Australian Standard 4024 describes an emergency stop as “a device which, regardless of the power source, e.g. electrical pneumatic or hydraulic, requires deliberate action to bring a machine to rest when danger is recognised”.
Here, Pilz Safe Automation's Frank Schrever explains the basics of how the Plant Regulations and the Australian Standard for safeguarding of machinery apply to emergency stop devices.
There are a number of emergency stop devices that may be used on plant or machinery, the preferred form of device being a mushroom-type push button, operable by palm. Other forms are acceptable such as wires, ropes, bars and handles so long as they provide equivalent levels of safety.
Each Australian state has its own plant regulations but for simplicity’s sake, we’ll focus on the Victorian Occupational Health and Safety (Plant) Regulations 1995 (in terms of emergency stop devices, the regulations are the same across the states).
The Plant Regulations and the Australian Standard 4024.1601: Design of controls, interlocking and guarding – Emergency Stop – Principles for design overlap to some degree.
Plant Regulations:
Under the Plant Regulations, designers and employers must ensure the following if the design of the plant includes an emergency stop device:
Location & Look
The device must be prominent, clearly and durably marked and immediately accessible to each operator. The actuating element of the device must be coloured red.
Operation
The device cannot be affected by electrical or electronic circuit malfunction .
Australian Standard AS 4024 Part 1601
While not legally binding, the Australian Standard is often relied on in court to show that reasonable steps have been taken to ensure safety, which means compliance is extremely important.
The Standard specifies that emergency stops:
• shall override all other functions in all operating modes;
• shall not be possible for any start command to be effective until emergency stop is reset;
• shall not be used as a substitute for safeguarding;
• shall not increase the risk of injury from another source;
• shall function as either a category 0 or category 1 stop (as per AS 60204-1) ;
• suitably marked, prominently located and readily accessible from all operator positions;
• be mushroom-head latch-in or lock-in manual reset types and push-buttons are preferred;
• be positioned at each operator control station and other locations where emergency stop is required;
• shall apply principle of positive mechanical action i.e. Normally closed, forced open, contacts;
• the actuator should be coloured red, and the background, as far as is practicable, should be coloured yellow;
• shall remain active at all times;
• shall not be used for normal stopping or relied on as a means of isolation and immobilisation;
For further reading, Pilz suggests:
• AS 4024 Safety of Machinery, Part 1604: Design of controls, interlocks and guarding – Emergency stop – Principles for design.
• AS 60204.1 Safety of Machinery – Electrical equipment of machines
• Occupational Health and Safety (Plant) Regulations 1995. Statutory Rule No. 81/1995.
About the author: Frank Schrever has 24 years’ experience in the instrumentation and automation markets and established Pilz Safe Automation, now Australasia’s leader in safe automation products and services. Mr Schrever also sits on the AS 4024-1 review committee (SF041).
