On Fri, 11 Feb 2005 09:50:46 -0000, Alan B. Pearce wrote:

>...<
> Incidentally out of this course I got some strange bits of information. One
> I specifically remember is that while most of the world uses a whacking
> great red button as the emergency stop button on equipment, the Italians use
> a green one - why? because it is putting the machine into a state where it
> is safe, so you use green. You use red when the machine is going into an
> unsafe state - e.g. setting a spindle rotating so it is not safe to allow
> hands, etc, into the area. When you stop and think about it, it is quite
> logical - after all this is how traffic lights work - green light is safe to
> proceed, red light not safe to proceed.


Of course, this is one of those situations where something "intuitive" is actually nothing of the sort!  I did 
wonder what the large green mushrooms were for at ski-lift stations in Italy - I can't say I would have 
immediately hit one if there was a problem unless they were marked "Stop" in some language or other!

You could look at the switch colours the rest of the world uses as meaning "go" and "stop", not "safe" and 
"danger".  Or that by pressing green you are telling the equipment that it is safe to start...

I don't know who decided that Green/Red were to be the colours for Safe/Danger (presumably someone on the 
early railways) but they have done us a great disservice.  Red/green colourblindness is the most common type 
and train drivers and pilots are tested to ensure they can distinguish them, for obvious safety reasons.  
Drivers, at least as far as I know, aren't!  Yellow is nature's danger signal (ask any wasp or bee!) and it 
would have been the best choice for a "Danger" signal/traffic light.  Too late to change it now, though!

I always thought that Bomb Disposal would be the worst job to have if you're colourblind... "I'm about to cut 
the reddy-greeny-greyish wire..."   ;-)

Cheers,


Howard Winter
St.Albans, England


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