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Managing mine earthing related risk
Bill Carman Director, Bill Carman Consulting
[email protected] 0411140577
25th Electrical Engineering Safety Seminar NSW Resources and Energy
4-5 November 2015
The new AS2067 approach
What is the new approach and will it really help?
• “Back in the day …”
• Mindset matters
• AS2067: Risk analysis is not a dirty word
• Once upon a time …. case studies
Where did it all begin?
• “Just give me the practical …”
• Since early 80’s - NSW safety push - coal and metalliferous mines
• Option #1: Reduce the hazard level and eliminate risk: 60 volts should be OK shouldn’t it?
• Solution: E/F reduction and segregation
• But not so easily achieved in many cases
• Roof bolting
• Cable movements
• Bath houses
• Miner operators
High exposure tasks
Mine substationVent fan
Drift
Mine earthing systems• Large geographical area
• Many power supply and metalwork configurations, variable soil conditions
• Sparse, poor earthing points
• Hazardous (gassy) environment
• Industrial complex on-site
• Long metallic structures above and below ground (pipelines, conveyors, rail lines, 11kV cables, control cabling)
• 3rd party interaction - transmission lines, supply s/s, lightning, traction systems
• Electrical plant operated in wet areas
• HV in flexible cables to large mobile machines
• HV cables confined areas
• Deep shafts with winders and/or cased bores
• HV installations and equipment in areas where people stand in mud/water to operate and maintain
• Little opportunity to escape
• Temporary and/or continuously moving
Mindset matters
• Big power - no time to ‘muck around’
• Electrical supply - ancillary service
• Competing interests - safety and production
• Hazardous materials and Safety critical systems
• Earthing systems are safety critical systems
• Where failure of the system may result in injury, loss of life or serious environmental damage
• Low probability …. high consequence events
Hazardous material
17 Management of risks A duty imposed on a person to ensure health and safety requires the person: (a) to eliminate risks to health and safety, so far as is reasonably practicable; and (b) if it is not reasonably practicable to eliminate risks to health and safety, to minimise those risks so far as is reasonably practicable.
Work Health and Safety Act - 2012
Magnitude of the risk
Probability of
occurrence
Severity of harm
Expense Difficulty/
inconvenience
Utility of conduct
Sappideen, C., Stillman, R.H., ‘Liability for Electrical Accidents: Risk,
Negligence and Tort’. Engineers Australia (1995).
Reasonably practicable…taking into account and weighing up all relevant matters including: A. the likelihood of the hazard or the risk concerned occurring; B. the degree of harm that might result from the hazard or the risk; C. what the person concerned knows, or ought reasonably to
know, about: the hazard or the risk; and ways of eliminating or minimising the risk;
D. the availability and suitability of ways to eliminate or minimise the risk;
E. after assessing the extent of the risk and the available ways of eliminating or minimising the risk, the cost associated with available ways of eliminating or minimising the risk, including whether the cost is grossly disproportionate to the risk.
Care%and%the%issue%of%DutyThe test for negligence under duty of care may be expressed in terms of four questions:
Causa1on:!Did!the!injury!or!situa0on!occur!because!of!the!‘unsafe’!ma7er!or!situa0on!on!which!the!claim!of!negligence!is!based?%Foreseeability:!Did!you!know?!Ought!you!to!have!known?!Could!this!have!been!foreseen?!(i.e.!via!prior!incidents,!complaints,!wide!or!common!knowledge,!or!expert!advice).%Preventability:!Is!there!a!prac0cal!way!or!alterna0ve!to!how!things!were!done?%Reasonableness:!The!balance!of!the!significance!of!the!risk!against!the!effort!required!to!reduce%
LI015 — Legislation 8 Revised'November 2005 Alberta WH&S Bulletin
Mines RegsCM(Gen)R 1999 - 28 Electrical equipment and installations
• (1) All electrical equipment at a mine or declared plant must be designed, installed, commissioned, operated, maintained (including servicing, repairing and overhauling) and decommissioned in such manner as to control any risks from fire, explosion, electric shock or unintended movement of equipment.
GR 2000 - 68 Requirements as to electricity The general manager of a mine must ensure that:
• (a) electrical installations at the mine are designed, installed and maintained to minimise the potential for any electric shock or for burns, injury, explosion, fire, overheating or mechanical damage,
Health and Safety in NSW metalliferous mines is governed by the Mines Inspection Act (MIA) 1901, and the General Rule (GR2000) 2000. The provisions relating to an electrical installation and electrical work can be summarised as follows:
• A general manager must prepare a Mine Safety Management Plan
• The general manager must ensure that people performing work at the mine have the necessary skills and competence
• Electrical installations must comply with AS 3000 and AS 3007
• Electrical equipment must be installed in such a manner as to control risk of fire, explosion, electric shock or unintended movement during the whole life cycle of the equipment.
Where to from here?
