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UNL Safety Colloquium

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UNL Safety Colloquium Laboratory Electrical Safety Fall, 2006 Robert W. Hayden, M.A., PMP Lincoln Electric System (LES) Why is this relevant to me? – PowerPoint PPT presentation

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Title: UNL Safety Colloquium


1
UNL Safety Colloquium
  • Laboratory Electrical Safety
  • Fall, 2006
  • Robert W. Hayden, M.A., PMP
  • Lincoln Electric System (LES)

2
Why is this relevant to me?
  • You work in a laboratory
  • (Electrical accidents are)
  • Accident stats
  • Injury stats difficult to find,
  • Fatality stats probably rare
  • (but, why be famous?)

3
Major characteristic of electrical accidents
  • You work in a laboratory
  • Accident stats
  • Injury stats difficult to find,
  • Fatality stats probably rare
  • (but, why be famous?)
  • RATIO of fatalities to injuries is HIGH 1
  • for ALL electrical type injuries.

4
Electrical hazards in a lab
  • Electrocution from INSTALLED equipment
  • Electrocution from TEMPORARY wiring
  • Electrocution from APPARATUS or POWER SUPPLIES
  • But, first some basics . . . . .

5
Electricity comes in only two flavors, AC and DC
  • AC is Alternating Current. It flows both
    directions, in varying potential, at a given
    frequency. In the U.S., 120v at 60 Hz is the
    standard. In other countries both the voltage
    and frequency may be different. (230v _at_50Hz)
  • DC is Direct Current. It flows in only one
    direction, at a set potential.

6
What Alternating Currentlooks like on an
oscilloscope
Frequency (one cycle or hertz)
7
What Direct Current (steady state) looks like on
an oscilloscope

0
8
What a Direct CurrentPULSE looks like on an
oscilloscope
0
9
But lets talk safety.
  • Both AC and DC need a path in order to complete
    a circuit. Only when a circuit is completed
    will current flow.
  • PEOPLE get hurt when THEY get in the path
    (circuit).
  • HOWEVER- electricity travels at (nearly) the
    speed of light, therefore ALL your precautions
    have to focus on preventing a path because after
    a path (circuit) is established it may be too
    late.

10
(No Transcript)
11
The risks?
  • There are four types of electrical-related
    injuries
  • Electrocution (death due to electrical shock)
  • Electrical shock (may cause tissue damage,
    initially invisible).
  • Burns (visible, obvious)
  • Falls (secondary injury)

12
Electrical Burns
  • A common, nonfatal shock-related injury
  • May occur when you touch electrical wiring or
    equipment that is improperly grounded, used, or
    maintained
  • Typically occurs on the hands
  • Electrical burns are very serious injuries that
    need immediate attention

13
Falls or Contact injuries
  • Electric shock can also cause indirect or
    secondary injuries
  • Workers in elevated locations who experience a
    shock can fall, resulting in serious injury or
    death
  • OR, workers can be thrown into others or into
    solid or sharp objects

14
So, how much electricity does it really take to
hurt me?
  • It varies. Sex, weight, skin moisture,
    hydration, and path through the body all
    contribute.
  • Some general threshold values
  • Sensation. 1 mA AC / 5mA DC
  • Let-go. 15 mA AC / 75 mA DC
  • V-fib. 75-100 mA AC / 300 mA DC

15
COMPARE
  • The values in the previous slide are in units
    called milliamps (mA). One milliamp is 1/1000 of
    an amp.
  • What is the TYPICAL current rating (in amps) of a
    120v circuit breaker?

16
COMPARE
  • the TYPICAL current rating (in amps) of a 120v
    circuit breaker? Lets say 15 amp.
  • 15 amp 15,000 mA / 150 mA
  • 100 times enough current to kill you
  • (without tripping the breaker, of course)

17
So, if the circuit breaker doesnt protect me,
whats it for?
18
Electrical Protective Devices
  • Protective devices shut off the flow of
    electricity in the event of either an over
    current or a ground-fault condition in the
    circuit. They include fuses, circuit breakers,
    and ground-fault circuit interrupters (GFCIs).
  • BUT, they protect different things.

