Machinery Safety & Hazard Guidance

Demystifying e-stops

STOP! It’s hammer time?

Over the years I have written many technical articles and regularly they have included safety requirements for various types of machinery. Of the safety requirements in these articles perhaps the most common and often asked about is the emergency stop. The questions I get range from what is it through to the application of emergency stops on specific machines.


Let’s begin with what is an emergency stop?


AS4024.1604:2014 Safety of Machinery – Design of controls, interlocks and guarding —Emergency stop—Principles for design contains the definition and other information for emergency stop devices.


Definition: An emergency stop device as a manually actuated control device used to initiate an emergency stop function.


Type: The types of actuators that may be used include the following: – mushroom-type pushbuttons;
– wires, ropes, bars;
– handles;
– in specific applications, foot-pedals without a protective cover.


Colour: The actuators of the emergency stop must be coloured red and where a background exists be yellow as far as is practical.


Location: An emergency stop device shall be located at each operator control station.


This seems quite straight forward, a red device with a yellow background located at the operator position. I think that most people involved with machinery already know this. The most common question I get is not what but how to apply an emergency stop to a machine.


The definition of an emergency stop device above contains the words “initiate an emergency stop function”. An emergency stop function is defined as – a function that is intended to:

– avert arising, or reduce existing, hazards to persons, damage to machinery or to work in progress,

– be initiated by a single human action


It is this definition that allows us to determine how to apply an emergency stop to a machine or more simply to answer the question, which parts of a machine should be affected by the emergency stop?


As an example, in AS 1418.8-2008 Cranes, hoists and winches – Special purpose appliances Section 4 mandates the inclusion of an emergency stop device on all tipping truck hoist systems. I am often asked how a truck could be driven once the emergency stop is actuated. Knowing what we do now we can consider which parts of the machine the emergency stop will affect to meet the definition above. If the emergency stop was applied to the engine of the truck then additional hazards would be created and the definition “avert arising, or reduce existing, hazards to persons, damage to machinery…” would not be met due to the loss of steering and braking as additional hazards such as collision and crushing would be created. However, if the emergency stop function was applied only to the tipping hoist power system then the definition would be met.


If you have a particular question regarding emergency stops please contact us.

Disclaimer: This information is intended to provide general information on the subject matter. This is not intended as legal or expert advice for your specific situation. You should seek professional advice before acting or relying on the content of this information. 

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