Spring balances - a note of caution

If you've skimmed this blog, you know I like salvaging old building materials for new projects.  Such was the case with a set of 60s era windows, still in frames, out of a house up by the lake.  Disassembling the frames to free up the sashes is pretty straightforward - you just need a little patience to separate the pieces without splitting to much of the wood.  The reason for this post is just a bit of fair warning about the object on the top right of the frame in this picture:

These are spring balances - one per sash - a technology still very much in use today.  They are just a strap wound and spring loaded in the case, and attached about a quarter of the way down each sash:

I've seen a few of these with rubber straps, but typically they are thin, flat metal. With very sharp edges. The safest way I found to approach these is to relieve the tension on the spring - free the sash from the frame and tilt it so the strap can retract almost all the way (see next to last photo).  Then and only then should you try and release it from the hook inside the sash.  Wear gloves (seriously) and safety goggles (no reason not to).