I have spawned my pasterized dung/straw compost and covered it with plastic sheet with a few drilled holes. It's in the dark and at 26,27 degrees Celzius (82 F). I wait for micelium to colonize the compost and then I will do the casing. Is there any danger of contamination if I wait for complete colonization without fanning?
There is always a danger of conatimnation with any grow.
Though at this colonizing stage there are no massive air exchanges needed, so what you have done is ok.