5 Whys Health and Safety | Incident Root Cause Analysis NZ

27 Jan Using the 5 Whys to Find the Real Cause of Health and Safety Incidents

Posted at 13:32h in Articles by Rachel Bell

When a health and safety incident occurs, it’s tempting to stop investigating once you’ve found an obvious cause.

“Someone wasn’t paying attention.”
“They didn’t follow the procedure.”
“It was just human error.”

But if you stop there, you’ll probably see the same incident happen again.

That’s where the 5 Whys methodology comes in. It’s a simple but powerful problem-solving tool that helps businesses dig beneath the surface and identify the true root cause of incidents – not just the symptoms.

What is the 5 Whys methodology?

The 5 Whys is a root cause analysis technique that involves asking “Why?” repeatedly – usually around five times – until you uncover the underlying cause of a problem.

This technique is now widely used across industries, including health and safety, manufacturing, construction, logistics and professional services.

The idea is straightforward:

Each answer becomes the basis for the next “Why?”

You stop once you reach a cause that the business can control, fix, or improve.

Why the 5 Whys works for health and safety

Health and safety incidents rarely have just one cause. They’re often the result of:

Gaps in training;
Poor systems or processes;
Inadequate supervision;
Time pressure or workload;
Outdated procedures; and
Unsafe equipment or environments.

The 5 Whys helps shift the focus away from blame and onto system improvements, which aligns well with New Zealand’s health and safety approach under the Health and Safety at Work Act 2015 (HSWA).

Example: Using the 5 Whys after a workplace injury

Let’s look at a simple example.

Incident:
An employee strains their back while lifting a heavy box.

Why #1: Why was the employee injured?
→ Because they lifted a heavy box incorrectly.

Why #2: Why did they lift it incorrectly?
→ Because they didn’t use a mechanical aid or team lift.

Why #3: Why didn’t they use a mechanical aid or team lift?
→ Because no equipment was readily available, and they were working alone.

Why #4: Why was no equipment available and no support provided?
→ Because the task wasn’t identified as a manual handling risk.

Why #5: Why wasn’t the risk identified?
→ Because the task hadn’t been assessed or included in a hazard or risk register.

Root cause:
The issue wasn’t just poor lifting technique – it was a failure to identify and manage a manual handling risk.

That root cause is something the business can fix.

When should you use the 5 Whys?

The 5 Whys can be used after:

Workplace injuries;
Near misses;
Property damage;
Equipment failures;
Unsafe behaviours or trends; and
Repeated incidents of the same type.

It works particularly well for low to medium-complexity incidents where the cause isn’t immediately obvious.

For serious or complex incidents, the 5 Whys can still be useful – but it may need to be combined with other investigation methods.

How to run a 5 Whys investigation effectively

To get meaningful results, keep these tips in mind:

1. Focus on systems, not people
Avoid stopping at answers like “human error” or “they didn’t follow the rules”. Ask why the system allowed that to happen.

2. Use evidence, not assumptions
Base each “Why” on facts from the incident, not guesses or opinions.

3. Involve the right people
Workers often know where processes break down. Including them improves accuracy and buy-in.

4. Document the findings
Record each question and answer so the reasoning is clear and traceable.

5. Link findings to corrective actions
The goal isn’t just understanding – it’s prevention. Each root cause should lead to a practical improvement.

How the 5 Whys supports compliance in NZ

Under the Health and Safety at Work Act, PCBUs must take reasonably practicable steps to eliminate or minimise risks. Investigating incidents properly is a key part of that duty.

Using a structured method like the 5 Whys helps demonstrate that your business:

Takes incidents seriously;
Looks beyond surface causes;
Acts to prevent recurrence; and
Continuously improves health and safety systems.

This can be particularly important if WorkSafe ever reviews how incidents were managed.

Common mistakes to avoid

Stopping too early (one or two Whys isn’t enough);
Treating “training” as the default answer;
Turning the process into a blame exercise; and
Failing to follow up with real changes.

If the same type of incident keeps happening, it’s a sign the root cause hasn’t truly been addressed.

Putting the 5 Whys into Practice

The 5 Whys methodology doesn’t require specialist software, long workshops, or complicated forms. It’s simple, practical, and effective – when done properly.

By using the 5 Whys to investigate health and safety incidents, businesses can move beyond surface-level fixes and make changes that genuinely reduce risk and prevent harm.