It causes silicosis, a life threating, cronic lung disease.

ALWAYS wear the correct mask rated for fiberglass or use a respirator. Use safety glasses. Use clothes that you don't mind disposing of afterwards. Take a shower after your done.

The shop should be cleaned from top to bottom using a HEPA vacuum and damp mopped after allowing the air in there to settle for a few hours.

For these reasons, I always do glass work outside WITH a mask.

Do I sound paranoid? Yep ... I have a close relative that has permanent lung damage due to not wearing a mask. All this from one fiberglass job, a small telescope tube.