Monday, June 3, 2013

About different ideas about technical risks

When my family and I lived in the United States in the mid-'90s, I bought a drill press. It was a cheap, somewhat wobbly Taiwanese import that served my purposes most of the time. Under a cover, one can put a v-belt on one of five pairs of pulleys, thereby getting one of five different drill speeds. The engineers had also thought a little bit about potential hazards and had identified an important one: If the chuck key were left in the drill chuck and I started the machine, the key would be hurtled away with high speed, potentially hurting me or someone. So, the key is spring-loaded to "self-eject" itself out of the chuck if it is not pushed in (here is an example of such a key—no advertising intended).

When I moved on to Germany, I had to get rid of my American-Taiwanese model (wrong voltage etc.). I bought a new cheap, somewhat wobbly Taiwanese import that serves my purposes most of the time. Again, there are five pairs of pulleys under a cover for different speeds, and of course, there's a drill chuck with corresponding key. And also the engineers of this machine had thought about potential hazards and come up with one important one: If one lifted the pulley cover while the machine was running, one's clothes or fingers could be caught by the v-belt, with potentially harmful results. So, there is a switch on the cover which breaks the circuit when the cover is opened. However, the chuck key ... is without any spring—just as the U.S.-side cover was without any circuit breaker.

What is the morale of this story? Simple:

What counts as dangerous and what not is largely a matter of previous experiences (including, I assume, lawsuits of one kind or the other). It seems that Americans hurt themselves by shooting drill keys through their workshops, whereas Germans cut off their fingers in running pulleys, but not the other way round ... or the like.

Why is this interesting for interlockings? Because it seems that at least some of the rules in that area were equally founded on some local experience that might be just the opposite of what someone nearby found. Here are two examples:
This remained so even though many other railways successfully moved their points with wires.
  • Austrian railways prohibited the use of DC electric locks for route locking from 1906 onwards and instead used combined AC-DC locks (see e.g. Hager, "Eisenbahnsicherungsanlagen in ├ľsterreich", vol.1, p.19). A little later, the German "Einheitsstellwerk" used only DC locks for route locking.
The reason for such rules is most probably that specific types of a device lead to problems, but the rules were formulated as if every variant of that device was problematical. The DC locks on my 12SA actually might not be without problems, but the improved version of the Einheitsstellwerk certainly was acceptable in any interlocking. Moving points with a single wire is certainly a bad idea (in contrast to signals and even barriers), but with two wires, it was definitely possible to build safe interlockings.

Still, the rules were as they were (and are as they are), and most of the time signalling companies complied with them (and maybe even could charge a little more because certain alternatives were not allowed to compete).

And what I learn is that even in an "objective field" like signalling, sometimes asking that question "But why didn't they ...??" can only be answered with "Well, they just didn't."

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