View
221
Download
0
Category
Preview:
Citation preview
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??
Recommended