Re: Safe for personnel?
I am sure the 'lack of oxygen' would be noticed by your body and appropriate 'actions' would be taken.
Nope. Not for most people. In most people the breathing reflex is triggered by build-up of carbon dioxide, not lack of oxygen. There are some medical conditions that can result in oxygen depletion being detected instead, but they take a long period of bodily adjustment (we're talking months, not minutes). Confirmation of this can be seen in simulations of aircraft decompression where people pass out without realizing there's anything wrong, particularly if the change in pressure is gradual rather than fast.
To quote text on 'Inert gas asphyxiation' :
Largely depends on the "inert" gas. Nitrogen and carbon dioxide, although it takes a lot to get them to react, do have nasty biological effects (with nitrogen you need a lot higher partial pressure than in the atmosphere, but then you get nitrogen narcosis). As do several other "inert" gases, including xenon. Xenon (despite being a noble gas) is, bizarrely, an anaesthetic (so a good choice for killing people painlessly).
Lack of oxygen alone isn't going to have any nasty side-effects. Unless, for example, you suffer from chronic respiratory acidosis, in which case your breathing reflex will be triggered by low oxygen rather than high CO2 and then you'll know there's something wrong.