sadly, with flash bangs and grenades the only limiter is "common sense" and "world reactions"
Meaning, you have to look at the world and how it would react to such things. FBs make A LOT of noise! They are going to attract a lot of unwanted attention! (Same as grenades). Also, that attention isn't just going to be your typical beat cop... it's going to be HTR teams.. which means heavy ordinance and hardened armor, lots of drones, and magical support.
Corp Security isn't going to be throwing around grenades (well maybe flash bangs) because of collateral damage... they are there to
protect Corp property, not blow it to bits with explosives. At the same time, if Runners are using grenades on Corp Security, they are breaking the unwritten rules of Shadowruns (meaning: "We know shadowruns are a cost of doing business, and we will try to stop you, but if you keep it professional, we won't hold a grudge")
(the larger the body count, and collateral property damage, the more runners "force" a Corp's hand into revenge tactics..... After all, losing a prototype is just business... losing a prototype, AND two dozen dead employees..... yea, someone's gotta pay!)
IRL Explosives kill through the compression wave. The wave ruptures the alveoli, preventing them from collecting oxygen, and filling the lungs with blood. In effect, your drown in your own blood and die of asphyxiation. Often with out any other marks on the body. Then there is the shrapnel.. which just tears through the body, severing arteries and organs...
IRL, the only REAL defense against grenades is to NOT be in the area of effect, or, baring that, make sure there is a hardened structure between you and the explosion. which is why always fighting from cover is a great idea

(but even that may not save you)
Basically, with grenades, the only defense is to clear the area... which with many of the wireless grenades in SR can be almost impossible.
