You ask:"Does washing your hands in (bearably) hot water kill bacteria?"
Yes it does. A better question would be: "How effectively does it clean your hands of dangerous bacteria?" The answer is that it is better than nothing and that it is better than cold water, but it is not really very good. Only very heat-sensitive microbes would be killed to a great extent, and those do not include many dangerous ones. Also, if there were dangerous ones on your skin, there probably would be plenty left, enough to be dangerous still.
"Bearing
in mind the hot water is only in contact with the hands for a few
seconds. I appreciate the question may be irrelevant if soap removes all
bacteria anyway."
It is not as irrelevant as you might think. The hot water does increase both the effectiveness of soap at removing microbes and killing them.
"Is soap 100% effective?"
Nothing is 100% effective, and certainly not plain soap and water, hot or cold, nor any other aids that would leave flesh on bone, however genuinely useful they might be in other ways. Use proper cleansers and disinfectants, scrub properly when it matters, and take matters further when it is sensible to do so.
"Even so, if soap wasn't
available, would hot water provide an adequate substitute to ensure the
hands are free of potentially harmful bacteria?"
No. Better than nothing, but no. Nor would soap alone, hot or cold. But the question supplies too little information. If you are talking of washing before dinner, that is one thing; if you are talking of scrubbing up before a surgical procedure, that is another. These are all matters of context. You need to bear in mind what it is you want to achieve and what it is you want to avoid, and what your options are. And when you cannot do everything you need to, do what you can to improve your chances and reduce avoidable damage and risks. The best anti-microbial procedures are those that you have available. Those that are not available are of no use whatever, no matter how magical they might have been if you had in fact had them at your disposal.