19
Over Current Devices
  • Fuses and circuit breakers are over current
    devices.
  • When there is too much current
  • Fuses melt
  • Circuit breakers trip open
  • Fuses and circuit breakers protect WIRING and
    EQUIPMENT.
  • They are designed to prevent fires.
  • Their primary purpose is NOT to protect people.

20
Ground Fault Devices
  • In contrast, GFCIs protect against imbalanced
    loads (wrong path to ground) also known as a
    fault, or a ground fault.
  • Only GFCIs are designed to protect PEOPLE.

21
BarbiDEMO
  • a.k.a. Why you need a GFCI

22
Electrocution from INSTALLED equipment
  • Non-UL (Underwriters Laboratory) equipment.
  • Improperly installed (wired) equipment (for
    example switching the neutral wire).
  • Ungrounded equipment (two prong)
  • Unprotected (non Ground Fault) equipment or
    outlets
  • Especially around liquids/water/plumbing.

23
Electrocution from TEMPORARY wiring
  • Contributors Include
  • Non-GFCI cords or non-GFCI outlets
  • Damaged cords
  • Modified cords
  • Improper use or application of cords

24
The path to ground from circuits, equipment, and
enclosures must be permanent and
continuous.
25
Permissible Uses of Flexible Cords
Stationary equipment-to facilitate interchange
Pendant, or Fixture Wiring
Portable lamps, tools or appliances
26
Prohibited Uses of Flexible Cords
Substitute for fixed wiring
Run through walls, ceilings, floors, doors, or
windows
Concealed behind or attached to building surfaces
27
Electrocution from POWER SUPPLIES or APPARATUS
  • In these cases (most often) the apparatus or
    power supply is doing just what its supposed to.
    It is putting out voltage at a given current
    and/or frequency.
  • BUT People (you) have managed to get yourself
    into the circuit (path).

28
The Results? They range from . . .
  • Ooops / Ouch (small shocks)
  • Secondary injuries or damage
  • Sparks
  • Fires
  • Falls or cuts
  • Breakage or equipment damage
  • Big shocks. Burns or even death.

29
  • Electrocution
  • Minor shock
  • Major shock
  • _at_ approximately let-go threshold invisible
    (often latent) tissue damage begins to occur
  • Visible burn(s)
  • Fatality
  • Most often due to V-fibrillation
  • Can also be from the burn (internal or external)

30
Known POWER SUPPLIES or APPARATUS values
  • Electrophoresis (power supplies)
  • Various manufacturers spec models from 0 to
    6000v, 0 to 2000mA.
  • Electroporation (equipment itself)
  • Pulses of 1,000s of volts
  • Other (physics) power supplies
  • Lasers
  • Particle study equipment (Especially anything
    with large capacitors)
  • QUITE capable of injury if not properly handled.

31
The Barriers
  • Installed equipment
  • Purchase UL listed equipment, if possible
  • Have equipment installed by a licensed
    electrician. (if its not plug-in type)
  • Have any non-UL equipment checked for
    grounding/wiring by a licensed electrician
  • STRONGLY consider having all equipment circuits
    operating around liquids or in proximity to
    plumbing (sinks) plugged into GFCI outlets or
    GFCI pigtails
  • LABEL all outlets/circuit breakers

32
The Barriers
  • Temporary wiring
  • Use only cords with proper ratings (amperage as
    well as environment wet W)
  • Jacket codes in Natl Electric Code (NEC)
  • Again, all equipment circuits operating around
    liquids or in proximity to plumbing (sinks)
    should be plugged into GFCI outlets or have GFCI
    pigtails
  • Dont daisy-chain cords.
  • Especially multiple outlet cords

33
The Barriers
  • Technique / procedure
  • Follow procedural guidance (SOPs) for setting up,
    terminating, and adjusting equipment / apparatus
    (for example )
  • Power OFF before touching wires
  • Double check connections before powering ON
  • Dont defeat electrical interlocks
  • Be especially careful whenever working with both
    electricity and any liquid or plumbing

34
Summary
  • Know that electricity can hurt or even kill you
  • Dont get too comfortable around electricity,
    especially when also around liquids
  • Inspect your equipment/apparatus (frequently)
  • Follow procedures for setup, adjustment, etc.
  • If you have Safety questions, ask the
    Occupational Health and Safety department staff

35
Questions ?
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