Arc Flash Hazards in Metering

Transcription

1 NWEMS Arc Flash Hazards in Metering 9/2018 Seattle Arc Flash Hazards P. Connolly PSE (e Hazard slides) Order of the Day» Electrical/Arc Flash Facts» Arc Flash Hazards & Protection Strategies Arc Flash: Hazards & Protection Strategies Personal Protective Equipment» Hazard Assessment» Safety Related Work Practices 2 Slide 1

2 Electrical Workplace Safety Why Arc Flash Protection? 3 - Electrical Workplace Safety 4 Slide 2

3 FR Flash Coat/leggings with Cotton Jeans ~80 cal/cm cal/cm 2 in crotch area; some from jean ignition Mannequin at 12 from arc source ~80 cal/cm 2 100% Cotton Ignition ( ) 6 Slide 3

4 By the Numbers Annually, U.S. Averages +1,200 2,000 Top Occupations Workers admitted to burn centers/ hospitals for fire/flame and electrical burns* electrical injuries requiring days away from work 31% Installation, Maintenance, Repair 25% Construction, Excavation * Based on NBR 2016 Report data ** , bls.gov In last 10 years +1,800 ** Workplace fatalities from exposure to electricity Every other day 1 Worker is electrocuted Study Finding: Arc Plays a Major Role in Electrical Injuries Results of an electrical industry 10 year study of 120,000 workers: 125 electrical injuries per year 77% arc injuries 21% permanent disabilities 2.4% fatalities Based on ED France data, IEEE Presentation from M. Capelli-Schellpfeffer, M.D. Electrical Trauma Research Program (University of Chicago) Slide 4

5 Electrical Workplace Safety Electrical Hazards & Protection Strategies Arc Flash What is it Types of Hazards Protection Strategies 9 - What are the Electrical Hazards? Arc flash Arc blast (Electrical shock) Associated hazards: Falls Smoke inhalation Confined space entry 10 Slide 5

6 What Is an Arc Flash? Arc Flash: an electrical breakdown of a gas which produces an ongoing plasma discharge, resulting from a current flowing through normally nonconductive media such as air Wikipedia Plasma temperature can reach 10,000 F Fatal burns can occur at distances over 10 feet Over half of all arc flashes occur at 277 volts Infrared Radiation from an Arc Event /480 Self-Contained Meter 20 cal/cm 2 electric arc in open air 12 inches away from worker Slide 6

7 Arc in a Box 3. Arc-in-a-box energy can be two to twelve times greater when the arc is in an enclosure situation. 13 Watch the disconnect door. Tracking Arc 4. Tracking arcs are arcs which conduct through skin and pop out between skin and clothing. Can cause ignition of clothing underneath FR in an electrical contact Usually occurs at higher voltages 14 Slide 7

8 Interacting with Equipment An arc flash hazard is a state that occurs when exposed parts are present OR when you are interacting with a piece of equipment in such a way that you could cause an arc flash.» Opening or closing doors or removing a cover» Operating switches or circuit breakers» Using tools or test equipment 15 What Causes an Arc Blast? Pressure wave caused by the rapid heating of surrounding air A blast:» Strips outer shell electron of air and metal; super heated air becomes plasma accounting for heat and blast Vaporized metal accounts for little of the blast.» Creates a shock wave capable of exploding circuit parts 16 Slide 8

9 Arc Blast Pressure/Sound Waves 40 50kA can:» Produce a 1,000 lbs. of pressure across the body which can throw a person several feet» Create a 165 db sound wave ka, 10 cycle <6 cal/cm² Watch disconnect door & mannequin. Common Places for a Fault Meter Bases and Meter Banks Higher fault currents of secondary side. Longer clearing times if phase to phase. Shorter clearing times if phase to ground since the lower voltages tend to self extinguish when they go through zero. 18 Meter de-energized but clip fell into energized EXCHANGING meter EXPERTISE SINCE below Slide 9

10 Common Places for a Fault 19 Meter Bases and Meter Banks PSE 10/8/12. On new 480 meter-base, neutral wire-tied to B-Phase - 5/12 Common Places for a Fault Low Voltage Testing»Higher fault currents of secondary side.»longer clearing times if phase to phase.»phase to ground often clears ½ cycle self extinguishing at zero.»drawing arc phase to phase.»common mistake: testing on primary voltage (i.e. 7200V to 13800V with a low voltage meter). 20 Two workers exposed Slide 10

11 19 Years Ago at Baker Arc Flash Boundary (AFB): determined distance arc energy could be projected from the source AFB assumes exposure to 2 cal/cm 2.in. 22 Slide 11

12 Minimum Approach Distance (MAD) & Arc Flash Boundary (AFB) 23 AFB MAD What Work Practices Protect You from Arc Flash Injuries? Creating an electrically safe work condition Arc resistant equipment Arc Flash Boundary (use remotes or live line tools) Arc Rated PPE Automation 24 Slide 12

