1. Construction Safety Talks
Electrical Some Things To Know Before You Give Your Talk.
Grounding How many times, as a supervisor, have you heard these words
spoken about electrical power tools?
No. 73
"It's only 110 - it can't hurt me."
There are many accident reports that show that a 110 volt shock
How This Talk can be fatal. It's not the voltage that will get you; it's the current
Applies To My (measured in amps). This chart shows your body’s reaction to
Crew: various levels of current. A fatal electrocution can occur around
100 milliamps - one tenth of an amp!
less than .001 amp no sensation.
.001 to .002 amps threshold of perception - very slight tingle
.002 to .010 amps muscular contraction (mild to strong.)
.010 to .025 amps painful shock - inability to let go due to
strong muscular contractions.
over .025 amps violent muscular contraction.
.050 to .100 amps ventricular fibrillation (can be fatal) -
irregular heart beat and pumping
over .100 amps paralysis of breathing (fatal)
The skeptics in the crew are right. A number of conditions must be
in place for this to occur.
• the body’s resistance is low because the worker is hot and
perspiring.
• the path of the current crosses through or near the heart.
• contact with the energized source and ground must last
several seconds or longer. The body may move upon initial
shock, breaking the path.
An electrical grounding system helps to prevent electrocution.
Check if your job is using an assured grounding system or GFCI.
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2. Explain to your crew the importance of using one of these two systems.
Ground Fault Circuit Interrupters (GFCI)
This device measures current of the hot (black wire) and the neutral (white wire)
conductors - they should be the same. If they are not, it means that current is leaking
through another path to ground. The GFCI will trip when it senses a difference as little
as 5mA (milliamperes).
Nuisance tripping of a GFCI can be corrected with some simple investigation. If a long
extension cord is used, the diameter of the conductors may be too small or there may
be internal problems between the conductors. A 14 gage 25 foot cord can handle your
13 amp circular saw, but a 50 foot cord such be 12 gage. Look at all connections, are
any wet or in water? Test the tool, it may have a fault in it. Test the GFCI, they can also
break. But don't bypass it! Never move the GFCI to the tool end of the cord! This leaves
the extension cord unprotected.
Assured Grounding System
This requires frequent checking and marking of all tools and cords. Normally done on a
job by the electrical sub-contractor. If used on your job, you should explain the operation
in detail.
For assured grounding to be used, third wire grounding (complete with grounding prong)
devices such as outlets and extension cords, are necessary. This provides a low-
resistance path to ground. Should they come in contact with a fault in the cord or tool,
the current will take the path of least resistance. In reality it will split into two parallel
circuits going to the ground, most through the third wire but some through your body.
Try These For Show And Tell!
Point out the type of grounding you have at your site and explain how it works to the
crew. (OSHA allows both an assured grounding system or the use of GFCIs.)
Questions You Can Use To Get Them Talking:
• Do all tools/cords have a third prong (except double insulated)?
• How can I tell if my power tool is double insulated? (by the specification plate on
the tool)
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3. Attended By:
The illustrations, instructions and principles contained in the material are general in scope and, to the best of our knowledge, current at
the time of publication. No attempt has been made to interpret any referenced codes, standards or regulations. Please refer to the
appropriate code, standard or regulation making authority for interpretation or clarification.
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