pres09 - electrical hazards 3-02

Suggestion on How to Use

• Industry Trainers are encouraged to use this material in their sessions

• Download both the PowerPoint file (.ppt) and script file (.pdf)

• Print the script file (.pdf) and read the script as you view the PowerPoint presentation in the “Slide Show” view. In this way you see the slides in large format and have animation (if there is any)

• Must have PowerPoint and Adobe Reader application software on your system.

Electrical HazardsElectrical Hazards

Safety BASICsTM

Basic electrical theory

I = V / Z•What happens with shock?

•What happens when have fault?

•What happens with larger transformers

or low impedance transformers?

•What is difference between short-circuit

and arcing fault?

Who’s Responsible for Safety?

The “Employer” is responsible forOSHA requirements Electrical Safety ProgramSafety Policies and ProceduresSafety Training

The “Employee” is responsible forImplementing procedures

The “Owner” is inherently responsible forContractors on site

Safety BASICsTM

Safety BASICsTM

What are the hazards as you approach

electrical equipment to perform work?

Safety BASICsTM

Are you thinking that the National Electrical

Code and UL Standards are sufficient to protect a

person working on or near “live” equipment?

NEMAUnderwriters Lab.IEC (Electrotechnical

committee)

Product StandardsNational Electrical

ManufacturersAssociation

Safety BASICsTM

Example of UL 508 – Testing only w/ door closed

National Electrical Code®

National Electrical Safety

Code®

National Electrical

Contractors Association

IEC (International -60364)

Installation Standards

Safety BASICsTM

National Electrical

Code

1997ANSI/NFPA 70

• Requirements for safe work practices

• Addresses hazards:– Shock– Arc Flash

• Requirements forshock and arc flashboundaries

• Requirementspersonal protectiveequipment

NFPA 70E

Qualified electrical workers shall not be asked to work on equipment that is “hot” or “live” except for two demonstrable reasons :

1. Deenergizing introduces additional or increased hazards

such as cutting ventilation to a hazardous location

or2. Infeasible due to equipment design or operational limitations

such as doing voltage testing for diagnostics

NFPA 70E: Safety in Workplace

OSHA 1910.333 (a) (1) & NFPA 70E 2-1.1.1

• Shock

• Arc-Flash

– Heat

– Fire

• Arc-Blast

– Pressure

– Shrapnel

– Sound

Example of an arcing fault

Electrical Hazards

Safety BASICsTM

Safety-Related Work Practices1910.333 Selection & use of work practices

(a) General. Safety-related work practices shall be employed to prevent electric shock or other injuries resulting from either direct or indirect electrical contact, when work is performed near or on equipment or circuits which are or may be energized. The specific safety-related work practices shall be consistent with the nature and extent of the associated electrical hazards

Safety-Related Work Practices1910.335 Safe guards for personnel protection

(a) (2) (B) (ii) Protective shields, protective barriers, or insulating materials shall be used to protect each employee from shock, burns, or other electrically related injuries while that employee is working near exposed energized parts which might be accidentally contacted or where dangerous electric heating or arcing might occur.

Over 30,000 non-fatal electrical shock accidents occur each year

Over 600 people die from electrocution each year

Electrocution remains the fourth (4th) highest cause of industrial fatalities

Most injuries and deaths could be avoided

Shock

Safety BASICsTM

Safety BASICsShock (Resistance Table)

TM

Safety BASICs TM

Shock

(A) Touch Potential (B) Step Potential (C and D) Touch / Step Potential

Current passing through the heart and lungs is the most serious

Safety BASICs

Shock

Human body resistance (hand to hand) across the body is about 1000

Ohms Law: I = V / R (Amps.)I = 480 volts / 1000 = 0.48 amps (480 mA)

The National Electrical Code® considers 5 mA to be the safe upper limit for children and adults.

TM

mA Affect on Person

0.5 - 3 - Tingling sensations

3 - 10 - Muscle contractions and pain

10 - 40 - “Let-go” threshold

30 - 75 - Respiratory paralysis

100 - 200 - Ventricular fibrillation

200 - 500 - Heart clamps tight

1500 + - Tissue and Organs start to burn

Safety BASICs ShockCurrent, Not Voltage causes Electric Shock

TM

Note: Reaction will vary with frequency and time of exposure

As much as 80% of all electrical injuries are burns resulting from an arc-flash and ignition of flammable clothing

Arc temperature can reach 35,000°F - this is four times hotter than the surface of the sun

Fatal burns can occur at distances over 10 ft.Over 2000 people are admitted into burn

centers each year with severe electrical burns

Arc-Flash

Safety BASICsTM

Electrical Arc

Copper Vapor:Solid to VaporExpands by67,000 times

Intense Light

Hot Air-Rapid Expansion

35,000 °F

Pressure Waves

Sound Waves

Molten Metal

Shrapnel

Personnel Hazards Associated with Arc Flash

Heat – Burns & Ignition of Materials Arc temperature of 35,000 ºF Molten metal, copper vapor, heated air

