Is it safe to connect my own USB drive to an unknown PC?

You said,

I can not find information if it is dangerous to place a unit on another computer

Before anyone tries to answer that, we need to know what "dangerous" means.

If you are concerned about the contents of the files that you have placed in the unit (including the metadata that can be attached to them), you should abandon this whole idea, as there is not much you can do to ensure the security of that data Files should be considered compromised as soon as you connect the USB drive to the unknown PC. The software on that PC could easily copy, store, modify or send your files anywhere.

If you are concerned about making the USB drive safe in the future, you should be careful at least. Taking that disk home and putting it in an average personal computer would be dangerous, since the unit could have been infected by malware that could spread to your PC before it had the opportunity to format it. This malware could potentially cause problems by corrupting or stealing personal information on your PC through a variety of methods.

Information security professionals and enthusiasts commonly avoid this risk by "destroying it from orbit," either by literally destroying the USB drive after using it or accessing it from a system designed to deal with infected media and then deleting them safe. Many times, these specifically designed systems are just a boot disk with a lightweight operating system that is preloaded with security tools, but, most importantly, it lacks personal information and does not have access to your personal information.