What is ISO 14119?
ISO 14119 is the international standard for applying interlocking devices to movable guards on machinery. The standard covers the design, selection and use of safety switches, such as door interlocks and guard detection.
In OT environments, ISO 14119 supports the correct application of interlocks on covers, doors and hatches of machines so that access to hazardous parts is only possible under safe conditions.
🧠 Purpose of ISO 14119
- Preventing access to hazardous zones during operation
- Correct use of mechanical or electrical locking
- Resistance to manipulation or bypassing
- Selection of suitable technology per application
- Support for CE marking (Machinery Directive)
🔧 Types of interlocking devices (typology)
| Type | Description |
|---|---|
| Type 1 | Mechanical – directly actuated by the guard (e.g. tongue switch) |
| Type 2 | Mechanical – indirectly (e.g. via pin or lever) |
| Type 3 | Non-contact – magnetic or RFID, coded actuator |
| Type 4 | Non-contact – with coded and diagnostics-capable electronics |
Type 3 and 4 provide higher protection against manipulation and are often used in PL d/e applications under ISO 13849-1.
🔐 Tamper resistance
ISO 14119 requires interlocks to:
- Not be easily bypassed (e.g. with a loose magnet or second actuator)
- Be physically inaccessible or non-replaceable without tools
- Be placed in positions where they cannot be held open during operation
- Preferably be coded (mechanically or electronically) for higher security
The manipulation index is determined based on physical design, coding and placement.
✅ Safety and integration requirements
| Design requirement | Explanation |
|---|---|
| Positive opening | Contact opens on mechanical separation – prevents “sticking” |
| Fault detection | Detection of a loose actuator or faulty contact required at PL d/e |
| Locked vs. unlocked | Some applications require locking until a safe state is reached |
| Diagnostic function | Advanced interlocks such as type 4 require feedback |
🔁 Linkage with other standards
| Standard | Relation to ISO 14119 |
|---|---|
| ISO 13849-1 | Determines the required PL (Performance Level) for the application |
| IEC 62061 | Alternative SIL approach to functional safety |
| IEC 60204-1 | General electrical requirements for machinery |
| ISO 12100 | Risk assessment determines whether an interlock is required |
| Machinery Directive | ISO 14119 is harmonised and supports CE conformity |
⚠️ Common practical mistakes
- Interlocks easily bypassed (e.g. with a loose screwdriver)
- No positive opening – contact may stick in the closed position
- No status feedback on digital interlocks
- Wrong type chosen (e.g. type 1 used where type 3 is required)
- No validation of the required PL or SIL level
📌 In summary
ISO 14119 governs how and when interlocking devices should be applied. In OT systems, this is essential for safe access to machines, protection of personnel and CE Compliance.