an engineer’s guide to osha’s new recommendations for arc flash studies
TRANSCRIPT
An Engineer’s Guide to OSHA’s New Recommendations
for Arc Flash Studies
Before We Start q This webinar will be available at
www.windpowerengineering.com & email
q Q&A at the end of the presentation
q Hashtag for this webinar: #WindWebinar
Moderator Presenter
Paul Dvorak Windpower Engineering
& Development
Tahnee Miller Ulteig
An Engineer’s Guide to OSHA’s New
Recommendations for Arc Flash Studies
Tahnee Miller, PE Ulteig
Objective • Explain the impact of a new OSHA filing which affects the
calculation methods of arc flash risk assessment from the perspective of a consultant engineer.
Overview
• Basics of arc flash • How arc flash is calculated • Impact of OSHA 29 CFR Parts 1910 and 1926 final ruling • Incorporating OSHA ruling into arc flash studies
Arc Flash Basics • Defined by NFPA 70E-2015: a dangerous condition
associated with the possible release of energy caused by an electric arc.
• An arc flash risk assessment must include: o Incident Energy at a given working distance o Arc Flash Boundary o Personal Protective Equipment (PPE) that must be worn inside the AF boundary
Calculation Methods • NFPA 70E-2015 • IEEE 1584 • Ralph Lee Method • ANSI/IEEE C2 NESC, Section 410 • Etc.
OSHA 29 CFR 1910/1926 • Released in April 2014, became effective in July 2014 • Replaces the incorporation of these consensus standards
with a set of recommendations • Appendix E to Subpart V of Part 1926 summarizes OSHA’s
recommendations for calculation methods for equipment • Includes detailed comparison of the options
o Summary on following slides
NFPA 70E-2012 Annex D (Lee Equation)
• <= 600 V o Acceptable for open-air arcs (though not typically used at this voltage)
• > 600 V and <= 15 kV o Reasonable, but conservative, so PPE will be heaver and bulkier than needed
• > 15 kV o Should only be used to estimate incident energy if the employee exposure is
calculated to be less than 2 cal/cm2
• Estimates incident energy levels for three-phase arcs
Doughty, Neal, and Floyd • <= 600 V
o Conservative, but reasonable
• > 600 V o Not acceptable o Testing was performed exclusively with an electrode spacing of 32 mm at 600 V
IEEE Std 1584b-2011 • Refers to IEEE Std 1584-2002 including both amendments • <= 15 kV
o Reasonably estimates incident energy o Accounts for differences between single-phase and three-phase arcs and between
arcs in open air or enclosed arcs
• > 15 kV o Outside the range of the standard and thus not recommended
ARCPRO • Based on tested heat flux data in lab • <= 15 kV
o Can be used as long as arc is single phase and open air o Conversion factors for three-phase or enclosed arcs are not verified
• > 15 kV o Same issues as <= 15 kV, but since there is no reasonable alternative, OSHA
considers this method as a reasonable estimate if the conversion factors are used
• NESC tables in Section 410 based on ARCPRO calculations
Incident Energy Calculation Method
600 V and Less2 601 V to 15kV2 More than 15 kV 1Φ 3Φa 3Φb 1Φ 3Φa 3Φb 1Φ 3Φa 3Φb
NFPA 70E-2012 Annex D (Lee Equation) Y-C Y N Y-C Y-C N N3 N3 N3
Doughty, Neal, and Floyd Y-C Y Y N N N N N N
IEEE Std 1584b-2011 Y Y Y Y Y Y N N N ARCPRO Y N N Y N N Y Y4 Y4
Table 1 – Selecting Reasonable Incident-Energy Calculation Method1
Table 1 Notes
1Φ: Single-phase arc in open air 3Φa: Three-phase arc in open air 3Φb: Three-phase arc in enclosure (box) Y: Acceptable: produces a reasonable estimate of incident heat
energy from this type of electric arc N: Not acceptable: does not produce a reasonable estimate of
incident energy from this type of electric arc Y-C: Acceptable: produces a reasonable, but conservative, estimate of
incident heat energy from this type of electric arc
Incorporating Ruling • Equipment <= 15 kV
o IEEE Standard 1584b-2011 • Equipment > 15 kV
o ARCPRO calculations adjusted with conversion factors for three-phase arcs in open air or in an enclosure
o NESC Section 410 tables (based on ARCPRO test data)
Questions?
Paul Dvorak Windpower Engineering & Development [email protected] Twitter: @windpower_eng
Tahnee Miller Ulteig [email protected]
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