Accidents in safety management are rarely caused by one mistake alone. The Swiss cheese model explains that incidents happen when several small weaknesses line up — like holes in slices of cheese — creating a clear path for hazards to slip through.
Each slice is a layer of defence, whether it is equipment, procedures, or human behaviour. When these layers fail at the same time, the result is an accident.
What is the Swiss Cheese Model in Behaviour-Based Safety?
The Swiss cheese model shows that accidents occur when multiple system gaps align. Each layer – procedures, equipment, and behaviour – acts as a defence. Behaviour based safety (BBS) strengthens the human layer through bbs observation and safety behaviour observation. Combined with a strong safety work culture, it helps close those gaps and prevent accidents effectively.
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What Is the Swiss Cheese Model?
The Swiss cheese model is one of the world’s most recognised frameworks for accident prevention. It explains why incidents occur even when multiple safety controls are in place. Every control layer has weaknesses or “holes”. When these holes line up, an accident happens.
This simple idea helps organisations understand that safety is never based on one barrier alone. It is based on many layers working together.
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A Brief History of the Swiss Cheese Model
The Swiss cheese model was introduced by psychologist James Reason in the late 1980s. His research focused on human error and the deeper organisational causes of accidents.
Originally developed for aviation and healthcare, the model quickly gained acceptance in other industries. Today, it is widely used in manufacturing, construction, chemicals, energy, and transport.
Its appeal lies in its clarity. It shows that accidents are rarely caused by a single mistake. They result from a series of small failures that come together.
Key Components of the Swiss Cheese Model
Understanding the Layers or Barriers
In the Swiss cheese model of safety, each “slice” represents a barrier. Barriers may be physical (equipment), procedural (SOPs), or human (training, behaviour). These barriers aim to stop hazards from reaching people.
What Are the Holes?
“Holes” represent gaps or weaknesses. They may appear due to human error, poor design, unclear procedures, rushed decisions, or missing controls. Holes shift and change, depending on workload, environment, or organisational conditions.
When Do Accidents Happen?
An incident takes place when the holes in multiple slices align. This alignment allows a hazard to pass through every layer without being stopped.
Number of Swiss Cheese Layers — What is “Correct”?
There is no fixed, universally agreed number of layers in the Swiss Cheese Model.
Why?
James Reason, who developed the model in the 1990s, never specified an exact number.
The model is conceptual, not a rigid framework.
Industries adapt the layers based on their risk profile.
The 4 Classic Layers in Reason’s Swiss Cheese Model
However, most formally accepted versions use 4 core layers:
Organisational Influences (Latent Conditions)
Meaning: Long-term decisions, culture, resources, and policies that shape safety.
Example: Inadequate staffing, cost-cutting, poor maintenance budgets.
Unsafe Supervision
Meaning: Failures in oversight, instructions, training, and monitoring.
Example: Supervisor ignores repeated unsafe forklift practices.
Preconditions for Unsafe Acts
Meaning: Environmental or human-factor conditions that make errors more likely.
Examples:Fatigue
Stress
Poor lighting
High workload
Unsafe Acts (Active Failures)
Meaning: Errors and violations that directly lead to incidents.
Examples:Bypassing PPE
Over-speeding a forklift
Not isolating equipment before maintenance
Industry Variations (Why 3, 5, or 6 Layers Sometimes Appear)
Aviation often uses 3 layers (latent → preconditions → unsafe acts)
Healthcare sometimes adds layers like Team Factors, Equipment Factors, Patient Factors
Different sectors adjust layers to fit their context:
- Process Safety may add Engineered Barriers, Procedural Barriers
👉 So, it is correct to say the model has “multiple layers that represent organisational, supervisory, environmental, and human defence barriers”.
Modern Modified Swiss Cheese Models Used in Industry
Over time, industries found the classic model difficult to use on the shop floor. The four academic layers made sense for analysis but were not easy for training, toolbox talks, or practical risk assessment.
So organisations created a more practical structure based on familiar categories of control.
The modern version includes three proactive layers and one reactive layer:
Engineering Controls
Physical and technical safeguards such as machine guards, interlocks, alarms, ventilation, and fire systems.
These controls reduce risk before humans interact with it.
Administrative Controls
Policies, planning, SOPs, supervision, training, PTW systems, and documentation.
If these controls are weak, gaps appear across the organisation.
Behavioural Controls
What people actually do.
