Swiss Cheese Theory offers a powerful way to understand why fire safety incidents often stem from a combination of small lapses rather than a single glaring mistake. When you view fire safety through this lens, you see how good layered defences can stop problems before they become serious.

What Is Swiss Cheese Theory?

Swiss Cheese Theory (or the Swiss Cheese Model) describes how accidents occur in complex systems when multiple layers of safeguards each have weaknesses. These layers are like slices of Swiss cheese: they’re intended to block hazards, but each has holes — weaknesses that vary over time and circumstance. A harmful “initiating event” only gets through when the holes in several layers line up at the same moment, allowing risk to pass all the way through.

In fire safety, each “slice” is a control such as prevention measures, detection, compartmentation, escape routes, training, alarms, suppression systems, inspection routines, and management oversight. Any of these can have “holes” — absent or ineffective practices, poor maintenance, inadequate training, unclear procedures — and if multiple holes align, they can let a fire develop, spread, and harm people or property.

The Origin of the Model

The Swiss Cheese Model was developed by Professor James T. Reason, a British psychologist known for his work in human error and system safety. Reason argued that accidents are seldom caused by one mistake alone; instead, latent conditions within systems and active failures by individuals interact to create opportunities for things to go wrong. His work in the late 1980s and early 1990s, including the influential book Human Error and later research papers, made the model widely recognised across safety-critical fields. Reason’s model shifted the focus from “blaming the operator” to understanding how organisational processes, design choices, training, and management practices contribute to unsafe outcomes. The video below explains the model very well.

How This Applies to Fire Safety

Fire safety is inherently about managing risk through layers:

Prevention: keeping ignition sources and fuel apart.
Protection: fire-rated walls, doors, and compartmentation.
Detection and Alarm: systems that detect and alert early.
Suppression: sprinklers and extinguishers that control fire growth.
Escape and Evacuation: routes, signage, lighting.
Training and Procedures: staff know what to do when systems fail.
Inspection and Assurance: checks that systems work as intended.

If any one of these layers has gaps, there’s still a chance another layer will catch the problem. But when weaknesses align — for example, poor maintenance, inadequate training, and ineffective escape routes — fire safety can fail, even if each individual lapse seemed small on its own.

Le Constellation

The fire at Le Constellation bar on New Years Eve 2025 is a tragic demonstration of this theory. The fire was reportedly started when “fountain sparklers” ignited flammable ceiling foam. However, the magnitude of the event could have been greatly reduced if the proper layers of fire safety had been in place. For example, allegations now include a lack of venue fire safety inspections since 2019, even though annual checks were required, lack of staff fire safety training, obstructed emergency exits, and insufficient oversight of safety systems, to name just a few. Using Swiss Cheese Model, we can see that any one of these layers would have greatly reduced the loss of life and injury suffered on that night.

What This Means for You

Swiss Cheese Theory highlights three practical principles for robust fire safety:

1) Layered Defences Reduce Risk. Don’t rely on a single safety mechanism. If one layer fails, others should still protect people and property.

2) Change Creates New Holes. Renovations, changing usage patterns, new materials, or staffing changes can introduce latent weaknesses if not properly risk-assessed.

3) Regular Assurance Matters. Routine inspections, proactive maintenance, testing, and training shrink the holes in each layer, reducing the chance that they will align at an inopportune moment.

Common “Holes” to Look For

Fire doors wedged open or damaged.
Alarms with unresolved faults.
Blocked escape routes or poor signage.
Staff without formal fire safety training.
Delayed fire safety inspections or ignored action lists.
Use of combustible finishes without appropriate controls.
Missing, poorly placed or poorly maintained fire extinguishers.

Each of these is a relatively small issue on its own, but collectively they create a path for fire to overcome your defences.

What To Do Next

Seen through the Swiss Cheese lens, fire safety is about understanding how small gaps across prevention, protection, detection, evacuation and management can line up over time. A fire risk assessment is where those gaps are identified and dealt with before they align with an initiating event. At Fletcher Risk, we assess buildings as working systems, not static checklists. We look at how your premises is actually used, where controls have weakened, and which layers need strengthening to restore resilience. If you want confidence that the holes are not lining up in your building, speak to Fletcher Risk about booking a fire risk assessment. Please contact us today.

Disclaimer

This article is for general information only and does not constitute legal or professional advice. For specific premises fire safety compliance, consult a competent fire safety professional.

Fletcher Risk Team - 28 January 2026

Swiss Cheese Theory and Fire Safety: How Multiple Failures Combine to Create Risk