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BASIC ELECTRICAL SAFETY
Transcript of BASIC ELECTRICAL SAFETY
HAZARDS OF ELECTRICITY
Shock – Most common and can cause electrocution or muscle contraction leading to secondary injury which includes falls
Fires – Enough heat or sparks can ignite combustible materials
Explosions – Electrical spark can ignite vapors in the air
Arc Flash - can cause burns ranging from 14,000 degrees f. to 35,000 degrees f
Arc Blast – In a short circuit event copper can expand 67,000 times. The expansion causes a pressure wave. Air also expands adding to the pressure wave
Fundamentals of Electricity
Electrical current is the flow of electrons through a conductor.
A conductor is a material that allows electrons to flow through it.
An insulator resists the flow of electrons.
Resistance opposes electron flow.
Effect of Current Flow
Overhead Line Incident
He sweats- and he dies...
Summary - Hazards and Protection
Take Electricity Seriously!!!
Electricity is the second leading cause of death in construction.
Electrocutions make up 12% of construction fatalities annually.
Over 30,000 non-fatal shocks occur each year.
Over 600 deaths occur annually due to electrocution.
Contact with both conductors
Contact with one conductor and ground
With a tool: contact with “hot” metal part and ground (1), (2) & (3)
Severity of the Shock
Severity of the Shock depends on:
Amount of current
Determined by voltage and resistance to flow
Path through the body
Duration of flow through the body
Other factors such as general health and individual differences.
Current Flows in a
Loop or Circuit
Circuits are AC (alternating current) or DC (direct current).
Current is usually AC.
AC current has five parts:
(1) Electrical source
(2) HOT wire to the tool.
(3) The tool itself
(4) NEUTRAL wire returns electricity from the tool
Leading Causes of Electrical Accidents:
Drilling and cutting through cables
Using defective tools, cables and equipment
Failure to maintain clearance distance of 10 feet
Failure to de-energize circuits and follow Lockout/Tagout procedures
Failure to guard live parts from accidental worker contact
Unqualified employees working with electricity
Improper installation/use of temporary electrical systems and equipment
By-passing electrical protective devices
Not using GFCI (ground fault circuit interrupters) devices
Missing ground prongs on extension cords
How Shocks Occur
Current travels in closed circuits through conductors (water, metal, the human body).
Shock occurs when the body becomes a part of the circuit.
Current enters at one point & leaves at another.
Shocks occur in 3 WAYS
Effects of Current Flow...
More than 3 milliamps (ma): painful shock
More than 10 ma: muscle contraction
More than 20 ma: considered severe shock
More than 30 ma: lung paralysis - usually temporary
More than 50 ma: possible ventricular fibrillation (usually fatal)
100 ma to 4 amps: certain ventricular fibrillation (fatal)
Over 4 amps: heart paralysis; severe burns
Luling, La. - A man was electrocuted when his sweat dripped into the electric drill he was using to build a swing set in his backyard, the coroner said.
Richard Miller was pronounced dead Sunday at St. Charles Hospital, said David Vial, St. Charles Parish coroner. Miller, 54, had been using an electric drill in 90 degree heat, Vial said Monday.
“Apparently the man was sweating profusely,” Vial said. “He probably was pushing against the drill with his chest and his perspiration went into the drill itself and made a contact.”
The Associated Press
Controlling Electrical Hazards
Employers must follow the OSHA Electrical Standards (Subpart K)
Subpart K includes four proactive methods:
Safe Work Practices
We can be safe by keeping electricity away from us. We can:
Insulate the conductors.
Example: The insulation on extension cords.
Elevate the conductors.
Example: Overhead powerlines.
Guard the conductors by enclosing them.
Example: Receptacle covers, boxes, & conduit.
Insulating the Conductors
The first way to safeguard workers from electrically energized wires is through insulation.
Rubber and plastic is put on wires to prevent shock, fires, short circuits and for strain relief.
It is always necessary to check the insulation on equipment and cords before plugging them in.
Remember, even the smallest defect will allow leakage!
