The Stargate' iris, iirc, is some kind of really strong titanium alloy. It covers the 'Gate opening a few millimeters from the event horizon, preventing any matter from re-integrating upon passage through the wormhole. It is, of course, retractable (and very cool-looking).
Here's my question: do we know what SGC protocol about the iris is? Ie, do they often or usually put up the iris when there is an unscheduled off-world activation?
The one thing I'm pretty sure they don't do is keep the iris closed at all times (we always see the 'Gate standing "open" when we get shots from the control or briefing rooms). For one thing, if the iris was closed when a wormhole activates, that expensive piece of equipment would be vaporized just like any other piece of matter.
Thoughts? Input? Episode/scene references?