The purpose of the spot treatment is to expose the pathogen to high levels of ozone. This will do a couple of things:
Stop sporulation of pathogens for several days
Eliminate Ethelene ( ripening agent).
Spot treatment should be done in a closed of area were no people are entering the room during treatment. It can be done at night between shifts or it can be done in a purpose build room for example a pre-cooling room.
Precooling rooms are ideal locations since the produce is usually exposed to high airflows and systems are in place to make sure that the cooling also takes place in the center of the stack. This will also allow ozone to come in contact with this produce.