I'm going to have to say that given the current state of the average EMS provider, that EMS as a whole should not be allowed in active shooter scenarios.
Large picture is that most EMS providers are moderately to severely out of shape, do not carry the traits of continuous situational awareness, prone to complacency, could not handle the intensified stress to properly execute TTPs in a nonpermissive environment, couldn't be trusted with a squirt gun - let alone a firearm, not interested in learning/training adequately to perform such rare operations, and are not in this game to do such things. Generally, tacticool medicine and tactical medicine are vastly different from each other and vastly different from regular EMS calls. Not to mention- some EMS folks wouldn't walk into that building anyways with shots being fired- no matter what- it just isn't in them.
Trained tac medics train continually and are versed and reheared for such action, and even they don't get it right everytime (we're all human). Plucking a few "badass" heroes off the engine and putting a vest and helmet on them does not a tactical medic maketh.
Now if you want a few medics to rush in under a protection element (SWAT guys covering you) and put TQs on folks and needle decompress folks- that's still something that requires more than a vest and helmet, to avoid becoming a casualty yourself.
Proficiency in such operations require personnel of a higher caliber than that of your average EMS provider. Notwithstanding, sometimes it is the people who no one imagines anything of that do the most unimaginable things. But in the larger scale- tactical medicine is not our business.
Intense physical conditioning, firearms training, small team tactics training, movement under fire... Etc...
I'd suggest if you are truly interested in tactical medicine you take a TCCC course -which is a VERY minimalistic entry level view into the concepts surrounding care under fire. It's not a tactical medic cert or patch or some BS.
Anyways.
Would I volunteer to be one of those guys? Sure I would... In a damn second... But I would train like my life and my teammates lives depended on it, because it will. Not to mention, I'm not going into an active shooter environment without being armed- cut and dry, that's non-negotiable. I don't give a **** if I have a full body Ironman suit- no personal weapon, no go.
"Everyone wants to be an operator, until it's time to operate."