NFPA 70E 110.8(B)(1) requires that an electrical hazard analysis be performed to ensure that workers are properly protected whenever they work on or near equipment that is not in an "electrically safe condition" (see NFPA 70E Article 120 for guidance on putting equipment in an electrically safe condition). This includes work required to deenergize the equipment.

Part of an electrical hazard analysis is an arc flash hazard analysis. According to NFPA 70E Section 130.3, the goal of arc flash hazard analysis is to identify:

• The arc flash-protection boundary, defined in Article 130.3(A) as "an approach limit at a distance from exposed live parts within which a person could receive a second degree burn if an electrical arc flash were to occur."
  
  
• The proper personal protective equipment (PPE) and protective clothing necessary, based on the incident energy present at the working distance for the task to be performed, as described in Article 130.3(B) and Article 130.7.
  
  
• Appropriate safety-related work practices.
  
  

Performing an electrical hazard analysis provides you an additional benefit-an in-depth look at your plant's electrical system. Such an analysis gives you data you can use to improve overall system performance, reduce downtime and manage costs.

Appendix D of NFPA 70E and IEEE Standard 1584, Guide for Performing Arc Flash Hazard Calculations, identify a systematic, nine-step approach for performing a comprehensive arc flash hazard analysis.

The process begins with a short circuit study to determine the available "bolted" fault current at each location in the system. Arcing fault currents are less than the maximum bolted fault current and need to be estimated. All relevant overcurrent protection device data must also be obtained to accurately predict the duration (clearing time) of the arc fault current. Other factors that affect arc flash energies need to be weighed as well.

A choice of formulas for calculating arc flash protection boundaries and incident energy can be found in NFPA 70E and IEEE 1584. If a worker is required to be within the arc flash boundary, then PPE must be selected for the expected incident energy calculated.

Note that IEEE 1584 contains separate equations for calculating the dramatic reduction in arc flash energies possible with certain current-limiting fuses. Using these fuses can also reduce the category of PPE workers are required to wear.

NFPA 70E also offers a table method for selecting protective clothing and other PPE. But you must be sure that the parameters of your electrical system are covered by these tables, as indicated in the various footnotes of Tables 130.7(C)(9)(a) and Tables 130.7(C)(10).

For a discussion comparing PPE selection using the table method versus the analytical method, see "A Summary of Arc Flash Energy Calculations" by D.R. Doan and R.A. Sweigart, found in the July/August 2003 issue of IEEE Transaction on Industry Applications, or contact Ferraz Shawmut Technical Services.