Common Electrical Hazards in the Workplace Including Arc Flash.

Common Electrical Hazards in the Workplace Including

Arc Flash

This material was produced under grant number SH-16615-07-60-F-12 from the Occupational Safety and Health Administration, U.S. Department of Labor. It does not necessarily reflect the views or policies of the U.S. Department of Labor, nor does mention of trade names, commercial products, or organizations imply endorsement by the U.S. Government.

This material was produced by the Workplace Safety Awareness Council, a 501(c)(3) not-for-profit organization dedicated to safety in the workplace.For further information about the council or upcoming safety related training, please visit our website at www.wpsac.org or call us at (863) 537-4053.

Introduction

In February 1972, OSHA incorporated the 1971 edition of the National Fire Protection Association's (NFPA) National Electrical Code (NEC), NFPA 70-1971

On January 16, 1981, OSHA revised its Electrical standard with Part I of National Fire Protection Association's (NFPA) 70E - 1979

On August 13, 2007, OSHA revised its Electrical standard to reference National Fire Protection Association's (NFPA) 70E - 2000

What’s New

Common hazards when working with energized electrical equipment include:

• Electric Shock / Burns

• Blast

• Arc Flash

Fast Fact: It doesn’t take much for human skin to burn – in fact an exposure of 203 F for just one-tenth of a second (6 cycles) is enough to cause a third degree burn!

Common Hazards

Receptacles installed in bathrooms or on rooftops shall have ground-fault circuit-interrupter protection

for personnel.

GFCI Protection1910.304(b)(3)(i)

Receptacle outlets (including cord sets) that are not part of the permanent wiring of the building shall have ground-fault circuit-interrupter protection for personnel.

Note: A cord connector on an extension cord set is considered to be a receptacle outlet if the cord set is used for temporary electric power.

GFCI Protection1910.304(b)(3)(ii)(A)

Flexible Cords – Permitted Use1910.305(g)(1)(ii)(A)-(L)

• Pendants;

• Wiring of fixtures;

• Connection of portable lamps or appliances;

• Portable and mobile signs;

• Elevator cables;

• Wiring of cranes and hoists;

• Appliances to permit removal for maintenance and repair

Pendant, orFixture Wiring

Portable lamps,tools or appliances

Stationary equipment to facilitate interchange

Flexible Cords – Permitted Use1910.305(g)(1)(ii)(A)-(L)

• Connection of stationary equipment to facilitate their frequent interchange;

• Prevention of the transmission of noise or vibration;

• Appliances where the fastening means and mechanical connections are designed to permit removal for maintenance and repair;

• Data processing cables approved as a part of the data processing system;

• Connection of moving parts; and

• Temporary wiring as permitted in paragraph (a)(2) of this section.

Prohibited Uses of Flexible Cords1910.305(g)(1)(iv)(A)-(F)

Substitute for fixed wiring

Run through walls, ceilings, floors, doors, or windows

Concealed behind or attached to building surfaces

• As a substitute for the fixed wiring of a structure;

• Where run through holes in walls, ceilings, or floors;

• Where run through doorways, windows, or similar openings;

• Where attached to building surfaces;

• Where concealed behind building walls, ceilings, or floors; or

• Where installed in raceways, except as otherwise permitted in this subpart.

Extension cords must be visually inspected before each use on any shift. Examine the cord for

• Missing grounding pin

• Damaged other jacket (tear in insulation)

• Possible internal damage (pinched cord)

Flexible Cords1910.304(b)(3)(ii)(C)(3)

Ensure that grounding pin on extension cords is in place and operable

Grounding Pin1910.304(b)(3)(ii)(C)(4)(i) – (iii)

All equipment grounding conductors shall be tested for continuity: • Before first use• Before return to service (repairs)• Before use after an incident that may have caused damaged and• Intervals not to exceed three (3) months

Splices1910.305(g)(2)(ii)

Flexible cords may be used only in continuous lengths without splice or tap.

Note: Black electrical tape does not provide suitable insulation and is not acceptable

• Durably marked as to type, side, and number of conductors

• Strain relief must be provided

Flexible Cords1910.305(g)(2)(i)

Inadequate Wiring Hazards

Using a portable tool with an extension cord that has a wire too small for the tool:

• The tool will draw more current than the cord can handle, causing overheating and a possible fire without tripping the circuit breaker

• The circuit breaker could be the right size for the circuit but not for the smaller-wire extension cord

Wire Gauge

WIRE

Wire gauge measures wires ranging in size from number 36 to 0 American wire gauge (AWG)

Minimum Depth of Working Space1910.303(g)(1)(i)(A) Table S-1

Nominal voltage to ground

Minimum clear distance for condition2 3

Condition A Condition B

Condition C

m ft m ft m ft

0-150151-600

10.910.9

13.013.0

10.91.0

13.03.5

0.91.2

3.04.0

Condition A -- Exposed live parts on one side and no live or grounded parts on the other side

Condition B -- Exposed live parts on one side and grounded parts on the other side

Condition C -- Exposed live parts on both sides

Overcurrent devices or disconnecting devices:• shall be legibly marked to indicate its purpose• shall be of sufficient durability to withstand the

environment involved.

Labeling of Breakers

1910.303(f)(2) –(3)

• Conductors entering shall be protected• Openings shall be effectively closed• Cable is fastened within 12” from box or

raceway

Cabinets, Boxes and Fittings1910.305(b)(1)(i)

In completed installations, each outlet box shall have a cover, faceplate, or fixture canopy.

