 2008, "Trends in Electrical Injury in the U.S., 1992–2002", IEEE Trans. Indust. Appl., Vol. 44, No. 4, pp. 962-972.
• ? Cooper, M.A., Holle, R.L. & Andrews, C., 2008, “Distribution of lightning injury mechanisms”, Proc. 20th ILDC / 2nd ILMC, Tucson, AZ, USA.
• ? Pointer, S. & Harrison, J., 2007, “Electrical injury and death”, NISU Briefing, No. 9, Flinders University & Australian Government.
• ? WA Government, 2012, “Electrical Incident Safety Report Western Australia 2010-11”, Department of Commerce (Energy Safety), Report DP0281/2012.

ACKNOWLEDGEMENT

My thanks go to Dr Franco D’Alessandro of Physelec Solutions Pty Ltd (Co-Inventor of the EPR Safety Mat) for his trust in the initial concept presented, and for his significant efforts in championing this project throughout the projects development, field testing, methodology validation, technical elucidation, intellectual property issues, and manufacture.

Without his significant involvement this project would not have happened.

ABOUT THE AUTHOR

Grant Kirkby- Lightningman Pty Ltd

Director -Lightning Risk Mitigation Technologist

[email protected]