Transcript Power Supply Study Phase III

Fire Retardant (FR)
Clothing NESC Compliance
Brent McKinney, P.E.
Manager – Electric T&D
APPA Principal Member
NESC Subcommittee 8
Disclaimer
• Compliance with NESC, NEC, OSHA and / or all
applicable codes and rules are the responsibility of
each individual utility. This presentation merely
provides background information so that each
utility can make its own decision concerning
compliance.
Nothing contained in this presentation is intended
to constitute legal advice. We recommend that
you consult with qualified legal counsel regarding
compliance with all codes, laws, and regulations.
Percent of Applicants that Perform Arc Hazard Assessments
92%
90%
90%
88%
86%
85%
85%
84%
82%
79%
80%
78%
76%
74%
72%
Small
Medium
Large
Overall
Outline
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Consensus Standard
NESC, NEC Scope
NESC Subcommittee Structure
NESC Subcommittee 8 FR Clothing History
NESC FR Clothing Compliance 2009
NESC FR Clothing Compliance 2012
Questions
• Consensus Standard: Standard which is
generally agreed upon by all entities affected.
• NESC & NEC are Consensus Standards
• NESC – IEEE
• NEC – NFPA
• NEC is primarily for non-utility companies past
the meter.
• NEC Utility Exemption – See NFPA 70E
90.1.B.5
• NFPA is proposing to remove utility
exemption for NEC.
• NESC is minimum safety consensus
standard for electric utilities.
• States, cities may adopt.
• Accepted as national safety consensus
standard.
• NESC is governed by 7 subcommittees
• 1.Purpose, Scope, Application, Definitions and
References
• 2. Grounding Methods
• 3. Electric Supply Stations
• 4. Overhead Lines - Clearances
• 5. Overhead Lines – Strength and Loading
• 6. None
• 7. Underground Lines
• 8. Work Rules
• NESC subcommittees made up of utility
representatives, consultants, IBEW, NSPE,
TelCom industry and others.
• No one group can have more than 33%
representation.
• NESC Subcommittee 8 responsible for worker
safety rules.
• Responsible for FR clothing rules.
FR Clothing History
• Change Proposal (CP) submitted to SC8 by
IBEW in 2005
• OSHA told committee it needed consensus
standard for new 1910.269 Rule
• OSHA would use NEC 70-E if NESC did
not pass FR clothing rule.
FR Clothing History – cont’d
• Nearly all SC8 members now under OSHA
• SC8 companies felt FR clothing rule must
be passed
• Significant disagreement among committee
• Working group developed to write FR rule
and bring back to subcommittee
FR Clothing History – cont’d
• EEI, NRECA, APPA, OSHA, IBEW
representatives on committee 8-10 people
• Committee met three times
Issues
• APPA and NRECA insisted tables be
provided instead of requiring Arc hazard
analysis.
• Little and poor data on Arc hazard incidents
and tests.
• OSHA used ArcPro 2.0 to determine arcs.
Issues cont’d
• What arc distance should be used?
• Would regular jeans be allowed?
• Would the heat stress of the clothes be more
of a problem than the arc hazards?
• Who should pay for the clothes?
• When should the rule begin?
Issues cont’d
• What do we do for arcs under 1,000V?
• OSHA must accept.
• Finally consensus reached, no one
completely happy.
• APPA votes to reject rule.
Rules
1. Effective as of January 1, 2009, the employer shall
ensure that an assessment is performed to
determine potential exposure to an electric arc for
employees who work on or near energized parts or
equipment. If the assessment determines a
potential employee exposure greater than 2
cal/cm2 exists (see Neal, Bingham, and Doughty
[B59]), the employer shall require employees to
wear clothing or a clothing system that has an
effective arc rating not less than the anticipated
level of arc energy
Rules cont’d
2. When exposed to an electric arc or flame, clothing
made from the following materials shall not be
worn: acetate, nylon, polyester, or polypropylene.
The effective arc rating of clothing or a clothing
system to be worn at voltages 1000 V and above
shall be determined using Tables 410-1 and 410-2
or performing an arc hazard analysis. When an
arc hazard analysis is performed, it shall include a
calculation of the estimated arc energy based on
the available fault current, the duration of the arc
(cycles), and the distance from the arc to the
employee.
Rules cont’d
3. EXCEPTION 1: If the clothing required by this rule has the
potential to create additional and greater hazards than the
possible exposure to the heat energy of the electric arc,
then clothing with an arc rating or arc thermal performance
value (ATPV) less than that required by the rule can be
worn.
