Risk assessment is the structured process of identifying the hazards of a machine or application, estimating and evaluating their risks, and deciding whether further risk reduction is needed. In robot safety, it is the foundation of every compliant installation: it determines which safeguards, safety functions and operating procedures a robot cell or collaborative application requires.
A key point that newcomers often miss is that risk assessment applies to the robot application, not to the robot alone. The same arm can be harmless when moving a foam part slowly and dangerous when carrying a sharp blade, so the tool, workpiece, layout, speeds and human tasks must all be assessed together.
The risk assessment process
The general method for machinery is defined in ISO 12100, and robot-specific requirements are added by the ISO 10218 series for industrial robots and robot applications. The process is iterative: after each risk reduction measure, the assessment is repeated to confirm that the remaining risk is acceptable and that the measure did not introduce new hazards.
| Step | Key question | Typical output |
|---|---|---|
| Determine limits | What is the intended use, space, time and who is involved | Description of tasks, modes and users |
| Identify hazards | What can cause harm in every phase of life | Hazard list per task and operating mode |
| Estimate risk | How severe and how likely is the harm | Risk level per hazard |
| Evaluate risk | Is the risk acceptable as it stands | Decision on whether reduction is needed |
| Reduce risk | Which measures remove or lower the risk | Design changes, safeguards, information |
| Document and verify | Were measures implemented and effective | Risk assessment report and validation records |
Hazard identification must cover every life-cycle phase and operating mode, not just automatic production. Teaching, maintenance, cleaning, fault recovery and changeover are where many robot injuries occur, because people are inside the workspace while energy is still present.
Responsibility follows the application. In many jurisdictions, including under European machinery legislation, a documented risk assessment is a legal precondition for placing a machine on the market or putting it into service. For a robot cell, the integrator usually owns the assessment of the complete system, while the robot manufacturer supplies the information on its own residual risks and safety functions.
Estimating robot risk
Risk is a combination of the severity of possible harm and the probability of that harm occurring. The probability is usually broken down into the frequency and duration of exposure, the probability of the hazardous event and the possibility of avoiding or limiting the harm.
| Element | Typical levels | Robot-specific considerations |
|---|---|---|
| Severity of harm | Slight, reversible injury to serious or fatal injury | Payload, tool sharpness, speed, pinch points |
| Exposure frequency and duration | Rare and short to frequent or continuous | How often operators load parts or intervene |
| Probability of hazardous event | Low, medium, high | Reliability of control system, foreseeable misuse |
| Possibility of avoidance | Possible under conditions or scarcely possible | Robot speed, warning, space to step away |
Robot hazards include mechanical hazards such as impact, crushing, shearing and clamping; unexpected start-up; ejected parts or dropped payloads; electrical and thermal hazards; and ergonomic hazards in collaborative tasks. Hazards from the end effector and the process, such as welding, cutting or adhesives, often dominate the risk profile.
Reducing risk with the three-step method
ISO 12100 prescribes a strict order of preference for risk reduction, known as the three-step method. A lower step may be used only when the higher steps cannot reduce the risk sufficiently.
| Priority | Measure type | Robot examples |
|---|---|---|
| 1. Inherently safe design | Remove the hazard or reduce it by design | Rounded tooling, lower payload, limited force, larger gaps |
| 2. Safeguarding and protective measures | Guards and safety functions | Fences, light curtains, laser scanners, safety-rated speed and separation monitoring |
| 3. Information for use | Warnings, training, procedures | Signs, manuals, lockout procedures, operator training |
Safety functions such as an emergency stop, protective stop, safety-rated reduced speed or safe zones are implemented in a safety controller and must reach the required reliability. That requirement is expressed as a performance level (PL a to e) under ISO 13849-1 or a safety integrity level under IEC 62061, and the risk assessment is what determines the required level for each function.
Risk assessment for human-robot collaboration
In human-robot collaboration, physical separation is partly or fully replaced by safety functions, so the risk assessment carries even more weight. The guidance originally published as ISO/TS 15066 describes power and force limiting with body-region thresholds for transient and quasi-static contact, and the current ISO 10218 series includes requirements for collaborative applications.
Typical collaborative measures are speed and separation monitoring, in which a scanner slows or stops the robot as a person approaches, hand guiding, and safety-rated monitored stop. The assessment must check not only the robot’s contact forces but also the tool and workpiece, which frequently turn a low-risk collaborative robot into a high-risk application.
Common mistakes in robot risk assessments
Risk assessments fail most often through narrow scope and weak follow-through, not through incorrect formulas.
- Assuming a collaborative robot is safe by itself, without assessing the end effector, parts and task.
- Ignoring maintenance, teaching and fault recovery, where people are closest to hazards.
- Treating the assessment as paperwork completed after the cell is built, when design changes are expensive.
- Forgetting to repeat the assessment after changes to layout, tooling, speeds or software.
- Relying on training and warnings where guards or safety functions are technically feasible.
The idea in brief
A risk assessment is a careful look at everything that could go wrong around a robot before anyone works with it. The team asks who could get hurt, how badly and how often, and then decides what has to change.
The best fix is always to design the danger away, for example by using a softer tool or a slower motion. Fences and sensors come next, and warning signs come last, because they depend on people never making a mistake.
A practical scenario
A metalworking shop plans a collaborative robot that loads raw blanks into a CNC machine while an operator deburrs finished parts at a shared table. The integrator’s risk assessment lists hazards for production, changeover, clearing jams and cleaning, and finds that the robot itself is acceptable at reduced speed, but the sharp-edged blanks in the gripper could cause serious cuts in a collision.
The team changes the gripper to enclose the blank edges, adds a laser scanner for speed and separation monitoring at the shared table, and assigns a required performance level to each safety function. After validation tests confirm stopping distances, the residual risk is documented and the operators are trained on the new procedures, before the cell enters production.