Electrical Safety Standard

NFPA 70E

What is NFPA 70E?

NFPA 70E requirements for safe work practices to protect personnel by reducing exposure to major electrical hazards. Originally developed at OSHA's request, NFPA 70E helps companies and employees avoid workplace injuries and fatalities due to shock, electrocution, arc flash, and arc blast, and assists in complying with OSHA 1910 Subpart S and OSHA 1926 Subpart K.

NFPA 70 E STANDARD

What does NFPA 70E address?

Provisions encompass safety -related work practices, safety -

related maintenance requirements, and safety requirements

for special equipment. The Standard includes guidance for

making hazard identification and risk assessments, selecting

appropriate PPE, establishing an electrically safe work

condition, and employee training.

NFPA 70E

•Electrical Shock

•Arc Flash

•Arc Blast

INJURY CATAGORIES

Annually

•30,000 Non-Fatal

•1,000 Fatalities

More than half of these occurred while servicing

energized systems of less than 600 volts.

ELECTRICAL SHOCK:

APPROACH BOUNDARIES - FROM A 70E TABLE, BASED ON

THE VOLTAGE EXPOSURE, NO CALCULATIONS OR STUDIES ARE

REQUIRED.

•

Annually

2000 admitted to burn centers with severe

arc-flash burns.

The majority of hospital admissions due to

electrical accidents are from arc-flash, not

from shocks.

ARC-FLASH:

Extent of Burn Injury:

Temperature

Distance

Time

ARC-FLASH:

Based on:

Available fault current (Temperature)

Distance from the exposed equipment (Distance)

Fault clearing time (Time)

INCIDENT ENERGY :

DISTANCES:

Burns (Non FR clothing can burn onto skin )

Fire (could spread rapidly through building )

Flying objects (often molten metal )

Blast pressure (upwards of 2,000 lbs. / sq.ft)

Sound Blast (noise can reach 140 dB – loud as a gun)

Heat (upwards of 35,000 degrees F)

TYPICAL RESULTS FROM AN ARC FLASH

CLOTHING :

Hazard Risk Clothing Type

(= number of layers)

cal/cm2

0 Non-melting fabric Untreated

cotton fabric weight of at least

4.50oz/yd (1)

N/A

1 FR shirt and FR pants(1) or FR

coveralls.

4

2 Cotton underwear + FR shirt

and FR pants (1or2).

8

3 Cotton underwear + FR shirt

and FR pants+ FR coverall (2

or 3) or 2 FR coveralls.

25

4 Cotton underwear + FR shirt

and FR pants + multilayer flash

suit (3 or more).

40

PPE

Hazard Risk

Category 1

Hazard Risk

Category 2 Hazard Risk

Category 3

Hazard Risk

Category 4 Hazard Risk

Category 0

•Per OSHA Rule and NFPA 70E :

DO NOT WORK ON EQUIPMENT HOT

Equipment must be put in an electrically safe work condition prior to maintenance.

REGULATORY REQUIREMENT

But. . .

•We must test live circuits before repairs are done.

•Troubleshooting work requires that the power be left on.

•Even after Lock Out / Tag Out, we must verify the absence of voltage – “not dead until tested dead”.

•During this process, a worker could be exposed to electrical hazards.

IT’S THE LAW

Because of this there are two exceptions to

“THE RULE”.

1. Where killing power is “infeasible” due

to equipment design or operational

limitations (like voltage testing).

2. Where de-energizing would introduce

increased or additional hazards.

NECESSARY LOOPHOLE

Safety –Related Work Practices

Hazard Analyses for shock and flash

Approach boundaries

Personal Protective Equipment

Training

Safety -Related Maintenance Requirements

Maintaining electrical components, wiring, equipment in a safe

condition

Safety Requirements for Special Equipment

Batteries, Lasers and power electronic equip

Installation Safety Requirements

Truncated version of NEC

Not to be used in lieu of NEC

NFPA 70 E STANDARD

Major Work

Practice

Requirements

Electric arcs produce some of the highest

temperatures known to occur on earth – up to

35,000 degrees Fahrenheit. This is four times the

surface temperature of the sun

All known materials are vaporized at this

temperature. When materials vaporize they expand

in volume (Copper – 67,000 times, Water–1670

times). The air blast can spread molten metal to

great distances with force.

Rapidly expanding gases, extreme pressure and

sound waves, molten metal and metal plasma.

ARC FLASH HAZARDS

REMINDER

Pressure: Blast pressure waves have thrown workers across rooms and knocked them off ladders. Pressure on the chest can be higher than 2000 lbs/ sq. ft. – blows clothing off body.

Clothing can be ignited several feet away. Clothed areas can be burned more severely than exposed skin.

Hearing loss from sound blast. The sound can have a magnitude as high as 140 dB at a distance of 2 feet from the arc.

ARC FLASH HAZARDS

REMINDER

Dust and impurities - Dust and impurities on insulating surfaces can provide a path for current, allowing it to flashover and create arc discharge across the surface.

