I have struggled with using a still-air box (plus bleach spray, gloves, and sleeves) for sterile work with spotty success. I know some experienced people here have said that it can be done. Compared to these people, I am a rank amateur. I just want more consistently successful efforts at sterile transfers. So I decided to obtain a HEPA air source. After experiencing sticker shock at sites like Fungi Perfecti, I decided to build my own.
I got the HEPA filter from Damn Filters. The quote for 12 X 24 X 11.5 deep was $329 for quantity two (they would not quote one). Shipping was $105.
I first contacted Sustainable Supply. They handle a number of Dayton squirrel cage blowers. I was asking for 200 CFM at a back pressure of .8 inches. Those clowns refused to help me. Instead, they referred me to Grainger (apparently Grainger and Dayton are tight). So I called Grainger: first I spoke with a lady, giving her the specs. After some minutes, she said “let me give you to a real expert”. I thought “oh, good, someone who knows this stuff”: NOT. That guy said that it can’t happen: a back pressure of .8 inches will “burn up the motor”. Having seen specs for back pressure of up to 1.2 inches, I tried to argue with him, but he was adamant. So: back to Sustainable Supply, where I could, at least, view the specs for all “Direct Drive Radial” blowers and then pick one. I settled on the Dayton 1TDR7, which I got from Amazon for significantly less than I would have spent at Sustainable Supply or Grainger. The 1TDR7 produces a stiff breeze through the filter.
I used this hammock filter as a pre-filter. Some people position the pre-filter prior to the blower, but I decided to place it directly behind the HEPA filter. That way, it could be big, minimizing back-pressure. I uploaded a picture of the HEPA air source half finished.
I use some hardware cloth (coarse galvanized screen) held in place by wood chips and Weldwood contact adhesive to hold the cut hammock filter in place. I uploaded a picture of the finished air source.
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 BRF 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 the still air box.