[GreenKeys] [External] Model 20 caution!

[Jones, Douglas W]

From: Nick England [navy.radio at gmail.com] -- Sunday, June 23, 2024 2:35 PM

> Came across this in a BSP today -
> CAUTION: TAPES PRODUCED BY A REPERFORATOR
> BEING TESTED WITH THE
> TEST TAPE MUST NOT BE INTRODUCED
> INTO THE TELETYPESETTER OPERATING
> UNITS, SINCE, IF CERTAIN ERRORS
> HAVE BEEN PUNCHED IN THE TAPE, A
> LINE SHORTER THAN THE JUSTIFIED
> LINE LENGTH WILL BE CAST. THIS MAY
> CAUSE HOT LEAD TO BE SPRAYED FROM
> THE LINE CASTING MACHINE ENDANGERING
> PERSONNEL IN THE AREA. THEREFORE,
> THESE REPERFORATED TEST
> TAPES SHOULD BE DESTROYED OR IMMEDIATELY
> REMOVED.

Back in the 1970's, our lab at the U of Illinois had a Modcomp minicomputer.  The maintenance tech who came by periodically to do preventative maintenance had a number of stories about Modcomp computers.  They were used in the PAVE PAWS radars, so his territory included an installation on Hudson's Bay, and they were heavily used for process control in oil refineries and petrochemical plants.

He had a story about things that can go wrong in the latter environment.  Polyethylene is made from ethylene gas in a chemical reactor.  The reaction is exothermic, so when the reactor is running at its rated capacity, cooling water is needed and the polyethylene comes out in liquid form.  During startup, the temperature needs to be raised before the reaction will start, so process steam is needed to get the reactor up to temperature.

There are two basic failure modes that can be caused by a failure in the control system:

1) allowing the reaction rate to fall (cutting off the gas) while not cutting off the cooling water.  The reactor cools down, the reaction stops, and the polyethylene in the plumbing freezes.  At that point, they need to go in with cutting torches to cut out long runs of plumbing filled with solid plastic and rebuild the reactor.

2) allowing the rate of cooling water flow to fall while the ethylene gas continues to flow.  The reaction rate goes up and the reaction runs away.  The reactor explodes, sending shrapnel and dollops of molten plastic over the surrounding square mile of landscape.

He said he'd actually seen the results of the latter accident at one plastic plant somewhere in the upper Mississippi valley.  These kinds of industrial control failures can be very expensive.  The error with a Linotype described in the BSP you quoted is on the small side of the kinds of things that do happen.

            Doug Jones