MB Pro instantly gobbling up 70+ Gb SSD - How to track culprit? Mac OS 10.10.5, MB Pro 16 GB DDR, 500 Gb SSD.

Probable culprit app MS Excel for Mac 2011?

It seems that when I open up a spreadsheet with lots of formulas, within a few minutes I'm getting "Out of Disk Space" warnings. (before starting I have about 66 GB space)

How can I verify Excel is the culprit, and how can I manage it, other than buying a (very high priced) bigger SSD? I do keep my trash emptied, usually.

Are there any tools/utilities which show files accessed sorted by bytes-written first, then date?
It sounds like the operating system is swapping out.

Open Activity Monitor from the Utilities folder (inside Applications) and select the Memory tab.  Click on the Memory category until the little caret arrow points downward.  Then open Excel.

At the bottom, you can see if Swap Used increases.