This presentation reviews literature related to the prevention, detection, mitigation and response to events resulting from low voltage cable failures. The most serious outcomes are manhole fires, explosions and contact voltage electric shocks. Smoking manholes, stray voltage (contact voltage) and service quality complaints are less serious outcomes.

1. C34 – Mitigating Manhole Explosions
IEEE PES ICC Spring 2013 Meeting
Understanding Manhole Events
Stuart Hanebuth
Power Survey Company
shanebuth@powersurveyco.com
973-344-7116

2. C34 – Mitigating Manhole Explosions
IEEE PES ICC Spring 2013 Meeting
Do We Need a Trial Use Guide?
• There has been a lot of research into causes, prevention
detection, mitigation and response
• Little of this work has been consolidated to identify
beneficial strategies and best practices
• Significant maintenance and capital spending to prevent
and respond, oftentimes with limited benefit
• Events represent risk to employees and the public
• Industry and public do not always speak the same
language on these events
• Consolidation of prior research, along with utility best
practices will save utility and ratepayer dollars and
improve public safety
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3. C34 – Mitigating Manhole Explosions
IEEE PES ICC Spring 2013 Meeting
Manhole Event Sources
• Transmission and primary cable initiated events
• High fault energy
• Interrupted quickly by protective systems
• Incipient fault detection may be possible
• Transformer initiated events
• High fault energy
• Large fuel source
• Primary faults interrupted by protective systems, secondary faults
may or may not be interrupted
• DGOA, visual inspection, and cathodic protection are effective
preventative measures
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4. C34 – Mitigating Manhole Explosions
IEEE PES ICC Spring 2013 Meeting
Manhole Event Sources
• Natural gas initiated events
• Large fuel source
• Potential for collateral damage to electric facilities
• Methane and chemical related events
• Less common
• Hard to predict
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5. C34 – Mitigating Manhole Explosions
IEEE PES ICC Spring 2013 Meeting
Manhole Event Sources
• Low voltage cable events (>95% of manhole events1)
• Limiters designed to prevent damage to adjacent sections but not
to interrupt fault
• Large potential fuel source from cable insulation
• Toxic gases produced during decomposition of insulation
• Visual inspections provide limited benefit (less than 5% reduction)
• Arc fault detection may not provide adequate sensitivity
• Contact voltage detection locates conductive faults
• Venting demonstrates some benefit in reducing severity
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6. C34 – Mitigating Manhole Explosions
IEEE PES ICC Spring 2013 Meeting
Electrical Properties
• Low Current
• Gas generation with a little as 1.28 W/cm1
• Sustained Combustion at 18W/cm
• Distinctive waveform2-4
• May persist for short intervals of seconds to minutes
with long quiescent periods5
• Arcing events can energize street level objects and
can be detected with mobile contact voltage detection
systems6
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7. C34 – Mitigating Manhole Explosions
IEEE PES ICC Spring 2013 Meeting
Protective Systems
• Limiters
• Designed to protect adjacent
sections from thermal overloads
during three phase faults7
• Typically limit in the 1,000-5,000
amp range
• Not generally effective in
preventing or mitigating gas
producing faults
• Arc fault detection
• Most sensitive systems seem to
be in the 5 amp – 50 amp range6
• May not be able to detect gas
producing faults
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8. C34 – Mitigating Manhole Explosions
IEEE PES ICC Spring 2013 Meeting
Chemistry
• A variety of materials have been used for low voltage cable insulation8
• Paper Insulated Lead (PILC)
• Kerite
• Styrene Butadiene Rubber (SBR) 1940 - 1960
• Butyl Rubber
• Neoprene
• PVC
• EPR
• Variety of duct materials have been used9
• Wood
• Cellulose-Tar
• Concrete
• PVC
• Each represents different risks and benefits
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9. C34 – Mitigating Manhole Explosions
IEEE PES ICC Spring 2013 Meeting
Cable Failure Outcomes
• Majority of failures result in power
quality and contact voltage
related issues
• Smoking manholes are the most
probable manhole events as a
result of insulation degradation
• Manhole fires and explosions can
be further subdivided
• Electrically driven events
• Chemically driven events
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Energized Objects
Flickering Lights
Smoking Manholes
Manhole
Fires and
Explosions