EXCEPTION 2: For secondary systems below 1000 V,
applicable work rules required by this part and engineering
controls shall be utilized to limit exposure. In lieu of
performing an arc hazard analysis, clothing or a clothing
system with a minimum effective arc rating of 4 cal/cm2
shall be required to limit the likelihood of ignition.
Rules cont’d
4. NOTE 1: A clothing system (multiple layers) that
includes an outer layer of flame resistant material
and an inner layer of non-flame resistant material
has been shown to block more heat than a single
layer. The effect of the combination of these
multiple layers can be referred to as the effective
arc rating.
NOTE 2: It is recognized that arc energy levels
can be excessive with secondary systems.
Applicable work rules required by this part and
engineering controls should be utilized.
Rules cont’d
5. Employers shall utilize positive procedures to secure
compliance with these rules. Cases may arise, however,
where the strict enforcement of some particular rule could
seriously impede the safe progress of the work at hand; in
such cases the employee in charge of the work to be done
should make such temporary modification of the rules as
will accomplish the work without increasing the hazard.
If a difference of opinion arises with respect to the
application of these rules, the decision of the employer or
the employer's authorized agent shall be final. This
decision shall not result in any employee performing work
in a manner that is unduly hazardous to the employee or to
the employee's fellow workers.
6.
• NESC 2012 CP’s initial meeting
• Low voltage working group developed
update FR clothing rule including new table
under 1000 Volts
Table 410- 23: Live-line tool work clothing and clothing
systems—voltage, fault current, and maximum clearing time
for voltages 46.1 to 800 kV 1 AC
(See Rule 410A3)
• Supporting Comments
Currently, Rule 410A3 requires the use of clothing or clothing
systems with a minimum effective arc rating of 4 cal /cm2 for
voltages less than 1000 V, in lieu of performing an arc hazard
analysis.
• Subcommittee 8 established a Low Voltage Arc Flash Work
Group (WG) to evaluate the necessary minimum clothing or
clothing system requirements for employees working on
energized lines and parts operating at voltages less than 1000V
and to develop a Change Proposal, if needed, to revise Rule
410A3.
• The WG’s initial evaluations concluded that aside from
anecdotal evidence no technically substantiated data based
upon specific industry testing existed to justify the creation
of a new table, similar to existing Tables 410-1 and 410-2,
for voltages less than 1000V. However, during the spring
and summer of 2008, the Pacific Gas and Electric
Company initiated and completed a series of scientific tests
to determine the arc flash characteristics of 480V selfcontained metering equipment by creating fault conditions
at various kA levels (sans fault protection devices).
• Based on PG&E’s test results and the application of an
accepted industry standard (IEEE 1584-2002), the WG
submitted a report to Subcommittee 8 which included
revisions to Rule 410A3 and a new Table (410-1).
• The revisions to Rule 410A3 seek to clarify the difference
between performing an assessment and an arc hazard
analysis, the conditions under which an arc hazard analysis
is to be performed, and the employer’s requirements for
determining the necessary clothing or clothing systems.
• New Table 410-1 [Clothing and Clothing Systems (per
cm2) for voltages 50 to 1000 V (AC)] and existing Tables
(renumbered to 410-2 and 410-3) are cited in new text
410A3a to offer employers the option of using tabulated
values for clothing and clothing systems in lieu of
performing an arc hazard analysis.
• The supplemental notes to new Table 410 -1 identify certain
parameters that vary from the pre-existing tables (new 410-2 and 4103). One such difference is the use of an 18 in. worker separation
distance. On this particular topic, it should be noted that the supporting
test results are based on the application of IEEE Std. 1584 test
methodologies and typical working distances for low voltage motor
control centers and panel boards (Table 3 p. 9). It seemed prudent to
the workgroup to apply the 18 in. working distances to determine the
cal/cm2 values for other listed equipment and for other voltage ranges,
since Section 4.8 (IEEE 1584) states that arc flash protection is based
on the incident energy level on the worker’s face and body, not the
incident energy on the hands and arms.
• The supplemental notes to new Table 410-1 also include statements
identical to those in pre-existing tables (renumbered 410-2 and 410-3)
that allow the user to apply different methods of calculating arc
exposure values.
Revisions to Rule 410A3
3. Effective as of January 1, 2009, tThe employer shall ensure that an assessment
is performed to determine potential exposure to an electric arc for employees
who work on or near energized lines, parts or equipment.
