Arc Flash Protective Gear Personal Safety in Performing Stray - - PowerPoint PPT Presentation

Arc Flash Protective Gear

Personal Safety in Performing Stray Voltage Investigations

by Tom Seidl We Energies

Arc-Flash Hazard

• 5-10 incidences occur every day
• Burns
• Hot Gases can injure lungs and impair

breathing

• Hot Copper/metal
• Blast Pressure

General Duty Clause

Section 5(a)(1)

Requires an employer to provide an employee with a workplace free from recognized hazards.

OSHA 29 CFR 1910.132(d)(1)

• Requires employers to evaluate hazards
• Requires employers to select and require

use of PPE for employees.

Details are left to Consensus Standards

• NFPA 70
• NFPA 70E
• ANSI
• ASTM
• IEEE

NFPA 70E Covers

• Public and private premises
• Yards, lots, carnivals, parking lots and

industrial substations

• Installations of conductors & equipment

that connect to the supply of elecricity

• Installations used by the electric utility

….that are not an integral part of a generating plant, substation, or control cntr.

NOT Covered: Installations under exclusive control

• f an electric utility where such:
• Consist of service drops or service laterals

& associated metering

• Are located in …easements or rights-of-way

recognized (as under jurisdiction of a utility commission)

• Are on property owned by the electricity

utility for the purpose of …distribution of electric energy

NESC 410

• Assessment of the system is required.
• If >2 cal/cm2, clothing system adequate for

the anticipated level of arc energy.

• For voltages >1000 Volts, effective arc

rating of clothing system determined from Table 410-1 & 410-2 or Arc Flash Analysis

Systems Below 1000 Volts

• Engineering controls to limit exposure.
• Clothing system with a minimum 4

cal/cm2

Generally, when you go to work on a farm, even though you are a utility employee, your are governed by NFPA 70 E

Best Practice - De-energize

NFPA 70E Article 130.1: All equipment and

circuits shall be put into an electrically safe condition before working within the Limited Approach Boundary unless:

• Doing so presents a greater hazard
• Infeasibility
• Less than 50 Volts

FPN No. 2 Examples that might be performed w/i the Limited Approach Boundary … because

• f infeasibility …include

performing diagnostics and testing (e.g., troubleshooting)

Arc Flash Hazard Analysis

(Required: NFPA 70E, Article 130.30)

• Determine the Arc Flash Protection

Boundary

• Determine the personal protective

equipment that people within the Arc Flash Protection Boundary shall use.

Incident Energy

The amount of energy (cal/cm2) impressed on a surface, a certain distance from the source, generated during an electrical arc event.

Flash Protection Boundary

An approach limit at a distance from exposed live parts within which a person could receive a 2nd degree burn if an electrical fault were to occur. (1.2 cal/cm2)

Flash Hazard Analysis (130.3)

For systems 600 Volts or less, the flash protection boundary shall be 4 feet. (Assumes 2 cycle clearing time and 50 kA ASCC or any combination not exceeding 100 kA Cycles.

The incident energy exposure level shall be based on the working distance of the employee’s face and chest areas from a prospective arc source for the specific task to be performed.

Article 130.3, Exception No. 1: An arc flash hazard analysis shall not be required where all of the following conditions exist:

• 1. The circuit is rated 240 Volts of less.
• 2. The circuit is supplied by one transformer.
• 3. The transformer supplying the circuit is

rated less than 125 kVA

Equation of Arc in a Cubic Box

• DB = distance from arc electrodes, inches (for distances 18
• in. and greater)
• tB = arc duration, seconds (cycles/60 cycles)
• F = bolted fault short circuit current, in kA (for the range
• f 16 to 50 kA)
• EMB = 1038.7 x DB
• 1.4738 x tA x (0.0093 x F2 – 0.3453 x F +

5.9675)

• EMB = maximum 20 in cubic box incident energy

Equation of Arc in Open Air

• DA = Distance from arc electrodes, inches (for

distances 18” and greater.

• tA = arc duration, seconds (cysles/60 cycles)
• F = bolted fault short circuit, in kA (for the range
• f 16 to 50 kA)
• EMA=5271 x DA
• 1.9593 x (0.0016 x F2 – 0.0076 x F

+ 0.8938)

• EMA = maximum open arc incident energy in

calories/cm2

Arc Flash Protection (transformer) Boundary

• MVA = rating of transformer
• t = time of arc exposure in seconds, (cycles/60

cycles)

• DC = (53 x MVA x t)1/2
• DC = Curable Distance

Arc Flash Protection (bolted fault) Boundary

• MVAbf = bolted fault MVA at point involved
• V = Volts
• %Z = percent impedance based on transformer MVA
• T = time of arc exposure in seconds, (cycles/60 cycles)
• ISC = (((MVA Base x 106)/(1.732 x V)) x 100/%Z)
• ISC = Short Circuit Current
• P = 1.732 x V x ISC 10-6 x 0.7072
• P = maximum power (in MW) in a 3 phase arc
• DC = (2.65 x MVAbf x t)1/2
• DC = Curable Burn Distance

The incident energy should be calculated at the maximum and at 85 % of maximum arc fault. (A longer clearing time can result in more incident energy.

