Basic Electrical Safety Principles

Learning the following electrical safety principles will enable personnel to understand and be aware of dangers associated with electrical energy sources.

Basics of Electricity

Current:

Do NOT learn the hard way!

	is the flow, like water, of electrons in a conductor
	can flow through you and other conductors, such as metals
	A unit of current is the ampere (amp)
	can harm you when it flows through your body (electric shock)

Resistance:

	restricts the flow, like the pipe restricts the water.
	A unit of resistance is ohm
	The more resistance, the less the current flows

Voltage:

	is a force, like water hitting you.
	The more water and faster it comes at you, the larger the force
	The unit is volt. 50 volts is considered HIGH VOLTAGE.

Potential:

	When water is in a water tower, is has potential to drop and exert a force
	Stored electricity can have a potential to move and exert a force
	Capacitors are an example of stored electrical potential.

Basic Electrical Circuit Characteristics

The electrical circuit ( Example )
An electrical circuit is an unbroken path carrying electric current. Current originates from a defined source and travels through a piece of equipment and then back to the current source.

Hazards associated with electrical circuits
Four hazards are associated with electrical circuits: shock, fire, arc/blast, and burns.

[CRITICAL]

Shock
When the flow of electrical energy is interrupted and redirected through a human body, creating a new circuit, electrical shock occurs.

Fire
Electrical fire hazards occur when a circuit is overloaded. A typical example of an overloaded circuit is when too many appliances are plugged into one temporary power tap (TPT) and the TPT begins to generate heat.

Arc/blast
An arc/blast can occur when two points with different potential come in contact, or close proximity. A common example of an arc is when two exposed wires from one extension cord cross one another and a spark is produced. The spark or arc is really a low-level blast. A full-fledged "blast" event would occur when greater amounts of electrical energy were given off.
[PLUG-FIRE]

Burns
The most common shock-related injury is a burn. Electrical burns are one of the most serious injuries you can receive and should be given immediate attention. Additionally, Clothing may be ignited in an electrical accident and a thermal burn will result.

Burns suffered in electrical accidents are of three basic types:

TeslaCoil

electrical burns: Tissue damage may be to internal organs or the skin and is caused because the body cannot dissipate the heat due to RF absorption or to current flow. These burns are very slow to heal, skin burns are usually third degree (the tissue is actually charred).

arc/blast burns: Tissue damage is caused by exposure to the extremely high temperature gases produced by an electric arc. Temperatures generated by electric arcs can easily melt and vaporize nearby materials, and burn skin or ignite flammable materials at distance of several meters. Electric arcs can produce large amounts of ultraviolet light which can burn skin or damage the eye. Electric arcs also present a shock hazard because they are conductors and are at a voltage above ground.

thermal contact burns: Tissue damage is usually due to skin contact with the hot surfaces of overheated conductors.

Secondary Hazards

Voltage sources that do not have dangerous current capabilities are often treated in a causal manner because they do not pose a serious shock or burn hazard by themselves. However, these circuits are often used in conjunction with or adjacent to lethal circuits. A less severe shock might cause a worker to rebound into a lethal circuit. Such an involuntary action can cause cuts and bruises, bone fractures or even death from a fall.

Delayed effects: Damage to internal tissues may not be immediately apparent. Internal effects may include bleeding, tissue swelling and irritation, and heart fibrillation. Prompt medical attention is necessary to avoid death or long-term injury. Report all electrical shocks immediately to your manager and take the victim to medical, even if they appear to be fine.

Electrical Shock Dynamics

Shock is the passage of electrical energy through the human body. The primary factors affecting an electrical shock's severity are the path along which the current travels, the amount of current, and the duration of exposure to the current.

Path

Electricity will have greater or lesser effects depending on the path along which it flows through the body. For instance, when electricity enters the right hand and exits the left foot, the chest cavity (and thus the heart) becomes part of the path, providing the potential for cardiovascular damage. The same potential occurs in a hand-to-hand shock. In all instances of shock, the issue is the potential for vital-organ damage based on the points of entry and exit of the electrical current.

Amount of current or energy

Electrical current is measured in amperes (A). The human body begins to experience electrical shock and its effects at the milliamp level.

The amount of electrical current needed to run One 100-watt (W) light bulb, served by 110 volts (V) of electricity, is calculated at roughly 1 A (1,000 milliamps[mA]).
(Using Ohm's law for the calculation)

EFFECT OF CURRENT IN THE HUMAN BODY
While most people are aware of the danger from electric shock, few realize how little current and how low a voltage are required for a fatal shock. Current flows as low as 30 mA can be fatal (1mA=1/1000A). Let's look at at the effects of current flow through a "typical" 68 kilogram (150 pound) male:
	At about 10 mA, muscular paralysis of the arms occurs, so that he cannot release his grip.
	At about 30 mA, respiratory paralysis occurs. His breathing stops and the results are often fatal.
	At about 75-250 mA, for exporsure exceeding 5 seconds, ventricular fibrillation occures, causing discoordination of the heart muscles; the heart can no longer function. Higher currents cause fibrillation at less than 5 seconds. The results are often fatal.

Duration of exposure

The time (duration) of exposure to the electrical shock can determine the extent of the damage. As the duration of exposure increases, the resistance of the skin breaks down and more current flows through the body.

Current duration effects on humans (Graph and Text)

Electrical Hazard Identification

Environment

The environment in which the system operates is a major factor in hazard identification. You will need to determine if your area is:

wet or dry,
indoors or outdoors
open or cramped
well lit or dark

Non-conductive floor tile
(Click picture to enlarge.) [OUTLET-BOX]
Death Trap!
Unprotected cord and outlet box sitting precariously in wet place.

