An Introduction to Incident Investigation, Hazard Identification Techniques

 What Are Incident Techniques?

Incident investigation is a mandatory requirement of any management system as well as national legislation also demands that all kinds of incidents occurring at the workplace must be investigated. The main important problem here is that the incident investigation is complex and experience is required to perform the investigation process.

The main important reason behind carrying out an investigation is to learn the root cause of the accident and contributing factors instead of blaming someone. The main goal is to ensure that the incident doesn't occur again in the future and everyone is safe. 

Now the investigation can be performed using multiple techniques to learn the root causes. Few of these techniques are mentioned below;

1. Fault Tree Analysis
2. Event Tree Analysis
3. BowTie Analysis Method
4. Swiss Cheese Model
5. Root Cause Analysis

Each of the above-mentioned techniques is elaborated below for easy understanding. These techniques are not only for investigation, but are used for identification of hazards, preparing risk assessments also to check how system can fail.

1. Fault Tree Analysis - FTA

Fault Tree Analysis is an analytical technique used to identify the multiple causes behind the incident. Not only in incident investigation, but this technique is also used in detailed risk assessment. To understand this technique consider a tree upside down. The top side of the tree is called the Top Event. After it works is done logically downward by placing contributing factors leading to the incident. Each branch of the tree is developed further until the primary event is reached.

The main purpose or focus of carrying out the Fault Tree Analysis is to;

• Identify the multiple causes leading to an incident
• What preventive measures need to be taken

The diagram uses a set of symbols, labels, and identifiers. These are mentioned below;

• Event: It represents the top event or sub-event
• AND Gate: Output will exist only if all inputs are existing simultaneously
• OR Gate: Output will exist only if anyone input is existing
• Basic Fault: It represents the root cause of the incident

Here, an example is to explain how Fault Tree Analysis can be developed for any kind of case. 

Imagine a fire incident took place in the workplace and as an HSE officer you are tasked to perform the incident investigation and prepare a report. The diagram will be developed and every event will be mentioned.

For explosion 3 basic things are required;

• Fuel
• Oxygen
• Ignition Source

As the Fire is the top event, it will be mentioned on top of the diagram. The And Gate will be used to connect the Fire with the 3 basic elements. Each basic element will be further divided into sub-categories to develop a comprehensive diagram.

Through the diagram, it can be seen the main event is on top and is connected with basic elements through AND Gate, while further OR Gate is used to represent that if any of burning material with ignition source is available, the fire can erupt.

2. Event Tree Analysis - ETA

Event Tree Analysis is concerned with the identification and evaluation of consequences of an event after it has taken place. In Event Tree Analysis, the main event is called Initiating Event. The Event Tree Analysis is done to identify the consequences occurring due to loss-making incidents, evaluate them, and decide how to mitigate them to a reasonable level. 

The main purpose of the Event Tree Analysis is to investigate the consequences of loss-making events in order to make ways of mitigating them to reasonable level. 

Following states are involved in carrying out an investigation process;

• Identification of initiating event.
• Identification of controls assigned to deal with Initiating Event e.g., automatic fire safety system.
• Event Tree construction with the Initiating Event and proceeding through the conditions.
• Establish the resulting Loss-Event Sequence.
• Identification of critical failures.
• If data is available, quantify the tree to check the probability or frequency of each possible outcome.

There are lot of ways constructing an Event Tree Analysis. The typical way used is binary logic gate, e.g., a gate that has only two options such as Success/ Failure or Yes/ No, On/ Off. It is started from left side with the initiating event and move right with sub-events, branching progressively. 

The above picture indicates how the Event Tree Analysis is developed and each branch is divided into sub-events with two possible results. 

To learn the frequency or probability, each event will be quantified. 

3. BowTie Analysis

BowTie method is combination of Failure Tree Analysis & Event Tree Analysis. In this analysis technique, the failure threats and respective consequences are discussed together. When both techniques are combined, a BowTie like shape occurs. 

In BowTie, Initiating Events on the left lead to the critical event (Main Event). Hereafter, the Main Event leads to respective consequences towards right. These consequences need to be mitigated through the design of barriers.

The risk control concept relies on two methods listed below;

• Place barriers between realization of hazards/threats and Main Event (see FTA section in BowTie)
• Place barriers between Main Event and consequences (see ETA section in BowTie)

Each barrier should be assigned with a reference number for easily identification and if they are similar to multiple event initiators.

4. Swiss Cheese Model

In this technique piece of cheese is modelled as a barrier against threat. The holes in the slice of cheese is represented as weakness. These weaknesses are continuously varying in size and position in the system. If these holes align themselves so that hazard can pass through them easily, the system gets fail and incident takes place. 

5. Root Cause Analysis - RCA

Root Cause Analysis (RCA) is a method to analyse the basic preventable root cause behind any incident. Not only this, behaviour that triggered this incident and possible consequences are also established. 

Terms

FTA: Failure Tree Analysis
ETA: Event Tree Analysis
RCA: Root Cause Analysis