Corrosion - Corrosion of equipment creates impurities on insulating surfaces. Corrosion also weakens the contact between conductor terminals, increasing the contact resistance through oxidation or other contamination. Heat is generated on the contacts; sparks may be produced; can lead to arcing faults closest ground source.

Condensation - water vapor can drip causing tracking on the surface of insulating materials. Can create a flashover to ground.

Spark discharge – Accidental contact; dropping tools

Overvoltage across narrow gaps

Failure of insulating materials

Improper work procedures

ARC FLASH CAUSES

Don’t have to be “working on” a circuit for an arc flash to occur. Accidental contact is the most common cause of arc flash events.

For a low voltage system (480 V), a 3 to 4 -inch arc can become “stabilized” and persist for an extended period of time if circuit does not operate.

Energy released is a function of system voltage, fault current magnitude and fault duration.

Arcs in enclosures, such as a Motor Control Center (MCC) or panelboard, magnify blast and energy transmitted as the blast is forced to the open side of the enclosure and toward the worker (Arc -in-the-Box).

ARC FLASH IN OUR EQUIPMENT

Small arc – burn to

hand Medium arc – burn to

hand, arm and chest

Severe arc – whole

body burns

Ionization cloud

barely visible Clearly visible ionized

gas

Exploding plasma of

gases and vaporized

metal

ARC FLASH IN A PANELBOARD

480 VOLT ARCING FAULT ENERGY

Arc-In-A-Box from a disconnect

switch

Arcing fault in a panel board

Protects against Contact with energized equipment

Boundary distance based solely on voltage

Use highest voltage level of exposure if more than one voltage present

Boundaries drawn from table in standard – no calcs necessary:

Limited – a safe approach boundary. Only qualified employees and escorted unqualified employees may cross

Restricted – Only qualified employees may cross. When working within this boundary, must use special precautionary techniques and PPE

Prohibited – Only qualified employees protected by insulating materials

APPROACH BOUNDARIES

FLASH BOUNDARIES

Limited Shock Boundary: Qualified or Unqualified Persons*

* Only if accompanied by Qualified Person

Prohibited Shock Boundary: Qualified Persons Only. PPE as

if direct contact with live part

Restricted Shock Boundary: Qualified Persons Only

Note: shock boundaries dependent on system voltage level

Flash Protection Boundary (FPB)

Must wear appropriate PPE

FPB dependent on fault level and time duration. E

qu

ipm

en

t

APPROACH BOUNDARIES

Restricted

Approach

Boundary

Condition

Nominal System

Voltage Range,

Phase to Phase

Exposed

Movable

Conductor

Exposed Fixed

Circuit Part

Includes

Inadvertent

Movement

Adder

Prohibited

Approach

Boundary

1 0 to 50 Not Specified Not Specified Not Specified Not Specified

2 51 to 300 10 ft. 0 in. 3 ft. 6 in. Avoid Contact Avoid Contact

3 301 to 750 10 ft. 0 in. 3 ft. 6 in. 2 ft. 2 in. 0 ft. 1 in.

4 751 to 15kV 10 ft. 0 in. 5 ft. 0 in. 2 ft. 7 in. 0 ft. 7 in.

5 15.1kV to 36kV 10 ft. 0 in. 6 ft. 0 in. 2 ft. 9 in. 0 ft. 10 in.

Limited Approach Boundary

1. “Limited” Boundary - Must be Qualified Person

2. “Restricted” Boundary - Must wear Flash Protection PPE

3. “Prohibited” Boundary - Must wear PPE as if direct contact is being made.

Working with Control Panel door open – in Restricted Approach Boundary

Determines the Flash Protection Boundary Determines the required PPE 2 Methods available: 1. Can use Default Tables in the NFPA 70E Standard

Classifies work tasks in a specific Hazard Risk Category (HRC) Specifies required PPE as a function of HRC

2. Can calculate the incident energy to employees if a fault occurred. Can then specify the required PPE based on predicted hazard level.

FLASH HAZARD ANALYSIS

We compared default tables to calculated values:

Used conservative, but reasonably expected input parameters

Used 2 different calculation models (took highest values)

Found calculated values to be less than default tables

EXAMPLE FROM DEFAULT TABLE

Voltage-rated gloves

Voltage-rated tools

Doubled-layered switching hood and hearing protection

Untreated natural fiber: T-shirt & Long pants

FR Clothing: Long –sleeve shirt, Pants, Coveralls

FR Protective Equipment: Hard hat, safety glasses, leather work

shoes

Page 55, Table 3-3.9.1/ Page 59,Table 3-3.9.2

600 V Class MCC - Work on energized parts including voltage testing

- What is required?