Equipment condition

The condition of the equipment or hardware is another factor in hazard identification.

You will need to consider such things as:

the age of the equipment
the integrity of the grounding system to which the equipment is connected
the electrical wiring of the equipment and the loads incurred on the system
the presence and effectiveness of internal safety mechanisms (such as overcurrent devices, interlocks, and limit switches)
the voltage at which the equipment operates

Damaged surge supressor.
Don't use.

Inspect your equipment before use
Damaged equipment cord. Don't use. (Click picture to enlarge.)	Damaged plug strip. Don't use. (Click picture to enlarge.)	Damaged equipment cord. Don't use. (Click picture to enlarge.)
If you find damaged cords or equipment, unplug if necessary, cut the cord, and take them out of service immediately,	Damaged equipment cord. Cut off. (Click picture to enlarge.)

Electrical safety work practices

The electrical safety work practices applied by personnel in the environment and around the equipment is the third element in hazard identification.

Become familiar with the SNL Electrical Safety Manual,
Read and follow standard operating procedures,
Become familiar with lockout/tagout procedures,
Understand the required qualifications of personnel working on the equipment,
Wear required Personal Protective Equipment (PPE)
Do not wear loose chains or metal of any kind; this includes watches, rings, or earrings.

RF sources

Electricity at radio and microwave frequencies (RF sources) can travel without conductors.

The body is not completely transparent to high frequency electricity which means that some of the energy can be absorbed which may cause damage to body tissues. Table A gives the major biological effects of high frequency radiation.

TABLE A
frequency (MHz)	tissues targeted	biological effect
less than 150	body is relatively transparent
150-1200	internal organs	internal heating
1000-3300	lens of eye	internal heating, cataracts
3300-10,000	skin and eye lens covering	surface heating
greater than 10,000	skin acts as reflector

Microwave generators like this one are sources of invisible RF energy.
(Click picture to enlarge)

The hazard presented by RF sources depends on the frequency and the strength of the field (usually measured in millivolts/meter) which determines the amount of energy in the field.

The greatest hazards presented from RF sources are when the worker is near an RF radiator (for example near a broadcast antenna or a microwave cavity).

Electrical Hazard Mitigation

Physical barriers


Clear plastic covers used to isolate user from voltage source. (Click picture to enlarge.)

Physical barriers are most often engineered on the equipment itself. Energized electrical parts may be isolated or insulated by such means as:

wire insulation,
metal conduits over conductors,
enclosures over circuit-breaker connection points,
ground fault circuit interrupters,
solidly grounded systems enabling fault and overcurrent protection to operate,
locked rooms stopping unauthorized personnel from accessing hazardous electrical equipment, and
flagging and barricades.
obey warning notices.

Warning Sign
Warning Sign
Warning barricade

Administrative and Management barriers are site-specific program or task driven guidance documents that enable personnel to work safely.


Safe operating procedures are located in the ES&H Document Binder on all laboratory doors. (Click picture to enlarge.)	Recognize that high voltage sources are often associated with certain types of lasers and laboratory equipment. (Click picture to enlarge.)
Refer to Owner's Manual when necessary!

Safe work practices:

Hazard Level 1 - Work with fully enclosed electrical systems.

Hazard Level 2 - Work in physical contact with fully de-energized circuits.
The hazard is created by the possibility that the circuit is not really de-energized or the possibility that it might get re-energized without warning.

If you are not 100% sure that a circuit is dead or if you do not have complete control over the current supplies to the circuit, treat it as if it were energized.

	Verify that all power is removed from a circuit before working on it. Make sure it cannot be turned back on by someone else or automatically.
	Use appropriate Personal Protective Equipment (PPE); see PPE Section.
	Watch out for multiple electrical sources. A circuit may be energized through more than one connection.
	Use solid ground connections, not clip leads, to ground electrical system closures. Watch out for custom or old equipment that may have improper ground connections.
	Remove all electrical loads before connecting or disconnecting a power cord to avoid the possibility of arcing.

Fully enclosed electrical system
(Click picture to enlarge)

Hazard Level 3 - Work in physical proximity to energized circuits.
(example: active cavity alignments)

Hazard Level 4 - Work in physical contact with energized circuits.
(example: cleaning Brewster Windows on an Ion Laser)

The practice of working in contact with current carrying conductors should be avoided whenever possible. When necessary, work must be specifically covered by detailed procedures in an SOP.

Your manager must qualify and authorize you to work with energized circuits

"Energized" work SOP's must, at a minimum, include:

	Identification of the conditions under which Energized work is allowed and the reasons why such work can only be conducted with energized circuits.
	A description of any tools or instruments required for the work including the means by which the proper operation of these tools or instruments is validated prior to the work (example: tester is rated for the voltage being used).
	A statement of the minimum distance separation required between the live circuits and the workers as consistent with applicable rules and standards.
	A statement of the qualified personnel authorized to do such work. Note that a two-man rule ( buddy system) is required for such work.

[GetHelp]

Where To Get Help

8300 Elec. Safety Reps.

Alt: Tom Prast x4-2803

Mark Jaska x4-2151

[Video]
Arc/Blast Video

TAKE QUIZ

QUESTIONS? COMMENTS?

Last Update: Jan 30, 1999

	(Enter your comments in window below.)
Your email address	Your Name