I have struggled with using a still-air box (plus bleach spray, gloves, and sleeves) for sterile work with spotty success. So I decided to obtain a HEPA air source. Sticker shock → build my own.
I used a hammock filter as a pre-filter.That way, it could be big, minimizing back-pressure. Here is the HEPA air source half finished.
I used hardware cloth (coarse galvanized screen) held in place by wood chips and Weldwood contact adhesive to hold the cut hammock filter in place.
I added a couple pieces of wood to raise to work level to where the particle-free breeze is blowing.
I am delighted with the HEPA air source performance for sterile transfers. I was able to transfer mycelium from petri dish to syringe to culturing jars without contamination. I was also able to pour agar from a flask into petri dishes without any contamination. This perfect outcome was not possible using my still air box.
