1
Q
About how many workers are electrocuted every week?
A
5 workers
2
Q
What percent of worker occupational deaths are caused by electricity?
A
electricity causes 12% of young worker occupational deaths
3
Q
4 main types of electrical injuries: direct and indirect
A
Direct: - electrocution or death due to electrical shock - electrical shock - burns Indirect: - falls
4
Q
Levels of dangers of currents
A
- currents above 10 mA can paralyze or “freeze” muscles
- currents more than 75 mA can cause a rapid, ineffective heartbeat - death will occur in a few minutes unless a defibrillator is used
5
Q
old saying about voltage and current
A
voltage hurts, current kills
6
Q
what is the most common shock related injury?
A
burns
7
Q
Burns:
A
- occur when you touch electrical wiring or equipment that is improperly used or maintained
- very serious injury that needs immediate attention
8
Q
how does electricity work
A
- electricity is the flow of energy from one place to another
- requires a source of power - usually a generating station
- a flow of electrons (current) travel through a conductor
- travels in a closed circuit
9
Q
voltage definition
A
voltage is the fundamental force or pressure that causes electricity to flow through a conductor and is measured in volts
10
Q
resistance definition
A
resistance is anything that impedes the flow of electricity through a conductor and is measured in ohms
11
Q
definition of current
A
current is the flow of electrons from a source of voltage through a conductor and is measured in amperes
12
Q
Alternating Current (AC) definition
A
- the current flows back and forth (a cycle) through a conductor
- in each cycle, the electrons flow first in one direction, then the other
- normal rate is 60 Hz
13
Q
Direct Current (DC) definition
A
the current flows in one direction only (as in a car battery)
14
Q
is AC or DC used more often, and why?
A
AC is most widely used b/c it is possible to step up or step down the current through the transformer
15
Q
Ohm’s Law
A
current = voltage / resistance
16
Q
Ground (definition)
A
a conducting connection, whether or not unintentional, between an electrical circuit or equipment and the earth, or to some conducting body that serves in place of the earth
17
Q
electrical shock definition
A
- an electrical shock is received when electrical current passes through the body
- you will get an electrical shock if a part of your body completes an electrical circuit by:
- touching a live wire and an electrical ground, OR
- touching a live wire and another wire at different voltage
18
Q
shock severity depends on:
A
- path of current through the body
- amount of current flowing through the body (amps)
- duration of the shocking current through the body
19
Q
what is the “let go” threshhold of current?
A
10 - 15 mA
20
Q
3 principle ways that people experience shock:
A
- contact with a normally energized bare conductor (close proximity with a high voltage conductor is often enough)
- contact with a normally insulated conductor that the insulation has deteriorated or has been damaged
- equipment failure: results in an open or short circuit, causing the current to flow in an unwanted manner
21
Q
4 basic ways insulation may fail
A
- mechanically - as with friction, tearing, crushing, or animal attack
- excessive electrical stress - occurs when the equipment and/or wiring experiences currents significantly beyond what it is designed for
- temperature - excessive high or low temps, or temp cycling can cause differential expansion or contractions on the insulator
- chemical and physical reaction - oxidation, contamination, or leaching of important ingredients from the insulation
22
Q
electrical accidents are caused by a combination of what 3 factors
A
- unsafe equipment and/or installation
- workplaces made unsafe by the environment
- unsafe work practices
23
Q
control of electrical hazards: isolate electrical parts:
A
- use guards or barriers (guard live parts of electric equipment operating at 50 volts or more against accidental contact - SESEK DOESNT LIKE THIS B/C CURRENT HURTS YOU MORE)
