I place caps business (inside) side down on a sterile culture dish lid or bottom. This avoids touching the inside of the cap when picking it up.

Hello Pablo Menéndez

If the cap of a container is kept facing down, it could introduce contamination because the rim of the cap would come into contact with the contaminants, and you could introduce this into your flask, tube etc., when replacing the cap even though if you have placed the cap in the sterile area. It is too risky!

If the cap is placed facing up, then there could be an increased chance of contamination if your hands etc. went over the top of the exposed cap. You could place the up-facing cap as far away from the working area to minimize exposure. When picking the cap, you could slide your palm-facing up hand along the base of the hood, using two fingers to pick it up and then place onto the flask or tube.

I follow neither of the methods. When I work in the biosafety cabinet, I am able to hold the flask or tube, unscrew the cap as well as hold the cap in one hand, and work with the other hand. So, I need not worry about how to place the lid/cap on the surface of the biosafety cabinet.

I feel that lids/caps should always be held between the fingertips when doing any manipulations in the biosafety cabinet. However, learning this technique of holding the lids/caps would come only with practice.

Best.

I recommend placing lids facing up while working in a BSC for three reasons:

Like Malcom, I avoid setting the lid down on the work surface when possible. It minimizes movement (less disruption of air curtains, less chances to bump into things), requires less workspace (BSCs should be free of clutter), and encourages you to replace the lid as soon as possible once you are done manipulating the vessel.