"No Firearms or Weapons"
I work for a middle-sized company (100+) with a written policy of "No Firearms or Weapons" on the premises.
It's a deliberately ambiguous wording, allowing the management to declare, ad hoc, that [whatever] is a weapon.
It's a building full of geeks.
The guy whose desk is beside mine carries a Cold Steel folding knife that's bigger than any folder I own. Other guys carry various things clipped to their pockets (I've seen several different knives and tools). I myself carry a full-sized folder, a Leatherman Wave, and at least one other 3-inch knife on a daily basis. No one even blinks. I make salad with my "weapon," and other guys open boxes and envelopes with theirs. We have a 10-inch carving knife in a drawer in one of the kitchens on my floor, and a very pointy 4.5 inch tomato/bagel knife.
Evidently the "or weapons" phrasing doesn't include pocket knives -- even large ones -- in common application, neither does it include sizable kitchen knives.
I would imagine, however, if some sort of violent event were to happen and someone's knife became a significant component of that event, the "or weapons" clause certainly gives the company the justification for a firing.
There is always the question of "would I bring a gun into the building," and the answer would be "not usually."
If it became clear that there was a plausible threat to life & limb and that my personal security required my personal intervention, I might take measures to balance the threat.
Companies do what they can to employ policies to standardize practices and provide a foundation for common understanding, generally oriented toward the benefit of the group considered as a whole, and only incidentally its individual members. Policy establishes standards and guidelines, but frankly cannot account for every kind of thing that can happen, and this is where one's individual responsibility and judgment comes into play. A responsible employee will take any necessary measures to see to it that company assets -- and that includes other employees -- are not subjected to undue risk. There are circumstances where a responsible employee would arm himself by way of mitigating a risk of specific character.
I have worked in places where it was explicitly stated in policy that whenever it was found that policy, as written, would act to the detriment of production or personnel, policy can and must be set aside until it can be remedied.
Policy is not awareness, policy is not thought, policy is not judgment. Those are qualities only people possess.
And so, come the day that being armed is more prudent than "following the rules," that's the day I go armed. And should that result in a rigid and poorly calibrated response from management, then so be it.
A friend of mine, riding in a cab in Italy, was surprised that the cabbie would slow down somewhat, but not stop, for some red lights. He noticed that the practice didn't seem to be limited to the vehicle he was in. When he asked about it, the cabbie advised him, "the light, she cannot see; for this we have eyes."
And so it is in life.
For this we have eyes.
Also I am known by my good friends that it is understood that I am usually "live".
It's that simple! Weather or not the company cares about your welfare or not is NOT the issue! The issue is, THEIR company, THEIR rules, THEIR liability! 
