This document summarizes a practical arc flash risk assessment strategy conducted on 174 high and low voltage switchboards at a mining site. The assessment included a physical condition assessment to determine the likelihood of arc faults occurring, and an arc flash evaluation to determine the consequences of arc faults. The results were combined into a risk matrix to prioritize upgrade and mitigation efforts. The assessment found 37 switchboards requiring replacement within 2 years and 58 requiring replacement within 5 years based on their poor condition and increased risk.

1. A Practical Arc Flash Risk
Assessment Strategy
8th August 2012

2. Part 1: A Practical Arc Flash
Risk Assessment Strategy

3. Overview
 1. Why Assess the Risk ?
 2.Condition Assessment Overview
 3. Assessment Tool Features
 4. Risk Assessment Outcomes

4. 1. Why Assess the Risk ?

6. 1. Why Assess the Risk ?
Where should I spend the money and effort ?
 PPE quick and easy but may not be effective for all faults
 New switchboards effective but costly, time consuming to
install
 Remote switching good but racking/charging still a danger
 Protection mods improve detection but degrade security
supply
 Protection mods still require fast and capable circuit breakers

7. 1. Why Assess the Risk ?
 Arc faults present significant danger to man and machine
 OHS Regulations require risk assessment
 Aust Stds require arc flash consideration in design
 Available procedures target consequence and PPE

8. 1. Why Assess the Risk ?
 Any assessment of risk must include both ‘likelihood’ and
‘consequence’ factors
 Arc Flash Evaluation provides a measure for ‘consequence’ of
arcing faults
 A physical condition assessment of the switchgear can
provide a measure of ‘likelihood’ of arcing faults occurring
 Combining arc flash evaluation and physical condition
assessment can help determine overall risk.

9. 1. Why Assess the Risk ?
Arc Flash Exposure Consequence
Arc Flash
Probability Minor Moderate Major Severe Critical
Moderate High Extreme Extreme Extreme
Most Likely
Moderate High High Extreme Extreme
More Likely
Low Moderate High High Extreme
Likely
Low Low Moderate High High
Unlikely
Low Low Low Moderate Moderate
Very Unlikely

10. 2. Condition Assessment Overview
SKM currently use a simple methodology for
condition assessment of multiple SwBds:
 visual inspection of the switchboard and environment,
 Review of operating history, maintenance records &
drawings
 Interview of responsible site personnel
Allows multiple SwBds to be assessed and
ranked quickly.

11. 2. Condition Assessment Overview
Approx 50 criteria elements evaluated for each swbd
installation.
This is a Fault Exposure Likelihood assessment tool,
 NOT a maintenance tool
 Does NOT use statistical methods
 BUT operational/maintenance issues are recorded
Other methodologies could be equally valid.

12. 3. Assessment Tool Features
Major Switchboard Consideration Groups
(affecting safety & condition):
 Age & Fault Rating (Considered most Critical)
 Environment (Affecting SwBd Deterioration)
 Design and Installation (Capability & Design Safety)
 Service History (Maintenance/Documentation)
 Operational History (Loading/Switching/Failures)
 Protection Systems (Type/Condition)

13. 3. Assessment Tool Features
Desirable Protocol Considerations:
 Must allow for visual inspection only
 Simple identifiable checklist items
 Minimal interpretation confusion
 Easy criteria evaluation
 Simplified item scoring
 Score to include weighting for important items/elements.
Note: This is Not an exact science. Can be Tailored

14. 3. Condition Assessment Audit Protocol
 Criteria Scoring
– Three level process:
1. Criteria Element compliance score: 0, 1, 2; (best to worst)
2. Criteria Element weighting multiplier: 0% to 100%;
3. Weighted compliance score totalled for each switchboard;
– Possible scoring range: 0 to 200.
 Example Critical weighting criteria:
• Age 15%
• System/Design Fault 15%
• Failure History 10%
• Loading 5%
• Spares Availability 5%
• Balance 54 Elements 50%

