larry@uunet.uu.net (Larry Lippman) (10/20/89)
In article <telecom-v09i0461m07@vector.dallas.tx.us> amc-gw!ssc!tad@beaver.cs. washington.edu writes: > I enjoyed Larry Lippman's description of cable splicing and mining. > Wasn't it a cable mining operation that set off the Hinsdale fire? It could be, but I am not certain; I have encountered different versions of an explanation for the Hinsdale fire, both from public and "inside" sources, so I don't know what to believe. In any event, cable mining DOES INDEED provide an opportunity for a fire under some circumstances if care is not exercised. The problem is that in older CO buildings the -48 volt office battery is distributed using wires having RH and RHW insulation types. This insulation is rubber, and covered with varnished cloth. Prior to 1950, the rubber used was natural, with newer cable using neoprene or butyl rubber. Over the years much of this rubber will age and devulcanize, especially on cable which has been subject to excess heat from overload conditions. As a result, the insulation will deteriorate such that movement of the cable would cause the rubber and outer cloth covering to literally crumble to dust - thereby exposing bare conductor. DC power distribution in large electromechanical CO's results in some serious current. In WECO CO's, most major battery feeders use 750 MCM copper conductors, in which the copper is almost one inch in diameter. A heavy conductor is also used to keep the battery feed impedance to a minimum, thereby reducing impulse noise and crosstalk. A 750 MCM conductor may intermittently carry with safety about 750 amperes, and hence will be fused between 500 and 1,000 amperes, depending upon the power distribution design. Such a 750 MCM conductor has the capability of a *SERIOUS* amount of short-circuit current. Almost all battery feeders in older CO's are protected by fuses which have a certain amount of thermal delay before opening on an overload condition. The ability of such an exposed conductor to strike and maintain an arc - all before blowing a fuse - is simply *AWESOME*. While I did not witness the event, I have seen the aftermath of a 750 MCM conductor carrying -48 volts burn through a 5/8" steel threaded rod cable rack support - like a knife through butter, but instead spewing molten metal - BEFORE the fuse ever opened the circuit! Power cables run directly on cable rack, protected from the supporting metal only by a small, thin piece of fibre insulation. I have also, ahem, personally destroyed my share of small tools in past years due to accidental short circuits between -48 volt battery and ground. It is EASY to start a fire if one is careless. The risk associated with cable mining is that old power cables, whose insulation is being held together on a wing and a prayer, will then crumble upon being disturbed, thereby exposing the conductor to potential short-circuit. Power feeders will usually survive more than one generation of telephone apparatus, which is why power feeder cables many years old will still be in service. While ESS apparatus is usually installed with new batteries, power apparatus and power distribution wiring, older power feeders often remain to supply trunk circuits, carrier, transmission and ancilary facilities. As I see it, the former Bell System and present RBOC's must shoulder some responsibility for the risk of CO fires. It has only been in recent years that smoke detectors have been commonplace in CO's. The traditional method of fire detection - still in service in many CO's - is to run "fire wire" around cable rack and apparatus which is deemed to be vulnerable to fire. Fire wire is a low-melting point wire similar to solder; it is about 10 AWG in size. When the temperature reaches a certain point (I don't remember the setpoint), the fire wire melts and opens a circuit. The problem with fire wire is that it is fragile, easily damaged and the fire wire splices are often intermittent. The result is that fire wire causes many a false alarm - which is then ignored. Also by the time fire wire melts due to an actual fire, one is in *deep* trouble since this is hardly an early warning detection system. Another problem is that the Bell System has traditionally sought to "take care of its own" and has thereby tried to avoid any embarassment with a fire department due to false alarms. The net result is that it has been rare for a CO fire alarm to be called into a fire department without a craftsperson investigating the matter first - a situation which can lead to serious delay and damage in the event of a real fire. The above attitude of avoiding "embarassment" and "adverse publicity" still exists. I personally know of an example which rather shocked me. A few years ago an employee of a contractor accidentally fell off a truck at the New York Telephone Franklin St. CO in Buffalo, NY. The employee was knocked unconscious. The security guard (this is the main CO in Buffalo, so there are full-time guards) did NOT call 911 for an ambulance, but instead called a *private* ambulance service which resulted in a significant delay in response as opposed to 911. The security guards apparently have standing instructions to call a private ambulance, and NOT to call 911 unless it is a "dire emergency". Why a private ambulance? Because then there will be no public record of any accident and no risk of a police report. Not a good attitude. <> Larry Lippman @ Recognition Research Corp. - Uniquex Corp. - Viatran Corp. <> UUCP {allegra|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry <> TEL 716/688-1231 | 716/773-1700 {hplabs|utzoo|uunet}!/ \uniquex!larry <> FAX 716/741-9635 | 716/773-2488 "Have you hugged your cat today?"
Maynard) (10/23/89)
In article <telecom-v09i0467m01@vector.dallas.tx.us> kitty!larry@uunet.uu.net (Larry Lippman) writes: > The above attitude of avoiding "embarassment" and "adverse >publicity" still exists. I personally know of an example which rather >shocked me. A few years ago an employee of a contractor accidentally >fell off a truck at the New York Telephone Franklin St. CO in >Buffalo, NY. The employee was knocked unconscious. The security >guard (this is the main CO in Buffalo, so there are full-time guards) >did NOT call 911 for an ambulance, but instead called a *private* >ambulance service which resulted in a significant delay in response as >opposed to 911. The security guards apparently have standing >instructions to call a private ambulance, and NOT to call 911 unless >it is a "dire emergency". Why a private ambulance? Because then >there will be no public record of any accident and no risk of a police >report. Not a good attitude. (paramedic mode on) This kind of thing kills people. That security guard, unless he is an experienced street EMT, has little to no concept of the necessity of getting fast qualified help to seriously injured people. Anyone who is knocked unconscious for any period of time is seriously injured. He needed an emergency ambulance, right then. There are any of a number of serious injuries that can kill within the time it takes to get a non-emergency ambulance there, most of which are not obvious as such. Wouldn't OSHA have something to say about that? I do know that if such a thing were to happen at either of GTE's COs in League City, there'd be charges filed... Jay Maynard, EMT-P, K5ZC, PP-ASEL | Never ascribe to malice that which can jay@splut.conmicro.com (eieio)| adequately be explained by stupidity. {attctc,bellcore}!texbell!splut!jay +---------------------------------------- Send richard@gryphon.com your NO vote on sci.aquaria; it belongs in rec.