This is where behaviour based safety, bbs observation, and safety behaviour observation play a central role. Behavioural controls either strengthen or weaken all other layers.
Post-Incident Mitigation
Emergency response and recovery actions activated after the incident occurs. These include first aid, rescue, containment, and evacuation.
Why this version is widely used
It matches the real-world structure of workplace controls. It is simple to teach, simple to audit, and directly linked to behaviour, supervision, and engineering design.
How the Classic and Modern Models Work Together
Both versions of the Swiss cheese model offer valuable insights.
The classic model explains why failures occur by focusing on organisational and human factors.
The modern model explains how failures occur in day-to-day operations using engineering, administrative, and behavioural controls.
Here is a simple way to see the relationship:
| Classic Layer | Modern Industry Equivalent |
|---|---|
|
Organisational Influences |
Administrative Controls |
|
Unsafe Supervision |
Administrative Controls |
|
Preconditions for Unsafe Acts |
Engineering + Administrative Controls |
|
Unsafe Acts |
Behavioural Controls |
Together, they show that an incident only occurs when several defenses fail at the same time. This is why strengthening all layers — physical, procedural, and behavioural — is essential for accident prevention, behavior based safety, and a resilient H&S culture.
Swiss Cheese Model in Safety (Industry-Wide Adoption)
Industries adopted the Swiss cheese model safety approach because it offers a structured way to study incidents and prevent repeat occurrences. Safety teams began using it for:
- root-cause analysis
- near-miss investigation
- human error assessment
- training and awareness
- design of new safety controls
The model encourages organisations to look beyond operator error and examine system weaknesses.
Human Error and the Swiss Cheese Model
Human Error Assessment in Practice
This model supports human error assessment, helping organisations understand why people make mistakes. It emphasises that behaviour is influenced by workload, environment, tools, supervision, and culture.
It reminds leaders that blaming people solves very little. Improving systems and behaviours creates lasting change.
Behaviour-Based Safety — Strengthening the Human Layer
One of the most important slices in the model is the human layer. This is where behaviour based safety (BBS) plays a direct role.
Through bbs observation, safety behaviour observation, coaching, and feedback, teams identify unsafe acts early. They learn what drives risky decisions and how to reinforce safer habits. This proactive approach makes bbs in safety a powerful way to prevent alignment of holes.
BBS also helps workers recognise triggers, distractions, shortcuts, and habits that may lead to incidents.
Swiss Cheese Model Example in Behavioural Safety
Imagine a worker entering a restricted area without authorisation.
Why did the unsafe act happen?
- The barrier (signage) was unclear.
- The procedure was not emphasised in recent training.
- A supervisor was not present to intervene.
- The worker assumed “nothing will happen”.
Several holes existed. When they aligned, the unsafe act occurred.
This shows how behavioural safety and system design must work together.
The Swiss Cheese Model in Process Safety
Application in High-Risk Industries
In process industries like chemicals, oil and gas, power plants, and pharmaceuticals, the model is central to process safety.
Layers may include:
- engineering controls
- alarms and interlocks
- emergency response systems
- training and competence
- permits to work
- supervision and audits
When even one layer weakens—such as a faulty valve, a missed inspection, or a misread indicator—other layers must be strong enough to prevent escalation.
The model helps teams design multiple robust defences rather than relying on a single control.
Relationship Between Swiss Cheese Model and LOPA
The Swiss Cheese Model and LOPA (Layer of Protection Analysis) are related because both rely on the idea of multiple barriers preventing an accident.
How They Connect
- Swiss Cheese = Qualitative (visual model showing how failures align)
- LOPA = Semi-quantitative (probability-based assessment of each barrier)
Corresponding Concepts
| Swiss Cheese Layer | LOPA Equivalent |
|---|---|
|
Engineering defences |
IPLs (Independent Protection Layers) |
|
Procedures & supervision |
Administrative controls |
|
Human behaviour & competency |
Human reliability factors |
|
Organisational factors |
Management systems |
Important Point:
LOPA demands barriers to be independent, but Swiss Cheese accepts that barriers may influence each other.