Flash Hazard Analysis (130.3)

As an alternative, the PPE requirements of 130.7(C)(9) shall be permitted to be used in lieu of the detailed flash hazard analysis

• f 130.3A

600 Volt MCC’s

Arc Rating of a Material

• Maximum incident energy resistance prior

to breakopen or onset of 2nd degree burns.

• cal/cm2
• Break open - formation of 1 or more

holes in the innermost layer.

Clothing made from nonmelting flammable natural materials such as cotton, wool, rayon, or silk is permitted for Hazard/Risk Category 0 if flash hazard is <1.2 cal/cm2

Underlayers

Meltable fibers are not permitted. (an incidental amount of elastic is permitted.)

Acetate, acrylic, nylon, polyester, polyethylene, polypropylene, and spandex, either alone or in blends, shall not be used.

• FR clothing is required to be work within

the Flash Protection Boundary, which is generally considered to be 1.2 cal/cm2

• FR clothing for race car drivers or pilots is

not suitable for arc flash protection. Arc rated FR clothing is the only FR clothing marked with the cal/cm2 rating.

Clothing and other apparel (hair nets, hard hat liners) made from materials that do not meet the requirements of 130.7(C)(14) regarding melting, or made from materials that do not meet the flammability requirements shall not be permitted.

Foot Protection

• Shoes with an arc rating are not available.
• Foot Protection. Heavy-duty leather work shoes

provide some arc flash protection to the feet and shall be used in all tasks in Hazard/Risk Category 2 and higher and in all exposures greater than 4 cal/cm2.

• An incidental amount of elastic used on

nonmelting fabric underwear or socks shall be permitted.

Hands

• No method exists for determining the

degree of exposure for a worker’s hands.

• Leather of FR gloves shall be worn where

required for arc flash protection.

• Where insulating rubber gloves are used for

shock protection, leather protectors shall be worn over the rubber gloves.

Safety glasses must be worn under the face shield or viewing window.

Outer Layers

Garments worn as outer layers over FR clothing, (jackets or rain wear) must also be FR clothing.

Exposure of more than 40 cal/cm?

• task must not be performed until and

electrically safe work condition exists

• FR clothing with a very high incident

energy rating might me needed to perform the steps necessary to establish an electrically safe condition

• This is the only task that should be

accomplished with the equipment energized

• Inspection
• Manufacturer’s Instructions.
• Storage
• Cleaning

Care and Maintenance of FR Clothing and FR Arc Flash Suits

Other Personal Protective Equipment

• Eye protection
• Head protection
• Conductive Articles not worn
• Face shields w/o Arc rating shall not be

used.

• Eye protection always be worn under face

shields or hoods.

Proper PPE

• Does not guarantee the worker will remain

injury free

• The purpose is to reduce death
• Burns to the hands and arms aren’t

considered life threatening

Insulated Tools

Employees shall use insulated tools and/or handling equipment when working inside the limited approach boundary.

(Must be marked with a voltage rating.)

The best solution is to always do as much work as possible with the system de-energized.

Alternatives During SV Investigations

• Know the maximum fault current at the farm

where you are working.

• Measure line voltages at receptacles
• Open panels only when de-energized
• Connect the “panel neutral” lead to the grounding

electrode conductor externally from the panelboard

• Access the panel neutral at remote panels through

contact with the equipment grounding conductor at a nearby receptacle

Practices

• Measure at the lowest energy point

(smallest breaker)

• If you can, keep both hands free
• 1 PH measurements - connect neutral first

and remove last

• Three point method
• Use probes with minimum exposed metal
• Keep on hand in your pocket.

Table 130.7(c)(9)(a) requires you to know the bolted fault level and approximate fault clearing time.

VPRIMARY = ?

% Of Normal

Transformer Impedance Measurement

Ifull load current

+

• That percentage is the percent Impedance (%Z)

VPRIMARY =

Normal

Transformer Available Short Circuit Current

IShort Circuit

+

• ASSC = Ifull load current / %Z

100

OH XFMR Size

• Sec. Volt.

FL Amps %Z ASSC 15 120/240 62.5 1.5 4166 25 120/240 104 1.5 6933 50 120/240 208 1.5 13867 100 120/240 417 2 20850 167 120/240 696 2 34800

Other Rules

Equipment Contact

Employees standing on the ground shall not contact the vehicle or mechanical equipment or any of its attachments.

Equipment Grounding

Barricade or insulate to protect employees from hazardous step and touch potentials.

Set-up

• Assess the environment
• do not work alone
• Wear appropriate PPE - NFPA 70E
• Test Instruments - rated for environment

(CAT III or CAT IV)

• Know how to use the equipment

Prohibited Approach Boundary

An approach limit and a distance from an exposed live part within which work is considered the same as making contact with a live part.

Restricted Approach Boundary:

An approach limit at a distance from an exposed live part within which there is an increased risk of shock, due to electrical arc-over combined with inadvertant movement, for personnel working in close proximity to the live parts.

Limited Approach Boundary

An approach limit at distance from an exposed live part within which a shock hazard exists.

Shock Hazard Analysis