John, Your point is well taken.
As a child, I recall running my fingers through a candle flame. If you move fast enough, you do not absorb "feel" the heat of the flame. So it seems to me that the true definition of ignition would be something like "a cirmstance where a source of ignition is sustained long enough against a material to be absorbed and raise its temperature to the point where it begins to combust." The UL 94 test has standardized the available energy and time taken to ignite a sample, and samples can then be evaluated in comparison to other materials. Conversely, it seems possible to use a "standardized" ignitable material to evaluate ignition sources. And this has been done to some extent in IEC 610101-1 section 9.2 "Eliminating or reducing the sources of ignition within the equipment" and 9.4 "Limited-energy circuits". But the aspect of time is not considered in either case, only magnitude. So far what I see in the standards is the approach to identify long-term (greater than 30 seconds) sources of ignition or already burning materials when evaluating the spread of fire. In the end, I suppose my question could be phrased, "Aside from the rapid and devastating mechanical effects of an explosion, is it possible or even likely to start a fire with something like UL 94 HB material, simply with an explosion?" And if so, "Is the use of UL 94 HB enclosure material enough, even if it does not have direct contact with non-energy limited circuits?" (double negative, I know...) More comments? -doug On 8/15/12, John Woodgate <[email protected]> wrote: > In message > <cabyvtvny1rjvr5g8moofwhm43wpbooszi0yrefkimxx6dvg...@mail.gmail.com>, > dated Wed, 15 Aug 2012, Doug Powell <[email protected]> writes: > >>For example the UL 94 test is a 30 second exposure to a 50W flame. >>Would a 15 second 100W flame be equivalent? > > Sometimes, sometimes not. It depends on what the heat does to the > material. I know of three effects, but there may be more: > > 1. The material itself oxidizes rapidly with energy release, so may be > said to 'burst into flames'. Thin natural textiles may do this (but wool > is type 3). > > 2. The material rapidly decomposes with release of oxygen, so > 'instantaneously combusts'. Cellulose nitrate (Celluloid) is an example. > > 3. The material has to heat up a lot before it begins to decompose and > release combustible gases. ABS plastic is an example, so is wood. > > Clearly, time of exposure matters. > -- > OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk > Instead of saying that the government is doing too little, too late or too > much, too early, say they've got is exactly right, thus throwing them into > total confusion. > John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK > > - > ---------------------------------------------------------------- > This message is from the IEEE Product Safety Engineering Society emc-pstc > discussion list. To post a message to the list, send your e-mail to > <[email protected]> > > All emc-pstc postings are archived and searchable on the web at: > http://www.ieee-pses.org/emc-pstc.html > > Attachments are not permitted but the IEEE PSES Online Communities site at > http://product-compliance.oc.ieee.org/ can be used for graphics (in > well-used formats), large files, etc. > > Website: http://www.ieee-pses.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 <[email protected]> > Mike Cantwell <[email protected]> > > For policy questions, send mail to: > Jim Bacher: <[email protected]> > David Heald: <[email protected]> > -- Thanks, -doug Douglas E Powell [email protected] http://www.linkedin.com/in/dougp01 - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.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 <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
