Product category:
Safety relays, interlocks, control systems, electrical components
News Release from: Siemens Automation and Drives | Subject: SIGNUM family of E-STOPs
Edited by the Manufacturingtalk Editorial
Team on 30 June 2003
EC's EMERGENCY STOP standard is not a
'norm'
Since 1992, the European Community's Machinery Safety Standard for EMERGENCY STOP equipment, BS EN418, should have become the industrial norm but that, as yet, this is not the case.
Since 1992, the European Community's Machinery Safety Standard for EMERGENCY STOP equipment, BS EN418, should have become the industrial norm but Paul Easton of Siemens Automation and Drives is concerned that this is not the case It is acknowledged that safety is an increasingly hot topic on everyone's agenda, and hundreds of column inches have been devoted to the subject
This article was originally published on Manufacturingtalk on 9 Aug 2000 at 8.00am (UK)
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However, before a designer deploys cutting-edge solutions and state-of-the-art products to a new project, it is vital that he gives rigorous attention to the basic equipment, including the humble mushroom actuator.
The standard requires, in Section 4.1.11 of BS EN418, that red mushroom actuators applied as E-STOPs must latch when sufficient pressure is applied to generate an E-STOP command, a characteristic that is commonly referred to as being "tease-proof", "tamper-proof" or "trigger action".
So any actuator that has generated an E-STOP command without simultaneously latching fulfils neither the conditions nor the intentions of the safety standard.
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As such, equipment using non-tease-proof devices as E-STOPs can be restarted without the dangerous condition having necessarily been cleared.
Consider for a moment the situation of an operator who is inspecting a machine in a remote part of a factory.
A setting error has caused a dangerous build up of swarf and it looks like the tool head will soon be damaged, so the operator hits the nearest E-STOP.
However a trailing cable has been caught between the mushroom head and the panel surface, causing it to bounce without latching.
As the machine has stopped, the operator is unaware of this and leans over into the machine to start clearing the debris.
Meanwhile, a supervisor located in a control room, without line-of-sight vision, notices that the machine is off-line but the contact status on the display panel shows that nothing is amiss.
As production schedules are tight and there is nothing to prevent him from remotely restarting the machine, he does so; with his colleague still inside it! Clearly such an example identifies other failures in safe working practice that go beyond the choice of the correct command devices.
However, if the mushroom head had latched when the signal was generated, it would not have been possible for the machine to be restarted without the operator having first reset the E-STOP: "manually, individually and intentionally".
It was clearly the intention of the standard that tease-proof devices be deployed to prevent such accidents and component manufacturers such as Siemens have offered tease-proof E-STOPs for several years.
Unfortunately, it appears that some OEMs are still not complying with the regulations by continuing to provide plant that includes non tease-proof mushrooms as E-STOPs.
As Paul Easton, the UK Product Manager for Command Devices for Siemens Automation and Drives commented recently; "The lack of compliance with E-STOP standards is a cause for concern.
As part of our target account program, we assist customers by converting materials from their current suppliers' list to the equivalent Siemens devices.
We frequently see lists where the only red latching mushrooms listed are not tease-proof.
The root cause of this is unclear as the cost differences between compliant and non-compliant command devices are minimal.
What is obvious is that the companies supplying E-STOP devices should be doing a great deal more to ensure that machine builders fit equipment that complies both with the letter and the spirit of BS EN418." At Siemens, the catalogues and brochures of other manufacturers are seen to be unclear; the importance of tease-proof functionality often being hidden away in the small print.
This fault can be compounded, as there are instances where distribution partners of reputable suppliers fail to list their tease-proof devices, even though these have been available for many years.
In the absence of clear advice, buyers often choose a non-tease-proof device, even though the cost advantage is seldom more than a few pence.
The consequences of choice are however now very onerous, as ignorance of safety standards is not a defence if an incident occurs.
Under The New Approach, everyone in the supply chain has a legal obligation to ensure that safety standards are met; an obligation that applies not only to component manufacturers but also to distributors and to the designers of machines themselves.
The SIGNUM family of E-STOPs fully complies with BS EN 418 and is available from stock.
E-STOPS come in both conventional and AS-i Safe configurations and users will be aware that Siemens were the first to introduce "embedded chip" technology.
These products are part of the common safety platform known worldwide as Safety Integrated, a unique portfolio of safety products, applications knowledge, and specialist advice to end-users.
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