Electrical safety at work

Electricity is a familiar and necessary part of everyday life, but electricity can kill or severely injure people and cause damage to property. Electrical current exposes workers to a serious, widespread occupational hazard; practically all members of the workforce are exposed to electrical energy during the performance of their daily duties, and electrocutions occur to workers in various job categories. Many workers are unaware of the potential electrical hazards present in their work environment, which makes them more vulnerable to the danger of electrocution.

Electrical injuries consist of four main types: electrocution (fatal), electric shock, burns, and falls caused as a result of contact with electrical energy.

Electrical hazards can cause burns, shocks and electrocution (death).

Assume that all overhead wires are energized at lethal voltages. Never assume that a wire is safe to touch even if it is down or appears to be insulated.
Never touch a fallen overhead power line. Call the electric utility company to report fallen electrical lines.
Stay at least 10 feet (3 meters) away from overhead wires during cleanup and other activities. If working at heights or handling long objects, survey the area before starting work for the presence of overhead wires.
If an overhead wire falls across your vehicle while you are driving, stay inside the vehicle and continue to drive away from the line. If the engine stalls, do not leave your vehicle. Warn people not to touch the vehicle or the wire. Call or ask someone to call the local electric utility company and emergency services.
Never operate electrical equipment while you are standing in water.
Never repair electrical cords or equipment unless qualified and authorized.
Have a qualified electrician inspect electrical equipment that has gotten wet before energizing it.
If working in damp locations, inspect electric cords and equipment to ensure that they are in good condition and free of defects, and use a ground-fault circuit interrupter (GFCI).
Always use caution when working near electricity.

Why is it so important to work safely with or near electricity?

The electrical current in regular businesses and homes has enough power to cause death by electrocution. Even changing a light bulb without unplugging the lamp can be hazardous because coming in contact with the “hot” or live part of the socket could kill a person.

What do I need to know about electricity?

All electrical systems have the potential to cause harm. Electricity can be either “static” or “dynamic” Dynamic electricity is the uniform motion of electrons through a conductor (this is known as electric current). Conductors are materials that allow the movement of electricity through it. Most metals are conductors. This document is about dynamic electricity.

Note: Static electricity is accumulation of charge on surfaces as a result of contact and friction with another surface. This contact/friction causes an accumulation of electrons on one surface, and a deficiency of electrons on the other surface.

Electric current cannot exist without an unbroken path to and from the conductor. Electricity will form a “path” or “loop”. When you plug in a device (e.g., a power tool), the electricity takes the easiest path from the plug-in, to the tool, and back to the power source. This is also known as creating or completing an electrical circuit.

What kinds of injuries result from electrical currents?

People are injured when they become part of the electrical circuit. Humans are more conductive than the earth (the ground we stand on) which means if there is no other easy path, electricity will try to flow through our bodies.

There are four main types of injuries: electrocution (fatal), electric shock, burns, and falls. These injuries can happen in various ways:

Direct contact with the electrical energy. When electricity travels through our bodies, it can interfere with the normal electrical signals between the brain and our muscles (e.g., heart may stop beating properly, breathing may stop, or muscles may spasm).
When the electricity arcs (jumps, or “arcs”) through a gas (such as air) to a person who is grounded (that would provide an alternative route to the ground for the electricity).

o Arc flashes result in intense heat (causing burns), intense light (can cause blindness), or ignition of other materials.

o Arc blasts cause the same conditions as an arc flash, but are more intense and can also include a strong pressure wave. These pressure waves can damage machinery, throw a person, collapse a lung or rupture ear drums.

Thermal burns including flash burns from heat generated by an electric arc, and flame burns from materials that catch on fire from heating or ignition by electrical currents. High voltage contact burns can burn internal tissues while leaving only very small injuries on the outside of the skin.
Muscle contractions, or a startle reaction, can cause a person to fall from a ladder, scaffold or aerial bucket. The fall can cause serious injuries.

What are some general safety tips for working with or near electricity?