13 Current OSHA (l)(6)(iii) The employer shall ensure that each employee who is exposed to the hazards of flames or electric arcs does not wear clothing that, when exposed to flames or electric arcs, could increase the extent of injury that would be sustained by the employee. 25 What is Arc Rating/ATPV?» ATPV Arc Thermal Protection Value» Maximum heat energy resistance of material» Represented or shown as cal/cm 2*» FR Flame Resistant» Not all FR is Arc Rated» NEWER terms: Arc Rated or PPE Level *cal/cm 2 =The measurement of heat transferred to a person s skin from an arc flash. Slide 13

14 The Right Stuff Makes a Difference 27 Probability of Survival 25% Body Burn 50% Body Burn 75% Body Burn 100 Chance of Survival, % Arc Exposure w/arc rated clothing Shirt Burns Shirt & Pant Burns Age Range, Years 28 Source: American Burn Association ( Study) Slide 14

15 Florida 480V Accident 29 Use Hard Hats & Safety Glasses 50% Probability of Specific Class E Hard Hat Melting = 48 cal/cm² 30 50% Probability of Safety Glasses Melting = 55 cal/cm² Slide 15

16 Hearing Protection Ear Plug Type Probability of Ignition Dual design 10% at 10.7 cal/cm² Yellow foam >50 cal/cm² (does melt) Red foam 10% at 6.7 cal/cm ² Silicone >50 cal/cm² (no melting) 31 Balaclava and shield WITH Safety Glasses Prevented burns in ALL conditions 32 Slide 16

17 The Right PPE is Vital Fall Protection Tested to 40 cal. FR Lanyard is also required 33 Arc Flash PPE Protection Principles» Layering Outer layers Under layers (arc rated or non melting)» Coverage» Fit» Maintenance of equipment Laundering Follow manufacturer s instructions No chlorine bleach No fabric softener Inspecting for tears and frays 34 Slide 17

18 Not Using Arc Rated Underwear?» Cotton May use for under layers when no break open risk Is an ignition risk in tracking arc» Wool» Leather» Silk Arc rated options are available. 35 Arc Hazard Assessment» An engineering study shall be conducted to determine the effective arc rating requirement on clothing. If the exposure is greater than 2 cal/cm² (2 nd degree burn): employer shall require employees to wear clothing that has an effective arc rating not less than the anticipated level of arc energy. All systems including secondary voltage, must be included in the arc hazard assessment 36 NESC 410.A.3 Slide 18

19 Hazard Risk Categories (HRC) * * Required minimum Arc Rating of PPE De-energized lines/equip when practical Energized work is prohibited above HRC 4! Hazard Risk Category (HRC) PPE HRC: 0 Arc Rating: (cal/cm 2 ) FR Shirt & Pants or FR Coveralls Hard Hat Safety Glasses Leather Gloves & Boots NFPA has eliminated HRC-0 category Slide 19

20 Hazard Risk Category (HRC) PPE HRC: 1 Arc Rating: (cal/cm 2 ) FR Shirt & Pants or FR Coveralls Hard Hat Safety Glasses Leather Gloves & Boots Ear Plugs (optional) Hazard Risk Category (HRC) PPE HRC: 2 Arc Rating: (cal/cm 2 ) FR Shirt & Pants or FR Coveralls Hard Hat Safety Glasses Leather Gloves & Boots Ear Plugs (as needed) Arc-rated Face Shield PSE FR clothing = 8 (cal/cm 2 ) min Slide 20

21 Hazard Risk Category (HRC) PPE HRC: 3 Arc Rating: (cal/cm 2 ) FR Shirt & Pants plus FR Coveralls Hard Hat Safety Glasses Leather Gloves & Boots Ear Plugs (as needed) Arc-rated Face Shield plus Balaclava Hazard Risk Category (HRC) PPE HRC: 4 Arc Rating: (cal/cm 2 ) FR Shirt & Pants plus Flash Suit Hard Hat Safety Glasses Leather Gloves & Boots Ear Plugs (as needed) Flash Hood Note: There are currently no HRC 4 tasks in Electric Ops Slide 21

22 Protective Clothing after a 480v Arc Flash 43 Arc Rated PPE Does It Really Work? Sometimes. The only thing between you and this is PPE. 44 Slide 22

23 480 Self Contained Meter 3/15/ Self Contained Meter 3/15/18 Slide 23

24 480 Self Contained Meter 3/15/18 PPE is the Last Line of Defense Arc hazards can be reduced by: De energizing equipment Modifying equipment to reduce arc potential Modify protection schemes to reduce arc energy Replace equipment with safer designs Changing work rules to reduce or eliminate risk 48 Slide 24

25 Electrical Workplace Safety Hazard Assessment Arc Energy Theory/ Calculations Analysis Labeling 49 - Hazard/Risk Analysis Musts:» Establish shock protection boundary» Establish arc flash boundary» Select appropriate PPE» NESC Task tables 50 Slide 25

26 Arc Flash Hazard Analysis» System Voltage» Fault Current» Clearing Time» Arc Gap» Working Distance Equip Labels and Signs Remember. You are responsible for your safety. 52 Slide 26

27 Safety Related Work Practices Common Labels 53 NFPA 70E (C) Task Tables Meter 54 Slide 27

28 Think Safety Work Safely» Your face matters, Protect it.» Protect all of you. 55 Slide 28