- replace covers
24
Q
control of electrical hazards - isolate electrical parts - cabinets, boxes, and fittings
A
conductors going into them must be protected, and unused openings must be closed
25
control of electrical hazards - close openings
- junction boxes, pull boxes, and fittings must have approved covers
26
hazard - overhead powerlines
- usually not insulated
- examples of equipment that can contact power lines: crane, ladder, scaffold, backhoe, scissor lift, raised dump truck, aluminum paint roller, child retrieving knife with bamboo pole and razor blade
27
control - overhead power lines
- stay atleast 10 ft away
- post warning signs
- assume that lines are energized
- use wood or fiberglass ladders, not metal
- power line workers need special training and PPE
28
hazard - inadequate wiring
- hazard: wire to small for the current
- example: portable tool with an extension cord that has a wire too small for the tool. the tool will draw more current than the cord can handle, causing overheating and a possible fire without tripping the circuit breaker
29
control of inadequate wiring
- use the correct wire
- wire used depends on operation, building materials, electrical load, and environmental factors
- use fixed cords rather than flexible cords
- use correct extension cord
30
hazard - defective cords and wires
- plastic or rubber covering missing
| - damaged extension cords and tools
31
cords can be damaged by:
- aging
- door or window edges
- staples or fastenings
- abrasion from adjacent materials
- activity in the area
32
control - cords and wires
- insulate live wires
- check before use
- use only cords that are 3-wire type
- use only cords marked for hard or extra hard usage
- use only cords, connection devices, and fittings equipped with strain relief
- remove cords by pulling on the plug, NOT the cords
- cords not marked for hard or extra hard use, or which have been modified, must be taken out of service immediately
33
permissible use of flexible cords - do not use flexible wiring when.. and flexible cords must not be...
- do not use flexible wiring where frequent inspection would be difficult or where damage would be likely
- flexible cords must not be:
- run through holes in walls, ceilings, or floors
- run through doorways, windows, or similar openings (unless physically protected)
- hidden in walls, ceilings, floors, conduit or other raceways
34
Grounding creates what and how does it protect you
- grounding creates a low-resistance path from a tool to the earth to dispense unwanted current
- when a short or lighting occurs, energy flows to the ground, protecting you from electrical shock, injury, and death
35
hazard - improper grounding
- tools plugged into improperly grounded circuits may become energized
- broken wire or plug on extension cord
- some of the most frequently violated OSHA standards
36
control - ground tools and equipment
- ground power supply systems, electrical circuits, and electrical equipment
- frequently inspect electrical systems to insure path to ground is continuous
- inspect electrical equipment before use
- don't remove ground prongs from tools or extension cords
- ground exposed metal parts of equipment
37
Control - use GFCI
- ground fault circuit interrupter
- protects you from shock
- detects difference in current between black and white wires
- if a ground fault is detected, GFCI shuts off electricity in 1/40th of a second
- use GFCI's on all 120 volt, single-phase, 15- and 20- ampere receptacles, or have an assured equipment grounding program
38
control - assured equipment grounding conductor program
- program must cover: all cord sets, receptacles not part of a building or structure, and equipment connected by plug and cord
- program requirements include: specific procedures adopted by employer, competent person to implement the program, and visual inspection for damage of equipment connected by cord and plug
39
hazard - overloaded circuits - hazards may result from...