The second way to safeguard workers from electrically energized wires is by elevating them.
Wires are often elevated by the power company.
It is always necessary to check the location of overhead lines before you begin work each day.
Clearance of worker and any equipment, tools, materials, or scaffold near uninsulated lines is 10 feet!
A worker was attempting to move mobile scaffold.
Scaffold made contact with 7200 volt line.
The worker died.
Guarding the Conductors
The third way to safeguard workers from electrically energized wires is by guarding them.
Covers, boxes, and enclosures are often put around conductors to prevent worker contact.
It is always necessary to check that electrical boxes and panels are covered and free from missing “knock-outs”.
Remember, electric equipment operating at 50 volts or more must be guarded!
We can be safe by providing a separate, low resistance pathway for electricity when it does not follow normal flow (ground prong).
Grounding gives the stray current somewhere to go and keeps you from becoming part of the circuit.
What Must be Grounded?
All circuits and extension cords.
All non-current carrying metal parts.
Portable & semi-portable tools and equipment unless double insulated.
We can be safer by automatically shutting off the flow of electricity in the event of leakage, overload, or short circuit.
Ground Fault Circuit Interrupters (GFCI) are circuit protection (or “overcurrent”) devices that protect you, the worker.
Circuit breakers & fuses protect equipment, not you, because they take too much current & too much time to trip.
Circuit Protective Devices
Circuit Breakers and Fuses
Only protect the building, equipment, and tools from heat build-up!
Never depend on circuit breakers or fuses to prevent shocks!
Ground Fault Circuit Interrupter (GFCI)
Is the only device which will protect the worker from shock and electrocution!
All temporary circuits are required to have GFCI protection and
Equipment & cords must be included in an Assured Equipment Grounding Conductor Program
An extension cord is a temporary circuit.
Types of GFCIs: receptacle, circuit breaker
Must be wired correctly and tested.
Assured Equipment Grounding Conductor Program
Requires the following:
-Written program and specific procedures
-Program implemented by a Competent Person (one who is capable of identifying existing and predictable hazards in the surroundings or working conditions which are unsanitary, hazardous, or dangerous to employees, and who has authorization to take prompt corrective measures to eliminate them.
-Equipment grounding conductors must be tested (tools, extension cords, and circuits):
At least every three months for cords & tools
At least every six months for receptacles
There must be separate circuits for electric tools and lighting, each labeled as such.
Light circuits do not require a GFCI. Unless used in a wet location.
Test branch circuits before use.
Maintain vertical clearances.
Insulate wires from their supports.
Extension Cords and Cables
Must be in good shape without splices.
Cannot be secured with staples, nails or bare wire.
Must be protected from damage.
Must have a ground pin.
Should be inspected regularly and pulled from service if defective.
Cannot be repaired with electrical or duct tape. Must be repaired with heat-shrink sleeve or bonding/vulcanizing tape to retain original insulation properties.
Acceptable Cord Types
All cords must meet the National Electric Code’s (NEC) requirement for Hard/Extra Hard type.
Look for markings stamped on cords.
Acceptable Cord Types:
Extra Hard Use Markings: S, ST, SO, STO
Hard Usage Markings: SJ, SJO, SJT, SJTO
No flat cords allowes on construction sites!!!
Safe Work Practices
Before work begins, the employer must determine where exposed and concealed electrical circuits are located.
Once found, warning signs/labels must be posted.
Workers need to know the location, hazards, and protective measures.
Competent Person determines if performance of work could bring contact with energy.
Distance of the worker to the energy source should be considered first.
Tools, materials, and processes should also be considered to see if they could potentially shorten the safe separation distance.
Must not permit work near electric circuits unless the worker is protected by:
De-energizing the circuit and grounding it.
Guarding it effectively by insulation.
Other means (maintaining safe separation)
De-energized circuits and equipment must be locked/tagged out.
No metal ladders for or near electrical work.
No wet hands when plugging or unplugging cords/equipment.
No raising or lowering tools by the cord.
Unless equipment is designed for it, cannot be used in damp and wet locations.
