[1] : Jargon File (4.3.1, 29 Jun 2001)

scram switch n. from the nuclear power industry an
   emergency-power-off switch see big red switch, esp. one positioned
   to be easily hit by evacuating personnel. in general, this is _not_
   something you frob lightly; these often initiate expensive events
   such as halon dumps and are installed in a dinosaur pen for use in
   case of electrical fire or in case some luckless field servoid should
   put 120 volts across himself while easter egging. see also
   molly-guard, tmrc.

   a correspondent reports a legend that "scram" is an acronym for "start
   cutting right away, man" another less plausible variant of this legend
   refers to "safety control rod axe man"; these are almost certainly both
   backronyms. the story goes that in the earliest nuclear power
   experiments the engineers recognized the possibility that the reactor
   wouldn't behave exactly as predicted by their mathematical models.
   accordingly, they made sure that they had mechanisms in place that would
   rapidly drop the control rods back into the reactor. one mechanism took
   the form of `scram technicians'. these individuals stood next to the
   ropes or cables that raised and lowered the control rods. equipped with
   axes or cable-cutters, these technicians stood ready for the literal
   `scram' command. if necessary, they would cut the cables, and gravity
   would expeditiously return the control rods to the reactor, thereby
   averting yet another kind of core dump.

   modern reactor control rods are held in place with claw-like devices,
   held closed by current. scram switches are circuit breakers that
   immediately open the circuit to the rod arms, resulting in the rapid
   insertion and subsequent bottoming of the control rods.


see also:
big red switch frob dinosaur pen field servoid easter egging molly-guard 
tmrc backronym core dump 

[2] : The Free On-line Dictionary of Computing (27 SEP 03)

scram switch
     
         from the nuclear power industry an emergency
        power-off switch see big red switch, especially one
        positioned to be easily hit by evacuating personnel.  in
        general, this is not something you frob lightly; these
        often initiate expensive events such as halon dumps and are
        installed in a dinosaur pen for use in case of electrical
        fire or in case some luckless field servoid should put 120
        volts across himself while easter egging.
     
        scram stands for safety control rod ax man.  in the early days
        of nuclear power, boron moderator rods were raised and lowered
        on ropes.  in the event of a runaway chain reaction, a man
        with an axe would chop the rope and drop the rods into the
        nuclear pile to stop the reaction.
     
        see also molly-guard, tmrc.
     
        jargon file
     
        2003-05-17
     
     
see also:
big red switch frob dinosaur pen field servoid easter egging molly-guard 
tmrc jargon file 

Scram Switch >> S Words
Scram Switch, definition of term: Scram Switch
scram+switch_pag1.html

Scram >> S Words
Scram, definition of term: Scram
scram_pag1.html

Switch >> S Words
Switch, definition of term: Switch
switch_pag1.html

Switch Back >> S Words
Switch Back, definition of term: Switch Back
switch+back_pag1.html

Switch Over >> S Words
Switch Over, definition of term: Switch Over
switch+over_pag1.html

Toggle Switch >> T Words
Toggle Switch, definition of term: Toggle Switch
toggle+switch_pag1.html

Context Switch >> C Words
Context Switch, definition of term: Context Switch
context+switch_pag1.html

Ignition Switch >> I Words
Ignition Switch, definition of term: Ignition Switch
ignition+switch_pag1.html

Safety Switch >> S Words
Safety Switch, definition of term: Safety Switch
safety+switch_pag1.html

Dip Switch >> D Words
Dip Switch, definition of term: Dip Switch
dip+switch_pag1.html

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