Cabinets, Boxes and Fittings1910.305(b)(2)(i)

Arc Flash Event

A dangerous release of energy created by an electrical fault

Release will contain: Thermal energy Acoustical energy Pressure wave Debris

Arc Flash Intensity

Variables that effect the size and energy of an electric arc flash:

Amperage Voltage Arc Gap Closure time Distance away from arc 3 phase v single phase Confined space

Arc Energy Basics

Exposure energy expressed in cal/cm2

½ to 1 cal/cm2 = hottest part of lighter in 1 sec

1-2 calorie exposure will cause second degree burn on

human skin

Typical non-FR workwear can ignite @4-5cals

Arcs typically release 5-30 cals - energies of 30-60 cals are

not uncommon

Arc Flash Events

Can reach 35,000 F Fatal burns >10 feet Majority of hospital

admissions are arc flash burns, not shock

30,000 arcs and 7000 burn injuries per year

Over 2000 people admitted to burn centers yearly with severe arc flash burns

What Is Important

Three factors are critical when discussing burns:

Extent (% of body burned – related to survivability)

Severity (linked to quality of life) Location (linked to quality of life)

What Is a Burn?

A chemical process which progressively injures skin; severity relates to depth

1st : redness, pain – not permanent

2nd: blistering – skin will regenerate

3rd: total skin depth destroyed. Will not regenerate – requires grafting

4th : Underlying muscle damaged

Burn Survival

Burn percentage, more than severity, predicts survival because skin is infection barrier

2nd and 3rd degree break skin, providing an infection pathway

Most hospital deaths 2-4 weeks post-exposure are infection (gram-neg staph)

Burn Survival Factors

Odds of survival fall with total % burn Odds of survival fall precipitously above 50%

burn Odds of survival fall as age increases

Burn Injury

Burn treatment requires approx. 1.5 days hospitalization per % burn

Average hospitalization is 19 days, at costs exceeding $18,000/day

Total hospitalization cost typically ranges from $200,000 to $750,000, with many over $1,000,000 USD

The most effective and fool-proof way to eliminate the risk of electrical shock or arc flash is to simply deenergize the equipment. . .

Deenergized Equipment

A lock and a tag shall be placed on each disconnecting means used to deenergize circuits and equipment on which work is to be performed.

Lockout / Tagout

Note: Electric equipment that have been deenergized but have not been locked out or tagged shall be treated as energized.

OSHA has also made allowances for not deenergizing electrical equipment when it would increase current hazards or create additional hazards, for example: • interruption of life support equipment, • deactivation of emergency alarm systems, • shutdown of hazardous location ventilation equipment, • removal of illumination for an area.

Working live is also allowable due to infeasibility of deenergization (i.e. testing of electric circuits)

Working Live

Employer must develop and enforce safety-related work practices to prevent electric shock or other injuries resulting from either direct or indirect electrical contacts.

These safety related work practices could include:

• Energized Electrical Work Permit• Pre-work Job Briefing• Personal Protective Equipment• Insulated Tools• Written Safety Program• Qualified Person Training• Flash Hazard Labeling

Hot Work Requirements

A number of “approach boundaries” exist and both qualified and non-qualified persons must understand these definitions.

Definitions

Flash Protection Boundary (outer boundary): The flash boundary is the farthest established boundary from the energy source. If an arc flash occurred, this boundary is where an employee would be exposed to a curable second degree burn (1.2 calories/cm2)

Flash Protection Boundary

Limited Approach BoundaryLimited Approach: An approach limit at a distance from an exposed live part where a shock hazard exists.

“Working Near Live Parts”

Occurs when any activity inside the Limited Approach Boundary is undertaken

Restricted Approach: An approach limit at a distance from an exposed live part which there is an increased risk of shock.

Restricted Approach Boundary

Prohibited Approach (inner boundary): A distance from an exposed part which is considered the same as making contact with the live part.

Prohibited Approach Boundary

“Working On Live Parts”Occurs when coming in contact with live parts, including test equipment, body, PPE, tools etc. . .

Flash Protection Labeling

Arc Flash Hazard labeling must be posted which identifies:

• Approach boundaries• PPE required

NFPA Tables: Refer to NFPA 70E – 2000 Table 3-3.9.1 or Table 130.7(C)99)(a) NFPA 70E – 2004.

Pro: Easiest and quickest method

Con: Provides the least amount of accuracy. Limited tasks are covered in tables

How to Determine Boundaries

Formula Method: NFPA 70 E and IEEE Standard 1584 provides formulas that can be used to accurately determine the approach boundaries.

Pro: More accurate and all inclusive than NFPA tables

Con: Is time consuming, requires an engineer level of expertise and is subject to human error.


Approach Calculator: IEEE and others have provided a spreadsheet based calculator to assist in determining approach boundaries.

Pro: Quicker than formula method

Con: Still requires detailed information about the equipment and circuit often requiring the use of an electrical engineer.


Software: There exists on the market various software products that can simplify and expedite the approach boundary calculations.

Pro: Creates one-line diagrams and arc flash labels based on data entered

Con: Cost and equipment / circuit knowledge is still required often requiring an engineer.


Qualified person: One who has received training in and has demonstrated skills and knowledge in the construction and operation of electric equipment and installations and the hazards involved.

Qualified Persons

Qualified Person Training1910.332(b)(3)(i) – (iii)

Qualified persons shall at a minimum be trained in the following areas:

•The skills to distinguish exposed live parts from other parts of electric equipment.

•The skills to determine the nominal voltage of exposed live parts, and

•The clearance distances specified in 1910.333(c) and the corresponding voltages to which the qualified person will be exposed.

Common Electrical Hazards in the Workplace Including Arc Flash.

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