10. C34 – Mitigating Manhole Explosions
IEEE PES ICC Spring 2013 Meeting
Collateral Damage Concerns
• Primary damage from
low voltage faults
• Damage to nearby
natural gas facilities10
• Building explosions from
carbon monoxide
accumulations
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Danny Iudici/for New York Daily News

11. C34 – Mitigating Manhole Explosions
IEEE PES ICC Spring 2013 Meeting
Event Prevention Strategies
• Post installation testing11
• Duct sealing to minimize
airflow12
• Filling manholes with inert
materials to minimize gas
accumulation
• Contact voltage testing to
find incipient faults
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12. C34 – Mitigating Manhole Explosions
IEEE PES ICC Spring 2013 Meeting
Visual Inspections
• Analysis of over 55,000
visual inspections found
small reduction in
secondary related
events such as13
• Smoking manholes
• Contact voltage
• Power Quality Events
• No reduction in manhole
fires or explosions
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Structure Category
EventProbability

13. C34 – Mitigating Manhole Explosions
IEEE PES ICC Spring 2013 Meeting
Mitigation Strategies
• Several cover designs and restraining approaches have been implemented14
• Tethering
• Self restraining
• Venting
• Deployment strategies not well established
• Is 100% installation the optimal approach?
• High density areas
• Dense structures
• Duct or Cable driven installation
• Analysis needed on impacts of deployment
• Water
• Primary Joints
• Customer basements
• Debris accumulation
• Access
• Civil design
• Increased duct airflow
• At least one “standard” exists for deployment of vented covers15
• Office of the Telecommunications Authority Hong Kong. (2010, June, 30). Implementation
Guidelines on Mitigating the Risk of Gas Explosion in Telecommunications Manholes [Online].
Available: http://tel_archives.ofca.gov.hk/en/report-paper-guide/guidance-notes/gn_201003.pdf
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14. C34 – Mitigating Manhole Explosions
IEEE PES ICC Spring 2013 Meeting
Response Strategies
• Area of little consideration by most utilities
• Fire department approaches problem different than utility
• Variety of agents are available on the market
• Some firefighters have written on the topic
• Battalion Chief Frank C. Montagna, “Manhole Fires”, http://www.chiefmontagna.com/Articles/manhole%20fires.htm
• Battalion Chief Frank C. Montagna, “What You Should Know About 10-25 Reponses”, http://www.chiefmontagna.com/Articles/pdf/Manhole.pdf
• Boston Fire Department, “SOP #49B Special Procedures and Precautions for Incidents Involving Manholes”, http://www.firesops.com/wp-
content/uploads/2012/02/BFD_SOP_49B_Special_Procedures_and_Precautions_Involving_Manhole_Incidents.pdf
• D. Leihbacher, “Managing Manhole Fires”, Fire Engineering Magazine, January 2008, http://www.fireengineering.com/articles/print/volume-161/issue-
1/features/managing-manhole-fires.html
• Conflicting strategies
• Remove covers or leave in place
• Flood Structures or leave dry
• Apply other firefighting agents
• Isolation
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15. C34 – Mitigating Manhole Explosions
IEEE PES ICC Spring 2013 Meeting
Manhole Events Outline
• Event taxonomy
• Definitions
• Literature Review
• Low Voltage Cable Insulation Initiated Events
• Electrical Properties
• Protective Systems
• Early Detection Methodologies
• Cable Failure Outcomes
• Collateral Damage Concerns
• Severity Mitigation Strategies
• Response Strategies
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16. C34 – Mitigating Manhole Explosions
IEEE PES ICC Spring 2013 Meeting
Manhole Events Outline
• Transformer Initiated Events (With similar subtopics from
above)
• Electrical Properties
• Protective Systems
• Early Detection Methodologies
• Outcomes
• Severity Mitigation Strategies
• Response Strategies
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17. C34 – Mitigating Manhole Explosions