Inspect tools, power cords, and electrical fittings for damage or wear prior to each use. Repair or replace damaged equipment immediately.
Always tape cords to walls or floors when necessary. Nails and staples can damage cords causing fire and shock hazards.
Use cords or equipment that is rated for the level of amperage or wattage that you are using.
Always use the correct size fuse. Replacing a fuse with one of a larger size can cause excessive currents in the wiring and possibly start a fire.
Be aware that unusually warm or hot outlets may be a sign that unsafe wiring conditions exists. Unplug any cords to these outlets and do not use until a qualified electrician has checked the wiring.
Always use ladders made of wood or other non-conductive materials when working with or near electricity or power lines.
Place halogen lights away from combustible materials such as cloths or curtains. Halogen lamps can become very hot and may be a fire hazard.
Risk of electric shock is greater in areas that are wet or damp. Install Ground Fault Circuit Interrupters (GFCIs) as they will interrupt the electrical circuit before a current sufficient to cause death or serious injury occurs.
Make sure that exposed receptacle boxes are made of non-conductive materials.
Know where the breakers and boxes are located in case of an emergency.
Label all circuit breakers and fuse boxes clearly. Each switch should be positively identified as to which outlet or appliance it is for.
Do not use outlets or cords that have exposed wiring.
Do not use power tools with the guards removed.
Do not block access to circuit breakers or fuse boxes.
Do not touch a person or electrical apparatus in the event of an electrical accident. Always disconnect the current first.

What are some tips for working with power tools?

Switch tools OFF before connecting them to a power supply.
Disconnect power supply before making adjustments.
Ensure tools are properly grounded or double-insulated. The grounded tool must have an approved 3-wire cord with a 3-prong plug. This plug should be plugged in a properly grounded 3-pole outlet.
Test all tools for effective grounding with a continuity tester or a ground fault circuit interrupter (GFCI) before use.
Do not bypass the switch and operate the tools by connecting and disconnecting the power cord.
Do not use electrical tools in wet conditions or damp locations unless tool is connected to a GFCI.
Do not clean tools with flammable or toxic solvents.
Do not operate tools in an area containing explosive vapours or gases, unless they are intrinsically safe and only if you follow the manufacturer’s guidelines.

What are some tips for working with power cords?

Keep power cords clear of tools during use.
Suspend power cords over aisles or work areas to eliminate stumbling or tripping hazards.
Replace open front plugs with dead front plugs. Dead front plugs are sealed and present less danger of shock or short circuit.
Do not use light duty power cords.
Do not carry electrical tools by the power cord.
Do not tie power cords in tight knots. Knots can cause short circuits and shocks. Loop the cords or use a twist lock plug.

What is a Ground Fault Circuit Interrupter (GFCI)?

A Ground Fault Circuit Interrupter (GFCI) works by detecting any loss of electrical current in a circuit. When a loss is detected, the GFCI turns the electricity off before severe injuries or electrocution can occur. A painful shock may occur during the time that it takes for the GFCI to cut off the electricity so it is important to use the GFCI as an extra protective measure rather than a replacement for safe work practices.

GFCI wall outlets can be installed in place of standard outlets to protect against electrocution for just that outlet, or a series of outlets in the same branch. A GFCI Circuit Breaker can be installed on some circuit breaker electrical panels to protect an entire branch circuit. Plug-in GFCIs can be plugged into wall outlets where appliances will be used.

When and how do I test the Ground Fault Circuit Interupter (GFCI)?

Test the GFCI monthly. First plug a “night light” or lamp into the GFCI-protected wall outlet (the light should be turned on), then press the “TEST” button on the GFCI. If the GFCI is working properly, the light should go out. If not, have the GFCI repaired or replaced. Reset the GFCI to restore power.

If the “RESET” button pops out but the light does not go out, the GFCI has been improperly wired and does not offer shock protection at that wall outlet. Contact a qualified electrician to correct any wiring errors.

What is a sample checklist for basic electrical safety?

Inspect Cords and Plugs

Check power cords and plugs daily. Discard if worn or damaged. Have any cord that feels more than comfortably warm checked by an electrician.

Eliminate Octopus Connections

Do not plug several power cords into one outlet.
Pull the plug, not the cord.
Do not disconnect power supply by pulling or jerking the cord from the outlet. Pulling the cord causes wear and may cause a shock.

Never Break OFF the Third Prong on a Plug

Replace broken 3-prong plugs and make sure the third prong is properly grounded.