• “Back in the day …”
• Mindset matters
• Risk analysis is not a dirty word
• Once upon a time …. case studies
Earthfault%Current%Flow
Presence%of%Person
Voltage%Gradients
Absence%of%Series%Resistance
Conditions%for%Danger
Fundamental%rela1onships
= Pfibrillation x Pcoincidence
Pfibrillation = f(Vapplied,Rseries, contact configuration, duration)
Pcoincidence = f(fault and contact frequency and duration)
Pfatality
0.001 0.01 0.1 1 10
Clearing time (secs)
10
100
1000
10000
Fib
rilla
tio
n C
urr
en
t (m
A)
0.5%5%25%50%
75%90%99%
Fibrillation%Current%Criteria
Based!on!work!by!Kouwenhoven!and!Kiselev!
Argon
Critical Risk Criteria SelectionRisk level Fatality Risk Increase Recommended Risk Management
Response
High ≥10-4 Mitigate risk
Intermediate 10-6 ≤ Risk < 10-4 Mitigate risk wherever possible, using ALARP principles
Low < 10-6 Risk generally tolerable
Societal Risk
Individual Risk
Societal RiskSocietal Risk is the risk associated with multiple, simultaneous fatalities within an exposed population. Required where it is realistic (on average) for 2 or more people to be simultaneously exposed to a shock hazard, for example:
showers at a public pool commercial sites near major substation sub-transmission tower in the grounds of a football stadium hospital access points schools - class entry points, playground areas cattle saleyards theme parks
Applied risk analysisENA EG-0:2010 Power system earthing guide
AS7000:2010 - Overhead line design - Detailed procedures AS/NZS 4853:2012 - Electical hazards on metallic pipelines AS2067:2015? - Switchgear Assemblies and Auxiliary Equipment for Alternating Voltages Above 1kV AS3007.2 - Electrical Installations for Outdoor Sites Under Heavy Conditions AS3835 - Coordination of Power and Telecoms – EPR
IEC61936:2010 EN 50522:2010
ANSI/IEEE Std 80 ENA-EG1 (2,3,4?)
Was AS3007.2 ‘safe’? Clearing time reduction?180 volts no series impedance - f(tc)
P(fib
rilla
tion)
0.001
0.01
0.1
1
10
100
1000
Fault duration (sec)0 0.3 0.5 0.8 1
PfibChance of survival
0.15 0.00592 0.4 0.0359
1 0.307
AS2067!–!HV!Installations
The!following!cases!are!not!covered!in!the!case!studies!and!require!case!specific!design!to!be!undertaken:
• Residential!distribution!–!including!aquatic!centres!and!commercial!centres!
• Light!industrial!–!sawmill,!batching!plant,!abattoir!• Large!interconnected!systems!–!power!stations,!
heavy!industrial,!wind!turbines!• Mining!\!!–!surface!operations,!underground!coal,!
underground!metals,!open!cut,!road!tunnelling
• Long!overland!conveyors!• Railway!systems!• Theme!parks IEC61936!=!parent!std
AS2067 - G5: Mining operationsMining operations may be broken up into several general areas of operation or types of plant for the purpose of understanding hazard scenarios and applicable criteria as follows:
(a) Surface plant operations area—workshops, offices, washeries, crushers.
(b) Underground coal operation.
(c) Underground metal mining operation.
(d) Open cut mining, quarrying and mineral sand extraction.
(e) Road tunnels—construction and operation.
AS2067!–!Underground!metalliferrous!mining
Draft
AS2067!–!Underground!metalliferrous!mining AS2067 - Underground coal
Learning from the past
• “Back in the day …”
• Mindset matters
• Risk analysis is not a dirty word
• Once upon a time …. case studies
Case studies• Conductive coupling through soil
• Capacitive coupling
• Inductive coupling
• Lightning
To bond or separate?
HV substation
Transfer Hazard Risks
• 0.5 sec fault/5 yrs - Vt tolerable = 182 volts
• 0.5 sec fault/10 yrs - Vt tolerable = 219 volts • 0.2 sec fault/5 yrs - Vt tolerable = 471 volts
• 0.2 sec fault/10 yrs - Vt tolerable = 548 volts
Segregated mine earthing system
Inadequate insulation level!
Old drift
Pipes
11kV switchroom and
mine earth
Bathhouse
33kV yard - High EPR, slow
tc
Induction and transfer hazards
Maintenance – what could possibly go wrong? Case studies• Conductive coupling through soil
• Capacitive coupling
• Inductive coupling
• Lightning
Mine processing plants
Case studies• Conductive coupling through soil
• Capacitive coupling
• Inductive coupling
• Lightning
Induction Risks
Induction Risks What needs to be done?
What can be done?
Case studies• Conductive coupling through soil
• Capacitive coupling
• Inductive coupling
• Lightning
Methane drainage systems
Sago WVA mine disaster Jan 2006 12 fatalities
Earthing system risk management framework
Earthing systems are required to manage the transfer of energy in such a manner as to limit the risk to people, equipment and
system operation to tolerable levels
Safety > Practicality > Cost