Managing mine earthing related risk - Bill Carman

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?


• Mindset matters

• Risk analysis is not a dirty word


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


• Mindset matters

• Risk analysis is not a dirty word


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



• Lightning

Mine processing plants




• Lightning

Induction Risks

Induction Risks What needs to be done?

What can be done?




• 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

Managing mine earthing related risk - Bill Carman

Government & Nonprofit

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