NGI-Cause Tree Analysis

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CAUSE TREE ANALYSIS

INCIDENTINCIDENT MANAGEMENT MANAGEMENT

WITH THE WITH THE “CAUSE TREE “CAUSE TREE ANALYSIS” ANALYSIS” METHODMETHOD

INCIDENTINCIDENT MANAGEMENT MANAGEMENT

WITH THE WITH THE “CAUSE TREE “CAUSE TREE ANALYSIS” ANALYSIS” METHODMETHOD

INCIDENTS RESULT FROM

THE CONJUNCTION OF SEVERAL

CAUSES

METHODOLOGY OF THE « CAUSE TREE » ANALYSIS

THE METHOD IS LOGICAL,

CREATIVE AND BASED ON

TEAMWORK

THE METHOD IS FACT-FINDING,

NOT FAULT-FINDING

1. COLLECTION OF CONCRETE FACTS & PRECISE DESCRIPTION OF THE EVENT

1. COLLECTION OF CONCRETE FACTS & PRECISE DESCRIPTION OF THE EVENT

FILL IN THE SEVERITY MATRIX

2. BUILD-UP OF THE CAUSE TREE2. BUILD-UP OF THE CAUSE TREE

3. LISTING & SELECTION OF THE PREVENTIVE ACTIONS

3. LISTING & SELECTION OF THE PREVENTIVE ACTIONS

4. IMPLEMENTATION & FOLLOW-UP OF THE SELECTED ACTIONS

4. IMPLEMENTATION & FOLLOW-UP OF THE SELECTED ACTIONS

FILL IN THE CAUSE MATRIX


THE TREE IN THE THE FOREST


1. COLLECTING FACTS

WHO ?WHO ?

• TOTAL SITE SUPERVISOR / MANAGER

• HE KNOWS PERFECTLY THE SITE, PEOPLE IN PLACE, INHERENT HAZARDS & RISKS, AND THE RUNNING ACTIVITIES

• THIS IS HIS RESPONSIBILITY (CARE OF PEOPLE HEALTH & SAFETY) AND FALLS WITHIN HIS AUTHORITY & COMPETENCE (CONTROL OF THE SITUATION)CREATION OF AN AMBIANCE OF CONFIDENCE

• HE SHOULD SEEK ASSISTANCE FROM THE CONTRACTOR’S SITE MANAGEMENT TO CARRY OUT THIS TASK

HOW ?HOW ?

• LISTEN TO WITNESSES, ONE BY ONEInformations stem from independent sourcesThe average resultant of opinions is avoided

• COLLECT Facts only, without interpretation nor judgement of value (ex.n°2)

In the chronological orderLook for the « unusual »

• WRITE UP A DETAILED REPORT Gathering all collected informations

Reconstructing the undesirable event

• BUILD UP A LISTING OF THE ELEMENTARY FACTS CONTAINED IN THIS REPORT Each fact retains one -and only one- information

1. COLLECTING FACTS

WHEN ?WHEN ?

AS SOON AS POSSIBLE !!

• memory fades away quite quickly

• witnesses usually build up a sequence of events from the only facts they remember (seeking after a « global » logic)

• one remembers only wilful actions, not spontaneous ones nor reflexes

IT IS THUS NECESSARY TO QUICKLY RE-ISOLATE THE FACTS SO AS TO RECONSTRUCT THE INCIDENT

1. COLLECTING FACTS

EXERCISE 1

Here is a situation which appears to be quite straightforward and which may be encountered at any time in business, family life or in the street.

John Smith, a contractor, arrives at the building site in the Boston Street. In the yard a worker is calling out in Spanish, waving his hand around frenziedly and looking up in the air. Then he goes back into the room and plasters the wall. By the porch a young man with a beard is talking affectionately to someone with long hair and wearing blue jeans.

Everything in this story is absolutely correct and cannot be doubted.

Now read the statements listed below and see whether each of them appears to you to be :

• true (T),• false (F),• arguable and uncertain (?).

Ring the one which corresponds to your answer.

The objective of this exercise is to show that :

• our replies can be modified by the way we “embroider” the facts,• memory quickly changes,• we are not always able to distinguish between facts and interpretations.

EX. n°1 : COMPANY « SMITH »

EXERCISE 1 - RULES OF THE GAME

- answer the questions in numerical order.- do neither go back and re-read propositions after replying, nor correct a previous answer.

