Have you ever wondered what the differences are between biological safety cabinets, fume hoods and laminar airflow hoods? Or are you looking to purchase safety equipment for your laboratory to prevent contamination? Either way you have come to the right place. This article will explain what the different types of hoods and cabinets are designed to protect against, their individual features, and the advantages and disadvantages of each of them. By the time you have finished reading you should have a comprehensive understanding about which safety hood would be best for you.

Biological Safety Cabinets

Biological safety cabinets, also known as biosafety cabinets, come in three main classes: Class I biosafety cabinets, Class II biosafety cabinets and Class III biosafety cabinets. Selecting the right class of biosafety cabinet is dependent upon what you need to protect from contaminants: yourself, your materials, the environment or a combination therein as well as the level of protection required which is dependent upon the materials you’ll be working with. Biosafety cabinets work by providing an inward turbulent airflow and all biosafety cabinets, regardless of class, are fitted with HEPA filters to protect the environment from chemical pollution.

Class I biosafety cabinets are used when working with low to medium risk materials only. Class I biosafety cabinets have an air velocity of 75 FPM and are used to protect you from your experimental materials, but they DO NOT offer protection to your materials.

Class II biosafety cabinets contain the most variation within a given class. Class II biosafety cabinets protect you against harmful materials AND they protect your materials. There are 4 different types to consider which are classified by both their air-flow properties and the level of protection that they offer. They are: Class II A1, Class II A2, Class II B1, and Class II B2. Class II A1 biosafety cabinets have a minimum air velocity of 75 FPM. They exhaust 30% of air and recirculate the remaining 70%. All other classes exhibit a minimum off 100 FPM airflow. Class II A2 biosafety cabinets are the leading seller of all biosafety cabinets combined. They have the same airflow properties as the A1 class but uses a negative pressure system. Class II B1 biosafety cabinets exhaust 60% of air and recirculate 40%. Class II B2 biosafety cabinets exhaust 100% to the laboratories exhaust ducts. Both the B1 and B2 classes permit the use of small quantities of volatile/toxic chemicals and radionuclides, so long as they are within the section of the cabinet where the fumes are exhausted.

Class III biosafety cabinets provide the highest degree of protection and can be used with materials of all hazard levels. They also protect your materials and the environment. They are completely sealed and secure cabinets which are fitted with a glove box to ensure that you are fully protected against the most hazardous/infectious materials. Decontamination ports are used as entrance and exit points for your materials/equipment.

Fume Hoods

Chemical fume hoods work by extracting air and noxious fumes away from the user and out of the fume hood where upon the air is filtered and returned to the outside environment via a duct system. The main class of fume hoods available on the market today are ducted fume hoods and come in 3 main varieties:- constant air volume (CAV), reduced air volume (RAV) and variable air volume (VAV).

Choosing a suitable fume hood is based on two basic requirements- what is your requirement for the removal of noxious fumes? And, is energy consumption a consideration within your laboratory?

All three types work in a very similar way, differentiated only by their air flow properties. CAV fume hoods exhaust the same amount of air, all of the time, and provide a stable and constant air flow with no need for re-balancing. The most common types contain a bypass opening which allows the air flowing through the hood to remain constant (wherever the sash is placed). Bypass openings are also used to combat the air velocity issues that can occur with conventional fume hoods. Also, because the fume hood has a constant operating procedure, the energy consumption remains constant.

RAV’s have all the basic principles that CAV’s do but the bypass opening is partially obstructed. This leads to a reduction in airflow which lowers the energy consumption of the RAV fume hoods. However, they can only be used with less noxious compounds because the air extraction is not as powerful. This means that there is the potential that some of the noxious fumes could escape the fume hood.

VAV’s are essentially a more advanced version of CAV’s and are becoming the fume hood of choice due to their airflow versatility. In VAV fume hoods, the air flow is kept constant but is variable in velocity dependent upon your requirements. VAV fume hoods regulate the air flow based on the sash height to maintain a given velocity at any sash height. This gives you control of the amount of air you want exhausted from your fume hood without worrying about any drop in air velocity. They have also been designed to be very user friendly and all parts that need to be changed periodically are easily accessible to you.

If you will be working with substances such as perchlorates, hydrofluoric acid or radioisotopes then specialized fume hoods are required, as each of these requires the fume hood to have different material properties to alleviate any dangers that could occur within the fume hood.

Laminar Airflow Equipment

Laminar airflow cabinets (or laminar flow hoods) work by controlling particulates that would otherwise contaminate your work. Removal of particulates provides a sterile, dust-free work area. There are two different types of laminar flow cabinets, which is determined by their directional airflow properties: Vertical laminar airflow hoods and horizontal laminar airflow hoods. Laminar hoods work by passing air through a HEPA filtration system in a laminar (single) direction with uniform velocity, towards a stainless steel work surface. Laminar hoods can be used for many applications where foreign particulates could present a problem to your experiment.

Vertical laminar airflow hoods work by reinforcing the gravitational effect on particles and helping them to move quicker so they get swept out through holes or a front access area. By using a vertical laminar airflow hood both yourself and your materials are protected but they can only to be used with hazard levels 2 and 3 (hazard level 4 materials need a class III biosafety cabinet as mentioned previously). Vertical laminar airflow hoods are also an ideal choice when your laboratory space is limited as the filter is installed on top allowing the hood to be installed on a standard laboratory workbench. Other advantages of the vertical laminar airflow hood include the ability to compound sterile products, easy access to the filter and low turbulence when air comes into contact with large equipment.

Vertical laminar flow hoods have some potential disadvantages as well. Notably, placing your hands, materials or equipment on top of other items obstructs the airflow and creates turbulence which reduces their ability to remove particles, leading to a greater risk for contaminating your work. Depending on the Vertical laminar flow hoods placement, doing a routine filter change can pose a safety risk if a stepladder is required to gain access to the overhead filter on top of the vertical laminar flow hood.

The second type of laminar flow hood is the horizontal laminar airflow hood which directs airflow from the cleanest air source, which is at the back of the hood, towards you, the user. Unlike their vertical airflow counterparts, horizontal laminar airflow hoods are designed to protect your work, but not you. You are positioned downstream of your work to protect it but you are left exposed to any contaminants that are not filtered out before reaching you. For this reason, horizontal laminar flow hoods can only be used with hazard level 2 and 3 materials.

Because the airflow is directed horizontally across the work surface rather than directly at it, the air turbulence that occurs in vertical laminar airflow hoods is not a factor. However, larger samples can disrupt the airflow or contaminate downstream samples. Other advantages of the horizontal laminar airflow include allowing you easier access to your work because there is no sash to open and close; and any particulates picked up by your gloves are less likely to contaminate the sample because you are downstream of it.

However, because the filtration system is placed at the back of the laminar hood instead of stacked vertically, more laboratory space is required for horizontal systems. Another disadvantage of horizontal laminar airflow hoods is that the whole cabinet usually needs to be moved in order to change the filter.

Each class of cabinet offers some form of protection, be it to you as the user, your materials, or the environment. As with anything, they all have their advantages and disadvantages but some will be more suited to your application. There is enough scope with these 3 classes of safety equipment to cover most experiments in a laboratory environment; you just need to decide which one is the right one for you.