SECTION 5: Electrical Safety
Electrically powered equipment, such as hot plates, stirrers, vacuum pumps, electrophoresis apparatus, lasers, heating mantles, ultrasonicators, power supplies, and microwave ovens are essential elements of many laboratories. These devices can pose a significant hazard to laboratory workers, particularly when mishandled or not maintained. Many laboratory electrical devices have high voltage or high power requirements, carrying even more risk. Large capacitors found in many laser flash lamps and other systems are capable of storing lethal amounts of electrical energy and pose a serious danger even if the power source has been disconnected
Electrical Hazards (top)
The major hazards associated with electricity are electrical shock and
fire. Electrical shock occurs when the body becomes part of the electric
circuit, either when an individual comes in contact with both wires
of an electrical circuit, one wire of an energized circuit and the ground,
or a metallic part that has become energized by contact with an electrical
The severity and effects of an electrical shock depend on a number
of factors, such as the pathway through the body, the amount of current,
the length of time of the exposure, and whether the skin is wet or dry.
Water is a great
conductor of electricity, allowing current to flow more easily in wet
conditions and through wet skin. The effect of the shock may range from
a slight tingle to severe burns to cardiac arrest. The chart below shows
the general relationship between the degree of injury and amount of
current for a 60-cycle hand-to-foot path of one second's duration of
shock. While reading this chart, keep in mind that most electrical circuits
can provide, under normal conditions, up to 20,000 milliamperes of current
Slight shock felt; not painful but disturbing
||Painful shock; "let-go" range
||Extreme pain, respiratory arrest, severe muscular contraction
||Cardiac arrest, severe burns, and probable death
In addition to the electrical shock hazards, sparks from electrical
equipment can serve as an ignition source for flammable or explosive
Even loss of electrical power can result in extremely hazardous situations.
Flammable or toxic vapors may be released as a chemical warms when a
refrigerator or freezer fails. Fume hoods may cease to operate, allowing
vapors to be released into the laboratory. If magnetic or mechanical
stirrers fail to operate, safe mixing of reagents may be compromised.
Preventing Electrical Hazards (top)
There are various ways of protecting people from the hazards caused
by electricity, including insulation, guarding, grounding, and electrical
protective devices. Laboratory workers can significantly reduce electrical
hazards by following some basic precautions:
- Inspect wiring of equipment before each use. Replace damaged or
frayed electrical cords immediately.
- Use safe work practices every time electrical equipment is used.
- Know the location and how to operate shut-off switches and/or circuit
breaker panels. Use these devices to shut off equipment in the event
of a fire or electrocution.
- Limit the use of extension cords. Use only for temporary operations.
In all other cases, request installation of a new electrical outlet.
- Use only multi-plug adapters equipped with circuit breakers or
- Place exposed electrical conductors (such as those sometimes used
with electrophoresis devices) behind Plexiglas shields.
- Minimize the potential for water or chemical spills on or near
All electrical cords should have sufficient insulation
to prevent direct contact with wires. In a laboratory, it is particularly
important to check all cords before each use, since corrosive chemicals
or solvent vapors may erode the insulation.
Damaged cords should be repaired or taken out of service immediately.
Live parts of electric equipment operating at 50 volts or more (i.e.,
electrophoresis devices) must be guarded against accidental contact.
Plexiglas shields may be used to protect against exposed live parts.
Only equipment with three-prong plugs should be used in the laboratory.
The third prong provides a path to ground that helps prevent the buildup
that may result in an electrical shock or spark. This does not guarantee
that no one will receive a shock, be injured, or be killed. It will,
however, substantially reduce the possibility of such accidents, especially
when used in combination with other safety measures.
Circuit Protection Devices
Circuit protection devices are designed to automatically limit or shut
off the flow of electricity in the event of a ground-fault, overload,
or short circuit in the
wiring system. Fuses, circuit breakers, and ground-fault circuit interrupters
are three well-known examples of such devices.
Fuses and circuit breakers prevent over-heating of wires and components
that might otherwise create hazards for operators. They disconnect the
circuit when it becomes overloaded. This overload protection is very
useful for equipment that is left on for extended periods of time, such
as stirrers, vacuum pumps, drying ovens, Variacs and other electrical
The ground-fault circuit interrupter, or GFCI, is designed to shutoff
electric power if a ground fault is detected. The GFCI is particularly
useful near sinks and wet locations. Since GFCIs can cause equipment
to shutdown unexpectedly, they may not be appropriate for certain apparatus.
Portable GFCI adapters (available in most safety supply catalogs) may
be used with a non-GFCI outlet.
In laboratories where volatile flammable materials are used, motor-driven
electrical equipment should be equipped with non-sparking induction
motors or air motors. Avoid series-wound motors, such as those generally
found in vacuum pumps, rotary evaporators and stirrers. Series-wound
motors are also usually found in household appliances such as blenders,
mixers, vacuum cleaners and power drills. These appliances should not
be used unless flammable vapors are adequately controlled, unless they
are equipped with redundant safeguards for work in such environments.
Safe Work Practices (top)
The following practices may reduce risk of injury or fire when working
with electrical equipment:
- Avoid contact with energized electrical circuits.
- Disconnect the power source before servicing or repairing electrical
- When it is necessary to handle equipment that is plugged in, be
sure hands are dry and, when possible, wear nonconductive gloves and
shoes with insulated soles.
- If it is not unsafe to do so, work with only one hand, keeping
the other hand at your side or in your pocket, away from all conductive
material. This precaution reduces the likelihood of accidents that
result in current passing through the chest cavity.
- Minimize the use of electrical equipment in cold rooms or other
areas where condensation is likely. If equipment must be used in such
areas, mount the equipment on a wall or vertical panel.
- If water or a chemical is spilled onto equipment, shut off power
at the main switch or circuit breaker and unplug the equipment.
- If an individual comes in contact with a live electrical conductor,
do not touch the equipment, cord or person. Disconnect the power source
from the circuit breaker or pull out the plug using a leather belt.
High Voltage or Current
Repairs of high voltage or high current equipment should be performed
by trained electricians. Laboratory workers who are experienced in such
tasks and would like to perform such work on their own laboratory equipment
must first receive specialized electrical safety related work practices
training by EHS staff. Contact the University
Safety Engineer at 258-5849 for more information.
The following additional precautions should be taken:
- Always assume a high voltage potential exists within a device while
servicing it, even if it is de-energized and disconnected from its
- Avoid becoming grounded by staying at least 6 inches away from walls,
water, and all metal materials, including pipes.
- Use voltmeters and test equipment with ratings and leads sufficient
to measure the highest potential voltage expected to be found inside
the equipment being serviced.
- After servicing, check equipment with a multimeter or appropriate
device to ensure it is grounded before reconnecting to the power source.
- Consider the need for shielding, particularly where exposure to an electrical arc is possible. Contact EHS for assistance.