If the assessment determines a potential employee exposure greater than 2
cal/cm2 exists (see Neal, Bingham, and Doughty [B59]), the employer shall:
a. Perform a detailed arc hazard analysis, or use Table 410-1, Table 410-2, or
Table 410-3 to determine the effective arc rating of clothing or clothing system
to be worn by employees working on or near energized lines, parts, or
equipment at voltages 50 – 800,000 volts.
When an The arc hazard analysis is performed, it shall include a calculation of
the estimated arc energy based on the available fault current, the duration of
the arc (cycles), and the distance from the arc to the employee.
b.Require employees to wear clothing or a
clothing system that haswith an effective arc
rating not less than the anticipated level of
arc energy.
When exposed to an electric arc or flame,
clothing or a clothing system made from the
following materials, unless flame resistant,
shall not be worn: acetate, nylon, polyester,
or polypropylene.
• EXCEPTION 1: If the clothing or clothing
system required by this rule has the
potential to create additional andor greater
hazards than the possible exposure to the
heat energy of the electric arc, then clothing
with an arc rating or arc thermal
performance value (ATPV) less than that
required by theis rule canmay be worn.
NOTE 1: Assessments performed to determine potential exposure
to an electric arc consider the affected employee’s assigned
tasks and/or work activities.
NOTE 12: A clothing system (multiple layers) that includes an
outer layer of flame resistant material and an inner layer of nonflame resistant natural fiber material has been shown to block
more heat than a single layer. The effect of the combination of
these multiple layers canmay be referred to as the effective arc
rating.
NOTE 23: It is recognized that arc energy levels can be excessive
with secondary systems. Applicable work rules required by this
part and engineering controls should be utilized.
Engineering controls can be utilized to reduce arc energy levels
and work practices can be utilized to reduce exposure levels.
New Table 410-1
Table 410-1: Clothing and Clothing Systems (per cm2) for voltages 50 to 1000 V (AC)
(See Rule 410A3.)
Nominal Voltage Range and Calories/Cm 2
Equipment Type
50 – 250V
251 – 500V
501 – 1000 V
Self-contained Metering
Pad-mounted transformers/
Panels & cabinets
42
204
308
CT Meters and
control wiring
42
45
68
Metal-clad Switchgear /
Motor Control Centers
83
406
608
Subsurface/ Pedestalmounted Equipment
42
87
12 8
Open Air (includes lines)
42
42
68
Notes:
1.
This table is based on maximum fault current of 51kA.
Calculations are based on an 18-in separation distance from the arc to the employee.
See IEEE 1584-2002.
Other methods are available to estimate arc exposure values and may yield slightly
different but equally acceptable results.
The use of the table in the selection of clothing is intended to reduce the amount or
degree of injury but may not prevent all burns.
2.
Industry testing by two separate major utilities has demonstrated that voltages 50 240V will not sustain arcs for more than 0.5 cycles thereby limiting exposure to less
than 4 calories/cm2.
3.
Value based on industry test results and IEEE Std. 1584-2002 formula for Motor
Control Centers. (Gap = 1 in.) (Xd = 1.641) (18 in. distance) 51kA (Based on a 208V,
1000kVA, 5.3% Z, served from a 500mVA system) Maximum duration (from tests) is
10 cycles: 46.5 cal/s/cm2 * 0.167 sec = 7.8 cal/cm2
4.
Industry testing on 480V equipment indicates exposures for self-contained meters do
not exceed 20 calories/cm2.
5.
Industry testing on 480V equipment indicates exposures for
CT meters and control wiring does not exceed 4 calories/cm2.
6.
Value based on industry test results and IEEE Std. 1584-2002
formula for Motor Control Centers. (Gap = 1” and Xd =
1.641, 18 inch distance) 12.7kA at 480 V (worst case energy
value from testing). Maximum duration from tests is 85
cycles: 26.2 cal/s/cm2 * 1.42 sec = 37 cal/cm2
7.
Incident analysis on this equipment indicates exposures do
not exceed 8 calories/cm2.
8.
Incident analysis and industry testing indicates that applying a
150% multiplier to the 480V exposure values provides a
conservative value for equipment and open air lines operating
at 501 – 1000V.
Questions?
Contact Information:
Brent McKinney
Manager, Electric T&D
City Utilities of Springfield
Phone: 417/831-8762
Email: [email protected]
Nathan Mitchell
Director of Engineering Services
American Public Power Association
Phone: 202/467-2925
Email: [email protected]
Mike Hyland
VP of Engineering Services
American Public Power Association
Phone: 202/467-2986
Email: [email protected]
Additional Information Available at:
• E&O Conference – March 22-25,
2009 Austin, Texas
• The 14th Edition of the APPA
Safety Manual – Available Now at
APPAnet.org