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 word areas. These devices can pose a significant hazard to workers, particularly when mishandled or not maintained. Many 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.
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 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 flow
In addition to the electrical shock hazards, sparks from electrical equipment can serve as an ignition source for flammable or explosive vapors.
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 work area. If magnetic or mechanical stirrers fail to operate, safe mixing of reagents may be compromised.
Preventing Electrical Hazards
There are various ways of protecting people from the hazards caused by electricity, including insulation, guarding, grounding, and electrical protective devices. Workers can significantly reduce electrical hazards by following some basic precautions:
All electrical cords should have sufficient insulation to prevent direct contact with wires. 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, 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. The third prong provides a path to ground that helps prevent the buildup of voltages 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 equipment.
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 areas 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.
Safe Work Practices
The following practices may reduce risk of injury or fire when working with electrical equipment:
High Voltage or Current
Repairs of high voltage or high current equipment should be performed by trained electricians. Individuals who are experienced in such tasks and would like to perform such work on their own equipment must first receive specialized electrical safety related work practices training by EHS staff. Contact the University Safety Engineer, Greg Cantrell, at 258-5849 for more information.
The following additional precautions should be taken:
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