NFPA 96 code 18.104.22.168.1 states- Upblast fans shall be supplied with an access opening of a minimum 4 in. on the curvature of the outer fan housing to allow for cleaning and inspection of the fan blades.
Outside of being code, this access is amazing for a hood cleaner. This fan was wobbling due to the outside build up, after the access was installed the blades could be cleaned properly. This access install cost much less than a new fan or any downtime.