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)

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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?)

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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.

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Electrical hazards in a lab

• Electrocution from INSTALLED equipment
• Electrocution from TEMPORARY wiring
• Electrocution from APPARATUS or POWER SUPPLIES
• But, first some basics . . . . .

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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.

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

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What a Direct CurrentPULSE looks like on an
oscilloscope
0
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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.

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(No Transcript)
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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)

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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

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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

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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

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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?

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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)

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So, if the circuit breaker doesnt protect me,
whats it for?
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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.

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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.

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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.

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BarbiDEMO

• a.k.a. Why you need a GFCI

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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.

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Electrocution from TEMPORARY wiring

• Contributors Include
• Non-GFCI cords or non-GFCI outlets
• Damaged cords
• Modified cords
• Improper use or application of cords

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The path to ground from circuits, equipment, and
enclosures must be permanent and
continuous.
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Permissible Uses of Flexible Cords
Stationary equipment-to facilitate interchange
Pendant, or Fixture Wiring
Portable lamps, tools or appliances
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Prohibited Uses of Flexible Cords
Substitute for fixed wiring
Run through walls, ceilings, floors, doors, or
windows
Concealed behind or attached to building surfaces
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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).

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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.

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• 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)

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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.

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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

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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

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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

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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

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Questions ?