Risk assessment per EN ISO 12100: complete guide
The risk assessment is the core of every CE marking in mechanical engineering. EN ISO 12100 describes the basic methodology with which manufacturers systematically identify and evaluate all hazards of their machine and reduce them through suitable protective measures. This guide explains the entire process step by step.
What is EN ISO 12100?
EN ISO 12100 ("Safety of machinery. General principles for design. Risk assessment and risk reduction") is the A standard (basic standard) in mechanical engineering. It defines the basic terminology, the methodology of risk assessment and the three-step method for risk reduction. Every risk assessment in mechanical engineering is based on this standard.
The standard is not product-specific. It provides the methodological framework within which product-specific C standards and safety standards (B standards) are applied. EN ISO 12100 is harmonised under the Machinery Directive 2006/42/EC; for the new EU Machinery Regulation (EU) 2023/1230 the first list of harmonised standards is only expected to take effect from 20 January 2027.
The risk assessment process
EN ISO 12100 divides the risk assessment into three consecutive phases: risk analysis, risk evaluation and risk reduction. Together they form an iterative process that is repeated until all risks have been adequately reduced.
Phase 1: Risk analysis
Risk analysis comprises three sub-steps:
- Determination of the limits of the machinery: Define the use limits (intended use and reasonably foreseeable misuse), space limits (space requirement, access area), time limits (service life, maintenance intervals) and other limits (e.g. environmental conditions, qualification of operating personnel).
- Hazard identification: Systematically identify all hazards that can arise from the machine. EN ISO 12100 lists the types of hazard: mechanical, electrical, thermal, noise, vibration, radiation, materials and substances, ergonomic hazards and hazards associated with the environment in which the machine is used. Consider all life phases in doing so.
- Risk estimation: For each identified hazard, estimate the risk. The risk results from the combination of severity of harm and probability of occurrence. The probability of occurrence is made up of: frequency and duration of exposure, probability of occurrence of the hazardous event and the possibility of avoiding the harm.
Phase 2: Risk evaluation
After risk estimation you decide whether the remaining risk is acceptable or whether further protective measures are required. In doing so you take into account the state of the art (documented by harmonised standards), the practicability of the measures and the principle of proportionality. A risk matrix helps to document this decision systematically.
Phase 3: Risk reduction with the three-step method
If a risk is not acceptable, you must take protective measures. EN ISO 12100 prescribes a mandatory order of precedence:
Step 1: Inherently safe design
Eliminate the hazard by design measures or reduce the risk by choosing suitable design features. Examples: avoiding sharp edges, limiting forces and speeds, using inherently safe materials.
Step 2: Safeguarding and complementary protective measures
If hazards cannot be eliminated by design, use technical protective measures: guards (enclosures, fencing), protective devices (light curtain, two-hand control, safety-related control systems per EN ISO 13849) and complementary measures (emergency stop, safe isolation of energy).
Step 3: Information for use
For remaining residual risks, inform the user: warnings and hazard signs on the machine, residual risks in the operating instructions, information on personal protective equipment (PPE), training recommendations. Information for use must never be used as a substitute for design or technical measures.
The risk matrix explained
A risk matrix is a graphical tool for visualising the risk level. It combines two dimensions: the severity of the possible harm (e.g. minor injury, serious injury, death) and the probability of occurrence (e.g. unlikely, possible, likely). The result is a risk level that makes it easier to decide on the necessary measures.
EN ISO 12100 does not prescribe a specific matrix format. 3x3, 4x4 or 5x5 matrices are common. What matters is that the criteria for severity of harm and probability of occurrence are clearly defined and applied consistently. The risk matrix must document both the initial risk (before measures) and the residual risk (after measures).
Consider all life phases
A common mistake: the risk assessment considers only normal operation. EN ISO 12100 requires the analysis of all life phases of the machine:
- Transport and installation: Hazards during lifting, moving, installing and anchoring to foundations
- Commissioning and setting up: Initial commissioning, adjusting, teaching, testing
- Normal operation: Intended use including loading and unloading
- Maintenance, inspection and cleaning: Regular maintenance work, lubrication, adjustment
- Troubleshooting and fault clearance: Interventions in the event of malfunctions, clearing material jams
- Decommissioning and disposal: Dismantling, removal, safe disposal of operating fluids
Typical pitfalls in risk assessment
Risk assessment only at the end of the design phase
The risk assessment must accompany the design. Anyone who only prepares it after the machine is finished can address hazards only with expensive technical measures or mere warnings. The effective step 1 (inherently safe design) is then hardly possible any more.
Misuse not considered
EN ISO 12100 requires reasonably foreseeable misuse to be considered. The operator will open doors, defeat safeguards and use the machine differently than intended. These scenarios must be included in the risk assessment.
Measures only on paper
Every measure in the risk assessment must be verified. A safeguard that appears in the assessment but is not correctly implemented or tested provides no protection. Document the implementation and validation of every measure.
No iteration after measures
The risk assessment is an iterative process. After defining protective measures you must check whether new hazards have arisen as a result and whether the residual risk is now acceptable. Only then is the assessment complete for that hazard.
FAQ
Frequently asked questions about risk assessment per EN ISO 12100
What is EN ISO 12100?
How does a risk assessment per EN ISO 12100 proceed?
What is the three-step method for risk reduction?
How does a risk matrix work in a risk assessment?
Which life phases must be considered in the risk assessment?
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