PROPOSITIONSREPLIES

1. Smith is a contractor

2. There are only four people on the building site in the Boston Street

3. The contractor is on the building site in the Boston Street

4. The contractor saw the worker cry out

5. One of Smith’s employees was plastering the wall

6. There was a Spanish worker in the yard

7. The worker who calls out in the yard is addressing a workmate on an upper floor

8. He is calling out to warn his workmates that the contractor had arrived

9. After calling out the workman starts plastering again the room wall

10. The workman who cried out in the yard does not then go back into the room

11. The plasterer is plastering the room wall

12. The bearded workman is having a short rest

13. The bearded man is talking affectionately to the woman in blue jeans

14. If the person with long hair and wearing blue jeans is a young man, could it be that the bearded man is in love with him ?

Has the picture which you had formed of the scene changed having answered these questions ?

T F ?T F ?T F ?T F ?T F ?T F ?T F ?T F ?T F ?T F ?T F ?T F ?T F ?

T F ?

YESNO

PROPOSITIONS REPLIES

1. Smith is a contractor

2. There are only four people on the building site in the Boston Street

3. The contractor is on the building site in the Boston Street

4. The contractor saw the worker cry out

5. One of Smith’s employees was plastering the wall

6. There was a Spanish worker in the yard

7. The worker who calls out in the yard is addressing a workmate on an upper floor

8. He is calling out to warn his workmates that the contractor had arrived

9. After calling out the workman starts plastering again the room wall

10. The workman who cried out in the yard does not then go back into the room

11. The plasterer is plastering the room wall

12. The bearded workman is having a short rest

13. The bearded man is talking affectionately to the woman in blue jeans

14. If the person with long hair and wearing blue jeans is a young man, could it be that the bearded man is in love with him ?

Has the picture which you had formed of the scene changed having answered these questions ?

T F ?T F ?T F ?T F ?T F ?T F ?T F ?T F ?T F ?T F ?T F ?T F ?T F ?

T F ?

YESNO

SOLUTION TO EXERCISE 1

ref 239 A

AMONG THE FOLLOWING HEADLINES, UNDERLINE THOSE WHICH, IN YOUR OPINION,

TRANSLATE JUDGEMENTS OR INTERPRETATIONS RATHER THAN FACTS :

1. Non-use of the individual protection made available2. Inadequacy of work organization3. Lack of instructions on working methods4. Dangerous omission5. Physical failure6. Proceeding without adequate precautions7. Work instruction not observed8. Acting without giving warning9. Neglecting to use individual protection10. Working in a not very safe position11. Inadequate vocational training12. Dangerous act13. Neutralizing a safety device Only facts, no interpretation, no judgement !Only facts, no interpretation, no judgement !

EXERCISE 2

IN BOLD : WORDING NOT TO BE USED

1. Non-use of the individual protection made available2. Inadequacy of work organization3. Lack of instructions on working methods4. Dangerous omission5. Physical failure6. Proceeding without adequate precautions7. Work instruction not observed8. Acting without giving warning9. Neglecting to use individual protection10. Working in a not very safe position11. Inadequate vocational training12. Dangerous act13. Neutralizing a safety device 1, 7, 8 and 13 are facts (5 is under medic competence)1, 7, 8 and 13 are facts (5 is under medic competence)

2, 3, 4, 6, 9, 10, 11 and 12 are judgements / interpretations2, 3, 4, 6, 9, 10, 11 and 12 are judgements / interpretations

SOLUTION TO EXERCISE 2

2 BUILDING THE CAUSE TREE

WHERE ? :For a given incident, several CTA can be done, provided that all causes are found and prevention targets identified.

WHEN ? : 2 to 3 days after the event, as soon as possible, in order to :• Implement immediate corrective actions• Avoid the changes of memories

Even in the case of a very simple story.

METHODOLOGYMETHODOLOGY

When 2 causes are simultaneously necessary to produce an incident: look for what could have prevented these two to combine. A protection device, like a safety helmet, for instance. This absence of the safety barrier constitutes in itself a particular cause.

HOW ? : • From right to left• Using proper symbols• Note that, in conjunctions, all causes have

not the same “weight”. Eliminating one cause will have an effect on the risk which may differ from another cause.

