Yet there were many casualities deaths of the war prior to the Battle of Big Bethel which would not be classified as "Combat deaths". Col Elmer Ellaworth would not be considered as a "Combat" death even though he was engaged in an invasion which was countered by a civilian acting as militia and defending his home. Several Civilian deaths such as John Browns raid. even those that raid was surpressed by a military force. And I believe that the first death in that action was ironically a free blackman who was a railroad telegrapher. And as for military deaths would you consider the Union soldier who was killed by the bursting cannon while firing the final salute of the surrender ceremony of Fort Sumter. Even though the Bombardment of Fort Sumter could be classified as a "Combat", with two military combatant forces, the only "human" death did not occur during the bombardment itself.
Just as a side note why do you think that Fort Sumter Cannon burst?
Was it possiblely damage during the Bomdardment? If so these were trained artillerymen and should have inspected the weapon before using it. Why would you use a damage gun.
Was it a flaw in the casting? If so had it never been proof fired? Therefore a failure of the Ordance Department.
Or was it mistakenly overloaded? Again these were trained artillerymen. Why would you use a projectile for a salute anyway which would increase the likelyhood of an overload situation? Where would that shell have landed if it had been loaded? A bursting gun is the results of overpressure and would be far less likely with a blank charge no matter what the cause of the failure, defect, damage, or even an accidental overload.