What caused the flashes in the video footage of Chernobyl? There is video footage of nearby villages in Pripyat, in the first week after the Chernobyl disaster. When I watch it there are villagers leading normal lives in normal clothing. Some Russian nuclear scientists pass by in full radioactive suits. Then there these clearly visible "flashes" in the air; I have looked on youtube but haven't found the video that I watched a long time ago. My layperson understanding is that these flashes are caused by an extreme amount of radiation.  

Here's footage that shows the flashes in the air. They are subtle orangish flashes that are quick. But there's one for instance just after 3 minutes. 
This isn't the original one that showed the flashes better. Anyway:
Chernobyl 

From Wikipedia "Ionized-air glow":


  Within minutes after the steam explosion that caused the Chernobyl
  accident at 01:23 local time, a number of employees at the power
  station went outside to get a clearer view of the extent of the
  damage. One such survivor, Alexander Yuvchenko, recounts that once he
  stopped outside and looked up towards the reactor hall he saw a "very
  beautiful" LASER-like beam of light bluish light, caused by the
  ionization of air, that appeared to flood up into infinity.


My questions are: 


What amount of radioactive material is needed to make those flashes in the air happen?
Is radiation alone enough?
Are other factors such as weather, temperature or other prior chemical elements in the air needed to allow this flashing to happen?
The white flashes seen in the video are the result of radioactive contamination of the original film. Airborne radioactive particles were deposited onto the film and caused a local overexposure of the negative, quite similar to the historic experiment of Antoine Henri Becquerel. That's why the flashes only appear in individual spots in individual frames of the film. (This is also explained in the documentary The Battle of Chernobyl, which also contains these film excerpts.)



There was no corresponding visual phenomenon in the air that could be directly observed by people in Pripyat.

The ambient dose rates measured in 26 locations in Pripyat on 26 April 1986 at noon (i.e. about the time when the film was recorded) were about 0.038–1.9 R/h (i.e. about 0.38–19 mGy/h; with a geometric mean of 2.4 mGy/h). Such dose rates cannot cause any directly visible effects in air.

The flashes on the film are not related to any visual phenomenon that was caused by nuclear reactions, radiation, fire or other chemical reactions at the open reactor during the night of the accident.