Guild Wars 2

To clarify:
I understand traits/sigils give you a chance to proc which then automatically casts whatever ability is tied to said trait/sigil. My question refers to the fact that I noticed that two things can not or will not proc at the same time. Is my testing of the abilities flawed?

Example:
Engineer’s Explosive V trait is 33% chance to burn on crits
Engineer’s Firearm Sharpshooter trait is 30% chance to bleed on crits
+
Sigil of Superior Air is 30% chance to cause Lightning Strike on crits

I have never seen them all go off at the same time. Only 1. Can someone confirm or deny this?