Arcflash.ppt

ARC FLASH AND OTHER ELECTRICAL SAFETY HAZARDS

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Electrical Safety Hazards 

Primary hazards: – Electric shock – Exposure to Arc-Flash

– Exposure to Arc-Blast – Exposure to excessive light and sound energies •

Secondary hazards: ‒ burns, release of toxic gases, molten metal, airborne debris and shrapnel.

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Electric Shock When personnel come in contact with energized conductors with current flowing through their skin, muscles and vital organ. Severity of the shock depends on: Path of current through the body Amount of current flowing through the body Length of time the body is in the circuit LOW VOLTAGE DOES NOT MEAN LOW

HAZARD! 3

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3 Basic Pathways Electric Current Travels Through The Body

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1.

Touch Potential (hand/hand path)

2.

Step Potential (foot/foot path)

3.

Touch/Step Potential (hand/foot path)

What is an Arc Flash Hazard? “. . . a dangerous condition associated with the release of energy caused by an electric arc.”

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35,000 degrees Fahrenheit (F), or 4 times the temperature of the sun’s surface.

What is an Electric Arc? 

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An electric arc is a short circuit through the air.

Arc Flash Hazards -- Construction Safety Association of Ontario

PB/RH -- March 3, 2009

Characteristics of an Electric Arc

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An electric arc will oscillate and escalate if not constrained.

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A single-phase electric arc can engulf a second or third conductor in only two cycles.

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An electric arc’s current propels the arc away from the power source.

What Causes Arc Flash? 

Dust, impurities, corrosion, condensation, animals

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Spark discharge from: – Accidental touching – Dropping tools

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Over-voltages across narrow gaps

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Failure of insulating materials

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Equipment failure

What is Arc Blast? 1. The flash causes an explosive expansion of air and metal. – For example: When copper vapourizes it expands by a factor of 67,000.

2. The blast produces dangerous: – Pressure waves – Sound waves – Molten steel and shrapnel. 10

Arc Flash Events Electric arc

Arc flash

Arc blast

Compliments of Salisbury Electrical Safety L.L.C.

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Arc Flash Injuries  Electric shock  Severe burns

 Blindness  Blast injuries – Shrapnel wounds

– Lung blast injuries – Ruptured eardrums – Pressure wave injuries 12

Electric Shock Injury – Burn

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Severe Burns from Arc Flash

Arc flash Sun 14

up to 35,000°F 9,900°F

Blindness 

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Flash of light is so intense it can damage vision.

Shrapnel Wounds

Material and molten metal can hit the body at over 700 miles per hour. 16

Blast Lung Injury (BLI) Arc blast can cause inhalation injuries. For example: – Inhaling high temperature copper vapour. – More than 100 toxic substances can be found in the fumes.

BLI + Burns = Greater chance of death 17

Arc-Flash Metrics 

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In order to determine the potential effects of an ArcFlash, we need to understand some basic terms. An Arc-Flash produces intense heat at the point of the arc. Heat energy is measured in units such as BTU’s, joules, and calories.

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Severity Factors

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Severity Factors Current-limiting devices such as Littelfuse type LLSRK_ID or JTD_ID fuses will open in . AC cycle (8.33 milliseconds) or less under short circuit conditions. Studies have shown that many existing molded case circuit breakers take up to 6 AC cycles (100 milliseconds) or longer to open under short circuit conditions.

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Hearing Damage

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Arc blast at 2 feet

145 decibels

Jet engine at 200 feet

132 decibels

Pain threshold

130 decibels

Pressure Wave Injuries Arc blast can throw a worker: – Off a ladder – Into nearby walls or equipment.  2000 lbs/ft2 pressure on the body can cause: – Concussion – Collapsed lungs – Other internal injuries

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Common Causes Faulty electrical equipment can also produce a hazard while being operated. Electrical safety hazards such as exposure to shock and Arc-Flash can be caused by: 1.Carelessness 2.Worn or broken conductor insulation 3.Exposed live parts 4.Loose wire connections 5.Improperly maintained switches and circuit breakers 6.Obstructed disconnect panels 7.Water or liquid near electrical equipment 8.High voltage cables 9.Static electricity 10.Damaged tools and equipment

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The severity and causes of electrical hazards are varied, but the best protection is to deenergize equipment before working on it.