METHODOLOGYMETHODOLOGYWHO ? : The investigation Team with the the Site Manager

2 BUILDING THE CAUSE TREE

2. BUILDING UP THE CAUSE TREE - METHODOLOGY

HOW ? (2) :HOW ? (2) :

FOR EACH FACT, ASK THE FOLLOWING 3 QUESTIONS :FOR EACH FACT, ASK THE FOLLOWING 3 QUESTIONS :

A POSITIVE ANSWER TO THE 3rd QUESTION MEANS THAT ALL POSSIBLE A POSITIVE ANSWER TO THE 3rd QUESTION MEANS THAT ALL POSSIBLE ANTECEDENTS HAVE BEEN TAKEN INTO ACCOUNTANTECEDENTS HAVE BEEN TAKEN INTO ACCOUNT

It is strongly recommended to be creative at that stage, looking in particular for non-listed but plausible and widely admitted facts, e.g. the absence of any kind of safety barrier related to hardware or human awareness.

« WHAT HAS BEEN REQUIRED ?… to get the incident »« WAS IT NECESSARY ?… to its occurrence »« WAS IT SUFFICIENT ?… aren’t there other antecedents ? »

HOW ? (3) :HOW ? (3) :

FOLLOW THE « CHAINING » METHODOLOGY :FOLLOW THE « CHAINING » METHODOLOGY :

THESE SIMPLE FACTS, WHICH ARE THE SOUGHT-AFTER ELEMENTARY THESE SIMPLE FACTS, WHICH ARE THE SOUGHT-AFTER ELEMENTARY AND INDEPENDANT CAUSES, REPRESENTSAND INDEPENDANT CAUSES, REPRESENTS

THE PREVENTION TARGETSTHE PREVENTION TARGETS..

Using the detailed report and related list of elementary facts, start from the ultimate undesirable event(s)

and seek for the logical and direct antecedents of each fact going back, in the chronological order, to the single facts beyond which

nothing can be done or for which there is no plausible nor known antecedent

2. BUILDING UP THE CAUSE TREE - METHODOLOGY

2. BUILDING THE CAUSE TREE - OPERATING STRATEGY

ref 354 A

HOW ? (4) :HOW ? (4) :

BUILD UP THE TREE COLUMN BY COLUMN, ANTECEDENT BY ANTECEDENT,BUILD UP THE TREE COLUMN BY COLUMN, ANTECEDENT BY ANTECEDENT,

TICK OFF FACTS FROM THE LIST AS SOON AS INTEGRATED INTO THE TREE,TICK OFF FACTS FROM THE LIST AS SOON AS INTEGRATED INTO THE TREE,

prevents from rushing straightforward to so-called obvious targets, and from missing a lot of things,

prevents from forgetting some facts, if for instance a fact leads to several other ones

CHECK THE TREE FROM THE LEFT TO THE RIGHT.CHECK THE TREE FROM THE LEFT TO THE RIGHT.

EXAMPLE OF LOGICAL CHAINING : ex.n°3EXAMPLE OF LOGICAL CHAINING : ex.n°3TRAINING FOR THE METHOD : ex.°4TRAINING FOR THE METHOD : ex.°4

DOCUMENT

TYPES OF CONNECTIONS BETWEEN FACTS - SYMBOLIC SYSTEMTYPES OF CONNECTIONS BETWEEN FACTS - SYMBOLIC SYSTEM

B has a single cause A, which is necessary and sufficient for it to happen.

1. LINK1. LINK

An event has a number of causes :• either independent :A or B are necessary and sufficient for D to happen,• or necessary simultaneouslyA and B simultaneously are necessary for D to happen.

2. CONJUNCTION2. CONJUNCTION

3. DISJUNCTION3. DISJUNCTION

A number of events have the same cause :C is necessary and sufficient to produce A and (or) B.

