The famous ESO hierachical keywords are unfortunately not compatible with many FITS readers (including the one in IRAF at the date of writing). If you badly need a software to read information from a file FITS header but the information is located in an HIERARCH ESO keyword, you want to use hierarch28. To use it, create a simple correspondance table translating ESO keywords to your own, then apply the command. Since this command works locally on the file, it does not need to load it into memory, working extremely fast.
hierarch28 man page