Unfortunately CHMS haven't worked on a network without jumping through some hoops for a very long time. The only time you see the "Unblock" option is when you have perhaps downloaded a CHM file from the internet. When that happens, the operating system considers the file suspect until you pat it on the head and tell it that things will be okay.
If you really want the CHM to work from a network drive, you will have to adjust the registry of any and all PCs that will be accessing it. And that process is described on my dear friend Peter Grainge's site at the link below:
I believe that it was back in 2006 that Microsoft changed the security policy for Internet Explorer, which suddenly caused all the CHM files to display blank pages when viewed across a network. The situation has not changed, as it was a deliberate security workaround by Microsoft.
The only way for your departments to view your CHM file is for them to copy that CHM over to their local machine.
As an alternative to CHM, another standalone output would be Printed Documentation to a PDF file. That would work fine when viewed across the network.
Roderick, it's technically incorrect to state that the only way to view the CHM is to copy it locally. One can still make CHMs work on a LAN drive by taking steps to relax the security on the PCs that need to see it.
Oh yes, I forgot to mention that one's users could go into their security settings for Internet Explorer, and ramp down the security to allow viewing of the CHMs across a network. However, this would be a foolish endeavor, and it would be prudent to resort to PDFs for viewing across a network.