AA BB

AA

BBDD CC

AA

BBCC

AA

BBDD CC

Exercise AExercise A

1. Receives phone call.2. Does not turn the oven off.3. Talkative caller.4. Roast burned.

AA

BB

CC

33 11 22 44

22 4433

11

441122

33

EXERCISE 3 (1/2)

Exercise BExercise B

1. Misses train.2. Car breaks down.3. Arrives late at station.4. Forgets to fill up with petrol.

AA

BB

CC 44 22 33 11

1122

3344

1122

33

44

Exercise CExercise C

1. Forgets to put on his safety helmet2. Does not change footwear.3. Arrives late.4. Fog.

AA

BB

CC

1122

3344

2244

3311

44 3311

22

Exercise DExercise D

1. Forflift truck driver absent.2. Foreman drives truck.3. Urgent loading job.4. No replacement forklift truck driver.

AA

BB

CC

2244

3311

4411

3322

11

33

4422

EXERCISE 3 (2/2)

Exercise AExercise A

1. Receives phone call.2. Does not turn the oven off.3. Talkative caller.4. Roast burned.

AA

BB

CC

33 11 22 44

22 4433

11

441122

33

Exercise BExercise B

1. Misses train.2. Car breaks down.3. Arrives late at station.4. Forgets to fill up with petrol.

AA

BB

CC 44 22 33 11

1122

3344

1122

33

44

EXERCISE 3 - SOLUTION

Exercise CExercise C

1. Forgets to put on his safety helmet2. Does not change footwear.3. Arrives late.4. Fog.

AA

BB

CC

1122

3344

2244

3311

44 3311

22

Exercise DExercise D

1. Forklift truck driver absent.2. Foreman drives truck.3. Urgent loading job.4. No replacement forklift truck driver.

AA

BB

CC

2244

3311

4411

3322

11

33

4422


EXERCISE A

1 - Floor wet2 - Falls3 - Slips4 - Injures himself

EXERCISE C1 - Deep trench, slides not shored2 - Collapse3 - Heavy rain4 - Heavy vehicle passes close to the edge of the trench (just before the collapse)

EXERCISE B

1 - Floor wet2 - Véhicle breakdown3 - Drivers slips4 - Drivers walks

EXERCISE D

1 - Another accident2 - No warning of first accident3 - Crowd gathers4 - Traffic accident

EXERCISE 4

EXERCISE A

1 - Floor wet2 - Falls3 - Slips4 - Injures himself

EXERCISE C1 - Deep trench, slides not shored2 - Collapse3 - Heavy rain4 - Heavy vehicle passes close to the edge of the trench (just before the collapse)

EXERCISE B

1 - Floor wet2 - Véhicle breakdown3 - Drivers slips4 - Drivers walks

EXERCISE D

1 - Another accident2 - No warning of first accident3 - Crowd gathers4 - Traffic accident

1 3 2 4

2 4

1

3

4

1

3

2

4 3

2

1


CTA - OCIAR INTERFACE

1° INCIDENT REPORT

2° CTA

SEVERITY MATRIXSEVERITY MATRIX

CAUSES MATRIXCAUSES MATRIX

REAL SEVERITY LEVEL 3OR

POTENTIAL SEVERITY LEVEL 4

3 - LISTING & SELECTING PREVENTIVE ACTIONS

WHO ? The investigation team, plus the concerned technical manager and someone who can « decide » on investments

WHEN ? • After completion of the CTA• Within 2 weeks time• No need for rush, let things get mature as long as

immediate corrective actions aimed at preventing the re-occurrence of the incident have been implemented

WHERE ? At the affiliate’s office

HOW ? USING THE BRAIN-STORMING TECHNICS

• Look for solutions to the identified prevention targets (at least one per target)• List all realistic & workable suggestions• Give free rein to imagination, avoid « sterilizing » & systematic criticism• Check, through the multicriterion decision matrix, if the proposed solutions :

Do no shift / transfer the problem elsewhere (imagine the possible negative consequences, hence the new resulting risk level). Appeal mainly to common sense and practical field experience

Comply with legal requirements Are long lasting, i.e. are stable (if not it’s only “partial” prevention) Are widely applicable (general in scope) Are acceptable to operators (who should thus be part of the brain storming session to be motivated)

• Estimate their potential efficiency (i.e. large probability to eliminate the undesirable event)

• Evaluate cost & deadlines• Additional site-specific criteria may be added• Eventually decide

MULTICRITERION DECISION TABLE (1/2)

CRITERIACRITERIA

PROPOSED PRENVENTIVE ACTIONSPROPOSED PRENVENTIVE ACTIONS1a1a 1b1b 1c1c 2...2...

