ISO 14119

What is ISO 14119?

ISO 14119 is the international safety standard that sets out the principles for the design, selection and mounting of interlocking devices (interlocks) on movable machine guards, so that a hazardous machine function cannot operate while a door, cover or hatch is open. The standard covers safety switches, guard locking devices that hold a guard closed, and trapped-key systems, and it pays close attention to preventing defeat. The current second edition was published in September 2024 and replaces the 2013 version. In Europe the text has been adopted as EN ISO 14119:2025.

In OT environments, ISO 14119 is the link between the physical door and the safety control system: the switch provides the signal that a safety relay or safety PLC uses to stop the machine or keep the door locked.

🧠 What exactly does ISO 14119 cover?

ISO 14119 is a so-called type B2 standard: a safety standard for one specific kind of safeguard that applies across many types of machinery. It answers four questions:

• Which type of interlocking device suits the application? - mechanical or non-contact, coded or uncoded, with or without guard locking.
• How do you prevent the device from being defeated? - an assessment of the motivation to defeat, plus matching countermeasures.
• How do you mount the switch and actuator? - non-detachable fixing, positions out of reach, and no use of the switch as a mechanical stop.
• How do you integrate the device into the control system? - together with ISO 13849-1 or IEC 62061, including fault masking in series connections.

The standard therefore does not decide whether a guard is needed; that follows from the risk assessment under ISO 12100. The required safety level (PL or SIL) also comes from that analysis. ISO 14119 makes sure the chosen guard monitoring actually achieves that level in daily practice.

🔧 Which types of interlocking device does the standard define?

The type classification is the best-known part of ISO 14119. It is based on the actuation principle and the kind of actuator. The 2024 edition added type 5.

The type therefore says mostly something about susceptibility to defeat, not about reliability. An uncoded type 3 sensor tolerates dirt and misalignment well, yet a fridge magnet can fool it. It is the coded types 2 and 4 that offer better protection against bypassing.

For coded actuators the standard distinguishes three coding levels:

The higher the coding level, the fewer additional mounting measures are needed, such as concealed mounting or an extra plausibility check.

For type 5, Annex K sets its own requirements: each key is coded so that separate interlocks do not share the same key, keys must not be easy to copy, and keys and locks must be clearly marked. Every trapped-key system also needs a key transfer plan in the instructions for use.

🔐 How does ISO 14119 prevent defeat?

Bypassed guard switches are one of the best-known causes of serious machinery accidents. A German study by the HVBG published in 2006, based on around 1,000 health and safety experts, estimated that protective devices are temporarily or permanently defeated on at least 37 per cent of stationary industrial machines. Operators rarely defeat a switch out of malice; they do it because setting up or cleaning the machine is quicker with the door open. ISO 14119 tackles this in a fixed order:

1. Remove the motivation - analyse which tasks (setting up, clearing faults, cleaning, observing) lead to opening the guard, and make them possible with a safe working method, for example a reduced-speed operating mode.
2. Choose a suitable type and coding level - where motivation remains, use a coded device; coding adds a layer of security against deliberate tampering.
3. Mount it smartly - out of reach, shielded or concealed, so a spare actuator or magnet cannot be used.
4. Fix it permanently - one-way screws, welding or rivets for the actuator.
5. Monitor plausibility - let the control system check that the door genuinely opens and closes in every cycle.

The 2024 edition extended the scope to measures that minimise reasonably foreseeable bypassing. It also states explicitly that a switch must not act as a mechanical stop unless that is its intended use; otherwise separate stops are needed that limit the impact energy to what the switch manufacturer permits.

🔒 What is the difference between interlocking and guard locking?

ISO 14119 distinguishes an interlocking device (the machine stops as soon as the door opens) from an interlocking device with guard locking (the door stays closed until the hazardous motion has stopped). Guard locking is needed when the run-down time of the machine is longer than the time a person needs to reach the danger zone. That trade-off is linked to the safety distances in ISO 13855.

For protecting people, the spring-applied principle is preferred. Where someone can be trapped behind a guard, an escape release on the inside is required. The standard also defines an emergency release and an auxiliary release (operated with a tool) for the outside.

🔄 How does ISO 14119 relate to other standards and legislation?

