.i5Z files are substance export files from the IUCLID5 software application. This application is used to enter data for chemical substances and ultimately submit a technical dossier to ECHA (Eurpoean Chemicals Agency).
The format is a ZIP file format. If you rename the file extension to .zip, you can open the file with WinZip. Inside this file are a number of zip entries with a .i5d extension. These are pure XML files.
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