March 27, 2026

Safety Alert 136: Swiss Cheese Model

What is the Swiss Cheese Model?

The Swiss Cheese Model is a widely used safety concept that explains how accidents happen when multiple layers of defence fail at the same time.

Each slice of cheese represents a barrier or control measure, such as training, SWMS, JSA or tool inspection. The holes in the slices represent failures to complete the risk assessments/controls in each layer.

An accident occurs when the holes in all layers line up, allowing a hazard to pass through all the defences, resulting in injury, damage or loss.

Real-world example

Training for the task was not completed (hole in the training layer)
SWMS not followed correctly (hole in SWMS layer)
The worker was distracted and forgot the JSA (hole in the JSA layer)
Tools not inspected and PPE not worn properly (hole in the tool inspection layer)

These combined gaps result in an injury/accident that may have been prevented if any single layer had held.

Key takeaways

In every control matter, never assume someone else will catch the error.
Follow procedures exactly, shortcuts create holes.
Report hazards or near misses, help close the gaps in the system.
Always wear your PPE correctly and ensure all equipment is up to date, properly maintained, and safe to use. It's your personal layer of protection.
Be aware of your surroundings and speak up if something seems off or unsafe.

Further information

This safety alert references the work of Professor James Reason, whose research forms the foundation of the Swiss Cheese Model. You can read more in the original article here: "Human Error: Models and Management" by Professor James Reason.

For a visual explanation of this topic, watch the EGT video below.