Electrical Safety III: Electrical Fires

Tue, 2011-12-27

Whether it's faulty equipment or improper installation, electrical fires are one of the main causes of fires in the workplace every year.

In our previous articles in this series we discussed the importance of proper lockout-tagout procedures, and went into depth about arc flashes, their causes, and 
how to prevent them
.

The best line of defense to prevent electrical fires
 in the workplace is a three-step process:

  1. Knowing what can cause an electrical fire.
  2. Identifying warning signs that could lead to an electrical fire.
  3. What measures you can take to prevent a fire altogether.

This article takes a look at each of these steps in detail!

NOTE: The information presented in this article is gathered from multiple sources cited below and is intended for general discussion only.  Information contained in this article should not be used for compliance purposes.

Use these links to jump to the information you are interested in:
 

The Fire Triangle
Hazards That Start Electrical Fires
Detecting Potential Electrical Hazards
Preventing Electrical Fires in the Workplace

 


The Fire Triangle

Before we step into specifics on electrical fires, let's take a look at the components required for a fire to start.  A fire naturally occurs when the three elements below are combined in the right mixture.  Conversely, if you remove any of these components, the fire will be extinguished.

Heat

Without sufficient heat, a fire cannot begin, and it cannot continue. Heat can be removed by the application of a substance which reduces the amount of heat available to the fire reaction.

Turning off the electricity in an electrical fire removes the ignition source.
Fuel
 
Without fuel, a fire will stop. Fuel can be removed naturally, as where the fire has consumed all the burnable fuel, or manually, by mechanically or chemically removing the fuel from the fire. 
Oxygen
 
Without sufficient oxygen, a fire cannot begin, and it cannot continue. With a decreased oxygen concentration, the combustion process slows. In most cases, there is plenty of air left when the fire goes out so this is commonly not a major factor.

When you combine these three elements in the right proportions, you have a potential to start a fire like this one:

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Hazards that Start Electrical Fires

The first step to prevention is to identify what types of electrical hazards cause electrical fires. 

To begin, we wanted to show you examples of some dangerous wiring installations.  Installations like the ones you see in this video can easily cause an electrical fire.  If you see anything like this around your workplace, contact a qualified electrician at once!
 

 

The images above were extreme cases, but they highlight three main problem areas to consider when identifying where an electrical fire could start.

Inadequate Wiring

An electrical hazard exists when the wire is too small a gauge for the current it will carry. Normally, the circuit breaker in a circuit is matched to the wire size. However, in older wiring, branch lines to permanent ceiling light fixtures could be wired with a smaller gauge than the supply cable.

Let’s say a light fixture is replaced with another device that uses more current. The current capacity (ampacity) of the branch wire could be exceeded. When a wire is too small for the cur­rent it is supposed to carry, the wire will heat up. This condition has the potential to cause a fire.

When you use an extension cord, the size of the wire you are plac­ing into the circuit may be too small for the equipment. The circuit breaker could be the right size for the circuit but not right for the smaller-gauge extension cord.

A tool plugged into the extension cord may use more current than the cord can handle without tripping the circuit breaker, which can cause the wire to overheat and catch fire.

Improper Grounding

The most common OSHA electrical violation is improper grounding of equipment and circuitry.  The metal parts of an electrical wiring system that we touch (switch plates, ceiling light fixtures, conduit, etc.) should be grounded and at 0 volts.

When a circuit is not grounded properly, a hazard exists because unwanted voltage cannot be safely eliminated. If there is no safe path to ground for fault currents, exposed metal parts in damaged appliances can become energized.

Electrical systems are often grounded to metal water pipes that serve as a continuous path to ground. If plumbing is used as a path to ground for fault current, all pipes must be made of conductive material (a type of metal).

Many electric shocks and fires occur when parts of metal plumbing are replaced with plastic pipe
during renova­tion or repair.  Since plastic does not conduct electricity, the path to ground is interrupted by nonconductive material.

