Keep in mind that the 28% oxygen index pertains to individual materials within the equipment (PWB's, etc.), rather than some sort of overall empirical measurement during the system fire test.
In a nutshell, materials are tested in an oxygen-controlled environment to see if they will support combustion in a >28% oxygen concentration. The idea is that if the materials require >28% oxygen concentration to combust, the material is considered more fire-resistant, and will therefore contribute less fuel to the fire. Dwight John Juhasz wrote: > > Good Answer (with respect to the standards noted below). > > However, I would like to expand on this discussion, if I may, with regards > to > telecom equipment in a CO (Central Office) environment and meeting Bellcore > specifications (realize that typically equipment that will go into a CO > environment will also need to meet UL 19503rd ed.). > > In the case of Bellcore NEBS GR-63, the content of smoke is measured with > regard to > 'Oxygen rating index' (should be 28% or greater) during the Fire Resistance > testing. The previous version of the specification (TR-NWT-000063) > specifically measured all the content of the smoke to determine smoke > corrosivity. > Although the current standard (GR-63) is relaxed, the RBOCs (Regional Bell > Operating Companies - becoming less numerous of late) reserve the right to > view the video tape of the fire test when considering a product, and if they > feel that the product is producing too much smoke (regardless of the oxygen > index) they become concerned. > They're concerned about bringing down a central office to 'clean' the > surrounding equipment from the corrosive elements of the smoke. > > So those of you who will also need to meet the Bellcore NEBS requirements > (telecom equip to be located in a CO) in addition to UL1950 3rd Ed., this > will be a concern. > > John A. Juhasz > Product Qualification & > Compliance Engr. > > Fiber Options, Inc. > 80 Orville Dr. Suite 102 > Bohemia, NY 11716 USA > > Tel: 516-567-8320 ext. 324 > Fax: 516-567-8322 > > -----Original Message----- > From: Rich Nute [mailto:ri...@sdd.hp.com] > Sent: Wednesday, April 21, 1999 2:30 PM > To: jeff.jenk...@aei.com > Cc: emc-p...@ieee.org > Subject: Re: Excessive smoke > > Hi Jeff: > > > If a component abnormal test generates excessive and sustained smoke > > (several minutes), but does'nt breach reinforced or double insulation, > nor > > emit flame from the enclosure, is it considered a failure? Intuitively, > it > > seems like it would be, because of toxicity, but I have been unable to > find > > anything in the safety standards to support this. I have checked EN > 60950, > > EN 50178, UL 1012, and CSA C22.2 No. 107.1. > > For the purposes of product safety and compliance with safety > standards, smoke is a "permitted" emission during fault testing. > > The safety issue is whether a safeguard is damaged or breached > due to the heat which produced the smoke. If insulation is not > damaged (as per the hi-pot test), and excessive heat or flame > does not breach the enclosure (as per the cheesecloth test), > then the product is considered acceptable for the purposes of > product safety. > > Typically, product safety standards do not address the toxicity > of smoke. This is because all smoke contains toxic materials. > The only solution to smoke toxicity is to eliminate smoke, which > means eliminating all overheating situations. Which is nearly > impossible. > > However, any smoke from a product is likely create fear and > anxiety in the mind of the user and nearby persons. Any smoke > in a clean room will likely be cause for scrapping all stock in > the clean room. > > While smoke always contains toxic materials (e.g., carbon monoxide), > the concentration of the smoke (toxic material) in the volume of > the room together with the room ventilation determines whether or > not inhalation of the smoke is likely to cause an injury. If the > volume of smoke is small compared to the volume of the room, then > it is likely the concentration of toxic material will be below the > TLV (threshold limit value) for that material. > > So, it is a good idea (for the satisfaction of your customers) to > eliminate or reduce any significant smoke emissions that might > occur during fault testing. > > Best regards, > Rich > --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to ed.pr...@cubic.com, j...@gwmail.monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
