May white arrows be printed on an emergency-stop switch as release indicator?

May an emergency-stop be marked with white arrows – for example to indicate the direction of release? This question appears surprisingly often in the field.

Something that many people do not know: Even a small arrow on the red mushroom head can be critical for safety – and can make the machine non-compliant. DIN EN ISO 13850 has a clear objective: The emergency-stop has to be clearly recognisable – without any additional coloured symbol. A haptic or visible symbol on the actuator that does not have any differing colour, however, is permitted.

What does that mean regarding the white arrows? They are generally prohibited. Why? We will explain this in the following post.

What does the norm require?

An emergency-stop is a safety-related function to prevent a dangerous situation on machines and plants as quickly as possible. The relevant basics are:

• DIN EN ISO 13850 – design and functional principle of the emergency-stop
• DIN EN ISO 13849‑1 – safety-related control functions

The current legal framework is the Machinery Directive 2066/42/EG which will be replaced in the future by the Machinery Regulation (EU) 2023/1230. 

What design must the actuator have?

Die DIN EN ISO 13850 requires for safe, easy and quick use a clear, globally recognisable design:

• red actuator
• yellow background
• mushroom-shaped design
• mechanical locking mechanism
• manual release

The design is deliberately simple and internationally established. The goal is a reflexive perceptibility – regardless of language or qualification. 

Are white arrows on an emergency-stop permitted?

To keep it short: No.

The norm does not allow for any additional coloured symbols on the red actuator as it can negatively influence the clarity of the emergency-stop function.

White arrows change:

• the look of the emergency-stop
• the normative colour combination
• the perceptibility under stress

Why are white arrows problematic for the safety of machines and operators?

1. Danger of misinterpretation

Usually, arrows are linked with movement or twist directions – such as prompting to twist instead of push. However, especially in case of danger, a clear prompt to action is crucial. 

2. Danger of confusion with other pushbuttons

• direction of twisting
• travel motion
• navigation buttons
• reset buttons

An emergency-stop must be clearly distinguishable from that. 

3. Disruption of the normative coloured signalling effect

The combination of the safety colour red for the actuator and yellow for the background is an internationally established warning signal. Additions in white weaken this clarity. 

What is the correct way to mark the direction of release?

If an indicator how the mushroom heads have to be released is necessary, they may not be added in a different colour on the red actuator. 

What is allowed?

• haptical highlighting or an engraving on the actuator without colour highlighting
• inscription on the housing or front ring
• optical marking beyond the actuator

If an additional explanation is required, it should be described in the operating instructions.

Example for norm-compliant and reliable solutions

Modern emergency-stop switches (e.g. from Schlegel) meet the requirements of DIN EN ISO 13850 and offer:

• mechanical locking with twist or pull to release
• status and diagnostic units for monitoring the status (optional)
• integration into safety-related bus systems

Since the EN ISO 13850:2015 came into effect emergency-stops can also indicate the actual operating status by a corresponding red illumination of the mushroom head. For a better recognisability of inactive emergency-stop devices, Schlegel developed emergency-stops which signal the active and inactive status by using their illumination (status indication).

• Active (illuminated): device is ready for use (red colouring)
• Inactive (not illuminated): device is deactivated or without function (and can be recognised as being inactive due to the grey colour)

Important: The safety-relevant basic design for reliability of the emergency-stop function remains unchanged.

Conclusion

White arrows or other symbols that are distinguishable by their colour on the red head of an emergency-stop are not in accordance with the norms and thus prohibited in general. The norm DIN EN ISO 13850 requires a clear and distinctive design without additional coloured symbols. Each optical addition that can lead to misinterpretation contradicts the purpose of emergency-stop devices.

FAQ

May additional symbols in another colour generally be placed on an emergency-stop?

No, not on the actuator itself.

Where may the remark for direction of release be placed?

On the enclosure, the front ring or the operating instructions. A symbol may be placed on the mushroom as long as it has no differing colour. 

Is there a norm that allows white arrows?

No. DIN EN ISO 13850 does not allow any additional symbols on the red mushroom head.