Post on 15-Jun-2015
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Lightning, “What’s the story?”September 2014
WealthUnearthed
Simon Tose – Global Mining Optimisation Manager
“Lightning, What’s the story?”
• Unusual number of incidents in Africa past 2 years
• Multiple hole events
• No major change in weather patterns
• Quoted research 10 to 20 years old
• Electric & Old technology
• Published articles conclude that a direct lightning strike on a single charged hole could cause an event
• Hence regulations/safety policies require evacuation of blast area when storm approaches
“Clouds, Lightning, Airlgow and Lights of Civilization in Africa” by NASA
Lightning…
• Lightning is a massive electrostatic discharge
• Within clouds
• Between a cloud and the earth
• Commonly referred to as a strike if it hits an object on the ground
• It is estimated that an average bolt of lightning carries:
• An electric current of 30000 amperes (30kA)
• Transfers 15 coulombs of electric charge
• 500 megajoules of energy
• Useless fact: enough energy to toast 100000 slices of bread…
Storm season approaching
• 250 people are killed by lightning in South Africa each year
• SA Weather Service
• In perspective 15000 are killed on our roads
• That’s 1 person in the half hour of this presentation
• Arrive Alive
Lightning Ground Flash Density Map- Southern Africa - CSIR
Commonly accepted risk to an individual being hit by a lightning strike
Around 1 in 10 million
Parts of South Africa
Around 1 in 650000
Risks to avoid…
• Open areas like soccer fields, golf courses, or parking lots
• You are the tallest thing around and the easiest target
Risks to avoid…
• Stay away from forms of metal
• Lightning is electricity and metal is a conductor of electricity
• Stop swimming and get away from water
• Water is a conductor
Risks to avoid…
• Don’t fly kites
• Don’t stand under tall objects like trees or towers
Risks to avoid
• Don’t carry an umbrella
• Better to get wet…
Review of recent mining papers…- Impact on people, equipment and infrastructure
International Society of Explosive Engineers, ISEE
“Mining world wide has been impacted by significant lightning-caused production delays and safety issues”
Mine-wide mobile radio communications fail following a lightning strike to a central radio tower
Surge protection is absent (Canada)
Five maintenance workers are injured when lightning strikes a stationary vehicle
The lightning early warning system is low cost and old technology (Peru)
A central computer system is damaged by a lightning strike, important geological data is lost
Grounding methods are in violation of codes and standards (Ghana)
More than $US one million is spent on some 350 unconventional-design lightning rods. The product is not approved by USA or international lightning protection codes and standards
Safety to all buildings is compromised (Peru)
Miners are killed when lightning explodes methane gas inside a subsurface mine. A comprehensive approach to lightning safety is absent
Many hundreds of deaths in coal mines in China, Russia, & historically USA
Tumbler Ridge, B.C.
• On July 15, 2012
• Driver of 777F haul truck was parked at the 1135 waste dump waiting out an electrical storm
• Truck was struck by lightning causing significant damage to the rear of the truck
No operator injury when this D-‐‐‐‐9 Cat took a
direct lightning strike, Peru
Review of recent papers…- Impact on people, equipment and infrastructure
Four of eight gas turbine generators suffer lightning-induced failures, production losses at the mine are $600,000/day
Power shortage lasts three months
Earthing is poor (Papua New Guinea)
Lightning causes failure of a primary water pumping system, underground flooding closes the mine for 45 days
Surge protection was absent (South Africa)
A smelter operation is “frozen” after lightning hits a substation
164 pots have to be dug out by hand, production is shut down for seven weeks
Earthing is poor (USA)
A large haul truck is struck by lightning with consequential tire explosion. Grenade like fragments kill two workers (Mexico)
A mine superintendent standing outside during a thunderstorm is killed by lightning, he ignored weather warnings (Australia)
A radio operator inside a building is killed by lightning
Grounding is poor (Indonesia)
Two workers are killed, with seven injured in two separate incidents
There is no employee lightning safety training (Laos)
Two exploration crew members struck by lightning are airlifted to hospital
The lightning detector fails to warn of threat in time for evasive action (Haiti)
NSW Department of primary industries
• Large rear dump truck (RDT) was struck by lightning while stationary and unattended. No employees or personnel were injured. September 2010
NSW Department of primary industries
US Mine Safety and Health Administration (MSHA)
• Statistics show average of ten recorded premature blasts per annum
• Two related to lightning
• Based on 4500 mines operating in the US
• Mining Journal online
• The chances of a blasthole being struck directly by lightning are less than that of a direct strike on a person
On an open bench in the mining area…
• Most exposed to a risk of being struck by lightning
• Aside from the equipment
• It is obvious that its people
Water
Lightning warning systems
• The rule of thumb, in the absence of such a system, is to withdraw when the interval between a lightning flash and the thunder is less than ten seconds. This represents about 3.5km
Campbell Scientific
Lightning Safety for Outdoor Worker recommendations
Detectors are to be monitored continuously
If thunder is heard, suspend operations
Notify all affected personnel via radio, texting, voice, sirens, etc.
Three stage Alert Program:
Yellow at 30-60 km radius
Orange at 16-30 km radius
Red at 0-16 km radius
Re-Assess threat
Sound All Clear
After one half hour of no thunder or lightning
Single blasthole
Unwise to state that a direct lightning strike could not initiate a single blasthole
Due to the energy contained within the lightning
The many sensitive explosive components particularly within the detonator and booster
However with the rapid decay and loss of energy from the ground strike
Difficult to explain the propagation by direct conduction through the rock to multiple blastholes
Typical burden and spacings make it very unlikely for sympathetic detonation
AELs experience – Shocktube
No detonations have been recorded
Experienced melted tubing
The only instance was an instantaneous electric detonator, IED
Fastened to the connected shock tube layout on a fully charged blast
Obvious cause was the high voltages and currents pushed through the ground by the lightning
Resulted in initiation of the whole blast
AELs experience – Electronics- No Initiation of blasts
A number of direct lightning strikes
Resulting in some instances in the failure of the units and melted cables on surface
• Operating and supplying explosive and initiating products to 1000’s of monthly blasts, mining types and countries
• We have not had a single lightning strike be implicated in the cause an unplanned initiation of explosives
AELs experience, since introduction of electronics
Lightning, “What’s the story?”September 2014
Thank You