ISO 14119 replaced the European standard EN 1088 at the end of 2013, with an eighteen-month transition period. EN ISO 14119:2013 is harmonised under the Machinery Directive and gives a presumption of conformity for CE marking. CEN published EN ISO 14119:2025 in March 2025, followed by an editorial amendment A11 in June 2026. At the time of writing, the new edition had not yet been cited in the Official Journal of the EU. From 20 January 2027 the Machinery Regulation replaces the Machinery Directive; harmonised type B standards such as ISO 14119 remain the usual route to conformity under it.

🏭 How do you apply ISO 14119 in practice?

A typical step-by-step approach for a new or modified machine:

1. Risk assessment - establish for each guard which hazards lie behind it and which PL is required.
2. Measure the run-down time - is the machine at rest before anyone can reach it? If not, guard locking is needed.
3. Task analysis - list why and how often people open the door; this determines the motivation to defeat.
4. Choose type and coding - for example a type 4 RFID switch with high coding on a frequently opened door.
5. Define the architecture - usually two channels (category 3 or 4) for PL d or e, with diagnostics in a safety relay or safety PLC.
6. Assess series connections - with several potential-free switches in one chain, a fault can be masked. Annex J helps estimate the achievable diagnostic coverage. Electronic switches with self-monitored outputs (OSSD) limit the problem.
7. Validate and document - test every door, simulate faults and record the choices in the technical file.

For existing machinery in the Netherlands, the Working Conditions Decree (Arbobesluit) also applies: the employer must keep work equipment safe and includes guarding in the RI&E. A substantial modification can turn the owner into a manufacturer, triggering a new CE assessment. In cobot and robot cells, door switches are often combined with light curtains and an emergency stop.

⚠️ What mistakes are commonly made?

• Uncoded switch on a frequently opened door - type 1 or 3 where the motivation to defeat is high.
• No positive opening - a mechanical contact without positive opening can stay closed if it welds.
• Loose actuator - fixed with ordinary screws, so it is easy to remove and hold against the switch.
• Switch used as a stop - the door hits the switch every time and damages it.
• Unassessed series connection - ten door switches in one chain without considering fault masking.
• No validation - the required PL or SIL was calculated but never tested with fault simulation.

A paper compliance check is therefore not enough; the real test is whether an operator can and wants to defeat the device.

❓ Frequently asked questions

Which edition of ISO 14119 is current?

The current edition is ISO 14119:2024, the second edition, published in September 2024. It replaces ISO 14119:2013. In Europe it has been adopted unchanged as EN ISO 14119:2025.

What is the difference between type 3 and type 4 in ISO 14119?

Both types in ISO 14119 are non-contact, but type 3 is uncoded and type 4 is coded. A type 3 switch responds to any magnet or metal object, whereas a type 4 switch, such as an RFID switch, responds only to a matching actuator.

What is type 5 in ISO 14119?

Type 5 is the trapped-key interlocking system, which has been included in Annex K of ISO 14119 since the 2024 edition. A key is only released once the energy has been isolated, and that key is needed to open the access door. The requirements previously came from ISO/TS 19837.

Is ISO 14119 mandatory?

ISO 14119 is not legally mandatory as a standard, but EN ISO 14119 is harmonised under the Machinery Directive. Following it gives a presumption of conformity with the essential health and safety requirements for CE marking. Another solution is allowed, but the manufacturer must then prove that it is equally safe.

When is guard locking required under ISO 14119?

Under ISO 14119, guard locking is required when the hazardous motion continues after the door is opened while a person can already reach the danger zone. The lock keeps the door closed until the machine is safely at rest. A spring-applied lock is preferred for protecting people.

What did ISO 14119 replace?

ISO 14119 replaced the European standard EN 1088 for interlocking devices at the end of 2013. The 2024 edition also absorbed content from ISO/TR 24119 on fault masking and from ISO/TS 19837 on trapped-key systems.

📌 In summary

ISO 14119 defines how you reliably monitor machine doors and covers: with the right type of switch, sufficient coding, smart mounting and, where the machine runs down, guard locking. The 2024 edition added type 5 for trapped-key systems and requirements on fault masking. Together with ISO 13849-1 and the Machinery Regulation, the standard forms the basis for safe access to machinery.

ISO 14119 makes sure a guard works not only on paper but in practice: an interlock that nobody can or wants to defeat.