Posts Tagged ‘electrical injuries’

Arc Flash Dangers

Sunday, September 13th, 2009

     Imagine being hit by a bolt of lightning.  Like lightning, an arc flash can unexpectedly release tremendous amounts of energy, resulting in serious injuries and even death.

     An arc flash is the result of a short circuit or electrical fault in energized equipment.  Current flows through the air and creates an electrical arc, very much like the phenomenon of lightning.  But unlike lightning, arc flash dangers are present in a myriad of circumstances that do not require storm conditions to manifest.

     Over 80% of electrically related injuries involve some type of arc flash.  They can be caused by a wide variety of factors, including:  equipment malfunctions, inadequate safety procedures, carelessness, lack of training, dropped tools, etc.   The amount of energy released by the electrical arc depends on the amount of electrical current flowing through the arc and how long the current will flow before it is interrupted by a circuit breaker or fuse.

     The radiation released in an arc flash can be so intense and so rapid that it can instantly burn skin and ignite clothing.  Temperatures at the electrical arc can rapidly climb to tens of thousands of degrees.  At temps this extreme metal becomes liquid, then vaporizes, and the air surrounding the arc becomes superheated to approximately 30,000°F.  The superheated air and metal vapor together expand with explosive force.  This creates a dangerous and potentially lethal pressure wave of hot gas, molten metal droplets, and solid metal shards that can create burns and shrapnel wounds. 

arc4 Temperatures at the electrical arc can rapidly climb to tens of thousands of degrees, creating a dangerous and potentially lethal pressure wave of hot gas, molten metal droplets, and solid metal shards that can create burns and shrapnel wounds.

      The Occupational Safety and Health Administration (OSHA) requires employers to assess the workplace for arc flash hazards that are present or that are likely to be present.  Assessment is done using standards developed by the National Fire Protection Association (NFPA) and the Institute of Electrical and Electronics Engineers (IEEE) to specifically address arc flash hazards.

     If hazards are identified, employers must mitigate risks by adhering to a six point compliance plan such as the following:

1.  Implement a worker safety program with defined responsibilities.

2.  Perform engineering studies that include calculations to determine the degree of arc flash hazards.  These studies also must be updated when any changes to the electrical system are made by the employer or the electric utility. 

3.  Provide workers with the correct personal protective equipment (PPE) based on the study results.  These PPE must then be maintained on site to protect workers.

4.  Provide worker training on the hazards of arc flash. This training must be documented and workers must demonstrate proficiency through testing.  Worker training must also be updated whenever any changes occur to the electrical system.

5.  Provide appropriate tools for safe working.

6.  Place conspicuous warning labels on equipment to warn workers about potential arc flash hazards.

     OSHA, like other government agencies, expects employers to keep up with regulations and take the necessary steps to remain compliant.  For example, OSHA won’t send notices out to employers to inform them that they must implement an arc flash program in their plant.  It’s up to the employers to know that and institute the necessary precautions on their own. 

     It must also be noted that OSHA doesn’t walk employers through the steps of setting up an effective worker safety program.  This means that workers can be exposed to arc flash hazards simply because their employer is ignorant of regulatory requirements and is operating based on misconceptions.

     Some workers are unfortunate enough to work for employers that don’t take potential dangers like arc flash seriously enough to implement an effective safety program.  When their wakeup call comes, it’s often too late.


Do you want to know more about implementing an effective Arc Flash Program in your facility? Phil O’Keefe developed and presents a 90-minute webinar entitled: “Arc Flash Program Fundamentals.”  Contact him for more information about conducting this webinar for your organization. 

A Few Words About Electric Shocks

Sunday, July 26th, 2009
     For an electric shock to occur, a person must become a part of an electrical circuit in such a way that electric current passes over their skin or through their body.  Under certain conditions, even momentary contact with an energized metal object can result in serious injury and even death.  According to an article in the American Journal of Industrial Medicine:

“Contact with live electrical wiring, equipment, and light fixtures was the main cause of electrical deaths and injuries among electrical workers, followed by contact with overhead power lines. Among non-electrical workers, contact with overhead power lines was the major cause of death. Other causes included contact with energized metal objects, machinery, power tools, and portable lights.”

     From an engineering viewpoint, the body’s electrical resistance is an important variable.   Electrical resistance of an object is a measure of how freely electrical current can flow across the object when a voltage is applied across it.  Resistance is measured in units called “Ohms.”    Resistance of a person’s body can depend on skin dryness, perspiration level, thickness of the skin, the distance that the electrical current travels through the skin, and other factors. The typical human body has a hand-to-hand electrical resistance somewhere between 1,000 and 2,000 Ohms, but resistance across other parts of the body can be much higher.  There is a wide variation in body resistance between individuals, so the same voltage level may result in different effects.

     Most electrical injuries occur from alternating current (AC) at levels above 50 Volts at the low frequencies typically maintained by electric utilities.  The North American utilities normally generate power at a frequency of 60 cycles per second.  The “cycles per second” unit of frequency is also referred to as “Hertz,” usually abbreviated as “Hz.”  At 60Hz frequency, the threshold for perception occurs with electrical currents as low as 0.0001 Amps.  The “can’t let go” electrical current for adults is approximately 0.010 to 0.015 Amps. This is the current that causes involuntary muscle contractions severe enough to prevent the person from letting go of the source of the electrical shock. 

     Electric currents as low as 0.050 Amps at 120V, 60Hz, have been known to cause death.  Just to give you an idea of how small that current is… a table lamp with one 40 Watt incandescent bulb draws 0.333 Amps from a 120 Volt, 60 Hz household electrical outlet!  In the interest of electrical safety, the National Electrical Code (NEC) considers 0.005 Amps at 120V, 60Hz to be the safe upper limit for children and adults.