IEEE PES ICC Spring 2013 Meeting
Manhole Events Outline
• Transmission and Primary Cable Insulation Initiated
Events
• Electrical Properties
• Protective Systems
• Early Detection Methodologies
• Cable Failure Outcomes
• Collateral Damage Concerns
• Severity Mitigation Strategies
• Response Strategies
• Natural gas Initiated Events (With similar subtopics from
above)
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18. C34 – Mitigating Manhole Explosions
IEEE PES ICC Spring 2013 Meeting
Manhole Events Outline
• Natural gas events
• Protective Systems
• Early Detection Methodologies
• Outcomes
• Collateral Damage Concerns
• Severity Mitigation Strategies
• Response Strategies
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19. C34 – Mitigating Manhole Explosions
IEEE PES ICC Spring 2013 Meeting
Conclusion
• General need to define common terms to discuss the
issue
• Low voltage cable failures are at root of most of these
events
• Need wider focus than simply mitigating manhole events,
also need to consider:
• Prevention
• Early detection
• Maintenance
• Response
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20. C34 – Mitigating Manhole Explosions
IEEE PES ICC Spring 2013 Meeting
Bibliography1. L. Zhang, “Mitigation of Manhole Events Caused by Secondary Cable Failure,” Ph.D. dissertation, Dept. of Elect. and Electronic Eng., Univ.
of Conn., Storrs-Mansfield, CT, 2011
2. D.G. Ece, F.M. Wells and H.G. Senel, “Analysis and Detection of Arcing Faults in Low-Voltage Electrical Power Systems,” in 7th
Mediterranean Electrotechnical Conference., Antalya, Turkey, 1994, pp. 929-935
3. W. Charytoniuk et al., “Arcing fault detection in underground distribution networks feasibility study,” in Industrial and Commercial Power
Systems Technical Conference, Clearwater Beach, Fla, 2000, pp.15-20
4. B. Koch and Y. Carpentier, “Manhole Explosions Due to Arcing Faults on Underground Secondary Distribution Cables in Ducts,” IEEE
Trans. Power Del., vol. 7, no. 3, pp. 1425-1433, Jul 1992
5. Hamel, A. Gaudreau, and M. Cote, “Intermittent Arcing Fault on Underground Low-Voltage Cables” IEEE Trans. Power Del., vol. 19, no. 4,
pp. 1862-1868, Oct 2004
6. N. Weisenfeld, Y. When, “Arcing Fault Detection Projects”, 2010 Jodie S. Lane Public Safety Conference, New York, NY
7. F. Heller, and I. Matthysse, “Limiters, Their Design Characteristics and Application” IEEE Trans. Power App. Syst., vol. 74, pp. 924-950, Oct
1955
8. C. Zuidema et al., “A Short History of Rubber Cables,” IEEE Electr. Insul. Mag, vol. 27, no. 4, pp 45-50, Jul/Aug 2011
9. L. Zhang et al., “The Electro-Chemical Basis of Manhole Events,” IEEE Electr. Insul. Mag, vol. 25, no. 5, pp. 25-30, Sep/Oct 2009
10. T.J. Parker and D. J. Ward, “Insuring Adequate Spacing Between Underground Distribution Conductors in Conduit and Gas Lines,” IEEE
Trans. Power Del., vol. 18, no. 1, pp. 291-294, Jan 2003
11. J.Côté, “Manhole Explosions Discussion Group Hydro-Québec Experience”,
http://www.pesicc.org/iccwebsite/subcommittees/subcom_c/C34/Presentations/2011Spring/C17.pdf
12. L. Zhang, S.A. Boggs and S. Livanos, “Manhole Events Caused by Secondary Cable Insulation Breakdown,” in Annual Report Conference
on Electrical Insulation Dielectric Phenomena, Quebec City, Canada, 2008, pp. 107-110
13. Consolidated Edison Co. of NY, Inc. Stray Voltage Test and Inspection 2010 Annual Report 04-M-0159, Consolidated Edison Co. of NY,
Inc., New York, NY, 2011
14. W. Black, J.Côté, “Mitigating Manhole Explosions”
http://www.pesicc.org/iccwebsite/subcommittees/subcom_c/C34/Presentations/2012Spring/C-21.pdf
15. Office of the Telecommunications Authority Hong Kong. (2010, June, 30). Implementation Guidelines on Mitigating the Risk of Gas
Explosion in Telecommunications Manholes [Online]. Available: http://tel_archives.ofca.gov.hk/en/report-paper-guide/guidance-
notes/gn_201003.pdf
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