Overloads

Overloads in an electrical system are hazardous because they can produce heat or arcing. Wires and other compo­nents in an electrical system or circuit have a maximum amount of current they can carry safely.

If too many devic­es are plugged into a circuit, the electri­cal current will heat the wires to a very high temperature. If any one tool uses too much current, the wires will heat up, and the temperature of the wires can climb high enough to cause a fire. 

If wiring insulation melts, arcing may occur. Arcing can cause a fire in the area where the overload exists, even inside a wall.  In order to prevent too much current in a circuit, a circuit breaker or fuse is usually placed in the circuit.  If there is too much current in a cir­cuit, the breaker “trips” and opens like a switch to shut off the electrical current.

If the breakers or fuses are too big for the wires they are supposed to protect, an overload in the circuit will not be detected and the cur­rent will not be shut off.  Overloading leads to overheating of circuit components (including wires) and may cause a fire similar to this:

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Detecting Potential Electrical Hazards

Now that we have helped identify some of the risks that cause electrical fires, let's take a look at some warning signs of a potential electrical fire you can look for throughout your workplace.

  • Tripped circuit breakers and blown fuses show that too much current is flowing in a circuit or that a fault exists.  This condition could be due to malfunctioning equipment or a short between conductors.
     
  • If an electrical tool, appliance, wire, or connection feels warm, it may indicate too much current in the circuit or equipment, or that a fault exists.
     
  • An extension cord that feels warm may indicate too much current for the wire size of the cord or that a fault exists.
     
  • A cable, fuse box, or junction box that feels warm may indicate too much current in the circuits.
     
  • A burning odor may indicate overheated insulation.  Worn, frayed, or damaged insulation around any wire or other conductor is an electrical hazard because the conductors could be exposed.

    Contact with an exposed wire could cause a shock. Damaged insulation could cause a short, leading to arcing or a fire. Inspect all insulation for scrapes and breaks.

     
  • A Ground Fault Circuit Interrupter (GFCI)that trips indicates there is current leakage from the circuit. If a GFCI keeps tripping while you are using a power tool, there is a problem.  Resetting the GFCI repeatedly without determining what is causing the problem can cause an overload- and even a fire.

In addition, look for these warning signs of a potential overload- if you see any of these dangers in your workplace, be sure to inform a supervisor and hire an electrician to remedy the situation:

  • Feeling a tingle when you touch an electrical appliance.
     
  • Discoloration of wall outlets.
     
  • Sizzling sound at wall switches or outlets.
     
  • Flickering lights.

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Preventing Electrical Fires in the Workplace
 

To protect against electrical fires, business owners, managers and supervisors should use proper preventative measures and employee education in their safety program.  In addition, every business should consider special situations that may be unique to their facility.  For starters, some general suggestions are listed below:

  • Use and maintain wiring, tools, and equipment correctly. Keep everything oil- and dust-free.
     
  • Uncoil an extension cord fully before use. Find the amperage marked on it. Is it adequate?
     
  • Don’t use equipment that delivers mild shocks or gives off unusual heat or odd smells. If in doubt, have it checked and repaired or replaced.
     
  • Sweep up scraps and sawdust, and store flammable liquids in approved containers. Don't use electrical equipment when flammable gases, vapors, liquids, dusts, or fibers are present.

If there is a small electrical fire, be sure to use only a Class C or multipurpose (ABC) fire extinguisher, or you might make the problem worse. All fire extinguishers are marked with letter(s) that tell you the kinds of fires they can put out.

The letters are explained below (including suggestions on how to remember them).

A (think: Ashes) = paper, wood, etc.

B (think: Barrel) = flammable liquids

C (think: Circuits) = electrical fires

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Sources:

http://en.wikipedia.org/wiki/Fire_triangle

http://www.cdc.gov/niosh/docs/2009-113/pdfs/2009-113.pdf

http://www.humboldtrec.coop/othersites/ElectricalSafety/electrical/prevent_workplace_fires.html