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Explaining Flash Calculations to Workers
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Author:  dlb [ Wed Jun 23, 2010 9:09 am ]
Post subject:  Explaining Flash Calculations to Workers
We have completed arc flash studies, created a policy, installed labels, and issued PPE. Now personnel are questioning why, for example, all 480V bus are not labeled the same. The simple answer, the study results indicate X incident energy based on the available fault calculations and the protective device clearing time, has not been sufficient. The request is for the information available to personnel to explain why busses are different.

Do I provide a full copy of the fault current study and flash study. Will it have any meaning for the end user? Any recommendations or alternate approaches?
Author:  JBD [ Wed Jun 23, 2010 9:46 am ]
Post subject: 
Have you conducted any formal training classes yet?
Your workers are not considered "qualified" until they know how to select PPE for their respective tasks, this would include understanding the information on the arc flash labels.
Author:  dlb [ Wed Jun 23, 2010 10:18 am ]
Post subject: 
Thank you, forgot to include that piece of information. We have conducted training in two parts - background and policy overview and hands-on training on how to read labels and select clothing.
Author:  cbauer [ Wed Jun 23, 2010 10:28 am ]
Post subject: 
Throught training the qualified personnel should have a basic knowledge of the elements that go into the AF analysis that will affect the IE levels at any given point in the electrical system. I would question their qualification levels should they not understand how varying fault currents, impedances, etc can produce varying results.
Author:  dlb [ Wed Jun 23, 2010 11:19 am ]
Post subject: 
The training included the difference between bolted and arcing faults and information on the hazard analysis - outline of equipment included in the study, faults calculated, arc flash calculated, and PPE level determined.

I guess I am looking for a way to communciate the information effectively to personnel who may not have background in electrical calculations.

The main group requesting specifics is the Operations Staff who rack and operate breakers. They do not perform electrical maintenance activities.
Author:  JBD [ Wed Jun 23, 2010 11:43 am ]
Post subject: 
Racking breakers is one of the most dangerous activities that I can think of.

Your workers should not need a background in electrical calculations in order to accept the concept that different devices operate at different speeds and therefore 'let through' different amounts of energy. You may need to revisit your training program.
Author:  Zog [ Wed Jun 23, 2010 3:32 pm ]
Post subject: 
I agree, it does nto sound like you are getting the rigth concepts across in your training. Let alone the right hands-on stuff. Let's review,

According to the NFPA 70E, a “Qualified Person" is one who is trained and knowledgeable of the construction and operation of the equipment or the specific work method, and be trained to recognize the hazards present with respect to that equipment or work method.

Such persons shall also be familiar with the use of the precautionary techniques, personal protective equipment, insulating and shielding materials, and insulated tools and test equipment. A person can be considered qualified with respect to certain tasks but still be unqualified for others.

An employee that is undergoing on the job training and who, in the course of such training, has demonstrated the ability to perform duties safely at his or her level of training and who is under the direct supervision of a qualified person shall be considered to be a qualified person for the performance of those duties.

In addition, to be permitted to work within the limited approach of exposed energized conductors and circuit parts the person shall be trained in all of the following:
  • Qualified employees shall be trained and competent in:
  • The skills and techniques necessary to distinguish exposed live parts from other parts of electric equipment
  • The skills and techniques necessary to determine the nominal voltage of exposed live parts
  • The minimum approach distances specified in this section corresponding to the voltages to which the qualified employee will be exposed, and,
  • The decision making process necessary to determine the degree and extent of the hazard and the personal protective equipment and job planning necessary to perform the task safely

A few notes to add to the 70E definition.
  1. Only the employer can deem an employee qualified after they have had the proper training and have demonstrated profinency using the skills and method learned.
  2. There is no such thing as NFPA 70E certification, going to a training course does not make an employee qualified.
  3. The most misunderstood part of the "qualified" term is that it is all emcompassing, you are "qualified" to work on a specific type or piece of equipment.
  4. Neither a J-card, a masters license, or an engineering degree make you a "qualified person"
  5. The word "electrician" is not anywhere in the definition of a "qualified person" meaning these rules apply to all employees and you dont have to be an electrician to be "qualified"
Author:  arcflash71 [ Wed Jun 23, 2010 4:30 pm ]
Post subject: 
dlb wrote:
Now personnel are questioning why, for example, all 480V bus are not labeled the same.


How about a discussion/presentation that centers around the inverse time trip characteristic of a low voltage power circuit breaker? Using the time-current curve as a visual aid you could discuss how the arc impedance might cause different trip elements (LTPU, STPU, INST) to operate and how the clearing time varies in each case. That might be a good base from which to explore the relationship between clearing time, arcing fault current and incident energy.
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