I was thinking about this topic a little bit more and I thought it might be helpful to share 2 other stories from my experience. To me they reinforce the importance of thoroughly cleaning the hoods and challenges with the current hood designs.
At one of the hospitals I worked at very early in my career I was told not to ever clean the metal grate that protects the HEPA filter. Initially, I just took the information and obeyed the command. After several months of working I started to notice all sorts of dried crud on the grate. I assume that it was from vials that were over pressured and then squirted their contents onto the grate. The stuff on the grate was there for months. Looking back on it now with our current understanding of bacterial or mold growth, if water can get on the grate then it’s possible for things to grow on the grate, therefore, it’s important to clean the grate. It’s also a very real concern that without careful cleaning, the HEPA filter can be damaged. Damaging the HEPA filter would be disastrous for your ability to maintain an ISO 5 environment in the hood, and potentially put your compounding operation at risk. I don’t actually see this as either you clean the grate and damage the HEPA filter or you leave the grate uncleaned and accept the risk of contamination growth. I believe you can train the people that will cleaning the hood to do so in a way that does not damage the HEPA filter.
Speaking about hood design, early on in my experience as a technician I noticed that there were parts of the hood that were not easy to access and thoroughly clean. On the vertical flow hoods that I worked with there is an air intake on the front of the hood to allow air to pass under the Direct Compounding Surface and recirculate the air. The problem was that the opening allowed for the collection of all sorts of dirt and unclean things. Because there was an area under the Direct Compounding Surface it wasn’t routinely looked at or cleaned. I can’t find the pictures right now, but I lifted up the Direct Compounding Surface and cleaned that space. It was disgusting. One could argue that the risk of contamination would be low since the air passing through that part of the hood still passes through a HEPA filter before it gets to the Direct Compounding Surface, but to me there are a lot of ways that the situation could be problematic. These experiences are why I’m much more in favor of designing a clean room without using hoods, but building the HEPA filters into the ceiling and using a more architectural solution to creating the clean room. All parts of the clean room are easy to see and easy to clean. To me, it’s a much more elegant design and solution.