Transcript UNL Safety Colloquium - UNL | Office of Research

UNL Safety Colloquium
Laboratory Electrical Safety
Fall, 2006
Robert W. Hayden, M.A., PMP
Lincoln Electric System (LES)
Why is this relevant to me?
•
You work in a laboratory
(Electrical accidents are…)
•
•
•
Accident stats
Injury stats
Fatality stats
difficult to find,
probably rare
(but, why be famous?)
Major characteristic of
electrical accidents
•
You work in a laboratory
•
•
•
Accident stats
Injury stats
Fatality stats
difficult to find,
probably rare
(but, why be famous?)
RATIO of fatalities to injuries is HIGH 1
for ALL electrical type injuries.
Electrical hazards in a lab



Electrocution from INSTALLED
equipment
Electrocution from TEMPORARY
wiring
Electrocution from APPARATUS
or POWER SUPPLIES
But, first some basics . . . . .
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 @50Hz)
DC is Direct Current. It flows in only
one direction, at a set potential.
What Alternating Current
looks like on an oscilloscope
Frequency (one cycle or hertz)
What Direct Current (steady state)
looks like on an oscilloscope
+
0
What a Direct Current
PULSE looks like on an
oscilloscope
0
But let’s 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.
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)
Electrical Burns
•
•
•
•
A common, nonfatal shockrelated 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
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
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
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?
COMPARE
the TYPICAL current rating (in amps) of a
120v circuit breaker? Let’s say 15 amp.
15 amp = 15,000 mA / 150 mA =
100 times enough current to kill you
(without tripping the breaker, of course)
So, if the circuit breaker
doesn’t protect me,
what’s it for?
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 (GFCI’s).
BUT, they protect different things.
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.
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.
Barbi
DEMO
a.k.a. Why you need
a GFCI
Electrocution from
INSTALLED equipment


Non-UL (Underwriter’s 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.
Electrocution from
TEMPORARY wiring
 Contributors
Include:
–Non-GFCI cords or non-GFCI
outlets
–Damaged cords
–Modified cords
–Improper use or application of
cords
“The path to
ground from
circuits,
equipment, and
enclosures must
be permanent and
continuous.”
Permissible Uses of Flexible Cords
Pendant, or
Fixture Wiring
Portable lamps,
tools or appliances
Stationary equipmentto facilitate interchange
Prohibited Uses of Flexible Cords
Substitute for
fixed wiring
Run through walls,
ceilings, floors,
doors, or windows
Concealed behind
or attached to
building surfaces
Electrocution from POWER
SUPPLIES or APPARATUS
o
o
In these cases (most often) the
apparatus or power supply is doing
just what it’s 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).
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.

Electrocution
– Minor shock
– Major shock
@ 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)

Known POWER SUPPLIES or
APPARATUS values
•
Electrophoresis (power supplies)
•
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Electroporation (equipment itself)
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Various manufacturers’ spec models from 0
to 6000v, 0 to 2000mA.
Pulses of 1,000’s of volts
Other (physics) power supplies
•
•
Lasers
Particle study equipment (Especially anything
with large capacitors)
QUITE capable of injury if not properly handled.
The Barriers

Installed equipment
– Purchase UL listed equipment, if possible
– Have equipment installed by a licensed
electrician. (if it’s 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
The Barriers

Temporary wiring
– Use only cords with proper ratings (amperage
as well as environment [wet =‘W’])

Jacket codes in Nat’l 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
– Don’t ‘daisy-chain’ cords.

Especially multiple outlet cords
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

– Don’t defeat electrical interlocks
– Be especially careful whenever working with
both electricity and any liquid or plumbing
Summary
Know that electricity can hurt or even kill
you
 Don’t 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

Questions ?