Air vents

Hi Guys
So I finished making my horizontal oil drum bbq/grill/smoker but while I was burning it out for the first time to get rid of the outer paint and inner crud I had the lid wedged open with a piece of wood but when it slipped and the lid closed the fire started to go out. I obviously need some air intake holes but don't want to add too many, any suggestions please.
So I finished making my horizontal oil drum bbq/grill/smoker but while I was burning it out for the first time to get rid of the outer paint and inner crud I had the lid wedged open with a piece of wood but when it slipped and the lid closed the fire started to go out. I obviously need some air intake holes but don't want to add too many, any suggestions please.