Legal complianceLegal compliance

Non-transfer of the riskNon-transfer of the risk

Long-lasting (i.e. stable) measureLong-lasting (i.e. stable) measure

Deadline (compatible with operations)Deadline (compatible with operations)

CostCost

Widely applicableWidely applicable

Potential efficiencyPotential efficiency

Acceptable to operatorsAcceptable to operators

OVERALL RANKINGOVERALL RANKING

CO

MPU

LSO

RY

CO

MPU

LSO

RY

DES

IRA

BLE

DES

IRA

BLE

USED USED RATINGRATING

++ OO --

COSTCOST

DEADLINEDEADLINE

EFFICIENCYEFFICIENCY

OTHERSOTHERS

CHEAPCHEAP

SHORTSHORT

EXCELLENTEXCELLENT

YESYES

RELATIVELY RELATIVELY EXPENSIVEEXPENSIVE

RELATIVELY RELATIVELY LONGLONG

AVERAGEAVERAGE

DOUBTFULDOUBTFUL

TOO TOO EXPENSIVEEXPENSIVE

TOO LONGTOO LONG

POORPOOR

NONO

MULTICRITERION DECISION TABLE (1/2)

ELIMINATION OF INCIDENTS CAUSES

it’s freezing

no sweater

doesn’t know

has forgotten

CAUGHT A COLD

MAKES A MISTAKE

TO AVOID : ELIMINATE :

A

B

A

B

C

C

« C »

« C »

&&

oror

« A » « B »oror

« A » « B »&&

CREATES AN CREATES AN AMBIANCE OF AMBIANCE OF CONFIDENCECONFIDENCE

THE FOLLOW-UP PHASE IS FUNDEMENTAL :

There is usually a large gap between the number of decided actions and the number of actual achievements.

« Many safety initiatives fail because they never succeed in turning enthusiastic commitment into actions. »

The rigorous implementation of the CTA method should allow to not exclusively depend on the personnel’s enthusiasm, but to get convincing result thanks to a clever and efficient management of the incidents.

HAVING A BETTER KNOWLEDGE AND HAVING A BETTER KNOWLEDGE AND ASSESSMENT OF THE RISKSASSESSMENT OF THE RISKS

TAKING ADEQUATE MITIGATING & TAKING ADEQUATE MITIGATING & PREVENTIVE MEASURESPREVENTIVE MEASURES

4 - IMPLEMENTATION & FOLLOW-UP

IMPLEMENTATION AND FOLLOW UP MATRIX

Prevention Target

Contributing factor

(cause matrix)

Actionselected

PriorityApproval from Management

Implemented by

Follow up by

Target Date

ClosedYes / No

EXERCISE 7

BUILD UP THE CAUSE TREE FOR THE FOLLOWING INCIDENT :

FATAL CAR ACCIDENTFATAL CAR ACCIDENT

On 23/3/94, at around 18h30, a fatal car accident occurred between RlO CULLEN and CANADON ALPHA (Argentina).

In a road bend, the driver of the car - a NISSAN pick-up, apparently in good condition - lost control of the latter, meanwhile he was driving at a speed of about 80-100 km/h. The car overturned and rolled over several times.

The driver has been ejected at about 5m away from the vehicle, and has been deeply injured. He died a few days later. The passenger has not been ejected, and suffered only light injuries. None of them had the safety belt fastened.

The road was a stony track, narrow and dry. There was no wind nor rain, visibility was good.

These two people were working for a local company, just contracted by TOTAL AUSTRAL for the construction of a guardroom at the Canadon Alpha plant entrance. The purpose of the trip to RlO CULLEN was to meet with TOTAL staff and to define the electrical hardware and set-up.

TOTAL standard contractual terms clearly specifies as follows :

The driving speed shall not exceed 60 km/h on non-asphalted roads,

The use of the safety belt is compulsory.

NB At the time of the accident, wearing of safety belts was not yet compulsory in Argentina.

Rescue means ?

Driving skills ?

Road bend

Stony track

Narrow track

OR

OR

OR

OR


It is 18h30

Not informed

Has forgotten

Motivation ?Does not

applyinstructions

No speed limitation device

Urgent meeting

Comfort speed ?

High speed

Tiredness ?

Car condition ?

Lostcontrol

of the car

No rollover bar

Caroverturned

Not informed

Has forgotten

Framedeformation

Door opens

Ejection force

Safety instructionsnot enforced

No control

Meeting in R.Cullen

Doesnot know

instructions

Ejectedfrom the car

Deep injuries

Death

Hits carequipment

Passengerinjured

Has nosafety belt

OROR

Drives the car

EXERCISE 8

BEAM'S INCIDENT TOTALEXBEAM'S INCIDENT TOTALEX

After completion of the drilling operations, heavy beams are stacked on the roof of a porta-cabin with a large crane (20 m boom) located at 15 m from the porta-cabin. The purpose is to transport these beams laying on top of the porta-cabin to the next drilling location.

