The general advice for combating this is simply to be very careful, and I have developed a number of habits when working in Pure Data, such as always using external speakers so that (presumably) my machine's internal sound system would not take any damage, keeping my Windows volume control as low as feasible, and adjusting my speaker volume knob up from min volume whenever playing audio. However, these measures still rely on accurate, human execution. Having recently read The Design of Everyday Things by Don Norman, I have come to belief that this is a suboptimal design which makes human error very likely to occur.

I am running Pure Data on Windows 7. Is there a way I can have either Windows or Pure Data put a cap on the maximum volume it will play? To be clear, I do not want a way to turn the Windows volume down more, as I would then be unable to hear the desired output of Pure Data. The danger is that the difference between desired volume and potential erroneous volume is many orders of magnitude, so I would like to be able to either put a hard ceiling on volume, or simply have the audio automatically muted while it is above a certain volume threshold. In the former case, it would be nice to also have some signifier to indicate that the ceiling is being applied. Is it possible to do this in Windows or in Pure Data?

It is a system built of user, computer, os, puredata, soundcard, amplifier, speakers, and anything else you put in the chain, you designed the overall system and you are the only one who can make it optimal. Applying blanket standards to all things just does not work, the design of my kitchen knives are sub-optimal because they can cut me, but if they can not cut me they will not be able to cut up my pineapple. Get a book on audio engineering if you are worried.

Ultimately I came to accept this as inseparable from the nature of Pd as a programming language, in that it gives you the raw tools to do pretty much whatever you like (including things that may not be advisable, either for your ears or your computer). Nowadays I always approach any unfamiliar patch (a help patch, demo from this forum, or anything whatsoever) with caution; I always take a look at what's going into [dac~] first, as many of my past unpleasant experiences came from patches where the author simply connected a number box with no defined upper limit directly into the right inlet of [*~] as gain control, meaning that if you mouse directly on the number box to turn up the volume (without shift-clicking), it's quite easy to slip & blast your ears in an instant.

For my own patch, I used zexy's [limiter~], which lets you specify an output limit in dB; you could make an abstraction which wraps such a limiter, and make sure to always add it in before [dac~] as a safety precaution in any patch you open. Or, when opening patches, just watch out for sketchy output levels before turning on DSP, and if necessary edit the patch first (perhaps [*~ 0.1] or [/ 100] or [dbtorms] may come in handy in these situations, if you catch my drift).

It is worth noting though that accidental volume spikes in general are certainly not unique to Pd, and keeping headphone/speaker volume low at first when checking levels is simply good practice with any speaker in any application.