Scott, Although this is in the end a safety issue, I do not believe that NRTLs will be very useful to find root cause.
I would recommend treating it like any reliability issue - use the "Five Whys" technique. Keep asking "why?" and, usually within 5 layers, you will get to the root cause. (1) Why did the system fail? It caught on fire. (2) Why did it catch on fire? Part of cabinet melted and the pcb around the power rectifiers area burned out. (3) Why did the pcb burn out? [Here's where the real work starts] John W's suggestion of comparing the failure area against single-faults in the schematic is a good one. There can also be manufacturing issues as Brian K suggests. I've seen high-impedance board shorts cause a fire once (luckily in the lab). Also look at possible foreign material inside the chassis especially if there are air vents or other openings in the product. Children are known to insert dimes and other material in vent holes (not that I ever did that when younger!). Another avenue to consider is mechanical tolerances. Despite the best intentions of the creepages and clearance requirements, sometimes a mechanical bit or piece will find its way between two energized traces. I saw that once and it evacuated the lab (!). Nothing will replace a couple of competent engineers poring over the product and looking at all angles. Maybe the next closest would be using a reliability consultant - I use "Ops a la Carte" but don't know if they have expertise in this area. If you narrow down the Root Cause to a component, a full vendor SCAR is mandatory, IMO. Good luck and I'd be interested to know the results, if possible. This is a real "fire fight". ...Marko From: [email protected] [mailto:[email protected]] On Behalf Of Scott Xe Sent: Tuesday, June 26, 2007 9:11 AM To: 'Tarver, Peter'; [email protected] Subject: RE: Caught fire during stand-by mode Peter, Many thanks for your reply and advice. We had a bad experience in hiring the world largest accredited laboratory to do such investigation long time ago but unfortunately it came back with unsatisfactory result. Do you have any idea any public body available for similar specific service? Best regards, Scott From: [email protected] [mailto:[email protected]] On Behalf Of Tarver, Peter Sent: Tuesday, June 26, 2007 10:10 PM To: [email protected] Subject: RE: Caught fire during stand-by mode > From: Scott Xe > Sent: Tuesday, June 26, 2007 6:44 AM > > However, under such circumstances, > I have no idea how to start the investigation. Can someone > point me out somewhere to have such investigation reports for > reference/information or any guidance to such study can be shared. Scott - Failure analysis and root cause analysis can sometimes be tricky. You can do this yourself, but might miss something. If your company has no one on staff experienced in these tasks, it may be best to hire an outside consultant. If you insist on doing this yourself, it is possible, but can take quite a bit of time. Take small steps as you disassemble the product with greater care than you would otherwise use. Take photos and detailed notes at every step. Try to locate the sources of heat that caused ignition (there may be more than one or a cascading effect). Smoke, discolored metal, bubbled paint, charred boards, etc. Try internet searches on failure analysis and root cause analysis. Regards, Peter L. Tarver, PE [email protected] CONFIDENTIALITY This e-mail message and any attachments thereto, is intended only for use by the addressee(s) named herein and may contain legally privileged and/or confidential information. If you are not the intended recipient of this e-mail message, you are hereby notified that any dissemination, distribution or copying of this e-mail message, and any attachments thereto, is strictly prohibited. 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