OSHA lockout/tagout procedures must be completed before opening any enclosure
that may contain exposed energized components. Only a qualified worker may then
open the enclosure after donning the appropriate level of PPE as determined by
the Flash Hazard Analysis. All exposed live parts must then be tested to insure
that the equipment is in an electrically safe condition. There are only two
exceptions to this rule. See Littelfuse Whitepaper: Understanding
and Reducing Arc-Flash Hazards .
NFPA 70E places the responsibility on the employer to qualify employees who may
be required to work on energized equipment and to train unqualified persons in any
electrical safety-related practices that are necessary for their safety.
The information contained on this CD is believed to be accurate. However, it is
provided solely to help the user determine incident energy and the accompanying
arc-flash hazard. Since the user determines input values and other circuit
variables, Littelfuse expressly disclaims liability for any omissions or errors
in the software, or results of calculations or analysis. All arc-flash
calculations, including those in NFPA 70E, are based on a number of empirical
decisions. Results obtained by using various calculators may not be identical
due to different rounding of numbers, and selection of different opening times
for protective devices. When faced with options, Littelfuse has attempted to
select those values that result in higher incident energy. At best, all
calculating methods and results only provide a guide for determining the level
of PPE required. NFPA 70E cautions that additional developmental testing is
required, and calculation methods may require future revision.
The Littelfuse program calculates the incident energy, minimum required level
of Personal Protective Equipment (PPE), and Flash Protection Boundary and
Hazard Risk Category. These factors are an important part of the Arc-Flash
Hazard Analysis required by and described in NFPA 70E. A complete Arc-Flash
Hazard Analysis should help you increase employee safety and meet the
requirements of NFPA 70E, NFPA 70 “National Electrical Code,” and OSHA
Standards 29-CFR, Part 1910. Occupational Safety and Health Standards. 1910 sub
part S (electrical) Standard number 1910.333 “Standards for Work
Practices."
In addition, users are cautioned that the program only determines incident
energy under specified test conditions used in IEEE 1584. The recommended level
of PPE is the minimum recommended to reduce injury from burns that could occur
from an arcing fault. Workers may still receive burns while wearing PPE. Burns
from arc-flash are only one of the hazards of an arcing fault. Other potential
hazards include: direct and indirect pressure from arc blast, toxic vapors from
copper and metallic coatings, vaporized insulation (which may release chlorine
or other toxic gases), and particles of copper or other materials propelled by arc
blasts. Actual shock hazards must also be considered. These factors need to be
included in the documented plans for working on energized circuits.
While parts of the Standards, Regulations, and Codes (especially relating to
arc-flash hazards) are quoted or summarized herein, readers are cautioned that
only the complete Standards constitute the law or regulation and all parts must
be followed where applicable.
In performing an Arc-Flash Hazard Analysis, users are required to make a number
of empirical decisions regarding available fault current, distance from the
arc, etc. They are cautioned that choices made should reflect the most
conservative values that will produce the maximum arc-flash conditions. These
choices are further described and explained in the Calculator.
An Overview of Arc-Flash Hazards is contained in Littelfuse Document: Understanding and Reducing Arc-Flash Hazards located on this CD. It is highly recommended
that this paper be studied before using the Calculator.
In addition, some critics take the position that calculating methods contained
in the standards greatly understate the incident energy for systems under 600
volts. A question has also been raised concerning the effect conductor
orientation has on direction and magnitude of arc blast. Additional testing is
under consideration. The standards and regulations establish minimum
requirements for improving safety. These minimums may not be adequate, and it
may be necessary to use PPE with higher ratings than calculated.