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Thread: "Six nines" reliability vs. safety factor

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    "Six nines" reliability vs. safety factor




    Aircraft are supposed to have a 99.9999 % chance that they will work over some specified time interval.

    If a picture weighs 25# and you want the industry wide safety factor of four, the fastener should pull out at 100 # or more. Personal safety calls for factors of at least 10.

    Is there some way to correlate these two?

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    Re: "Six nines" reliability vs. safety factor

    what is the relationship between aircraft and picture?
    In the long run, we're all dead.

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    Re: "Six nines" reliability vs. safety factor

    Not with the data given.

    If you assume that the only relevent failure mode picture hanging is "fastener could not hold 25#", and you tell me that standard deviation of the maximum load, then I can corelate them. If we build picture fasteners to hold, on average, 100# but the SD around that spec is 33#, then they will not hold a 25# picture ~1% of the time, i.e. they will only be 99% reliable. If, on the other hand, the SD around that spec is just 11#, then only ~10^(-12) of them will fail, i.e. they will be 99.9999999999% reliable.

    Of course, I doubt that the assumption that this is the only relevent failure mode is a good one in practice.

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    Re: "Six nines" reliability vs. safety factor


    Mr. "I am", I think you have answered my question.
    Thanks.
    BTW, the SD of the pull out strength of fasteners is probably +/- a few pounds, depending on the wall material.

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