Part 1 – Introduction
Welcome back everybody to this series of modules on biorisk management. In this module, we will be discussing ventilated enclosures and biological safety cabinets. These are just boxes that move air and help to keep you safe while working in the laboratory.

 
Earlier we looked at various types of controls and we grouped them together in different baskets. This graphic shows these again, but in a different way. First, standard and special microbiological practices, which might be considered the first line of defense. This is shown as that blue line, close to the pathogen. Then we have safety equipment, which includes primary containment (such as the biosafety cabinet) and PPE. Then finally, the facility design as the third layer of defense, or secondary containment. This is the room that you work in along with all the engineering controls that are installed in the building to support the functions in that room.

In this module, we’re going focus a lot on one of the controls that we have at our disposal, which are the engineering controls. This is the equipment that’s used in the laboratory, such as the biological safety cabinet, the fume hoods and laminar flow cabinets. This also includes some of the facility design features, such as heating, ventilation and air conditioning machinery that help filter and move the air in the laboratory. All of these engineering controls supplement our work practices. Good microbiological practices are still the most important part of controlling the hazards that we face in the laboratory. 

So, let’s just take a look at the different kinds of hoods or ventilated enclosures you commonly see in the laboratory. They’re all just big metal boxes that move air, but they are not the same. The three most common ones that we see in the laboratory are the chemical fume hood, shown on the left-hand side, the biological safety cabinet shown in the middle, and laminar flow or clean air bench cabinet. Each one has a different function and moves air in a different way. We’ll look at all of them, but focus mostly on the biosafety cabinet. 

If you look at the diagrams shown for the way each cabinet moves air, you see that they are all different. The class II biological safety cabinet (shown on the left-hand side) moves air away from where the worker sits, recirculates some air back to the work surface through a filter and exhausts the remainder through a filter to the outside. The chemical fume hood, draws air away from the worker and then exhausts it directly outside. Lastly, we have the clean bench or laminar flow cabinet shown on the far right-hand side. You see air being drawn in before being cleaned and then directed to that work surface. You see, each type of ventilated enclosure handles air in a very different fashion for a different purpose.

Let’s start with the chemical fume hood. Most laboratories have these because they use chemicals. It’s very important to know where your chemical fume hood is and how to use it properly. We won’t spend a lot of time on this because we’re focusing mostly on biological safety, but I want to make sure you understand the difference between the chemical fume hood and a biological safety cabinet. 

The chemical fume hood moves chemical fumes and vapors away from your breathing zone. That’s its primary role and goal. Some have charcoal filters that allow the air to be recirculated back into the room. I prefer to have the air exhausted directly outside, because the charcoal filters may not always be catching all the chemical fumes that are being produced and then they don’t always get changed often enough. So, you may be getting chemicals exhausted back into the laboratory. Much better to have them hard ducted, to ensure the fumes and chemicals are removed from the laboratory. Their efficiency varies with the design, the location, the sash position, the face velocity and a couple of other factors. So, keep that in mind they’re, not all the same and they’re not for use with highly infectious materials, especially for environmentally dangerous organisms. They could exhaust air directly outside without any filtration and therefore not remove any infectious particles or aerosols that may be in your microbiology labs. They cannot be easily decontaminated because they have complex baffles and structures in them and they offer no product protection. Very different than a biosafety cabinet. They are really meant to be used for work with chemical fumes and should be directly exhausted outside. 

This graphic shows how the fume hood protects you as it draws air away from you. A typical cabinet has hundred feet per minute of airflow being drawn into the cabinet and exhausted directly outside. But it doesn’t provide environmental protection because there’s no filter on the exhaust. Everything that is being pulled out of the laboratory away from you, is directly exhausted outside or through a filter back into the laboratory.
Now, here is a video to show you on how a fume hood is to be used safely. So please watch this video.

Video

Now, let’s turn our attention to clean benches which are also known as laminar flow hoods or PCR stations. Most laboratories also have at least one of these. They typically only provide product protection and they do that by creating air flow through a HEPA filter over the product. They move air over the work surface which has been filtered and discharge this air directly back into the room. 

As shown in these diagrams, there are typically two types of laminar flow cabinets – vertical flow or horizontal flow. The one on the left-hand side shows how the air is brought in through the bottom and then exhausted directly in a horizontal fashion, straight out at the worker. The other cabinet is drawing air into the top and exhausting through a HEPA filter on to the work surfaces. Therefore, these cabinets should only to be used when the product is non-hazardous and must be kept sterile or contamination-free. They are really for preparation of media and other materials that you want to keep clean (for example growth media or PCR reagent mixes). Remember, anything you work with in this cabinet may end up in your breathing zone. Often these cabinets are used for cell culture work because you want to keep the cultures clean, but cell cultures are not sterile. They have advantageous pathogens in them and the cells themselves are cancerous cells. All of those could potentially be blown into your face and you may breathe them in. So please don’t use these cabinets for work with cell cultures.

Here is a short video that clearly shows the difference in the airflow patterns between a biological safety cabinet and a laminar flow cabinet. 

Video – no audio

In review. In the laboratory we typically see three different types of ventilated enclosures, the clean bench (laminar flow cabinet), the fume hood (chemical cabinet) and the biosafety cabinet. As you now know, each is very different, moves air differently and protects different aspects of the work. Make sure you know the difference between them and know when to use one and when to use the other. If you get them mixed up and use one for a wrong purpose, you may be putting yourself at greater risk.