Hello Chris To fulfill requirements of risk management according to ISO 14971, you have to identify all the hazard situations whhich could turn a hazard into harm. This means identifying all the foreseeable sequence or combinations of events that could led to the hazard situation.
Three points here: First: sometimes people think that they only have to identify the hazard (for example, electrical shock). But there are a lot of situations (probabilities) in which this hazard could arise, and there are a lot of outcomes (severities) if the hazard turn into harm. So you have to determine the risks of each hazard situation, not only of the more "general" hazard. Second point: Foreseeable. It means that, although theoretically there are an infinite number of hazard situations, you still have to limit it to some number to keep it manageable. In fact, "where to stop" really depends on manufacturer. It should be noted that there are some technoques for doing this, for example, taking into consideration the intented use and reasonably foreseeable misuse as initial parameters. Third: although IEC safety product standard (in which the IEC 60601 series are an example of) follow the single fault philosophy, ISO 14971 is not restricted to single faults. So yes, there could have doube or triple faults on your risk management (but try to use just the foreseeable ones, please:-)). Also, it´s always toog to keep in mind that the single fault philosophy in IEC 60601 can only be applied if the situation falls under some specific boundaries (these boundaries are explanied in the examplanation to 4.7 in Annex A). If the situation are outside these boundaries, then the single fault philosophy cannot be aplied. For more on this interaction i suggest the following paper: R.G. Mellish, "The single fault philosophy: How it fits with risk. management,"presented at ACOS Workshop VI, Safety of Electromedical Equipment—An Integrated Approach through IEC Standards, Toronto, May 6–7, 1998. Cheers! Best regards Marcelo Antunes Regulatory strategy consultant SQR Consulting - Safety and quality through risk management http://www.sqrconsulting.com.br <http://www.sqrconsulting.com.br/> Electromedicalinfo http://www.electromedicalinfo.com <http://www.electromedicalinfo.com/> Gtalk: mmantu...@gmail.com MSN: marcelo_antu...@hotmail.com - Show quoted text - Chris.Dupres@elek ta.com To 03/17/2008 09:06 ted.eck...@apcc.com AM cc emc-p...@ieee.org Subject Re: Protective Earthing Terminal Construction Requirements Ted Ekert said: <If a ground connection fails, there will be no indication of a problem to the user. The product will likely continue to operate perfectly normally. A second failure, such as a loose line wire, could lead to the sudden and unexpected energizing of exposed metal. The product has now become hazardous without warning.> This makes sense of course, but (going off track a little bit) this implies that the equipment has TWO faults, and the premise at the moment seems to be 'Safety under SINGLE FAULT conditions'. I guess I'm asking for opinions, in view of the latest standards leaning or Risk Analysis etc., (e.g. IEC 60601-1 Rev 3) is.. "How many stacked risks should we take into account?" when defining 'Risk'. I mean, it's perfectly feasible to lose a ground connection on a case (1 fault), and for a live wire to come loose and touch the case (2 fault). Do we have to take ALL scenario's like that into account? In other words, ensure the design is safe under double, or even triple fault conditions? I'm reminded of a mains plug on a piece of UK equipment, where the lead was tugged, the Earth wire pulled out and ended up on the Live wire. Of course the whole case became live.This was found because a secretary felt a 'tingle' when she touched the case. I guess her plastic high heels saved her that time. One event, but two faults. So how many levels of fault should we take into account in order to fulfil the Risk Analysis requirements? Regards, Chris. Chris Duprés Compliance Engineer Elekta Limited Linac House Fleming Way Crawley West Sussex RH10 9RR www.elekta.com tel: +44 (0) 1293 654311 fax: +44 (0) 1293 654260 *******************Internet Email Confidentiality Footer******************* The contents of this e-mail message (including any attachments hereto) are confidential to and are intended to be conveyed for the use of the recipient to whom it is addressed only. If you receive this transmission in error, please notify the sender of this immediately and delete the message >from your system. Any distribution, reproduction or use of this message by someone other than recipient is not authorized and may be unlawful. Elekta Limited is a company registered in England and Wales whose registered number is 3244454 and whose registered address is Linac House, Fleming Way, Crawley, West Sussex, RH10 9RR - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to emc-p...@ieee.org Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas emcp...@ptcnh.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald: emc-p...@daveheald.com All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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