MODIS product is generated by an automated algorithm and placed on the web page in near-realtime. It has not been quality controlled. For a quality controlled product, users are referred to the Hazard Mapping System (HMS) product created by SAB satellite analysts:
http://www.ospo.noaa.gov/Products/land/hms.html

Users should note:
Fire pixels represent the approximate location of a fire and do not represent the actual fire size. The MODIS instantaneous field of view at nadir for the channels used to make the fire product is 1x1 km, but the fire phenomena may be much smaller than that. We post this data as soon as we receive it, but the Near Real Time Processing System is not considered operational. We do not guarantee 24/7 access to this data at this time.

If no fires are detected for a given pass, a file is not placed on the server.