Where the Swiss Cheese Model Fits Among Modern Accident Causation Models
Comparative Table: Accident Causation Models
| Model | Core Idea | Focus Area | Strengths | How It Relates to the Swiss Cheese Model |
|---|---|---|---|---|
|
Swiss Cheese Model (James Reason) |
Accidents occur when multiple system weaknesses align. |
Human factors, organisational factors, supervision, defences. |
Simple visual concept, strong human-factors perspective, widely adopted. |
Baseline conceptual model showing how barriers fail together. |
|
Domino Theory / Loss Causation Model (Heinrich & Bird) |
Accidents result from a chain of causes — remove one domino to stop the sequence. |
Unsafe acts, underlying causes, lack of control. |
Foundation for modern safety thinking; easy to teach. |
Swiss Cheese expands Domino Theory by adding multiple layers & human factors, not just linear causes. |
|
Fishbone Diagram (Ishikawa) |
Breaks down complex causes into categories. |
People, process, equipment, environment, management |
Great for brainstorming and root cause analysis. |
Complements Swiss Cheese by helping identify “holes” in each layer. |
|
Fault Tree Analysis (FTA) |
Analyses how specific combinations of failures lead to a top event. |
Logical pathways and probability calculations. |
Highly structured; works well in engineering and process safety. |
Swiss Cheese is conceptual; FTA provides the quantitative pathway for the same alignment. |
|
Bow-Tie Analysis |
Visualises threats, controls, and consequences. |
Barriers, escalation factors, scenario management |
Superb for major hazard risk management. |
Both emphasise multiple controls; Swiss Cheese is broader and more behaviour/human factor-oriented. |
|
HEART (Human Error Assessment and Reduction Technique) |
Systematically estimates human error probability. |
Human reliability and performance shaping factors. |
Quantitative assessment of human error. |
HEART quantifies “holes” in the human-behaviour layers of Swiss Cheese. |
How Other Fields Use the Swiss Cheese Model
The power of the concept makes it useful in many fields, such as:
- Healthcare – preventing medication errors and surgical mistakes
- Aviation – flight safety and crew coordination
- Finance – fraud prevention
- Cybersecurity – layered defence strategies
- Public safety – disaster management
In every field, the message remains the same: good systems rely on multiple layers.
Using the Swiss Cheese Model in Organisations
Practical Ways to Apply the Model
Organisations can strengthen their safety systems by implementing a layered approach:
- Review and improve each barrier regularly.
- Conduct safety surveys to understand employee perceptions.
- Encourage open reporting of near-misses and unsafe acts.
- Use bbs observation to catch behavioural risks early.
- Strengthen leadership engagement to improve H&S culture.
- Communicate lessons learned across teams.
When every layer is strong, holes become smaller, and alignment becomes unlikely.
Building a Strong Safety Culture Around the Swiss Cheese Model
A strong safety work culture acts as a protective layer around all other controls. It encourages learning, accountability, respect, and shared ownership.
Leaders reinforce safe behaviour. Workers speak up. Teams collaborate.
This culture ensures that even if one slice weakens, the system remains resilient.
Bringing It All Together
The Swiss cheese model shows that effective safety is not about finding one root cause. It is about understanding how many small weaknesses can combine to create an incident.
By strengthening layers—technical, procedural, and behavioural—organisations build a dependable defence system. Combined with behaviour based safety, continuous improvement, and a strong safety culture, the Swiss cheese model becomes a cornerstone of modern accident prevention.
Swiss Cheese Model: Explains why accidents happen.
Behaviour-Based Safety: Provides a practical method to plug the human-behaviour gaps.
Safety Culture: Sustains those defences through shared values and collective vigilance.
FAQs on the Swiss Cheese Model and Behaviour-Based Safety
How does the Swiss Cheese Model help in accident prevention?
The Swiss cheese model shows how accidents happen when system weaknesses align. Strengthening every layer – process, equipment, and human behaviour – helps prevent incidents before they occur.
What is the link between the Swiss Cheese Model and Behaviour-Based Safety?
Behaviour based safety (BBS) strengthens the human layer of the Swiss cheese model through bbs observation and safety behaviour observation, reducing unsafe actions and closing behavioural gaps.
How does Behaviour-Based Safety support safety culture?
A strong safety work culture builds on behavioral safety practices and feedback. Regular safety surveys and bbs in safety initiatives promote ownership, shared responsibility, and continuous improvement within the H&S culture.
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About the author
Director – Sustainable solutions at Consultivo
Madhabi Guha specialises in the domains of ESG, Social Compliance, Business and Human Rights, Development Projects and focuses on supporting go-to-market teams along with customer and partner relationships. Madhabi has been working in the sustainability & business excellence advisory business for over 14 years.
Madhabi has been developing individuals, teams, and organisations in the areas of leadership, excellence and Human Factors in the field of sustainability, people and community.
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