The ABC’s of Emergency Stop Buttons…A Simple Concept that can get Really Complicated

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The IEC 60947-5-5 & ISO 13-850 which define the specifications of emergency stop buttons are regularly evolving to stay up-to-date with Safety needs. It’s often easy to get lost in this topics… So here are a couple of the latest evolutions and frequently asked questions:

  • Aesthetics & Ergonomics
This product should not be used on a yellow background anymore.

The standard is now clearly stating that a red button on a yellow background must be an emergency stop. It means that a standard red spring-return pushbutton must not be used on a yellow background, only emergency stop buttons with trigger action, latching and positive opening contacts can be used on such a background.This product should not be used on a yellow background anymore

Also the aesthetics of an emergency stop button should not lead to confusion about its actuation during a danger. In the past, turn-to-release emergency stop buttons had white arrows to indicate the release movement. However such white arrows could be confused with turn the button to be safe! Therefore white arrows are now forbidden. As it may still need to be important to indicate the unlocking direction, red arrows are still accepted as they are less visible and thus the risk of mistake is smaller.

An emergency stop button with red arrows indicating the unlocking direction.
  • Are monitoring contacts mandatory ? NO

Monitoring contacts are specifically design to stop the machine if the contacts are separated from the heads, especially when strong shocks are applied on the heads.

The standard is stating that violent shocks should not lead to the emergency stop losing its functions. However, the standard is not imposing a technical solution. Monitoring contacts are one of such solutions, but technical design preventing the contact separation or accessories keeping the contact in place are other solutions that could be as acceptable. The technical solution is just a question of taste and trust between the product manufacturing, the control interface designer and the end-user.

An emergency stop button with monitoring contacts.
  • Are guards forbidden ? NO

The standard is recognizing that accidental actuation could be an hindrance, so guards are not for forbidden. BUT the guard should not prevent the emergency stop button to accomplish its Safety function, which means that the guard should enable the emergency stop button actuation by the hand of the operator or bystander. More exactly by the palm of the hand, a finger is not enough.

There is several possibilities to fit that requirement:

Telescopic guards are not preventing activation and are used to prevent the release of the emergency stop button.
Large guard with specific design are fully using the usual diameter 60 yellow area of most common emergency stop legend plates to give enough space for voluntary actuation while preventing the accidental actuations by larger body parts (mostly the culprits are arms, back or buttocks ).

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