Second Degree Burn Threshold :

80 ºC / 175 ºF (0.1 sec), 2nd degree burn

Third Degree Burn Threshold:

96 ºC / 205 ºF (0.1 sec), 3rd degree burn

Intense Light

Damage eyes – cataracts

Personnel Hazards Associated with Arc Flash

Pressures From Expansion of Metals & Air

Eardrum Rupture Threshold

720 lbs/ft2

Lung Damage - Threshold

1728 - 2160 lbs/ft2

Shrapnel

Flung Across Room or From Ladder/Bucket

IEEE/PCIC & NFPA 70EArc Flash Hazard

• UsersUsers

• ConsultantsConsultants

• ManufacturersManufacturers

• Medical ExpertsMedical Experts

IEEE/PCICIEEE/PCIC

Arc Flash Hazard

• Following are some of the tests run by IEEE Ad Hoc Safety Committee

•All of the devices used for this testing were applied according to their listed ratings

Setup Area For TestsSetup Area For Tests #1 Through #4#1 Through #4

Close-up of Test AreaClose-up of Test AreaA

rc-F

lash

22.6 KA SymmetricalAvailable Fault Current

@ 480V, 3 Phase

Fault Initiated on Line Side of 30AFuse

30A RK-1Current Limiting Fuse

Size 1 Starter

Test No. 46 cycle STD

640A OCPDNon Current Limitingwith Short Time Delay

Set @ 6 cycle opening

TEST 4

TEST 4

TEST 4

TEST 4

TEST 4

TEST 4

TEST 4

22.6 KA SymmetricalAvailable Fault Current

@ 480V, 3 Phase

Fault Initiated on Line Side of 30AFuse

30A RK-1Current Limiting Fuse

Size 1 Starter

640A OCPDNon Current Limitingwith Short Time Delay

Results:Test No. 4

Opened in six cyclesNo CurrentLimitation

> 225 C /437 F> 225 C /

437 F

Results: Test No.4

T1

T2

P1

T3

Sound

141.5 db @ 2 ft.

50 C / 122 F

>2160 lbs/sq.ft

> Indicates Meter Pegged

22.6 KA SymmetricalAvailable Fault Current

@ 480V, 3 Phase

Fault Initiated on Line Side of 30AFuse

30A RK-1Current Limiting Fuse

Size 1 Starter

Test No. 3

601A.Class LCurrent Limiting Fuse

TEST 3

TEST 3

TEST 3

TEST 3

22.6 KA SymmetricalAvailable Fault Current

@ 480V, 3 Phase

Fault Initiated on Line Side of 30AFuse

30A RK-1Current Limiting Fuse

Size 1 Starter

601A.Class LCurrent Limiting Fuse

Results:Test No. 3

Cleared in 1/4 Cycle

Current-Limitation Reduced Energy

> 175 C/347 F

Results: Test No.3

T1

T2

P1

Sound

133 db @ 2 ft.

62 C / 143.6 F

504 lbs/sq.ft.

T3(No Change

From Ambient)

> Indicates Meter Pegged

X

22.6 KA SymmetricalAvailable Fault Current

@ 480V, 3 Phase

30A RK-1Current Limiting Fuse

Size 1 Starter

Test No. 1

601A.Class LCurrent LimitingFuse

Fault Initiated on Load Side of 30AFuse

TEST 1

TEST 1 Close-up

TEST 1 Close-up

TEST 1 Close-up

TEST 1 Close-up

TEST 1 Close-up

22.6 KA SymmetricalAvailable Fault Current

@ 480V, 3 Phase

30A RK-1Current Limiting Fuse

Size 1 Starter

Results:Test No. 1

601A.Class LCurrent Limiting Fuse

Class L FuseDid Not Open,System wasSelectivelyCoordinated

30 A RK-1 FuseCleared Fault inLess Than 1/4 Cycle

Fault Initiated on Load Side of 30AFuse

Results: Test No.1

T1

T2

P1

T3

Sound(No Change From Ambient)

(No Change From Ambient)

(No Change From Ambient)

(No Change From Ambient)

(No Change From Ambient)

Safety BASICsTM

Current-Limitation - Arc-Energy Reduction

Consider that:• Magnetic Force -- varies with the square of the Peak Current• Thermal Energy -- varies with the square of the RMS Current

Non-Current Limiting Current Limiting

Available Fault Current Reduced Fault Current

Safety BASICsTM

Current-Limitation: Arc-Energy Reduction

Non-Current Limiting

Reduced Fault Current

via Current-Limitation

Test 1

Test 4

Test 3

Safety BASICsTM

What are the hazards as you What are the hazards as you approachapproach

electrical equipment to electrical equipment to perform work?perform work?

• Shock

• Arc Flash

• Arc Blast

Safety Basics Video (VHS)Safety Basics Video (VHS)