ISO 3691-4 is the safety standard that most directly applies to autonomous mobile robots operating in industrial settings. If you are evaluating a floor robot for a warehouse or logistics facility in Japan, Europe, or North America, this is the document your facility manager or safety officer will eventually reference. It is also a document that vendors frequently cite without explaining what it actually requires.
This post is a plain-language walkthrough of ISO 3691-4:2020, focused on the requirements that directly affect how a mobile robot should behave around people. We are not making certification claims for our own product. We are explaining what the standard says so operators can have an informed conversation with any vendor about how their product addresses each requirement. We design toward conformance with ISO 3691-4 as an engineering target, not as a marketing badge.
Scope and what the standard covers
ISO 3691-4 covers "industrial trucks: safety requirements and verification" for driverless industrial trucks operating in industrial environments. It applies to vehicles that move autonomously under their own power and carry or tow loads. This includes AGVs (automated guided vehicles) that follow fixed paths, and AMRs (autonomous mobile robots) that navigate freely within a mapped environment.
The standard does not cover collaborative robots on fixed arms (that is ISO 10218), robots operating in open public spaces (separate regulatory territory in most jurisdictions), or manually operated powered vehicles. If a floor robot is not classified as an industrial truck under applicable regulations, ISO 3691-4 may not be the only or primary standard. But for most warehouse AMR deployments, it is the starting point that safety assessors use.
The speed-distance protection zone requirement
Section 5.5 of the standard addresses "protection devices for preventing persons from being struck." The core requirement is that a driverless truck must be equipped with detection devices that create a protective field in the direction of travel, sized such that the truck can be brought to a complete stop before reaching a person who enters the field boundary.
This is not a requirement to detect people at a fixed distance. It is a requirement that the combination of detection range plus stopping distance must be sufficient to prevent contact. The calculation is:
Required detection range = stopping distance from operating speed + safety margin
The stopping distance depends on operating speed and deceleration capability. At 1.2 m/s with 0.8 m/s² deceleration, the stopping distance is approximately 0.9m. At 1.8 m/s, it rises to approximately 2.0m. If your robot operates faster, your required detection range is proportionally larger. The standard requires that vendors demonstrate this calculation for their specified operating speed range, not just claim a detection distance number.
The safety margin added to the stopping distance accounts for sensor latency and detection uncertainty. ISO 3691-4 does not prescribe a specific margin number. Instead, it references the risk assessment methodology in ISO 12100 to determine what margin is appropriate given the specific use case. This is where vendor documentation should include a risk assessment, not just a distance spec.
Zone classification and what it means for mixed-traffic aisles
The standard recognizes different operating scenarios through a classification of "safeguarded areas" versus areas where coexistence with people occurs. For AMRs operating in mixed-traffic aisles, the relevant classification is where the robot and people share the same floor space without physical separation.
In this classification, the protective field must be active at all times during autonomous operation, not just in certain zones or at certain speeds. There is no provision in ISO 3691-4 for disabling protective detection in a "robot-only zone" while the robot is in motion. If a vendor is telling you their robot can be configured to run faster in a zone where people have been excluded, they need to demonstrate that the zone exclusion is itself rigorously enforced (typically by access control infrastructure, not just floor tape) and that the robot reverts to full protective behavior immediately upon zone exit.
What the standard says about operating speed
Section 5.4 requires that driverless trucks have a defined maximum operating speed and that the protective field is appropriately sized for that speed. There is no absolute maximum speed specified in the standard. The requirement is that whatever speed the vehicle operates at, the protective stopping performance is sufficient.
This means a faster robot is not inherently non-compliant. It means a faster robot requires either a larger protection zone or a faster stopping capability or both. In practice, larger protection zones cause operational disruption (the robot stops for objects that are not obstacles) and faster stopping at higher speeds puts more stress on drive hardware and cargo stability. These are engineering tradeoffs, not compliance shortcuts.
For robots operating in narrow aisles where the protection zone cannot be made arbitrarily large without causing constant stops, lower operating speed is typically the correct tradeoff. This is one reason why fast AMRs and narrow-aisle operations are sometimes a poor fit regardless of sensor capability.
Emergency stop and manual override requirements
Section 5.10 requires that every driverless truck have a means of emergency stop, operable by personnel in the area, that brings the truck to a stop and maintains that stop until manually reset. Emergency stop buttons must be clearly identified and accessible. For robots operating in mixed-traffic areas, the standard expects that workers can stop the robot without needing to contact a central control station.
For our deployment in retail and logistics environments, this typically means a physical E-stop button on the robot chassis and a secondary override through the fleet management interface accessible to shift supervisors. The key requirement is "manually reset" after emergency stop: the robot should not automatically resume after a stop triggered by the E-stop circuit. It should require a positive human action to restart. This prevents a scenario where the E-stop was triggered because something was genuinely wrong, the cause is not resolved, and the robot resumes because the trigger cleared.
Documentation requirements that operators often overlook
ISO 3691-4 Section 8 covers information for use, including the documentation that manufacturers must supply. This includes: a risk assessment conducted per ISO 12100, operating instructions specifying the intended operating environment, maximum floor gradient, surface requirements, minimum aisle widths, load specifications, and the protective field dimensions at different operating speeds.
Operators who receive an AMR without a risk assessment document should ask for it specifically. "Designed to comply with ISO 3691-4" is a design intent statement, not a delivered compliance artifact. The documentation is part of the conformance, not an optional supplement. A robot that meets all the behavioral requirements but ships without the required documentation does not fully satisfy the standard's delivery obligations.
We include a formal risk assessment, operating parameters documentation, and a deployment environment specification sheet with every Closer unit we deploy in a pilot. This is not a differentiator we expect credit for. It is a requirement that any serious AMR vendor should be meeting as standard practice.
What ISO 3691-4 does not cover
It is worth being direct about the standard's limits. ISO 3691-4 addresses the industrial truck's own safety systems. It does not prescribe the facility-side infrastructure changes needed to create a safe operating environment. Floor condition, aisle width, lighting, load height, and the behavior of other equipment in the facility are outside the standard's scope but are real factors in a safe deployment.
The standard also does not address fleet behavior: how two AMRs from different vendors should behave when their paths converge. This is an active area of work under ISO 23220 and related fleet management standards. If you are running a multi-vendor fleet, the inter-vehicle safety question requires separate assessment beyond what either vehicle's individual ISO 3691-4 conformance covers.
For an operator evaluating an AMR deployment, ISO 3691-4 is the minimum baseline for the robot itself. A thorough safety assessment also requires a site-specific risk evaluation per ISO 12100, a commissioning verification procedure confirming that the robot's actual behavior in the facility matches the documented performance envelope, and a maintenance schedule that preserves that performance over the robot's operational life. The standard is the starting point, not the full picture.
