Electrical safety in the laboratory. CHM 605, 2009. This lecture is mostly for “typical” labs, users of equipment.
Electrical safety in the laboratory CHM 605, 2009
This lecture is mostly for “typical” labs, users of equipment The typical laboratory contains a wide variety of electrically-powered equipment including stirrers, shakers, pumps, hot plates, heaters, power supplies, ovens, and electrophoresis equipment.
Atypical laboratories and users need to learn more, see Dr. Santini and/or his lecture notes.
Hazards, risks of electric shock (which btw can cause death) due to completing a circuit. fires due to poorly installed or maintained systems. due to sparks serving as an ignition source for flammable or combustible materials.
How to protect yourself? Understand some basic principles, guidelines. Do NOT “just use your "common sense.” ? Common sense
Basic principles A little “advanced” background Being prepared Receptacle safety Power supply safety Power cord safety Circuit protection and human protection Flammable materials General electrical safety
More than 3 ma painful shock More than 10 ma muscle contraction “no-let-go” danger More than 30 ma lung paralysis- usually temporary More than 50 ma possible ventricular fib. (heart dysfunction, usually fatal) 100 ma to 4 amps certain ventricular fibrillation, fatal Over 4 amps heart paralysis; severe burns. Usually caused by >600 volts Some background (1/5) (These are externally measured currents!Thirty micro-amps in the heart is lethal.)
Some background (2/5) AC, DC or AC+DC voltages above +/-30 volts peak value are potentially a risk Because current can flow through an internal path in the human body that includes the heart and or the chest muscles that control breathing. Usually, the overall circuit includes unpredictable parallel paths on the skin that reduce the risk.
Some background (3/5) The most likely source of exposure in the lab environment is to line power at plugs, receptacles and inside equipment. Typical line voltage values are 120, 208 and 240 VAC. DC power sources range from 5 VDC to over 1000 VDC. (Whole ‘nother lecture.)
Some background (4/5) Most common electrical shock accident factors: User is careless or circumvents safety devices and makes physical contact with high voltage. User creates unsafe condition that is not immediately obvious, such as a shock hazard or thermal run-away condition.
Some background (5/5) Single Phase AC Waveform: 60 Hz rate (50 Hz) Nominally, a sinusoid with an effective value of 120 VAC. Electrical components must withstand the peak voltage!DC to AC converters do not produce sinusoidal output unless specified clearly to have this capability.
Being prepared (1/3) Electrical panels should be locked and not used as emergency shut-offs. If you need an emergency shut-off, request an installation. Leave at least a 3-foot clearance around electrical panels for access by maintenance personnel.
Being prepared (2/3) Plan ahead for what steps will be taken in the event of a power loss. Think about potential vapor/gas release from vapor-generating processes or chemical fume hoods if power is lost.
Being prepared (3/3) Conduct a periodic inspection of laboratory electrical equipment to be sure it is in good condition. Remove equipment from service if in poor condition and replace or have it repaired by a qualified repair person
Outlet Receptacles Electrical outlets should have a grounding connection and accept three-prong plugs. Multiple plug outlet adapters are not allowed unless 15 amp fused and UL approved. Power strips must be 15 amp fused and UL approved. GFCIs in all wet locations.
Power Cords Power cords must have grounding plugs or be double insulated. Inspect power cords -- no damage, no fraying. Place cords carefully – avoid water, chemicals Avoid dangling cords and cords at floor. Take care to not smash or walk on cords. Keep cords away from hot surfaces. Never pull on or hang something by the power cord.
Power Cords photo Avoid dangling cords and cords at floor.
Power supplies Portable power supplies are common, are extremely high energy sources, must be used carefully. Never attach an exposed connector (such as an alligator clip) to a power supply. Extension cords are not allowed. Electrical power strips & surge suppressors (max 15 a fused, UL listed) are.
Circuit protection (1/2) Not more than two high current devices (e.g. oven, centrifuge, microwave) are to be plugged into the same outlet. Fuses and circuit breakers protect equipment, prevent fires. Not people.
Circuit protection (2/2) Ground-fault circuit interrupters (GFCI) protect people -- disconnect current almost instantly to protect when large current detected. GFCI outlets or portable GFCIs are used near sinks and potentially wet locations. Keep electrical equipment (and yourself while using it) away from water unless it’s rated for wet use. PEOPLE
Flammable materials Keep flammable materials away from electrical equipment. Receptacles providing power for equipment used inside a fume hood should be located outside the hood. Including power strips! Refrigeration: flammable materials may be stored in “lab safe” refrigerator or freezer. These have the obvious sources of ignition removed. Oven drying of organic materials has lead to explosions caused by electrical ignition. (&electricity)
Sparking appliances Most equipment IN YOUR HOUSE AND IN YOUR LAB, is not non-sparking.This has SERIOUS meaning as regards flammable liquids near by.