ISO 12100:2010 — Risk Assessment and Risk Reduction
Quick Start
For practitioners new to ISO 12100:
- Apply ISO 12100 first — before ISO 13849-1, IEC 62061, or any other safety standard. Those standards require ISO 12100 risk assessment outputs as inputs.
- ISO 12100 does not give you PLr — it gives you the risk assessment. The required Performance Level is estimated from the risk graph in ISO 13849-1 Annex A; a required SIL is determined by the method in IEC 62061. Cite the design standard, not ISO 12100, as the normative source of PLr or SIL.
- The three-step method is the harmonized route, not the legal text itself — EU machinery law requires a documented risk assessment and compliance with the applicable essential health and safety requirements. Applying EN ISO 12100 is voluntary but confers presumption of conformity for the requirements it covers.
- The process is iterative — after any risk reduction measure is applied, return to hazard identification and verify no new hazards have been introduced.
- Document everything — a risk assessment without adequate written records is non-compliant, even if the engineering decisions were correct.
Standard Overview
| Field | Value |
|——-|——-|
| Standard ID | ISO 12100 |
| Edition | 2010 |
| Publisher | International Organization for Standardization (ISO) |
| Jurisdiction | Global; Type A standard under EU Machinery Directive and EU Machinery Regulation 2023/1230 |
| Scope | Risk assessment and risk reduction for machinery |
| Repository | rag/international/functional_safety/iso_12100/ |
Purpose: ISO 12100 is the foundation standard for machinery safety. It provides the principles and methodology for risk assessment and risk reduction. All other machinery safety standards (ISO 13849-1, IEC 62061, IEC 60204-1) assume ISO 12100 has been applied first.
The Iterative Risk Assessment Process
ISO 12100 defines a closed-loop, four-step process. The loop repeats until residual risk is judged acceptable.
| Step | Activity | Clause |
|---|---|---|
| 1 | Hazard identification — systematically identify all hazards, hazardous situations, and hazardous events across the full machine lifecycle | 4.2 / Annex A |
| 2 | Risk estimation — characterise each hazard using severity (S), frequency of exposure (F), and possibility of avoidance (P) | Clause 5 |
| 3 | Risk evaluation — judge whether the estimated risk is acceptable, considering state of the art, legal requirements, and known incidents | Clause 6 |
| 4 | Risk reduction — apply measures in the mandatory three-step sequence; return to Step 1 to verify no new hazards introduced | Clause 7 |
The loop is exited only when all identified hazards have been evaluated as acceptable after reduction measures have been applied and verified.
Risk Estimation Elements (Clause 5)
ISO 12100 Clause 5 estimates risk from the severity of harm and the probability of its occurrence (exposure, occurrence of a hazardous event, and the possibility of avoiding or limiting harm). Clause 5 does not itself produce a PLr or a SIL.
The coded S/F/P parameters and the risk graph below belong to ISO 13849-1 Annex A, which is the normative source of PLr. IEC 62061 has its own, differently parameterised method for determining a required SIL. The ISO 12100 risk estimation is the engineering judgement those methods encode — the table maps one to the other.
| Parameter | Symbol | Level | Definition |
|---|---|---|---|
| Severity of harm | S | S1 | Slight — normally reversible injury (bruising, minor laceration) |
| S2 | Serious — normally irreversible injury including death (amputation, permanent disability, fatality) | ||
| Frequency and duration of exposure | F | F1 | Seldom to infrequent, and/or short duration |
| F2 | Frequent to continuous, and/or long duration | ||
| Possibility of avoiding or limiting harm | P | P1 | Possible under specific conditions (hazard visible, sufficient reaction time) |
| P2 | Scarcely possible (sudden action, high speed, person constrained) |
PLr lookup: The combination of S, F, and P determines PLr via the ISO 13849-1 Annex A risk graph — that annex, not ISO 12100, is the normative source. S2/F2/P2 yields PLr e (the highest requirement); S1/F1/P1 yields PLr a (the lowest).
The Three-Step Method (Clause 7)
The three-step method is mandatory in the order shown. A lower-priority step cannot substitute for a higher-priority step where the higher step is reasonably practicable.
