at a certain concentration hydrogen peroxide self combusts...what is that density?
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I have (very carefully) handled 99% pure hydrogen peroxide (frozen, using tongs, dropped into a container and let it melt up to room temperature). If it does self combust, the concentration would be higher than 99% and/or at higher than room temperature.
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Hydrogen peroxide will always tend to decompose on its own, depending on its concentration, the temperature, impurities, and what kind of container it's stored in. That's why HTP has to be stored in a vented container (see the updates to the article). There is no concentration at which it will spontaneously decompose very rapidly at room temperature. However, at higher temperatures it can reach a point where you can get runaway decomposition. 120F (49C) is generally considered the highest "safe" temperature at which to work with HTP. Higher temperatures can be maintained as long as something is removing heat from the peroxide to prevent it from getting any hotter due to its own decomposition.
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Incidentally, stainless steel is *not* an appropriate container in which to store peroxide. Both iron and chromium, which stainless steel contains, are incompatible with peroxide. I edited the page to take out the reference to stainless steel.