EN ISO 3691-4:2023 was approved by CEN on 5 May 2023, published July 2023, and member states had to withdraw conflicting national standards by January 2024 [S5]. It supersedes both EN ISO 3691-4:2020 and the older EN 1525:1997 that AGV/AGC builders had relied on for two decades [S3][S5].
The standard is a Type C machine-safety document under EN ISO 12100, scoped to driverless industrial trucks and their systems: automated guided vehicles, automatic guided carts, and the fleet/zone controllers that supervise them [S3][S4]. It applies to the truck itself, the operating environment, and the protective safety functions that link the two [S3].
What changed from EN 1525 to ISO 3691-4
EN 1525:1997 was the de facto AGV reference for years, but it was never harmonised to the EU Machinery Directive 2006/42/EC, so manufacturers had to build a bespoke risk file per installation [S3]. ISO 3691-4:2020 (and its 2023 revision) closes that gap by aligning the truck-level safety requirements with a Type C approach under EN ISO 12100, and by giving a single vocabulary for zones, hazards, and safety functions [S3][S4].
Where EN 1525 treated the AGV mostly as a vehicle, ISO 3691-4 treats it as a truck plus a system: the vehicle, the traffic environment, the fleet manager, and the personnel-detection devices that constrain it are all part of the safety case [S3][S6]. A 2026 explainer notes the standard defines how AGVs and autonomous mobile robots (AMRs) must behave across mixed-traffic zones, not only in fenced lanes [S6].
Scope, zones, and the three-pillar model
The standard frames the safety problem around three elements: the operating environment (with explicit human/truck interaction zones), the hazards and risk assessment, and the implementation of the safety (protective) systems [S3]. This is a meaningful shift from EN 1525, which leaned on warning devices and bumpers but did not codify a zone taxonomy at the same level of detail [S3].
For integrators, the practical effect is that the safety barrier between the truck path and pedestrians is now specified by the same document as the truck itself, instead of being a project-by-project deduction. ISO 3691-4:2023 explicitly requires verification of the protective systems, not just declaration of their existence [S4][S5].
Who each standard is for, and who it is not for
Use EN ISO 3691-4:2023 for any new build, retrofit, or major modification of a driverless industrial truck or its system intended for the EU market after January 2024 [S5]. It is also the reference for non-EU sites that follow CEN or ISO practice, which is most global AGV/AMR suppliers [S1][S2].
EN 1525:1997 only persists for equipment that was placed on the market before withdrawal and for service items on those units. It is not the right reference for new tenders, new risk assessments, or new CE marking under 2006/42/EC [S3][S5]. It is also not the right reference for autonomous mobile robots that are not classified as industrial trucks, which sit under ISO 13482 or other domain standards [S6].
Selection criteria: truck type, navigation, and load
Selection under ISO 3691-4 starts with the truck taxonomy: AGV (powered, steered, path-defined) versus AGC (typically simpler, smaller, often tug-style), and whether the unit is a fixed-path vehicle, a free-navigation AMR, or a hybrid [S3][S6]. Payload class matters because the standard's stopping-performance and personnel-detection distances scale with mass and speed, a constraint covered in depth in the AGV payload capacity selection guide.
Other binding criteria are the operating environment classification (restricted, supervised, open), the safety-rated sensor suite (LiDAR safety scanners, bumpers, E-stops), and the safety certification chain the vendor can already produce (TÜV, UL, third-party type examination) [S3][S6]. For navigation technology (magnetic tape, QR/2D codes, LiDAR SLAM, contour-based), ISO 3691-4 is technology-neutral; it specifies the safety outcome, not the means [S3][S4].
Comparison matrix: EN 1525 vs ISO 3691-4:2020 vs EN ISO 3691-4:2023
On regulatory alignment, EN 1525:1997 is not harmonised to the Machinery Directive; ISO 3691-4:2020 is a Type C standard under EN ISO 12100; EN ISO 3691-4:2023 adds the CEN layer and Annex ZA linking it directly to 2006/42/EC essential requirements [S3][S5]. On scope, EN 1525 covers the truck; ISO 3691-4 covers the truck plus its system and zones [S3][S6].
On personnel safety, EN 1525 relies on bumpers, audible warnings, and route planning; ISO 3691-4:2023 explicitly requires safety-rated protective devices with defined Performance Level/PL or Safety Integrity Level/SIL targets and verification methods [S4][S5]. On cybersecurity, EN 1525 is silent, while ISO 3691-4:2023 addresses software and parameterisation changes as a hazard source that must be risk-assessed [S7]. On mobile robot context, the 2023 revision is also the standard the industry now points to for AGV/AMR cyber and functional safety, replacing the vacuum left by EN 1525 withdrawal [S7][S8].
Real use cases and known limitations
Typical in-scope deployments are tote and pallet handling in automotive body shops, e-commerce fulfilment aisles, cross-docking tug trains, and cleanroom semiconductor material moves, all of which are covered by the standard's zone and hazard model [S3][S6]. A vendor pursuing a CE mark for a new AGV today will design against ISO 3691-4:2023 and use the corresponding test protocols for safety scanners, brakes, and emergency stops [S4][S5].
Known limitations are that ISO 3691-4 is a truck-level Type C standard, so site-level integration (fire egress, mixed traffic with manned forklifts, cybersecurity) still needs additional standards such as ISO 12100, ISO 13849-1, IEC 61508, and ISO 27001 for the fleet IT layer [S3][S7]. It is also still a CEN/ISO document, so a US-locked project may need to layer ANSI/ITSDF B56.5 on top, and the safety-rated safety glasses, audible warnings, and safety fence provisions must be integrated with local fire-safety rules such as those covered in fire safety [S3][S6].
Trackable signals going forward: monitor CEN/TC 150 and ISO/TC 110 for amendments or a new Part 5 covering cobot-style human-cooperative trucks, and watch notified-body guidance updates that begin referencing EN ISO 3691-4:2023 for AGV CE certification under 2006/42/EC [S5][S6].