My experience agrees with yours Gert - there is no simple formula to follow.
In my early days as a PSE I tried to draw a flow-diagram of product safety assessment and decisions. On the first line I had about 20 options and each of those dropped down to about 20 more - many of which interlocked.....after a couple of weeks I gave up. I believe there is a real danger when one tries to provide general guidance. There will always be exceptions - hence standardization and harmonization will (I believe) never satisfy all conditions. When I write product descriptions I deliberately over specify the safety aspects of critical components - or systems. There is one reason for this - to ensure that everyone on the project understands the impact of changing components. When the PD is cut down my the agency I send a file copy of my original for the manufacturing/design file. That way there is a history. (e.g. if I use an HB enclosure because the product if powered from and SELVEL PSU with current fold-back, then that goes into the general description AND the description of the PSU.) I get despondent reading some agency reports to do not include that level of detail - but a telephone call to the manufacturer usually gets the answer. I know that not everyone does writes descriptions the way I do and I am not suggesting that it is the best way (or ought to be standardized) - it just happens to work for me and my clients. Best regards Gregg P.O. Box 310 Reedville, Virginia 22539 Phone: (804) 453-3141 Fax: (804) 453-9039 Web: www.test4safety.com -----Original Message----- From: [email protected] [mailto:[email protected]]On Behalf Of CE-test - Ing. Gert Gremmen - ce-marking and more... Sent: Thursday, November 08, 2001 2:13 AM To: Doug McKean; EMC-PSTC Discussion Group Subject: RE: Definitions - Safety Critical, Safety Circuit Hi Dough, Group, I agree that is approach is much more simple to understand, but most definitions up to now have the problem of defining A LOT of components as safety critical. The safety critical parts need much more attention then just specification and name it. They need to be maintained in brand , type and material f.a. If an ECO (Engineering Change Order) is made, replacing a safety critical component needs re-assessment of the whole safety concept. Safety related components need however just fulfill their safety specs and they will do the job, and ordinary components may be replaced at will by the manufacturer by any other part that does the functional job. A similar reasoning can be made to measures, procedures, circuits (build from components) and construction. The approch i treid in an eralier mail made use of the double layer concept in safety (electrical mechanical chemical radiation heat and fire) to identify components. Those who bridge two layers of safety, or can invalidate the safety of a circuit are Safety Critical. (f.a. a cap that goes from hazardous voltageto an ungrounded accessible part) Those that bridge only one layer are Safety Related. (f.a. one of the two insulations in double insulation) Those that are redundant (from safety point of view) are ordinary components. What do you think of this: can this approach simplify the job ? Regards, Gert Gremmen, (Ing) ce-test, qualified testing =============================================== Web presence http://www.cetest.nl CE-shop http://www.cetest.nl/ce_shop.htm /-/ Compliance testing is our core business /-/ =============================================== >>-----Original Message----- >>From: [email protected] >>[mailto:[email protected]]On Behalf Of Doug McKean >>Sent: Thursday, November 08, 2001 4:07 AM >>To: EMC-PSTC Discussion Group >>Subject: Re: Definitions - Safety Critical, Safety Circuit >> >> >> >>Couldn't we just go to the front of the UL1950/60950 >>standard and agree that a "safety critical part or device >>or circuit or construction" is simply something used >> >>"... >>to prevent injury or damage due to: >>- Electric shock hazard >>- Energy hazards >>- Fire hazard >>- Mechanical hazard >>- Heat hazard >>- Radiation hazard >>- Chemical hazard >>..." >> >>Regards, Doug McKean >> >> >> >>------------------------------------------- >>This message is from the IEEE EMC Society Product Safety >>Technical Committee emc-pstc discussion list. >> >>Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ >> >>To cancel your subscription, send mail to: >> [email protected] >>with the single line: >> unsubscribe emc-pstc >> >>For help, send mail to the list administrators: >> Michael Garretson: [email protected] >> Dave Heald [email protected] >> >>For policy questions, send mail to: >> Richard Nute: [email protected] >> Jim Bacher: [email protected] >> >>All emc-pstc postings are archived and searchable on the web at: >> No longer online until our new server is brought online and >>the old messages are imported into the new server. >> >> ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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