You now analyse the information to find out how and why things went wrong. Your information gathering has told you what happened, now analyse this to learn what allowed it to happen.


To get rid of the weeds you must dig up the root. If you only cut off the foliage, the weed will grow again.


What will be the most effective way to stop similar incidents happening again?

  • If you deal with the immediate cause, then you can stop the same type of incident happening again. However, similar incidents may be rare, so this is not very effective. It can be a short term fix.
  • If you find the root cause of the incident and put actions in place to stop this, then you can prevent a wider range of incidents, possibly with more serious consequences. This is the best option.

Investigations that find human error is the sole cause (someone is to blame) have usually not looked at the underlying causes that make human errors inevitable.

How to find the cause of an incident

5 whys

5 whys is a simple methodology to look at what causes incidents.

  • Start by writing down the incident, and ask Why did this happen? This is the immediate cause.
  • Now ask again “why did this happen?’ This is the underlying cause.
  • Continue to ask “why did this happen?’ until there is no answer. This is the root cause.

The number of times you have to ask ‘Why?” is not important. Often it is 5…. but could be more or less.

Cause of incidents

To prevent adverse events, you need to provide effective risk control measures which address the immediate, underlying and root causes.

Root Cause Analysis

Immediate cause: the most obvious reason why an adverse event happens, eg the guard is missing; the employee slips etc. There may be several immediate causes identified in any one incident

Underlying cause: the less obvious ‘system’ or ’organisational’ reason for an adverse event happening, eg pre-start-up machinery checks are not carried out by supervisors; the hazard has not been adequately considered via a suitable and sufficient risk assessment; production pressures are too great etc.

Root cause: an initiating event or failing from which all other causes or failings spring. Root causes are generally management, planning or organisational failings.

An example

Using Proactively

The ‘why did this happen?’ section of the form is where you will carry out the root cause analysis.

To help decide which are the appropriate boxes to tick, click the blue info button for a more detailed description with examples of what each of the items mean.

Updated on March 8, 2022

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