Electrical Safety slides

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E L E C T R I C A L
S A F E T Y
September 28, 2014
Leo Koppel (QSET)
This talk is for your awareness. It is not
required, nor does it certify or qualify you to
do anything.
S H O C K
“High voltage is dangerous”
“Voltage isn’t dangerous, current is”
?
S H O C K
Depends on
• Current
• Pathway
through body
• Nature of
electrical
source
• Duration
• (and voltage)
Los Angeles Times. Jun 29, 1902
• Body becomes part of
circuit
• Danger from
– Burns
– Cardiac arrest /
filbrilation
– Fractures / trauma from
secondary falling down
T. Lanzisero. Electric Shock Hazards - Risk
Assessment and Safety Management (2012)
C U R R E N T
Current Level
(AC 60 Hz)
Effect
1 mA
Sensation that shock is occurring
5 mA
Upper limit of safe or harmless range
10–20 mA
Let-go threshold: flexor muscles are stronger than the extensor muscles;
subject cannot shake loose from the shock source; perspiration
30–40 mA
Tetany: sustained muscle contraction and cramping
50–70 mA
Extreme pain, physical exhaustion, fainting, irreversible nerve damage;
possibility of ventricular fibrillation (heart); respiratory arrest with
possible asphyxiation
100 mA
Ventricular fibrillation (heart) and death if the current passes through
the body trunk
>100 mA
Fibrillation, amnesia, burns, severe electrolysis at contact sites
>5 A
Little likelihood of survival
J.C. Whitaker, The Electronics Handbook 2nd ed. 2005
A C / D C
Bodily effect
DC
AC 60 Hz
AC 10 kHz
Slight sensation felt at hand(s)
Men
= 1.0 mA
Women = 0.6 mA
0.4 mA
0.3 mA
7 mA
5 mA
Threshold of perception
Men
= 5.2 mA
Women = 3.5 mA
1.1 mA
0.7 mA
12 mA
8 mA
Painful, but voluntary muscle
control maintained
Men
= 62 mA
Women = 41 mA
9 mA
6 mA
55 mA
37 mA
Painful, unable to let go of
wires
Men = 76 mA
Women = 51 mA
16 mA
10.5 mA
75 mA
50 mA
Severe pain, difficulty
breathing
Men
= 90 mA
Women = 60 mA
23 mA
15 mA
94 mA
63 mA
Possible heart fibrillation after
3 seconds
Men = 500 mA
Women = 500 mA
100 mA
100 mA
http://www.allaboutcircuits.com/vol_1/chpt_3/4.html
S H O C K
• “Let go” current – above this you can’t
let go (muscles contract)
• Interestingly, domestic AC happens to
the most dangerous
• Also body impedance is lower
• Resistance! Your skin resistance is >
100kOhm dry, but < 1 kOhm wet!
C. F. Dalziel, Electric Shock Hazard. IEEE Spectrum (1972)
• By the way – I’m not
sure why women have a
lower threshold; the
articles don’t seem to
think it’s worth
mentioning…
• This article is from 1972
• “So far, it has been
impossible to obtain
reliable values for
children; they just cry at
the higher values.”
• Again, 1972
• (Who among us will fill this
scientific niche?)
C. F. Dalziel, Electric Shock Hazard. IEEE
Spectrum (1972)
Also I’ll throw this in…
Remember it’s not just lethal shocks we want to
Electrical Safety Authority
avoid…
S O
W H A T
T O
D O ?
Working with 24 VDC, our biggest risk is
short-circuit -> overheating -> burns or fire.
• Watch out for leads
• Turn things off before working on them
• Don’t wear jewelry / watches when
working with power systems
S O
W H A T
T O
D O ?
• Use multimeter
correctly
• Watch out for correct
socket
• Only measure
resistance in deenergized circuit
• Careful not to short out
connections with the
leads
http://www.allaboutcircuits.com/vol_1/chpt_3/9.html
F U S E S
• Use the right one
• They protect equipment,
not you
F U S E S
https://www.youtube.com/watch?v=YCWdnjLqVWw
F I R E
https://www.youtube.com/watch?v=YCWdnjLqVWw
F I R E
• I can’t train you in fire extinguishing.. But
• If there’s a fire: warn others!
• If you’re not confident the fire can be put out pull
the alarm and leave.
• Even if you put it out, report it
• If something that’s plugged in starts smoking /
burning, unplug it first
• Lithium batteries are hard to put out / will reignite.
https://www.youtube.com/watch?v=YCWdnjLqVWw
W E A R
T H E S E
• When soldering
• Working with
moving parts
• Using tools
Exception!
• “It’s only for a second”
• “My parents have a shop”
• “I do more dangerous things all the
time”
…if you’re
this guy!
Then
it’s okay.
Just wear them
(QSET has some
you can borrow)
O T H E R
T I P S
• Working with the robot or robotic arm know
– Where it could move
– How you will turn it off
•
•
•
•
•
Be aware of what’s on (and don’t forget)
Don’t touch a hot iron
Don’t try to catch a falling iron
Keep workspace tidy
Report incidents
http://www.allaboutcircuits.com/vol_1/chpt_3/9.html
G E N E R A L
S A F E T Y
(Leigh Hunter)
QSET’s procedures will be posted.
Safety!
https://www.youtube.com/watch?v=U7Q06csDc7U

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