Electrical equipment now comprises a major part of the modern laboratory, thus posing a new set of possible laboratory hazards. Periodic laboratory inspections should pay particular attention to electrical safety. Incorporate electrical safety into the initial design and setup of laboratory equipment and apparatus. You must install and maintain all new electrical equipment, whether permanent or temporary, in accordance with the provisions of the latest edition of the National Electric Code (NEC) NFPA 70. Every replacement, modification, repair, or rehabilitation of any part of any electrical installation must comply with NEC standards.
Only Facilities Services may authorize modifications or changes to circuits or building equipment. All sources of electrical potential for either service or experiments must have adequate grounding and circuit breaking. University policy allows flexible extension cords only as temporary extension cords for portable equipment. Permanent wiring and receptacles are required for routinely used equipment or apparatus. Maintain all cords and plugs in a safe condition. You may use multi-outlet power strips for computer workstations, but not in any other part of the laboratory requiring multiple outlets. In this case, Facilities Services must install additional hard-wired outlets. A list of possible wiring hazard follows:
- spliced cords
- worn-out cords
- inadequate strain relief for plugs (causing cord to pull away from plug housing)
- tripping hazards from poorly positioned cords
- cords with missing ground pins
- cords draped near hot plates or open flames
- cords used near sinks or other wet locations unless protected with ground fault circuit interrupter (GFCI).
Grounding and Bonding
You must ground all exposed non-current-carry metal covers and other parts that are liable to energize. This includes the chassis of refrigerators, freezers, centrifuges, etc. When you transfer flammable liquids in metal containers, avoid static generated sparks by bonding between containers with the use of ground straps.
Power sources must be isolated to prevent accidental contact, which could result in serious electrical shock. Take the following precautions to isolate power sources.
- Ensure a labeled switch is in a readily accessible location for shutting off the power to laboratory equipment or apparatus in case of emergency. Make sure that all switches are accessible and not blocked by other equipment or lab clutter.
- All electrical equipment or apparatus requiring frequent attention must be electrically isolated with a fused disconnect switch.
- Enclose all power supplies for experiments, so that accidental bodily contact with power circuits is impossible. Access doors must have interlocks. Even for temporary arrangements, enclosures are required.
- Use lockout and tagout on appropriate disconnect switches to de-energize electrical power to equipment being worked on. A lockout/tagout system makes it impossible to energize a piece of equipment while the lock/tag is in place. Use a voltage tester to ensure the correct circuit is “dead.”
You should never work alone around energized electrical equipment. Know the procedure for removing a person from contact with a live electrical conductor, and the emergency first-aid procedures for persons who receive a serious electric shock.
Ground Fault Circuit Interrupters (GFCI): Additional Information
GFCI detect ground faults, also known as leakage currents, and in response open the circuit to halt the flow of electricity. GFCI can protect you if part of your body becomes a path for electrical current to ground. The leakage current threshold that “trips” a GFCI is typically five milliamps (5 mA). This is much lower than the threshold to trip a typical non-GFCI circuit breaker (usually at least 15 amps). GFCI can protect both equipment and personnel, whereas circuit breakers can only protect equipment. [Figure 3.7]
GFCI outlets usually have two small buttons labeled “TEST” and “RESET” in the center (Figure 3.7a). Outlets located near sinks or other wet locations are to be GFCI outlets. Some circuits have GFCI protection at the circuit breaker, rather than the outlet; thus, the outlet might look like a non-GFCI version but the circuit is GFCI protected. Functional GFCI systems ensure that the worst result if one becomes a path to ground is a brief 5 mA shock, which is painful but not fatal.
Keep in mind that GFCI circuits trip more frequently than non-GFCI. De-energization of experimental apparatuses could damage equipment, destroy research, or even cause accidents (e.g. spills or releases). Consider the potential consequences of de-energization before using GFCI circuits, especially for operations you leave unattended. Fail-safe designs might be necessary.
Contact EHS if you have questions about areas that might require GFCI protection. Contact Facilities Services to have GFCI outlets installed, or to report GFCI outlets that trip frequently. Alternately, you can plug GFCI adapters (Figure 3.7c) or GFCI cords (Figure 3.7d) into non-GFCI outlets in wet locations. Note that flexible extension cords (including GFCI cords) are for short-term use with portable equipment, and are not a substitute for permanent wiring.
Poor contacts at electrical connections and overloaded circuits can cause fires. Poor contacts between plugs and receptacles can cause arcing, which could lead to serious fire hazards. Overloaded circuits can cause fire by overheating. Extension cords or cube taps can overload circuits. Multi-outlet boxes with built-in switches, pilot lights, circuit breaker, and reset provide better protection than cube taps.
Disconnect electrical soldering irons, hot plates, and other electrical heating equipment when not in use. Use fire- resistant metal sheets under heating equipment to protect work surfaces. Electric heating equipment should be equipped with a temperature-sensing device that turns off the electric power if temperature exceeds the preset limit.
Unattended overnight operations (see Section II) of electric heating devices, stills, etc. should incorporate fail-safe devices that sense temperature, flow, liquid level or electrical overload. You should only use hot plates for heating liquids with flash points above 100 oC. Steam baths are required for heating liquids with low flash points, e.g., ethyl ether.
You must plug all electrical equipment used in a laboratory hood into a receptacle outside the hood. Rheostats used to control equipment in a laboratory hood must be located outside the hood, as it is a spark-producing device that is not constructed to protect against liquid splashes or spills.
Specially designed electrical equipment is necessary in areas where hazardous mixtures of explosive gases, vapor, or dusts are present (Article 500, National Electrical Code). Explosion-proof equipment, intrinsically safe circuits, purged enclosures, and positive-pressure ventilation are appropriate for operations in hazardous location. Some examples are:
- Flammable liquid storage rooms
- Flammable compressed gas storage rooms
- Motors and stirrers for solvents and oil baths
- Centrifuges using flammable liquids
- Refrigerators for storing flammable liquids
- Walk-in environmental chambers (i.e., cold or warm rooms)