Emergency stop blog

The emergency stop function is designed to reduce risk or eliminate an imminent or existing hazard that may affect the safety of people, machinery or work under progress.

In the hierarchy of preventive measures, as ruled in ISO 12100:2010 “Safety of machinery — General principles for design — Risk assessment and risk reduction”, emergency stop devices are classified in the Complementary Protective Measures category, and not in the category of Protective Measures. Therefore, emergency stops have the same hierarchal level as Personal Protective Equipment. The main differences lies in the voluntary aspect of triggering the stop of the machine by use of an emergency stop. The latter must be designed to be triggered by human action only.

In Quebec, the Regulation Respecting Occupational Health and Safety requires conception designers and users to take all aspects of the emergency stop function into consideration.

The emergency stop is mainly addressed in sections 192 and 193.

RROHS -Section 192 (2017)

Emergency stop

This section stipulates that, subject to section 270, any machine whose operation requires the presence of at least one worker shall be equipped with an emergency stopping device or switch.

This device or switch stops the machine, considering the machine’s design, in the shortest possible time. In addition, it has the following characteristics:

1. it is easily visible and within reach of the worker;
2. a single action activates it;
3. it is clearly identified.

The resetting of the emergency stopping device after it is used shall not by itself cause the machine to start up.

RROHS -Section 193 (2017)

Groups of machines

Any stopping device or switch for a machine belonging to a group of machines that are wired to operate in series, including an emergency shut-off switch, shall in addition be designed to stop serial upstream and downstream machines if their operations constitute a danger for worker safety.

Several standards deal with the function and emergency stop devices, for example:

• CSA Z432 – 2016 – Safeguarding of machinery
• NFPA 79 -2015 – Electrical Standard Industrial Machinery
• ISO 13850-2015 – Safety of machinery — Emergency stop function — Principles for design

Each of these standards to its own requirements, but broadly, one could summarize the them as follows. Emergency stop devices need to:

• Be red in color;
• The surface behind the control unit should be yellow (specified by NFPA 79 and ISO 13850);
• Be mushroom shaped;
• Must require unique human action in response to or in anticipation of a hazardous situation;
• Must stop the machine as quickly as possible in a safe manner;
• Must not provoke the start-up of the machine when it is returned to its original position
• The reliability of the emergency stop function must be determined and validated on the basis of a prior risk analysis (ISO 13849-2015 Safety-related parts of control systems – Part 1: General principles for design and Part 2 : Validation)

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