ANNUAL REFRESHER – electrical hazards SURFACE 2015

Electricity is the most widely used type of energy in mining. Electricity is so widely used because it is versatile. It can be transmitted long distances easily, its hardware is rugged, and its controls are rugged and well defined. Electricity is easily transformed to usable voltages (from large motors to horns, lights, phone signals, and fiber optics). It is also easily transformed into other forms of energy (mechanical-linear, mechanical-rotary, air-hydraulic, oil-hydraulic,). Furthermore, other forms of energy are easily transformed into it (chemical batteries, chemical sensors). Its cables are flexible, and can be quickly repaired KEEP THE PROMISE – 2015

Electricity 101 KEEP THE PROMISE – 2015

Electricity is the branch of physics that deals with the study of moving electrons. KEEP THE PROMISE – 2015

An electrical conductor, copper for example, is made up of copper atoms. Each atom has electrons spinning around it in all directions. KEEP THE PROMISE – 2015

When the conductor is connected to two terminals of a voltage source, the electrons begin to flow from the negative terminal to the positive terminal. KEEP THE PROMISE – 2015

The flow of electrons is called ELRCTRICAL CURRENT. The unit of measurement for electrical current is the ampere, commonly called “amps”. The symbol for electrical current is “I” or “i”. KEEP THE PROMISE – 2015

Basic electrical laws Ohm’s Law Power Law Voltage = Current X Resistance OR V = I X R Power Law Power (Watts) = Voltage X Current OR P = V X I

Mines use Alternating Current (AC) and Direct Current (DC) circuits & equipment Voltages: 120, 240, 480, 575, 995, 2,400, 4,160, 7,200, 13,200 Voltages: 12, 24, 36, 48, 128, 300, 500 Equipment: Substations, face equipment, power centers, belt drives, fans, pumps, hand tools, etc. Equipment: Trolley, face equipment, rubber-tired mantrips, track-mounted mantrips locomotives, scoops hand tools, etc.

There are approximately 300 coal electrical standards (Parts 7, 18, 75, and 77) in title 30 CFR

Ignition Source for Fires and Explosions Electrical Hazards Electrocution and Shock Flashes and Burns Ignition Source for Fires and Explosions

A ground fault occurs when a power conductor contacts a grounded metal frame or ground wire in a cable ANY ELECTRIC EQUIPMENT POWER CENTER IF ONE OF THE POWER CONDUCTORS CONTACTS THIS GROUNDED FRAME ... GROUND FAULT CURRENT FLOWS IN THE MANNER SHOWN BY THE RED ARROW

GROUND FAULT BEHAVIOR ANY ELECTRIC EQUIPMENT POWER CENTER IF A MINER CONTACTS THIS FAULT, HE/SHE CAN BE SHOCKED OR ELECTROCUTED

116 I= time 5 s 8.3 ms V=I X R Less than 1 mA - imperceptible 1 mA - mild sensation 3 mA - pain threshold 10 mA - cannot release grip, may be fatal 30 mA - respiratory paralysis, frequently fatal 75 mA - fibrillation threshold(depends on time, probably fatal 4A - heart paralysis, usually restarts when current is removed 5A and greater - tissue burns, not fatal unless vital organs are burned

Electrical burns come from some form of electrical arc Electrical burns come from some form of electrical arc. An electrical arc occurs when air becomes part of an electrical circuit. Currents as low as 2 to 20 Amps can generate temperatures from 3,600 to 7,200 degrees F. Circuit breakers, starters, and cables can fail and become a source of arcing. Once an arc is initiated, only 50 volts per inch is needed to sustain the arc. Humans cannot withstand the heat from uncontrolled arcing. Injuries result in very serious burns, permanent disability, or death.

Many ignitions and explosions have had electric equipment as an ignition source. 5 % to 15 % methane in 12 % or more oxygen will ignite and/or explode. Also, the proper density of coal dust will ignite or propagate an ignition. Well maintained non-permissible electric equipment can be an ignition source if an explosive mixture of air/dust surrounds it. Similarly, poorly maintained permissible equipment can have the same effect. Cables and circuit breakers can overheat, fail, and short out and start fires. Similarly, motors can be overloaded, start pulling too many amps, and catch fire.

Why Worry about Electricity? Electrocutions rand FOURTH in causes of industrial Fatalities. The National Safety Council estimate 600 people die every year of electrical caused. Most of there accidents involve low voltage (600 or Less) Roughly 3600 disabling electrical contact injuries occur every year in the US, along with another 4000 non-disabling injuries.

How Electricity can Harm YOU Current passing through your body can cause electric shock, resulting in 3 types of potential injuries: Burns (Arcs burn with heat and radiation) Physical injuries(Broken bones, falls, and muscle damage) At 10 mA, the muscle clamp on to whatever the person in holding. Nervous system effects (Stop breathing at 30 to 75 mA alternating current at 60Hz, fibrillation at 75 to 100 mA at 60Hz) Fibrillation = heat is “twitching” and there is no blood flow to the body!

How to keep from getting Electrocuted Always make sure that the power is locked and tagged out! The person doing the work must be the person to lock out the energy source. Always check your cable as you start your shift, looking for torn places or bad splices. Don’t take my work for it, lock it out, tag it out, and then try it out.