15. 3. Assessment Tool Features
Toolkit Sample
Checksheet.pdf

16. 3. Assessment Tool Features
Toolkit Sample Criteria Review.pdf

17. 4. Risk Assessment Outcomes
 SwBd condition “Likelihood” now quantified as a numerical
value
 Multiple SwBd condition values can now be compared and
ranked for attention.
 Condition “Likelihood” and arc flash “Consequence” can
now be combined into a Risk Matrix for mitigation
planning.
 The actual task can now also be considered vs the “risk”

18. 4. Risk Assessment Outcomes
Exposure Risk Assessment Matrix Example.pdf

19. Questions and Discussion

20. Part 2: Recent WA Case Study

21. Introduction
1. Hazard Recognition
2. Management
Resolve
3. Protocol Agreed
4. Condition Assessed
5. Arc Flash Assessed
6. Critical Learnings

22. 1. Management Hazard Recognition
 Aging switchboards
 Rising fault levels
 Deterioration in mechanisms
 Higher maintenance costs & delays
 Operator concerns
 Occurrence of actual arc faults
 Personnel injury from new switchboards

23. 2. Management Decision
 Progressive replacement or upgrade of all suspect swbds.
 Highest risk boards to be identified for schedule &
finance
 Safety & Condition Assessments to be undertaken
• Stage 1 ‐ Physical condition assessment (Likelihood)
• Stage 2 ‐ Arc Flash assessment (Consequences)
 Assess for condition/safety/reliability NOT life extension

24. 3. Stage 1 ‐ Audit Protocol Agreed
 Criteria and Checklists developed based on:
 Past experience of switchgear and minerals processing
 Recent condition audits for similar process site
 Knowledge of client requirements
 Main Protocol Considerations:
 150+ switchboards, 12 week time frame
 Multiple rotating inspection teams
 Must allow for visual inspection only
 Simple identifiable checklist items
 Minimal interpretation confusion
 Easy criteria evaluation with simplified scoring
 Weighted scoring for critical items/elements.

25. 3. Stage 1 ‐ Audit Protocol Agreed
 This matched the capability of the in‐house Assessment model
 Minor Changes made:
 Check Lists were refined to suit client preferences
 Plant Criticality factor included
 Priority Ranking for Condition Assessment modified

26. 3. Stage 1 ‐ Audit Protocol Agreed
 Client Preferred Condition Priority Ranking
• Group A – Unacceptable safety/commercial issues – replacement 0‐2yrs.
• Group B – Major commercial/safety risk issues – replacement 2‐5yrs.
• Group C – Minor commercial/safety risk issues – replacement 5yrs +.
• Group D – Safe to operate, but not arc fault contained. Address by risk
mitigation.
• Group E – Safe to operate, no upgrade works required.

27. 3. Stage 1 ‐ Audit Protocol
Agreed
Switchgear Condition Assesment Checksheet Rev 6_SKM Logo.pdf

28. 3. Stage 1 ‐ Audit Protocol
Agreed
Condition Assessment Checksheet Rev 6_wer.pdf

29. 3. Stage 1 ‐ Audit Completed
Total of 174 HV & LV switchboards inspected
Combined ranking assessment:
 Qualification data
incorporated in
spreadsheet;
 Spreadsheet data sorted by:
 SKM Final Ranking order
(Qualitative);
 Plant Productivity Priority
(Criticality);
 Assessment Score
(Quantitative).
Upgrade Order & Summary Overview.pdf Detailed Ranking Assessment Logo.pdf

30. 3. Stage 1 ‐ Audit Completed
What did we find ?
 Condition Assessment Summary:
– Switchboards inspected 174
– Priority group A 0‐2yrs 37
– Priority group B 2‐5yrs 58
– Priority group C 5+ yrs 56
– Priority group D mitigation 22
– Priority group E safe 0
– Non grouped decomm 1
– High Thermally loaded >80% 3
– High Fault level >90% 32
– High Fault level >100% 17

