Access condition
Know what must happen when the guard opens
The required behaviour starts with the hazard, the machine function and the reason people need access—not with a preferred switch from a parts catalogue.
Controlled access to hazardous machinery
ISO 14119:2024 interlocking devices for machine guards.
A practical guide to the standard engineers use when selecting and applying interlocking devices associated with guards—and when reducing the chance that those devices will be bypassed or defeated.
Understanding the standard
What is ISO 14119?
ISO 14119:2024 specifies principles for the design and selection of interlocking devices associated with guards. It also addresses measures intended to minimise foreseeable defeat. The standard sits beside ISO 14120: the guard provides the physical barrier, while the interlocking arrangement helps coordinate access through a movable guard with machine operation.
Device selection
Match the interlocking principle to the application
Guard construction, movement, environment, access frequency, alignment and foreseeable misuse all influence a suitable arrangement.
Defeat resistance
Design out incentives and opportunities to bypass
Good access, workable reset arrangements, appropriate device selection and considered installation help reduce pressure to interfere with safeguarding.
Interlocking versus locking
A stopped machine and an unlocked gate are not always the same decision.
An interlocking function coordinates the guard position with hazardous machine functions. Guard locking is an additional function that keeps the guard locked under defined conditions. Whether locking is needed depends on the risk assessment, the hazard and the time required for the dangerous condition to disappear.
Interlocked movable guard
The machine control system receives information about the guard state so hazardous functions cannot operate under the conditions defined by the safety function, and opening the guard initiates the required response.
The detail of signal processing belongs to the wider safety-related control system and is commonly addressed using standards such as ISO 13849-1 or IEC 62061.
Interlocked guard with guard locking
The guard is held closed until the conditions established by the safeguarding design allow access. This may be relevant where a dangerous movement or other hazard does not disappear immediately after a stop command.
The need for locking, release strategy and emergency or escape provisions must be determined for the actual machine and access scenario.
A practical selection sequence
Six questions before an interlock is specified
Treat the device as one part of an access-control system. These questions expose the decisions that are often missed when the conversation starts with hardware.
01
What hazardous functions are covered?
Define the machinery movements, energies and operating modes affected by opening the guard.
02
Why and how often is access needed?
Loading, cleaning, adjustment, jam clearing and maintenance can demand different access strategies.
03
Does danger remain after the stop command?
Stopping and run-down behaviour influence positioning and whether guard locking may be required.
04
Can the device be defeated foreseeably?
Review access pressure, actuator availability, mounting, visibility, diagnostics and operating incentives.
05
How will the gate and device stay aligned?
Hinges, frames, panel rigidity, gate sag, vibration and the working environment affect reliability.
06
How will the complete safety function be validated?
Confirm the mechanical arrangement, wiring, logic, stopping response, reset behaviour and installed operation.
Commercially workable safety
Defeat resistance starts with a layout people can use.
An interlock can be technically sophisticated and still sit in a poor safeguarding concept. If legitimate tasks are awkward, visibility is poor or access points are in the wrong place, operators and maintainers face avoidable friction.
Put gates where work happens
Plan around real loading, cleaning, fault-recovery and maintenance routes rather than placing one convenient gate after the fence layout is complete.
Protect alignment and mounting
A robust frame, suitable hinges and a deliberate mounting arrangement help the guard and device remain mechanically consistent in service.
Make reset and restart deliberate
The wider safeguarding design should consider who can see the danger zone, where reset occurs and how unexpected restart is prevented.
Related standards
ISO 14119 is one layer of the system
ISO 12100
Establishes the machinery risk-assessment and risk-reduction process used to define the required safeguarding outcome.
Risk assessment guideISO 14120
Addresses the selection, design and construction of the fixed or movable guard that carries or works with the interlocking device.
Guard design guideISO 13855
Addresses safeguard positioning in relation to human approach and is relevant when stopping performance affects safe access.
Safeguard positioning guideFrequently asked questions
ISO 14119 questions from guarding projects
What is the difference between ISO 14119 and ISO 14120?
ISO 14120 addresses the general design, construction and selection of fixed and movable guards. ISO 14119 addresses the interlocking devices associated with guards and measures intended to minimise foreseeable defeat.
Does every machine-guarding gate need an interlock?
Not automatically. The safeguarding arrangement depends on the risk assessment, access frequency, machine behaviour and applicable standards. A gate that exposes a person to hazardous machine functions commonly requires a coordinated safety function.
Does an interlock always need guard locking?
No. Guard locking is an additional function used where the risk assessment and machine behaviour require the guard to remain locked until defined safe conditions exist.
Does ISO 14119 set the required Performance Level?
ISO 14119 does not replace the safety-related control-system design process. The required safety functions and performance are determined from the risk assessment and addressed using the applicable control-system standards.
Can a guard interlock be added to an existing machine?
Yes, but retrofit work should assess the complete machine: stopping behaviour, control architecture, reset and restart, access, device mounting, foreseeable defeat and validation—not only the installation of a switch.
Practical information only. This page does not replace ISO 14119:2024, a machine-specific risk assessment, competent functional-safety engineering or local legal requirements.
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