Emergency stop button design (ISO 13850) — colour, shape and latching

The emergency stop categories guide covers what happens electrically when an emergency stop is activated (stop category 0, 1 or 2, per NEN-EN 60204-1). ISO 13850 governs a different, complementary aspect: the physical design of the emergency stop actuator itself — what it looks like, how it is operated, and how an activated emergency stop is prevented from being accidentally cleared.

Visual requirements

The actuator of an emergency stop device must be red. Where a background is present behind the actuator, and as far as practicable, that background must be yellow. This colour combination makes it possible to recognise an emergency stop device without having to read any text or symbols — recognition by colour alone is faster than recognition via text.

Shape of the actuator

ISO 13850 requires a mushroom-head-shaped actuator: large enough to be operated with the palm of the hand, a fist or the forearm, even under stress or while wearing gloves.

Latching until manual reset

Once the emergency stop command has been generated, it must remain latched until the button is deliberately and manually released — typically by twisting or pulling it out. The command must not be cleared automatically by restoring the power supply. Electrical emergency stop devices must additionally have a direct opening action mechanical contact mechanism: the contact is opened via a direct mechanical linkage, not solely via a spring or software logic.

Note: ISO 13850 governs the design of the button itself. Which stop category (0, 1 or 2) a specific machine must execute upon activation follows from that machine's risk assessment and is covered in the emergency stop categories guide — not in ISO 13850 itself.

Practical relevance

When replacing a worn or damaged emergency stop button on an existing machine on a factory floor, it is important to verify that the replacement unit meets both the electrical requirements (correct stop-category control) and the physical design requirements of ISO 13850 — a button that is red but has no latching, or that resets itself automatically after a power failure, does not comply, even if it appears to "work" as expected.

Common mistakes

Using a non-latching push button as an emergency stop — as soon as the button is released or power returns, the emergency stop command is unintentionally cleared without a deliberate reset action.
Using a green or black button as an emergency stop because a red one happened not to be in stock — this undermines the fast, text-free recognisability that the colour combination is specifically intended to provide.
Assuming that a correct ISO 13850 button automatically triggers the right stop category — the button itself only controls the command and the latching; which stop category is actually executed depends on the machine's control system.