31. 4. Stage 2 ‐ Arc Flash Evaluation Results
Principal Findings of Arc Flash Assessment – 173 swbds
 No definable relationship between voltage and arc flash “consequences”
were observed but Very High (Cat4+) more common at HV
Sorted by Voltage
 Seven (7) switchboards initially required higher than Category 4 PPE (40
cal) at 0.5m – Reduced by modifying settings

32. 4. Stage 2 ‐ Arc Flash Evaluation Results
 Safe working distance without PPE 6.0 m for 92% of switchboards
 13 Switchboards unsafe to approach at more than 10m without PPE.
(probable accuracy limitations)
Note 1: Assumes primary protection operates correctly
(Otherwise Double Jeopardy Rating Applies)
Note 2: Assumes live bus work or power terminals are exposed.
Note 3: IEEE 1584 has accuracy limitations

33. 5. Arc Flash Critical Learning’s
Critical Learning from Arc Flash studies for PPE Consideration:
 Category 3 (25 Cal) PPE adequate for approximately 80% of all
switchboards at 500mm.
 Specified ratings for some swbds assume normal operating configuration.
(but care required)
 Most common personnel injury due to Arc Flash is to face, arms and
hands.
 LV arc faults are just as dangerous as HV faults

34. 6. Risk Assessment Outcomes
The following outcomes have been achieved to date:
 All Client swbds audited for condition & arc flash hazards.
 Prioritised upgrade list prepared for funding & scheduling.
 Dedicated Switchboards Project Team established
 Several high risk switchboards already replaced
 Others in process
 Five year plan in place with forward funding

35. 6. Risk Assessment Outcomes
 Short term mitigation for 11 Cat 4+ swbds implemented
to reduce arcing time or current:
 Enabled/adjusted high set element (instantaneous element) to trip
for the calculated Arcing current
 Changed out relays in some instances with relays having a ‘hi‐set’
element.
 Modified system configuration to reduce parallel feeds
Note: Protection setting mods for max arc flash protection
can reduce reliability of supply by limiting grading.

36. 6. Risk Assessment Outcomes
 Action profile raised with workforce.
 Increase control of unauthorised access
 Flame Resistant clothing trialled by volunteers
 PPE Workshops undertaken
• Cat 2 FR clothing made standard for all EW’s
• Arc flash records to be strictly maintained
• Short form records to be located in subs
• Isolations to be implemented in accordance to risk
• Preferred signage for swbds agreed
• Training program was developed

37. 6. Risk Assessment Outcomes
Consequence
Probability Insignificant Minor Moderate Major Severe
Cat 0 Cat 1 Cat 2 Cat 3 Cat 4
Group A (0-2 Yrs) Moderate High Extreme Extreme Extreme
Group B (2-5 Yrs) Moderate High High Extreme Extreme
Group C (5+ Yrs) Low Moderate High High Extreme
Group D (Mitigate) Low Low Moderate High High
Group E (Safe) Low Low Low Moderate Moderate

38. 6. Risk Assessment Outcomes
Switchboard Sticker Layout _2_.pdf

39. WHERE TO FROM HERE ??

40. Case Discussion
Was this an accident waiting to happen or “Just one of those things” ??

41. Case Discussion
• What have YOU done?
• What could YOU do on
your site?

42. Case Discussion
 Poor Capability  Poor Regulatory Compliance
 Thermal and magnetic stresses  Arc fault containment design
 Containment of arcing fault  Safety interlocks
 Switchroom clearances
 Poor Operability (User  Safe working environment
Interface)
 Manual racking and/or spring
charging  Residual Risk Uncommunicated
 Open panel access requirement  Was arc flash energy considered ?
 Was residual risk of containment
communicated ?
 Poor Maintenance
 Adequate PPE and signage
 What went wrong and why ?
 Procedures
 Why was breaker fault not
discovered and repaired ?