Passive or Active Consent

I am conducting fire research in primary schools looking specifically at evacuation. This involves observing and recording on camera, fire drills which are conducted in the schools. The videos are then analysed to provide data on evacuation dynamics. I will have no active role in the evacuations as the teachers shall remain in control of each class throughout and they will conduct the drill in accordance with school procedures.
As the research is non-evasive and defined as less than minimal psychological and physical risk I am proposing the passive consent method. This would be in accordance with school policy for the use of photographs taken at school events, etc. All gatekeepers are happy with my approach

This has been questioned by my ethics committee who are looking for active consent. The big problem being that return rates for active consent in schools could be lower than 50% and will present a significant administration burden to the schools who have provided access by good will.

All comments are welcome.