Tripod Incident Investigations

The tripod method is a way of conducting incident analysis. It is mostly used for high risk, complex incidents, since it is a very extensive and detailed method. Training is highly recommended when using the tripod method.

The Three Step Principle of Use!

A Tripod Beta tree is built in three steps. The first step is to ask the question: ‘what happened?’. All the events that happened in the incident are listed as a chain of events. The next step is to identify the barriers that failed to stop this chain of events. The question that is asked in this step is: ‘How did it happen?’. When all the events and the failed barriers in between are identified, the reason for failure of these barriers is analyzed. The last question for this step is: ‘Why did it happen?’. For each of the failed barriers a causation path is identified.

One of the most important aspects of Tripod Beta is that it assumes that human behavior resulting in failures is influenced (determined) by latent failures in the context of an organization. If these latent failures are not addressed, only symptoms are being tackled. This is why a human behavior theory is a key element of Tripod Beta.

What is an Incident? A sequence of logically and chronologically

related deviating events involving an incident that results in injury to personnel or damage to the environment or material assets.

Three phases in Incident investigation

Collecting evidence and facts

• Human or testamentary evidence Human or testamentary evidence includes witness statements and

observations.

• Physical evidence Physical evidence is matter related to the Incident (e.g. equipment,

parts, debris, hardware, and other physical items).

• Documentary evidence Documentary evidence includes paper and electronic information,

such as records, reports, procedures, and documentation.

Analysis of evidence and facts

• What happened where and when?• Why did it happen?

types of causal factors: Direct cause Contributing causes Root causes

Methods for Incident investigation

• TRIPOD• Barrier analysis • Change analysis. • Events and causal factors analysis

OTHER Incident INVESTIGATION METHODS

• Fault tree analysis• Root cause analysis • Events and causal factors charting (ECFC) • Event tree analysis• MORT • Systematic Cause Analysis Technique (SCAT) • (Sequential timed events plotting) • MTO-analysis • Incident Analysis and Barrier Function (AEB) Method • Acci-map

TRIPOD _BETA

DefinitionAdvantages Phases:

• Diagram Tripod_beta• Hazard conduct• Incident causation model

Diagram Tripod_betaElements

• Event• Hazard• Target

Hazard conduct

Swiss cheese model

- Organisations manage risk using ‘barriers’

- Barriers – use of equipment, design of plant (redundancy, overflows, etc.), following rules, procedures, standards…

…… usually barriers are people doing a job

- Barriers are ‘functions’

Why incidents happen (1)

Why incidents happen (2)

Incidents happen when barriers fail.

Why do barriers fail? The Tripod causation path

An organisation

Error / violation promoting conditions

That influences the personCreates To take action or inaction

That causes barriers to fail

That result in

Incidents, incidents and business upsets

• SMS• Leadership• Culture

• Performance influencing factors (PIFs)

- Competence- Fatigue- Environment- Supervision- Task- Etc.

• Human action or inaction• slips, lapses,

mistakes, violations

Underlying causes

Immediate causes

Preconditions

Knowledge.energyinst.org

Why do barriers fail? The Tripod causation path

An organisation

Error / violation promoting conditions

That influences the personCreates To take action or inaction

That causes barriers to fail

That result in

Incidents, incidents and business upsets

• SMS• Leadership• Culture

• Performance influencing factors (PIFs)

- Competence- Fatigue- Environment- Supervision- Task- Etc.

• Human action or inaction• slips, lapses,

mistakes, violations

Underlying causes

Immediate causes

Preconditions

Types of human failure – the ‘immediate cause’

Intended actions Unintended actions

Violations Mistake SlipLapse

Errors

Human factors – the ‘PIFs’ (two similar models)

Job Individual

Organisation

Task complexity.Facilities.Environment

Culture, leadership, supervisors, rules and procedures

Personality, psychology, height, weight, competency, fatigue

1. Organisational change (and transition management) 2. Staffing arrangements and workload3. Training and competence (and supervision)4. Fatigue (from shiftwork and overtime)5. Human factors in design:

(a) General(b) Alarm handling(c) Control rooms(d) Ergonomics – design of interfaces(e) Ergonomics – health ergonomics

6. Procedures (especially safety critical procedures)7. Organisational culture (and development)8. Communications and interfaces9. Integration of human factors into risk assessment and investigations (including

Safety Management Systems)10. Managing human failure (including maintenance error)

Human factors Top 10 issues

EventFailed barrier

EventEvent - Agent

EventObject

Agent

Object

Failed barrierFailed barrier

Immediate causePreconditionUnderlying

cause

Investigation (e.g. Tripod Beta)