There are a few omissions here as well as some misinformation about the justicar's bubble and how it detonates combinations. The follow statements are completely true about biotic explosions:
1. A biotic primer never gets cancelled by a tech primer. Never. The tech primer simply overlays it.
2. Nearly all biotic detonators are also tech combo detonators, so they'll only trigger the most recent primer.
3. Reave is the exception. It ignores the tech primer and will always detonate a BE on a blue/green primed target.
4. The justicars bubble when deployed -- like any biotic detonator except reave -- will detonate the topmost primer.
5. The only biotic detonator that can cause two explosions is a cluster grenade and only because 2-3 get thrown at the same time. I.e. it's an exception that's not really an exception.
6. Lift grenades will only detonate biotic combos on unprotected targets. I don't know if they also detonate tech combos.
7. Obviously all this makes drell awesome biotic teammates.
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WRT to Beerfish's questions:
Reave-->Overload-->Bubble==> Tech Burst. If the bubble was specced for warp then a second reave would cause a BE regardless of preemptive tech primers.
Reave-->Overload-->Incinerate==> Tech burst, AND the target would be primed for a fire explosion. However, FE's take a few seconds to prime so a biotic detonator, quickly cast, would have a change to get you a biotic explosion.