Data collection : the art of isolating objective facts
Building a solid cause tree depends entirely on the quality of the information gathered during the field investigation. The OHS professional must act with the rigor of a technical investigator.
Distinguishing facts from opinions and judgments
This is the golden rule of the method : a cause tree is built only with objective, verifiable, measurable, and indisputable facts.
- An opinion is a personal interpretation ("The operator was tired and not paying attention"). It must be excluded from the investigation.
- A judgment is a value judgment ("The operator was careless"). It adds no technical value.
- A fact is an indisputable physical reality ("The operator was wearing new safety shoes", "The forklift speed was 12 km/h").
The investigation should be conducted as soon as possible after the event, directly on-site, by interviewing witnesses and the victim in an atmosphere of trust, completely removed from any disciplinary context.
Fact taxonomy: routine vs. non-routine
To populate the matrix, the collected facts must be classified into two categories :
- Routine facts : these represent the normal operating state of the workshop, machines, or company processes (e.g., the task is usually performed by two people).
- Non-routine facts (or variations) : these are the anomalies, incidents, breakdowns, or last-minute changes that occurred specifically on the day of the accident (e.g., the second operator was absent that morning).
It is almost always the combination of routine and non-routine facts that triggers the accident trajectory.
Rules for creating the tree diagram
The tree of causes is a graphic representation built from right to left. You start with the final event (the accident) and work backward through time by systematically asking the following question: "What was required for this fact to occur ?" and "Was this sufficient ?".
The three logical connection codes
To link facts together on the antecedent diagram, the method requires three types of logical connections :
- Direct sequence : fact A was necessary and sufficient to produce fact B.
- Conjunction : several independent facts (A AND B) were simultaneously necessary to cause fact C.
- Disjunction : a single fact A led to several distinct consequences (B AND C).
[ Organizational Antecedent A ] ──┐
├─► [ Technical Variation C ] ──► ( ACCIDENT )
[ Behavioral Fact B ] ─────────┘
When should you stop tracing causes ?
Theoretically, a tree could be traced back to the company's inception. In practice, the OHS professional should stop the investigation when they reach deep organizational or managerial root causes over which the company has real power to act and where corrective measures will benefit the entire system.
Translating the graphic matrix into an OHS prevention plan
The cause tree is a diagnostic tool. Its purpose is to identify breaking points where the company can insert safety "barriers." For every fact identified in the tree, the working group must seek concrete corrective actions.
To effectively manage the transition from graphic analysis to field action, using specialized digital solutions is essential. Using Symalean's workplace accident management software allows you to properly document your tree while automating the tracking of associated action plans, ensuring that investigation findings do not go to waste.
Furthermore, to ensure the long-term success of these action plans, it is essential to ensure that management and teams have the required safety skills. Integrating OHS training into the heart of your digital strategy by relying on software to manage declarations for the prevention passport ensures that the human barriers defined during the investigation remain operational and compliant with legal requirements.
.jpg)
The cause tree method transforms a negative event into a source of organizational learning. By replacing subjectivity with facts, it helps improve workplace social dialogue and mobilizes all stakeholders (management, safety officers, employee representatives) around a common goal: designing a safer work environment.