hazards may result from:
- too many devices plugged into a circuit, causing heated wires and possible fire
- damaged tools overheating
- lack of over-current protection
- wire insulation melting, which may cause arcing and a fire int he area where the overload exists, even inside a wall
40
Breakers and Fuses protection vs. GFCI protection
- breakers and fuses protect equipment, and your overall system from a fire, they dont protect people (by the time they melt or pop, youre melted or popped first)
- a GFCI is intended to protect people
41
control - electrical protective devices
- automatically opens circuit if excess current from overload or ground-fault is detected - shutting off electricity
- includes GFCI's, fuses, and circuit breakers
42
fuses and circuit breakers are:
overcurrent devices - when too much current:
- fuses melt
- circuit breakers trip open
43
power tool requirements
- have a three-wire cord with ground plugged into a grounded receptacle, or
- be double insulated, or
- be powered by a low voltage isolation transformer
44
tool safety tips
- use gloves and appropriate footwear
- store in dry places when not using
- dont use in wet/damp conditions
- keep working areas well lit
- dont carry tool by cord
- remove damaged tools from use
- dont yank cords to disconnect
- keep cords away from heat, oil, and sharp edges
- disconnect when not in use and when changing accessories such as blades/bits
- ensure cords are not a tripping hazard
45
preventing electrical hazards in tools
- inspect tools before use
- use the right tool, correctly
- protect tools
- use double insulated tools
46
double insulated tools
- hand-held tools manufactured with non-metallic cases are called double insulated
- if approved, they do not require grounding under the National Electric Code
- although this design method reduces risk of grounding deficiencies, a shock hazard can still exist
47
temporary lights
protect from contact and damage, and dont suspend by cords unless designed to do so
48
clues that electrical hazards exist
- tripped circuit breakers or blown fuses
- warm tools, wires, cords, connections, or junction boxes
- GFCI that cuts off a circuit
- worn or frayed insulation around wire or connection
49
lockout and tagout of circuits
- apply locks to power sources after de-energizing
- tag deactivated controls
- tag de-energized equipment and circuits at all points where they can be energized
- tags must identify equipment or circuits being worked on
50
to protect workers from electrical shock:
- use barriers or guards to prevent passage through areas of exposed energized equipment
- pre-plan work, post hazard warnings and use protective measures
- keep working spaces and walkways clear of cords
51
other safety-related work practices
- use special insulated tools when working on fuses with energized terminals
- dont use worn or frayed cords/cables
- dont fasten extension cords with staples, hang from nails, or suspend wire
52
preventing electrical hazards - planning
- plan work with others
- plan to avoid falls
- plan to lock-out and tag-out equipment
- remove jewelry
- avoid wet conditions
- avoid overhead power lins
53
why to avoid wet conditions
- if you touch a live wire or other electrical component while standing in even a small puddle, youll get a shock
- damaged insulation, equipment, or tools can expose you to live electrical parts
- improperly grounded metal switch plates and ceiling lights are especially hazardous in wet conditions
- wet clothing, high humidity, and perspiration increase chances of being electrocuted
54
preventing electrical hazards - PPE
- proper foot protection (not tennis shoes)
- rubber insulating gloves, hoods, sleeves, matting, and blankets
- hard hat (insulated - nonconductive)
55
preventing electrical hazards - proper wiring and connectors
- use and test GFCI's
- check switches and insulation
- use 3 prong plugs
- use extension cords only when necessary and assure in proper condition and right type for job
- use correct connectors
56
training
- de-energize electric equipment before inspecting or repairing
- use cords, cables, and electric tools that are in good repair
- lockout/tagout recognition and procedures
- use appropriate PPE
57
electrical fires - 3 principle ways in which electrical installations could cause fires
- electrical overloading
- electrical discharges (sparcs, arcs, or coronas)
- electrical heating appliances
58
electrical overloading
- current in circuit is greater than design levels
- excess current generates excess heat
- heat damages components
- may ignite flammable nearby materials, including insulation
- a fuse "blowing" or a circuit breaker "popping/snapping" means theres a problem
59
electrical discharges (sparcs, arcs, or coronas)
- spark: a rapid, heavy discharge of electrons. occurs any time an ionized path develops in the dielectric medium separating 2 conductors or a conductor and ground
- arc: a sustained stream of electrons flowing across a gap between conductors that were initially in contact or close together while current is flowing
- corona: occurs in high-voltage systems when the dielectric medium separating conductors partially breaks down (the potential difference reaches a level necessary to ionize gas in the dielectric medium, but not enough to produce a spark - produces faint glow in dark)
- may ignite flammable solid, liquid, vapors, dust, or powders
- electrical devices may need to be in explosion proof enclosures
- may cause electrical noise and interfere with electrical equipment
- spark caused by static electricity can cause fires in certain environments
60
electrical heating appliances
- commonplace both at home and in workplace
- not appropriate where flammable materials or atmosphere are expected
- may cause burns to person that makes contact with equipment
safety test 2
flashcards
Decks in class (8)
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