Using Method #1 Flash Hazard Analysis – NFPA

70E Default Tables:

ELECTRICAL PPE – HIGH

HAZARD

PPE SELECTION

FROM 70E TABLE

For Most Service and Maintenance Work Voltage Clothing Gloves Other PPE

Safety Glasses

Hard Hat

Safety Glasses

Class E Hard Hat with 8

Cal. ATPV Face Shield

2300-4160

Volts

Safety Glasses

Class E Hard Hat with 8

Cal. ATPV Face Shield

Class 1 Insulated Rubber

Gloves w/ Leather

Protectors

50 - 240 Volts 100% long-sleeve cotton

shirt and pants

Leather Gloves (Class 00 if

possibility of contact)

240 - 600 Volts 100% long-sleeve cotton

or FR shirt and pants

Class 00 or 0 Insulated

Rubber Gloves w/ Leather

Protectors

FR shirt and pants or FR

Coveralls - 9.4 ounce

Indura Ultra Soft

(minimum)

Synthetic fibers, such as polyester, nylon, acetate, rayon, either alone or in

blends are not permitted – they melt at low temperatures, adhere to the

skin and increase the extent of injury.

For outdoor work, outer layer must be natural fiber or FR

One Major Exception to the 100%

Cotton Rule for 480 Volt work:

When working on (e.g. voltage testing) the line

side terminal of a service disconnect, wear FR

clothing as the outer layer instead of 100%

cotton.

100% COTTON VS. FR CLOTHING

This is due to the uncertainty of available fault

currents and clearing times with on-site distribution

systems; alternate feeds; etc...

Voltage Testing

480 Volt Fused Disconnect Switch

Current-Limiting Fuse

Customized for HVAC Service and Contracting Business:

Work Procedures

Electrical PPE

Protective Clothing

Training

ELECTRICAL SAFETY PROCEDURE

1. Work Procedures: Lockout/Tagout whenever possible – Cardinal Rule

Approach Boundaries - Based on voltage

Use of conductive tools, materials, equipment

Insulated tools and equipment

Test Instruments and equipment

Protective Shielding Equipment

Potable Ladders

Safety Interlocks

Use of GFCIs

ELECTRICAL SAFETY

PROCEDURE

2. Electrical PPE

Required when working within the Limited Approach Boundary

Flash Hazard Analysis dictates what must be worn

Can use NFPA 70E default tables, or

Can perform customized analysis

Includes Hand; Head and Face; Whole Body protection

ELECTRICAL SAFETY

PROCEDURE

ELECTRICAL SAFETY PPE

Rubber Insulated Gloves

8 cal/cm2 Arc Resistant

Face Shield

Flame retardant garments

Basic requirements

1. Must have knowledge of construction and operation of equipment and specific work methods to recognize and avoid electrical hazards while performing work.

2. Must be familiar with the precautionary techniques, PPE, insulating and shielding materials, insulated tools and test equipment.

Specific requirements

1. Able to distinguish exposed energized parts from other parts

2. Able to determine nominal voltage of exposed live parts

3. Approach distances and corresponding voltages in the Standard

4. Determine degree of hazard and appropriate PPE

QUALIFIED PERSON TRAINING

Required by OSHA and NFPA 70E

Training can be either classroom, on-the-job, or a combination. OJT

requires direct supervision by a Qualified Person.

1. Reduce Fault Current and Duration of Arc Flash

Change type of fusing, where appropriate

Faster clearing times

Current-limiting fusing

Manufacture equipment with IP20 (Touch-Safe) components in control panels

Replace breakers with faster operating devices such as fuses

2. Reduce Exposure

Add barriers (installed or portable) eg 1kV plastic rolls

Add distance with different tools; extended probes; etc..

Install external measurement points

FOCUS ON ENGINEERING

AND ADMIN CONTROLS

Use of PPE to Control the Hazard is the Last Resort

1. Which of the following is an insulator of electricity?

Gold

Copper

Sweat

Pure water

TEST

2. Which of the following would increase the amount of current

in a circuit?

Heating up the conductors

Decreasing the voltage

Decreasing the work distance

Decreasing resistance

TEST

3. What makes a short circuit dangerous?

A larger load on the circuit

Little-to-no resistance

Less voltage

Decreased current

TEST

4. What is electrocution?

An electric shock that kills someone

A light shock

An arc flash that injures a worker

Electricity that resides in capacitors

TEST

5. All of the following about arc flash are true except:

Hot temperatures

Loud noises

Bright lights

Low currents

TEST

6. What determines the intensity of an arc flash?

The available current and how long it lasts

The voltage and humidity level

Air pressure and voltage level in the sensors

Energy and fault lines

TEST

7. What must be on all equipment that has an arc flash hazard?

An arc flash warning or danger label

A shock protection sign

A blue arc flash label with a yellow warning triangle

A green arc flash hazard stamp

TEST

8. What normally happens to PPE during an arc flash?

It sounds an alarm

It is destroyed instead of your skin

It burns cleanly and without much heat

It shrinks and fits better

TEST

9. What would a qualified worker look like with Level 4 PPE on?

Someone wearing a space suit

Someone wearing a suit of armor

Someone wearing a scuba diving outfit

Someone getting ready to run outside

TEST

10. What will an arc flash label usually have on it?

Panel destination and source current

PPE level required and flash protection boundary

Surge protection level and secondary relay boundary

PC3 data on voltage and wattage

TEST

Thank You – Questions??