Review the item:
Sima was so sleepy after her marathon studying session for calculus that
she ordered a triple espresso before going to class
once the caffeine kicked in, Sima knew that she would not doze off
on Professor Ribley.
A comma splice occurs when two complete sentences are incorrectly joined with just a comma. In the example above, no such comma exists. Sima was so sleepy … begins one sentence. Once the caffeine kicked in, Sima knew … starts the second sentence.
Because only empty space exists between the two, you should call this error a fused sentence.
To fix the problem above, you could put a period after class and begin once with a capital O.