Why it’s wise to heed warnings in user manuals

I’ve been reading through a manual for an IBM DS 3400 Disk Array, and found a pronounced warning:


Many people don’t read manuals at all (claiming it’s a waste of time). Even those who do, often don’t treat warnings seriously. The one above is however quite serious. During my SAN training I was told to never look into an operating fiber link. Why? It’s simple. A long-wave fiber interface (which means it’s both for long distance and uses long wavelength) emits an invisible, but nevertheless powerful laser beam. Why it’s invisible? Because the wavelength is in deep infrared 1310-1550nm. Cheap cameras, which don’t have an IR filter (for example mobile phone cameras) can easily detect such IR radiation. This turns mobile phones into cheap, portable devices to check if there is signal on the fiber:

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