If the triggers are fired twice for the same event, it means that these 2 events are dependent, so you probably have 1 event that triggers the email and that also triggers the second event that triggers the email (I am no sure I am clear here, so let me know )
You should examine the activity log of your persons to see what are the 2 concomitant events that fire the trigger twice and try limit this dependancy. AFAIK, "Person is created" does not trigger any data value change, nor does it trigger any segmentation change.
Another solution would be to use a static list to send the email.
As a lead cannot be added to a list if it is already there, the campaign would not be able to fire twice within this range of 5 or 10 seconds