UNL Safety Colloquium Laboratory Electrical Safety Fall 2006

UNL Safety Colloquium Laboratory Electrical Safety Fall, 2006 Robert W. Hayden, M. A. , PMP Lincoln Electric System (LES)

Why is this relevant to me? • You work in a laboratory (Electrical accidents are…) Accident stats • Injury stats • Fatality stats • difficult to find, probably rare (but, why be famous? )

Major characteristic of electrical accidents • You work in a laboratory • • • Accident stats Injury stats Fatality stats difficult to find, probably rare (but, why be famous? ) RATIO of fatalities to injuries is HIGH 1 for ALL electrical type injuries.

Electrical hazards in a lab n n n Electrocution from INSTALLED equipment Electrocution from TEMPORARY wiring Electrocution from APPARATUS or POWER SUPPLIES But, first some basics. . .

Electricity comes in only two flavors, AC and DC AC is Alternating Current. It flows both directions, in varying potential, at a given frequency. In the U. S. , 120 v at 60 Hz is the standard. In other countries both the voltage and frequency may be different. (230 v @50 Hz) n DC is Direct Current. It flows in only one direction, at a set potential. n

What Alternating Current looks like on an oscilloscope Frequency (one cycle or hertz)

What Direct Current (steady state) looks like on an oscilloscope + 0

What a Direct Current PULSE looks like on an oscilloscope 0

But let’s talk safety. n n Both AC and DC need a ‘path’ in order to complete a ‘circuit’. Only when a circuit is completed will current flow. PEOPLE get hurt when THEY get in the path (circuit). – HOWEVER- electricity travels at (nearly) the speed of light, therefore ALL your precautions have to focus on preventing a path because after a path (circuit) is established it may be too late.

The risks? There are four types of electrical-related injuries: – Electrocution (death due to electrical ( shock) – Electrical shock (may cause tissue damage, initially invisible). – Burns (visible, obvious) – Falls (secondary injury)

Electrical Burns • • A common, nonfatal shockrelated injury May occur when you touch electrical wiring or equipment that is improperly grounded, used, or maintained Typically occurs on the hands Electrical burns are very serious injuries that need immediate attention

Falls or Contact injuries • • • Electric shock can also cause indirect or secondary injuries Workers in elevated locations who experience a shock can fall, resulting in serious injury or death OR, workers can be thrown into others or into solid or sharp objects

So, how much electricity does it really take to hurt me? It varies. Sex, weight, skin moisture, hydration, and path through the body all contribute. n Some general threshold values: n – Sensation. ~1 m. A AC / 5 m. A DC – ‘Let-go’. ~15 m. A AC / 75 m. A DC – V-fib. ~75 -100 m. A AC / 300 m. A DC

COMPARE n The values in the previous slide are in units called milliamps (m. A). One milliamp is 1/1000 of an amp. n What is the TYPICAL current rating (in amps) of a 120 v circuit breaker?

COMPARE the TYPICAL current rating (in amps) of a 120 v circuit breaker? Let’s say 15 amp = 15, 000 m. A / 150 m. A = 100 times enough current to kill you (without tripping the breaker, of course)

So, if the circuit breaker doesn’t protect me, what’s it for?

Electrical Protective Devices Protective devices shut off the flow of electricity in the event of either an over current or a ground-fault condition in the circuit. They include fuses, circuit breakers, and ground-fault circuit interrupters (GFCI’s). BUT, they protect different things.

Over Current Devices § Fuses and circuit breakers are over current devices. § When there is too much current: § § § Fuses melt Circuit breakers trip open Fuses and circuit breakers protect WIRING and EQUIPMENT. They are designed to prevent fires. Their primary purpose is NOT to protect people.

Ground Fault Devices § In contrast, GFCIs protect against ‘imbalanced’ loads (wrong path to ground) also known as a ‘fault’, or a ‘ground fault’. § Only GFCIs are designed to protect PEOPLE.

Barbi DEMO a. k. a. Why you need a GFCI

Electrocution from INSTALLED equipment Non-UL (Underwriter’s Laboratory) equipment. n Improperly installed (wired) equipment n (for example switching the neutral wire). Ungrounded equipment (two prong) n Unprotected (non Ground Fault) equipment or outlets n – Especially around liquids/water/plumbing.

Electrocution from TEMPORARY wiring n Contributors Include: – Non-GFCI cords or non-GFCI outlets – Damaged cords – Modified cords – Improper use or application of cords

“The path to ground from circuits, equipment, and enclosures must be permanent and continuous. ”

Permissible Uses of Flexible Cords Pendant, or Fixture Wiring Portable lamps, tools or appliances Stationary equipmentto facilitate interchange

Prohibited Uses of Flexible Cords Substitute for fixed wiring Run through walls, ceilings, floors, doors, or windows Concealed behind or attached to building surfaces

Electrocution from POWER SUPPLIES or APPARATUS o o In these cases (most often) the apparatus or power supply is doing just what it’s supposed to. It is putting out voltage – at a given current and/or frequency. BUT – People (you) have managed to get yourself into the circuit (path).

The Results? They range from. . . Ooops / Ouch (small shocks) Ø Secondary injuries or damage Ø Sparks Ø Fires Ø Falls or cuts Ø Breakage or equipment damage Ø Ø Big shocks. Burns or even death.

n Electrocution – Minor shock – Major shock n@ approximately let-go threshold = invisible (often latent) tissue damage begins to occur n Visible burn(s) – Fatality n Most often due to V-fibrillation n Can also be from the burn (internal or external)

Known POWER SUPPLIES or APPARATUS values • Electrophoresis (power supplies) • • Electroporation (equipment itself) • • Various manufacturers’ spec models from 0 to 6000 v, 0 to 2000 m. A. Pulses of 1, 000’s of volts Other (physics) power supplies • • Lasers Particle study equipment (Especially anything with large capacitors) QUITE capable of injury if not properly handled.

The Barriers n Installed equipment – Purchase UL listed equipment, if possible – Have equipment installed by a licensed electrician. (if it’s not ‘plug-in’ type) – Have any non-UL equipment checked for grounding/wiring by a licensed electrician – STRONGLY consider having all equipment circuits operating around liquids or in proximity to plumbing (sinks) plugged into GFCI outlets or GFCI pigtails – LABEL all outlets/circuit breakers

The Barriers n Temporary wiring – Use only cords with proper ratings (amperage as well as environment [wet =‘W’]) n Jacket codes in Nat’l Electric Code (NEC) – Again, all equipment circuits operating around liquids or in proximity to plumbing (sinks) should be plugged into GFCI outlets or have GFCI pigtails – Don’t ‘daisy-chain’ cords. n Especially multiple outlet cords

The Barriers n Technique / procedure – Follow procedural guidance (SOPs) for setting up, terminating, and adjusting equipment / apparatus (for example …) n Power OFF before touching wires n Double check connections before powering ON – Don’t defeat electrical interlocks – Be especially careful whenever working with both electricity and any liquid or plumbing

Summary Know that electricity can hurt or even kill you © Don’t get too comfortable around electricity, especially when also around liquids © Inspect your equipment/apparatus (frequently) © Follow procedures for setup, adjustment, etc. © If you have Safety questions, ask the Occupational Health and Safety department staff ©

Questions ?