Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!kitty!larry From: larry@kitty.UUCP (Larry Lippman) Newsgroups: net.micro.pc Subject: Re: Hard disk shut-down (really terminal fires) Message-ID: <1397@kitty.UUCP> Date: Thu, 30-Oct-86 19:58:45 EST Article-I.D.: kitty.1397 Posted: Thu Oct 30 19:58:45 1986 Date-Received: Fri, 31-Oct-86 13:18:01 EST References: <302@neoucom.UUCP> <2475@gitpyr.gatech.EDU> <1379@kitty.UUCP> <220@polyslo.UUCP> Organization: Recognition Research Corp., Clarence, NY Lines: 95 Keywords: computer on, but monitor off please Summary: The _reality_ of computer product "fire safety"... In article <220@polyslo.UUCP>, npollack@polyslo.UUCP (Neal Pollack) writes: > In article <1379@kitty.UUCP> larry@kitty.UUCP (Larry Lippman) writes: > > There is nothing in a CRT monitor which is any more prone to catch > >fire than in a computer itself. > > CRT monitors have no more than 24 volts DC present in any circuit > >element, with the exception of the high voltage accelerating potential > >circuit. Now, THAT circuit may well have 12 to 25 kilovolts of DC, but will > >be so current-limited (a few microamperes), that one would be hard-pressed > >to start a fire by intentionally removing the anode wire and arcing between > >ground and a piece of paper! > > What else is there _different_ in a CRT that will burn? The > >deflection yoke? No way! > > No offense Mr. Larry Lippman, but you are giving users dangerous > advice indicating that it is not realistic for a monitor to cause > a fire. I have been a technician for 12 years, and an Engineer > for the last 7. I have seen numerous fires started by both 5 volt > logic, and high voltage in monitors. Netland people, do not fear > your low voltage logic, it is rare to start a fire with the 5 volt > levels. However, when it comes to the monitors, maybe Mr. Lippman > can explain to our Fire Department why he thinks they can not burn. First of all, I am referring to CRT monitors which are mass-produced and therefore _should_ be UL approved. Like something made by NEC, Amdek, Ball, Conrac, RCA, etc. If you are using a monitor which is homebuilt, surplus, or otherwise NOT UL-aprroved, then ANYTHING is possible! Second, I am referring to monitors which are PROPERLY MAINTAINED. It should be obvious to anyone using a monitor for any period of time that the electrostatic charge results in dust buildup, especially on the CRT surface. Dust, of course, also builds up INSIDE the monitor - which is why all monitors should be opened at least once per year and vacuumed. Such cleaning is part of what I consider to be "proper maintenance". There is no question that a monitor with huge dust balls inside is a potential fire hazard (which is no different than carelessly storing oily rags...). As long as we are talking about UL-approved monitors that are reasonably dust free (which SHOULD be the case for everyone!), I stand by my original posting - a monitor should be no more prone to catch fire than any other computer circuitry. Notice that I said "more prone", and NOT "never". In a UL-approved monitor, you will find virtually no component - including the case - that is not a self-extinguishing plastic. This means that printed circuit boards are NOT phenolic, but are something like a FR-4 fiberglass-epoxy construction. Some catastrophic fault may result in SMOKE until power is removed through operation of either internal or external overcurrent devices, but it is highly unlikely that FIRE will result. Why? Because in order for a self-extinguishing plastic to burn - like FR-4 - it is necessary that external energy be applied. With the operation of an overcurrent device, this external source is removed. Sure, I've seen charred FR-4 - especially on boards where a fault occured that resulted in a wire-wound resistor getting red-hot. But once the resistor opened under overload, or the power was cut, say by a blown fuse, any FR-4 burning abruptly stopped. > We have seen several monitor fires here over the last few years. They > have ranged across many brands. In most cases, the high voltage > section (10 -25 Kvolts) has started a fire by either arcing or > internals shorts in the transformers. In the case of arcing, arcing against _what_? Most monitors use a horizontal output transformer with the high voltage lead running to an inline silicon rectifier array, and thence to the CRT anode. These silicon rectifier arrays will open rather quickly under the overcurrent conditions associated with arcing - thereby removing the source of the arcing energy. Should the horizontal output transformer develop a significant internal short, then invariably either the horizontal output transistor will fail due to overload, or the power supply overcurrent device will actuate. What is going to burn? Is this any DIFFERENT than the power supply transformer in a computer developing an internal short? > In one case, a power resistor > in the power supply of a Tek Graphics terminal flamed out and set > the board on fire overnight. This is a POWER SUPPLY PROBLEM. Is this any different than the computer itself? > In all cases, our smoke > detectors alerted the fire crews before serious damage to the > laboratory complex. Did the fire burn through the terminal housing? If not, was the terminal housing hot enough to blister paint and ignite say, paper left in contact with the terminal. Look, I'm not saying that monitors won't catch fire, and I'm not denying that monitors haven't caught fire in the past. There is a possibility of fire ANY time line-operated electronic equipment is involved. All I am saying is that for what should be a NORMAL situation (i.e., a properly maintained, UL-approved monitor), there is no greater probability of it catching fire than in say, the computer itself. ==> Larry Lippman @ Recognition Research Corp., Clarence, New York ==> UUCP: {allegra|decvax|rocksanne|rocksvax|watmath}!sunybcs!kitty!larry ==> VOICE: 716/688-1231 {hplabs|ihnp4|seismo|utzoo}!/ ==> FAX: 716/741-9635 {G1,G2,G3} "Have you hugged your cat today?"