In October 2024, a master's student at a French university’s teaching lab experienced a serious chemical splash while filtering a digested soil sample containing concentrated nitric acid. The syringe filter detached under pressure, spraying the corrosive liquid into the student’s face and eye. The student was wearing safety glasses and working in a fume hood, yet still sustained a burn.
The case study, published in ACS Chemical Health & Safety, outlines how the teaching team used the cause tree method to unpack this incident—and in doing so, demonstrated the value of a systems-based lab safety approach that goes beyond individual error.
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Mapping the mishap: inside the cause tree method
Rather than identifying a single point of failure, the cause tree method starts at the incident and works backward by asking, “What made this possible?” Each contributing factor becomes a tree branch, allowing investigators to visualize how small missteps and oversights combine to cause an accident. Developed as a structured form of root cause analysis, this method categorizes influences—procedural, behavioral, and environmental—and helps teams identify where preventive actions could break the chain of events. We break down how to build a cause tree later in this article.
In this case, the teaching team linked the nitric acid splash to a combination of decisions and design flaws, rather than focus on human error or victim blaming, which destroys lab staff engagement:
- The use of a 10 mL syringe, which was not specified in the protocol, increased the risk of filter detachment due to excess pressure.
- The student’s position at the bench diminished the protective function of the fume hood sash.
- The safety glasses provided inadequate facial coverage, allowing for chemical exposure.
These were not isolated lapses—they were symptoms of a system with unclear expectations, inconsistent safeguards, and insufficient guidance.
"A single efficient action on one of the branches of the tree should be sufficient to avoid the accident. Nevertheless, we decided to act on as many branches as possible by keeping in mind that the human behavior variable is the hardest to control and that future action cannot rely only on education and formation and even less on common sense," the study authors wrote, underscoring the need for systemic prevention over reactive fixes.
Preventing the next lab safety incident with systems-based solutions
The true strength of the cause tree method lies in how it informs corrective action. By charting each branch of the incident, the teaching lab was able to implement broad, integrated improvements:
- Protocols were updated to include syringe size, dilution requirements, ergonomic positioning, and pressure warnings.
- Equipment was upgraded to include sealed safety goggles and Luer lock syringes that reduce the risk of disconnection.
- Training was restructured to emphasize procedural steps and the rationale behind each one, strengthening risk awareness.
These changes were not reactive patches—they were proactive system corrections aimed at eliminating the conditions that allowed the incident to occur in the first place.
Applying the cause tree method in your lab
To help lab managers translate this approach into their environments, the cause tree method offers a practical, visual tool for structured investigations:
How to conduct a basic root cause analysis using a cause tree:
- Start with the incident at the far right of a diagram.
- Ask “What made this possible?” and map out all contributing factors.
- Use rectangles for fixed facts and circles for variable or unusual ones.
- Continue asking “What allowed this to happen?” for each node.
- Identify intervention points and decide on actions based on feasibility and impact.
This process supports better decision-making in the moment and creates a living roadmap for building resilient lab safety systems.
A cause tree helps visualize contributing factors to an incident and highlights where interventions can prevent future occurrences.
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What lab managers can take away
The most meaningful lesson for lab managers is that lab safety incidents are rarely the result of a single misstep. Instead, they arise from weaknesses in the system—weaknesses that can be uncovered and addressed through structured, holistic tools like the cause tree method.
Another key lesson is that they didn’t simply blame the victim for the accident. By approaching safety as a system, they were able to identify root causes and improve the safety of everyone doing these lab activities.
This approach empowers managers to:
- Identify interdependent failures across policies, behaviors, and tools
- Guide corrective action that improves systems, not just responses
- Foster a culture of prevention, where lab safety is built into the process, not bolted on after an incident
Rather than focusing solely on the incident, this case shows how the right investigative method can transform lab safety into an ongoing, informed prevention practice.
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