Common OSHA Citations:
.404(b)(1)(i): Branch circuits: GFCI protection/Assured Equipment Grounding Conductor Program
.404(f)(6): Grounding path
.403(b)(2): Equipment installation and use
.403(i)(2)(i): Guarding live parts
Exposed electrical parts
Wires with bad insulation
Ungrounded electrical systems and tools
Damaged power tools and equipment
Using the wrong PPE and tools
Overhead power lines
All hazards are made worse in wet conditions
Damaged extension cords
Unqualified workers doing electrical work
Use fuses and circuit breakers
Guard live parts
Proper use of flexible cords
Close electrical panels by Competent Person
Ensure Competent Person on site
Use proper approved electrical equipment
Qualified person install electrical devices
What is SAFETY?
It is the state of being "safe" (from French sauf), the condition of being protected against physical, social, spiritual, financial, political, emotional, occupational, psychological, educational or other types or consequences of failure, damage, error, accidents, harm or any other event which could be considered non-desirable.
Safety can also be defined to be the control of recognized hazards to achieve an acceptable level of risk.
This can take the form of being protected from the event or from exposure to something that causes health or economical losses.
What is Electricity ?
It is the set of physical phenomena associated with the presence and flow of electric charge. Electricity gives a wide variety of well-known effects, such as lightning, static electricity, electromagnetic induction and electrical current. In addition, electricity permits the creation and reception of electromagnetic radiation such as radio waves.
History of electricity
Long before any knowledge of electricity existed people were aware of shocks from electric fish. Ancient Egyptian texts dating from 2750 BC referred to these fish as the "Thunderer of the Nile", and described them as the "protectors" of all other fish.
Several ancient writers, such as Pliny the Elder and Scribonius Largus, attested to the numbing effect of electric shocks delivered by catfish and torpedo rays, and knew that such shocks could travel along conducting objects. Patients suffering from ailments such as gout or headache were directed to touch electric fish in the hope that the powerful jolt might cure them.
Possibly the earliest and nearest approach to the discovery of the identity of lightning, and electricity from any other source, is to be attributed to the Arabs, who before the 15th century had the Arabic word for lightning (raad) applied to the electric ray.
Ancient cultures around the Mediterranean knew that certain objects, such as rods of amber, could be rubbed with cat's fur to attract light objects like feathers. Thales of Miletus made a series of observations on static electricity around 600 BC, from which he believed that friction rendered amber magnetic, in contrast to minerals such as magnetite, which needed no rubbing.
Electricity would remain little more than an intellectual curiosity for millennia until 1600, when the English scientist William Gilbert made a careful study of electricity and magnetism, distinguishing the lodestone effect from static electricity produced by rubbing amber.
Further work was conducted by Otto von Guericke, Robert Boyle, Stephen Gray and C. F. du Fay. In the 18th century, Benjamin Franklinconducted extensive research in electricity, selling his possessions to fund his work. In June 1752 he is reputed to have attached a metal key to the bottom of a dampened kite string and flown the kite in a storm-threatened sky. A succession of sparks jumping from the key to the back of his hand showed that lightning was indeed electrical in nature. He also explained the apparently paradoxical behavior of the Leyden jar as a device for storing large amounts of electrical charge in terms of electricity consisting of both positive and negative charges.
In 1791, Luigi Galvani published his discovery of bioelectricity, demonstrating that electricity was the medium by which nerve cells passed signals to the muscles.
Alessandro Volta's battery, or voltaic pile, of 1800, made from alternating layers of zinc and copper, provided scientists with a more reliable source of electrical energy than the electrostatic machines previously used.
While the early 19th century had seen rapid progress in electrical science, the late 19th century would see the greatest progress in electrical engineering.
n 1887, Heinrich Hertz discovered that electrodes illuminated with ultraviolet light create electric sparks more easily.
In 1905 Albert Einstein published a paper that explained experimental data from the photoelectric effect as being the result of light energy being carried in discrete quantized packets, energising electrons. This discovery led to the quantum revolution.