The operation is supervised by the crane driver ‘X’, and the helper ‘Y’ stands on the roof of the porta-cabin to receive and position the beams.

The porta-cabin is 3 m wide and is located at 1.5 m out of the vertical of a 20 kV electrical line supplying power to the site.

During the lifting operation, the crane wire came too close to this line : an electrical arc was created and burnt ‘Y’, who consequently Iost his balance. He then fell down onto the ground and was injured.

NB (non-reported but plausible facts, which rnay help to build the cause tree):

‘X’ and ‘Y’ probably knew that the electrical line was under tension, but didn’t take this fact into consideration.

‘X’ (crane driver) cannot simultaneously watch the top of the boom (to check if it comes close to the electrical line) and the Iift itself when the latter comes close to the porta-cabin’s roof.

Hazardous areas where the crane should not be allowed to work in are not properly identified and marked.

‘Y’ had no safety harness.

Apparently, this was the only usual way of transportation for these beams...

1/3

CRANE

PORTA-CABIN

20kV LINE

RD 373

1,5 m

20kV LINE

1,5 m

10 m

3 m

15 m

2/3EXERCISE 8

3/3

BUILDING AND CIVIL ENGINEERING WORKS AND ALL OTHER WORKS CONCERNING BUILDINGS.

Works near electrical lines, ducts or installations must comply with prescriptions of title 12 of decree 65-48 of 8 January 1965

MANOEUVRE NEAR BEAR LIVE PARTS

50 000 V or more : 5m

less than 50 000 V : 3m

EXERCISE 8


7

Beams transported Beams transported to next locationto next location

End of drillingEnd of drilling

Heavy Heavy beamsbeams

No other mean of No other mean of transportation ?transportation ?

Has no Has no protectionprotection

Using wire Using wire slingsslings

10

2

No other No other crane crane

available ?available ?

Site power Site power supplysupply

Not knownNot known

No pre-job No pre-job reminderreminder

No PTW reminderNo PTW reminder

No visual No visual warningwarning

4

X drives the X drives the cranecrane

Unknown Unknown regulationregulation

OR

ORNo TOTAL safety No TOTAL safety

supervisionsupervision2

8

9

9

5

6

Known but forgotten

20 kV not taken into account

11

Non-isolated line

Line under tension

Crane's wire too

close

Electrical arc

Holds the beam

Receives &

positions the beams Loses his

balance

Is on the roof

Falls down Y injured

Y burnt

Beams stacked on roofImpossible

to watch

Need a crane

Porta-cabin below HT line

Hazardous area not delimited

Saf. instr. not complied with

Crane gets closer to the

line

Crane high enough

20kV line @ 10m

3

1

EXERCISE 11 - PROPOSED PREVENTIVE ACTIONS

IDENTIFIED PREVENTION TARGETS PROPOSED PREVENTIVE ACTIONS

1. No protection To be supplied (harness, handrails ?) if this transportation means is still used.

2. Not possible to watch proper This operation requires a dedicated supervisor. When hazardous operations are conducted, it is recommended to request a safety officer.

3. Unknown regulation To be included In handling standing instructions.

4. Non-delimited hazardous areas for crane activities To be compulsorily done.

5. Crane’s size What is the sizing parameter (weight of beams or height of bungalow ?)

6. DriIIing location power supply from overhead electrical network A priori, nothing can be changed. Reconsider positioning of equipment close to HT lines.

7. No other means of transportation To be seriously questioned.

8. No warning signs To be done. Remind everyone with safety rules concerning work close to high-voltage lines.

9. No PTW nor pre-job safety reminders Enforce the use of PTW check-lists and organise pre-job meetings prior to starting up hazardous

operations.

10. Non-isolated line Isolation should not be required, if other precautions are properly taken.

11. Use of wire slings Better use nylon slings (isolating material).

Thank you Thank you for your for your

attention.attention.

Thank you Thank you for your for your

attention.attention.

NGI-Cause Tree Analysis

Education

Transcript of NGI-Cause Tree Analysis