It looked to me like the terrorists on the floor had a mechanical friction type detonator. He needed to pull a cord or something like a cord pretty far, judging by his arm movement upward, and then the explosion took about 2 more seconds.
If that is the case, if you are an armed security guard or armed citizen, you need to treat them like zombies and put some lead in their brain, instead of running away. It looks to me like it was the opposite of an electronic dead-man switch—this self-detonation took a pretty big effort by the wounded/dying terrorist. He had to roll around to find his cord, and get into a position to give it a big yank.
The security guard who ran away (if he was armed) should have shot him in the head and stopped the detonation.
In one report I heard that one of the perps blew himself up outside against a window wall to get the other guy inside. This might be the first “suicide bomb breaching” I’ve heard of. Turkish security was actually pretty good, much better than a U.S. airport, where all three suicide bombers could have been in the middle of big security lines inside of airport concourses where the blasts would be contained for much more power and effect.
One of these days they will orchestrate suicide bombers like a controlled explosion map, each bomber has a gps unit that detonates automatically when in a predetermined position and time. More than likely a simple app like facebook would work.
That still leaves a question of how easy, quick the trigger is; and also the possibility of a "heartbeat" type of switch, where if the switch doesn't get attention each minute (or whatever interval), the fuse is lit.