| Step | Method | Examples | Notes |
|---|---|---|---|
| Step 1 | Inherently safe design (ISD) | Eliminate nip point by geometry change; use SELV voltage; reduce travel speed to non-injurious level; substitute less hazardous material | Preferred — eliminates or reduces hazard at source; not defeatable by user behaviour |
| Step 2 | Safeguarding and protective measures | Fixed guards; interlocked movable guards (ISO 14119); light curtains / area scanners (IEC 61496); two-hand controls (ISO 13851); STO/SS1/SLS safety functions (IEC 61800-5-2) | Introduces safety functions — PL or SIL must be determined per ISO 13849-1 or IEC 62061 |
| Step 3 | Information for use | Warning labels (ISO 11684); operator manual; PPE specification; lockout/tagout procedure; training requirements | Addresses residual risk only — effectiveness depends on human compliance; weakest protection |
Key Clauses
| Clause | Topic | Key Output |
|---|---|---|
| 4 | Risk assessment principles | Iterative process definition; machine limits; documentation requirements |
| 5.3 | Severity of harm | S1/S2 classification |
| 5.4 | Frequency and duration of exposure | F1/F2 classification |
| 5.5 | Probability of occurrence of hazardous event | Reliability, human error factors |
| 5.6 | Possibility of avoiding or limiting harm | P1/P2 classification |
| 6 | Risk evaluation | Acceptability decision; state-of-the-art benchmark |
| Annex A | Normative hazard list | Checklist of 8 hazard categories with sub-categories |
When To Use ISO 12100
| Situation | Use ISO 12100? |
|---|---|
| Starting a new machine design | Yes — required before any other safety standard |
| Determining PLr for a safety function | As an input — the PLr itself comes from the ISO 13849-1 Annex A risk graph |
| Determining SIL target for a safety function | As an input — the SIL target itself comes from the IEC 62061 SIL determination method |
| Modifying an existing machine | Yes — reassess affected hazards; verify no new hazards introduced |
| Preparing CE marking technical file | Yes — EU machinery law requires a documented risk assessment; EN ISO 12100 is the standard methodology used to produce it |
| Machine-type-specific standard exists (Type C) | Recommended — use ISO 12100 to fill gaps not addressed by Type C |
| Product already has full Type C standard coverage | Conditional — ISO 12100 still governs hazards not covered by the Type C standard |
| Electrical safety design (wiring, enclosures) | Indirect — ISO 12100 identifies electrical hazards; IEC 60204-1 implements protective measures |
Common Mistakes
-
Starting with ISO 13849-1 instead of ISO 12100. The ISO 13849-1 Annex A risk graph cannot be applied meaningfully without a completed risk assessment behind it. Skipping ISO 12100 produces PLr values that are not grounded in a systematic hazard analysis.
-
Incomplete lifecycle coverage. Hazard identification limited to normal production operation misses maintenance, cleaning, setup, and decommissioning — where a disproportionate share of serious accidents occur.
-
Accepting S1/F1/P1 without justification. Each parameter must be supported by documented reasoning. Defaulting to the most favourable parameters without evidence is a common audit finding.
-
Using Step 3 to address hazards that Step 1 or Step 2 could reduce. A warning label on a machine that could have been guarded does not satisfy the three-step hierarchy and creates regulatory exposure.
-
Not re-entering the loop after applying protective measures. New hazards introduced by safeguards (e.g., a light curtain mounting bracket creating a new shear point) are missed if the iterative loop is not completed.
-
Treating the risk assessment as a document-after-the-fact exercise. ISO 12100 requires the assessment to drive design decisions. A risk assessment written after the machine is built cannot satisfy this requirement — it can only document decisions already made, not influence them.
Practical Checklist
Work through these items for each machine project:
- Machine limits defined: spatial, time, power, and use limits documented
- Intended use and reasonably foreseeable misuse documented
- Hazard identification completed using Annex A as checklist for all lifecycle stages
- Risk estimation completed for each hazard: S, F, and P assigned with documented reasoning
- Risk evaluation completed for each hazard: acceptable or not acceptable, with reasoning
- Step 1 (ISD) applied first for each unacceptable risk; design changes documented
- Step 2 (safeguarding) applied where ISD insufficient; safety function identified
- PLr or SIL determined for each Step 2 safety function (ISO 13849-1 or IEC 62061)
- Step 3 (information for use) addresses remaining residual risk only
- Iterative loop completed: re-assessed after each measure applied; no new hazards unaddressed
- Residual risks documented and addressed in operating instructions
Lifecycle Application
| Lifecycle Stage | ISO 12100 Activity |
|---|---|
| Concept | Define machine limits; define intended use and foreseeable misuse |
| Preliminary design | Initial hazard identification (Annex A); first risk estimation pass |
| Detailed design | Apply three-step method; determine PLr/SIL for safety functions; update hazard list |
| Prototype / commissioning | Verify risk reduction measures are effective; complete iterative loop |
| Production / normal use | Information for use in place; residual risks communicated to users |
| Maintenance and cleaning | Hazards at these stages assessed and addressed (lockout/tagout, safe isolation) |
| Modification | Re-enter risk assessment for affected hazards; verify no new hazards introduced |
| Decommissioning | Hazardous energy isolation, hazardous material disposal addressed |
Next Steps After ISO 12100
After completing the risk assessment, use the following standards to design and validate the safety functions identified in Step 2:
- ISO 13849-1 — Performance Level methodology for safety-related parts of control systems; its Annex A risk graph determines PLr, informed by the ISO 12100 risk estimation
- IEC 62061 — SIL methodology for electrical/electronic/programmable safety-related control systems; parallel path to ISO 13849-1
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