How many Confederates were killed by the explosion: 0 * to 6** to 50***
*According to this source ("The Mississippi and River Forts" · Volume 3, by Ron Field
[Link]) the author claims the Confederates had abandoned the area since they were aware of the Union Army's actions as they were digging so no one was present during the explosion however in the fighting that followed 21 lives were lost.
**And according to this source ("Life in the Confederate Army: being the observations and experiences of an alien in the South during the American Civil War", by William Watson
[Link]) he claims 6 lives were lost with 21 wounded. In the book ("Vicksburg and the War", by Gordon Cotton
[Link]) suggests "because of their foresight (the 3rd Louisiana) only about a half-dozen were killed.
***And according to this source (
https://www.historynet.com/americas-civil-war-digging-to-victory-at-vicksburg.htm) "A soldier in the 3rd Louisiana recalled: Suddenly the earth under our feet gave a convulsive shudder and with a muffled roar a mighty column of earth men poles spades and guns arose many feet in the air. About fifty lives were blotted out in that instant".
Members of What Regiment killed by the explosion: Third Louisiana Infantry Regiment
Yet again I am plagued with various answers. According to my first source it was the above;
[Source]
In another source ("Mississippi Civil War Monuments An Illustrated Field Guide byTimothy S. Sedore"
[Link]) I found a list of those killed (including one noted as 6 (buried by the firing of the mine) and it totals 17 a totally new number of deaths.
3rd Louisiana - 6
38th Mississippi - 1
43rd Mississippi - 6 (buried by the firing of the mine)
5th Missouri - 1
6th Missouri - 3 - including Confederate Colonel Eugene Erwin
And with that final word I throw in the towel and am finished searching for different answers. Unless I have the questioner's exact source (or I misread and misunderstood the question) I have no idea what the correct answers are.