How to turn off ALL alerts?

There is probably a simple answer to this, i just can't find it, i hope someone in the community can tell me.

I sometimes use my iPad to do a public presentation, and I have had embarrassing situations when a banner notification comes across the top of the screen. These can be tweets, iMessages from family or friends, notifications of incoming phone calls on my Comcast home phone, sports scores, news updates, my bank alerting me of a large withdrawal, and the like. And I've even gotten interrupted by FaceTime calls!

Is there any way to temporarily turn off ALL interrupting notifications from ANY app, during the time of the presentation, and then turn them back on afterward. I don't want to have to go into 14 different apps, turn off notifications, then turn them back on.

I simply can't find anything in Settings which will allow me to do this. I tried turning on "Do not disturb" setting, but that only quiets the phone, it doesn't turn off alerts.

BTW, FWIW, when I do these presentations I'm using Safari, not PowerPoint or Keynote, so I have to remain connected to the internet. I figured maybe Keynote for iOS would have a setting "Turn off outside notifications during slide show", but I can't even find that!

Any help would be appreciated! Thanks,
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