Joomla! version: 3.4.1
BF Syrvey version: 2.2.0

As the title suggests, it is possible to submit the firm without filling in any of the fields.
This issue has bee reported before and it remains actual, at least on Safari 8.0-6 / Mac OS X Yosemite.
On Chrome 43 it leaves as expected.

Do you have this issue with Firefox browser? If so, can you look to see if there are any javascript errors that might help pinpoint the problem using tools->web developer->browser console.

Does Safari have a similar feature that allows you to see Javascript errors? If so, what are the error messages you are seeing?

Safari's error console is not throwing any JS error, hence making it much harder to determine where the issue lies.

I do have a JS blocker in place, but the issue still happens when that browser add-on is completely switched off.
On FF, just like on Chrome, there is no problem whatsoever.
Same goes for Opera.

Can you see if you have the same issue using Safari with the survey on our demo site
http://demo.tamlynsoftware.com/bf-survey.html