Never Use Extension Cords as Permanent Wiring

Use extension cords only to temporarily supply power to an area that does not have a power outlet.
Keep power cords away from heat, water and oil. They can damage the insulation and cause a shock.
Do not allow vehicles to pass over unprotected power cords. Cords should be put in conduit or protected by placing planks alongside them.

What is static electricity and how is it generated?

Static electricity is the electric charge generated when there is friction between two things made of different materials or substances, like clothes tumbling in your dryer. Static electricity is what causes the sparks when you comb your hair or touch a metal object, like a doorknob, after walking across a carpet on a cold, dry day (especially during Canadian winters). It can also be generated by repeated contact and separation between unlike materials, like a flat belt on a rotating pulley.

Electric charges can build up on an object or liquid when certain liquids (e.g., petroleum solvents, fuels) move in contact with other materials. This can occur when liquids are poured, pumped, filtered, agitated, stirred or flow through pipes. This buildup of electrical charge is called static electricity. Even when liquids are transported or handled in non-conductive containers, something rubbing the outside surface of the container may cause a static charge to build up in the liquid. The amount of charge that develops depends, in part, on how much liquid is involved and how fast is it flowing or is being agitated or stirred.

Is static electricity hazardous?

Depending on circumstances it can be a nuisance or a hazard. Static cling in your clothes can be a nuisance but a spark that has enough energy to cause a fire or explosion is a definite hazard. To decide if static electricity is likely to be a hazard, you must consider several factors:

Can a static electric charge be generated under the operating conditions?
Can the charge accumulate?
If it discharges, will it cause a spark?

Is there an ignitable mixture (e.g., solvent vapour or dust in the air) in the area where a static electricity discharge can occur?

Will the discharge generate an incendive spark, i.e., a spark that has enough energy to ignite the mixture in air?

If the answer to the above five questions is yes where a solvent or fuel is used, then static electricity can be a fire / explosion hazard. It means that the spark can ignite a vapour/air mixture that is in its flammable range, the concentration range between the upper and the lower flammable limits.

What kind of solvents are likely to be a static electricity hazard?

Flammable and combustible liquids can present a static electricity hazard depending on their ability to generate static electricity, how well they conduct electricity (conductivity), and their flash point.

Solvents and fuels produced from petroleum (e.g., benzene, toluene, mineral spirits, gasoline, jet fuel) can build up a charge when they are poured or flow through hoses. They tend to hold a charge because they cannot conduct electricity well enough to discharge when in contact with a conducting material, like a metal pipe or container, that is grounded. When enough of a charge is built up, a spark may result. If the vapour concentration of the liquid in air is in the “flammable range” and the spark has enough energy, a fire or explosion can result.

According to the NFPA (Code 77), solvents that are soluble in water (or can dissolve some water themselves) do not build up static electricity. Examples of such liquids include alcohols and ketones like acetone. However, when liquids are transferred into non-conductive containers (e.g., plastic, glass), even conductive solvents may build up a charge because the plastic or glass containers decrease the rate at which the charge in the solvent dissipates.

The flash point and vapour pressure of the liquid and the temperature are other factors to consider. The vapour levels will be higher in the air around the container if you are working outside on a hot summer day than in the winter when the temperature is below 0°C (32°F) or colder.

At higher elevations in the mountains, the air pressure is significantly lower and solvents boil at lower temperatures. Under these conditions, the flash point and the temperature for the optimal vapour/air ratio are lower and some “combustible” liquids can become “flammable”.

A liquid like hexane has a low flash point and it is flammable when its temperature is in the range -33°C to -3°C (-28°F to +26°F) at sea level. At normal room temperatures, the vapour/air ratio at the surface of the solvent will be well above its upper flammability limit and would be “too rich” to burn. However, at some distance away from the solvent surface, there is a concentration of hexane vapour in the air that is in the flammable range.

A fuel like kerosene is a combustible liquid with a flash point above 38°C (100°F). Under hot weather conditions or if high flash point liquids are heated to temperatures around or above their flash points, a flammable vapour/air mixture will form.

Generally, the conditions for igniting a liquid are optimal when the liquid is used at a temperature that produces a vapour in air concentration (at the surface of the liquid) that is halfway between the upper and lower flammability limits. Recognizing that these conditions represent an “optimal” fire hazard, one has to take appropriate precautions.