SECTION 7: Safe Work Practices and Procedures
Electrically powered equipment, such as hot plates, stirrers, vacuum
pumps, electrophoresis apparatus, lasers, heating mantles, ultrasonicators,
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.
Accounts of incidents on campus that resulted in electrical shock, including
a near fatal incident, are described in Anecdotes.
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 conductor.
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
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 flow
||Slight shock felt; not painful but disturbing
||Painful shock; "let-go" range
||Extreme pain, respiratory arrest, severe
||Cardiac arrest, severe burns and probable
In addition to the electrical shock hazards, sparks from electrical equipment
can serve as an ignition source for flammable or explosive vapors or combustible
materials. See Anecdotes.
Loss of electrical power can create 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.
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
of a fire or electrocution.
- Limit the use of extension cords. Use only for temporary operations
and then only for short periods of time. In all other cases, request
installation of a new electrical outlet.
- Multi-plug adapters must have circuit breakers or fuses.
- Place exposed electrical conductors (such as those sometimes used
with electrophoresis devices) behind 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 solvents may erode
Damaged cords should be repaired or taken out of service immediately,
especially in wet environments such as cold rooms and near water baths.
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 for internal electrical short circuits, thereby protecting
the user from a potential electrical shock.
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. Ground-fault circuit interrupters, circuit breakers and fuses are
three well-known examples of such devices.
Fuses and circuit breakers prevent over-heating of wires and components
that might otherwise create fire hazards. 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
The ground-fault circuit interrupter, or GFCI, is designed to shutoff
electric power if a ground fault is detected, protecting the user from
a potential electrical shock. 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
In laboratories where volatile flammable materials
are used, motor-driven electrical equipment should be equipped with
non-sparking induction motors or air motors. These motors must meet
Safety Code (US DOC, 1993) Class 1, Division 2, Group C-D explosion
resistance specifications. Many stirrers, Variacs, outlet strips,
ovens, heat tape,
hot plates and heat guns do not conform
to these code requirements.
Avoid series-wound motors, such as those generally found in some 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.
Although some newer equipment have spark-free induction motors, the on-off
switches and speed controls may be able to produce a spark when they are
adjusted because they have exposed contacts. One solution is to remove
any switches located on the device and insert a switch on the cord near
the plug end.
The following practices may reduce risk of injury or fire when working with
- Avoid contact with energized electrical circuits.
- Use guarding around exposed circuits and sources of live electricity.
- 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
with insulated soles.
- If it is safe 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
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
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
from the circuit breaker or pull out the plug using a leather
Repairs of high voltage or high current equipment should be performed only
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 258-5294 for more information.
Any modifications to existing electrical service in a laboratory or building
must be completed or approved by either the building facility manager, an
engineer from the Facilities department or the building's Special Facilities
staff. All modifications must meet both safety standards and Facilities
Engineering design requirements.
Any unapproved laboratory facilities modifications discovered during
laboratory surveys or other activities are reviewed by EHS and facility
staff to determine whether they meet design specifications.
7H: Pressure and Vacuum Systems