What is barrier analysis?
Barrier analysis is an investigation technique based on a simple idea: harm happens when a hazard (an energy source or condition) reaches a target (a person, product, patient, asset or the environment) because the barriers that should have separated them did not work. By examining each barrier, you find out where the system's defenses broke down, which points directly to the root causes and corrective actions.
The technique comes from the MORT (Management Oversight and Risk Tree) tradition and is widely used in occupational safety, process safety, healthcare and quality investigations. It is the practical side of the "Swiss cheese" model of accident causation.
Types of barriers
| Type | Examples |
|---|---|
| Physical | Machine guards, walls, containment, packaging, segregated storage |
| Engineering | Interlocks, alarms, automatic shutdowns, poka-yoke devices, system validations |
| Administrative | Procedures, permits to work, checklists, supervision, second-person verification |
| Human | Training, qualification, experience, attention, fitness for duty |
| Natural / distance | Distance, time, location or isolation separating the hazard from the target |
Barrier status
- Effective: the barrier worked as intended, for example it limited the consequences.
- Weakened: the barrier was present but degraded, so it only partly worked.
- Failed: the barrier was in place and used, but did not work.
- Not used: the barrier existed but was bypassed, ignored or not applied.
- Missing: a barrier that should have existed did not.
Each status uses a distinct icon as well as a color in the diagram, so it stays readable in print and for color-blind readers.
Barrier analysis example
The example investigates a hand injury while clearing a conveyor jam. Of six barriers, the fixed guard was weakened by an unassessed modification, the door interlock was bypassed with a spare key, lockout/tagout was not applied because the SOP exempts "minor servicing", no jam-clearing tool was provided and training was out of date. Only the emergency stop worked, limiting the injury. Several barrier failures share one theme, changes made without assessment, which is a systemic root cause worth tracing further with a change analysis or a root cause tree.
Choosing better barriers
When recommending new or improved barriers, follow the hierarchy of controls: elimination, substitution, engineering controls, administrative controls and finally personal protective equipment. Physical and engineering barriers are more reliable than procedures and training alone. Several independent barriers are stronger than one barrier, because their weaknesses are unlikely to line up.
How to use this Barrier Analysis tool
- Describe the event. Summarize what happened and the harm or near miss that resulted.
- Identify the hazard and the target. Name the energy or source of harm (the hazard) and the person, product or asset that was affected (the target).
- List the barriers. Add every barrier between the hazard and the target, in order: physical, engineering, administrative and human. Include barriers that should have been there.
- Assess each barrier. Set each barrier's status: effective, weakened, failed, not used or missing, and describe how it performed.
- Ask why. For each barrier that did not work, record why. These answers point to the root causes.
- Recommend and export. Add recommendations to restore, strengthen or add barriers, then export the analysis to your incident or CAPA record.
Frequently asked questions
What is barrier analysis?
Barrier analysis is an incident investigation technique that identifies the hazard (the source of harm), the target (what was harmed) and every barrier that should have kept them apart. Each barrier is assessed to see whether it was effective, weakened, failed, not used or missing, and why.
What are examples of barriers?
Physical barriers include guards, walls and containment. Engineering barriers include interlocks, alarms and automatic shutdowns. Administrative barriers include procedures, permits and supervision. Human barriers include training, competence and situational awareness. Distance and time can also act as barriers.
How does barrier analysis relate to the Swiss cheese model?
James Reason's Swiss cheese model describes defenses as slices with holes; an accident happens when holes line up. Barrier analysis is the practical method for finding those holes in a specific event: which defenses existed, which failed and why they failed.
When should I use barrier analysis?
Use it for safety, environmental and quality incidents where harm reached a person, product, patient or asset that should have been protected, for example injuries, contamination, product mix-ups or data integrity breaches. It works well alongside change analysis and root cause trees.
Is barrier analysis the same as bowtie analysis?
They are related. A bowtie is a proactive risk tool that maps threats, preventive barriers, the top event, mitigating barriers and consequences before anything happens. Barrier analysis is usually reactive and examines how barriers performed in an actual event.
Can I export my barrier analysis?
Yes. Export a PDF report with the barrier diagram and table, a PNG image, an Excel workbook or a CSV, or save a .json file to keep working later. It is free and your data stays in your browser.