Part 2 – Field certification tests

So now, let’s just look at the tests that must be done and that you should look for. There are five primary tests or tasks that must be done by the certifier for a Type II, A2 BSC. These are the field certification tests that you should be familiar with and require be done. These are 1) the down flow velocity test which measures the velocity of air moving down into the cabinet from the supply filter: 2) the inflow velocity test which measures the velocity of air moving through that sash opening into the cabinet; 3) the filter tests which determine the integrity of the HEPA filters (both supply and exhaust); 4) the air flow smoke pattern test, which shows the cabinet certifier how the air is moving around the cabinet; and 5) the site installation integrity tests to verify that the cabinet is in the right place and it’s connected to your building correctly. For cabinets with canopy connections or B cabinets the certifier will also check the ducting, exhaust fans, and exhaust system performance alarms. In addition, there are some extra secondary tests like UV intensity, sound, vibration, and grounding that your certifier may do. But if your cabinet fails any of those tests it will still be certified because these are considered secondary tests and optional. All equipment the certifier uses, including the air flow measuring devices are certified and calibrated annually.

First, the cabinet certifier will test the down flow velocity. Here you see an example of the measurements that they’ll be taking. They are going to be using an air flow measuring device to test the amount of air moving from the top of the cabinet down onto the work surface. As shown in the picture, they will be testing this at multiple different places, to look for any dead spots (no air flow) or any places where the air flow may be too high, indicating that there might be a hole or leak in the HEPA filter. The certifier should be able to show you the exact amount of air flow at each of the different places within the cabinet, using their calibrated test equipment. In this case, you see that the cabinet passed this test.

Next, they will do the inflow velocity test, which shows the amount of air moving into and out of the cabinet. They can do this in two ways. They can measure the inflow velocity at the sash opening (as shown) or they can measure the amount of air at the exhaust. Again, they are going to use calibrated test equipment to measure the amount of air moving through the cabinet. For a BSC that is built to the NSF49 standard, this will either be 75 or 100 ft/minute. In this case, the cabinet failed as you see there at the bottom. The blower speed controller was faulty and they were unable to adjust the airflow. In this case the fan or blower motor or controller may need to be replaced before the cabinet can be certified.

The next test, is the air flow smoke pattern test. There is a video that shows you this later on. Basically, they’re going to use a piece of equipment that generates visual smoke and they’re going to look at the pattern of smoke movement in and around the cabinet. They are going to look all along the perimeter where the air goes in through the sash, the air flow in the work area for downward air flow or dead spots, and for air that’s potentially refluxing out through the gasket around the window sash or around the seals of the window. This test relies very much upon the experience and judgement of the certifier.

There are a variety of different smoke generating devices available to you or the certifier. The simplest is just using dry ice, if you have that available to you. Solid carbon dioxide put in water will generate a lot of carbon dioxide gas that you can easily see. Most commonly a small device heats a liquid which produces a harmless visible smoke. One of these is a child’s toy, called the wizard stick, as shown in the bottom left-hand picture. If you don’t have money for any of those things you can just buy incense sticks which are available in any country anywhere. When you put several of these together, they produce quite a bit of smoke that you could see.

This is an example of the findings of a smoke pattern test done by a cabinet certifier. You can see that they tested the downflow pattern, the viewscreen retention, the work opening edge retention, the sash seal and they found that it failed. They say that “when visual smoke was passed along the sash edge window, smoke was observed going through the gap on the sash edge”. In this case there was a leak around the sash windows and air was being drawn in. The smoke pattern tests are very important because it gives the cabinet certifier a good visual indicator of how the cabinet is performing.

This video that shows you an example of somebody doing those smoke pattern tests in a variety of different ways, so watch this video.

Video

As you may recall, biosafety cabinets have one or more HEPA filters. The filters must remove 99.97% of particles at 0.3 microns and so need to be evaluated to ensure that they are indeed filtering out particles and that they’re not leaking around the filter itself. Leakage cannot exceed 0.01% at any point in the filter. In order to test this, the cabinet certifier will use a machine that generates 0.3 micron particles. They will then test the filter for blockage or leakage through or around the filter. They use a photometer or laser aerosol spectrophotometer to detect the amount of these particles in order to determine if there’s more than 0.01% leakage. Because this is a precise test, calibration of that instrument is important. They calibrate their test equipment first against a known standard and then start to test for leakage or blockage across the entire surface area of the filter. This is called the filter leak test.

The HEPA filter leak test is done on both the supply and the exhaust filter and on the filter housing. This is where that seal is made between the filter frame and the biosafety cabinet. The certifier will use chemicals such as DOP or other accepted alternatives such as PAO to generate the particles of correct size. The particles are discharged on one side of the HEPA filer, as shown in the picture. Here you see the photometer that’s being passed across the HEPA filter surface to detect any particles coming through. 

This again is another example of the results from the HEPA filter leak test during certification. You can see in the picture, the photometer being passed across the surface of the supply HEPA filter to see if there’s any pinpoint leaks. In this case there was a problem and the filter failed. The report says leakages were found at multiple locations in the exhaust filter. This is a very important to test, because you should never assume that the filters in your BSC are working and retaining all those infectious aerosols that you may be generating. 

Here you see the photometer being passed over the surface of the HEPA filter and the readings being taken. In the bottom pictures, you can see some damage that occurred to the HEPA filter pleated fibers where the leaks were coming from. You should be aware, that small leaks can actually be fixed. You do not have to have the have the filter replaced. Certifiers are allowed to use a sealing material to repair the hole. After repair they will retest the filter to see if it passes. However, there is a limit to how much of the filter they can repair. If you find yourself in this situation, ask them if they can fix the filter instead of having it replaced.

I want to remind you that HEPA filters only remove particulates and not gases or odors. They are fragile and can be easily damaged or plugged. So, make sure that the HEPA filter leak test is being done correctly, to confirm that the filters are working to protect the product and the environment. HEPA filters should be changed as required by the test results and not on some fixed schedule.

Finally, the site installation test. When the biosafety cabinet certifier comes out to your location, they will be looking to make sure that the cabinet is installed in the right place in your laboratory and connected in the right way to the facility. This may be through a thimble connection or a hard duct connection or it may exhaust into the room. Another thing that the cabinet certifier will look for is the functionality of alarms, as described in the NSF 49 standard. The audio-visual sash alarm should trigger when the sash exceeds the manufacturer’s specified height. It is very important to have that sash at the right level so that the air inflow velocity is correct. Some biosafety cabinets have a down flow and exhaust flow monitors built in that will alarm if one of them fails. If you have B type cabinet, the BSC exhaust fan and the one in the facility pulling the air away from the biosafety cabinet have to be interlocked and there should be of audio-visual alarm if one of those fans fails. In addition, NSF issued a new regulation saying that if you have an A1 or A2 cabinet, that’s canopy connected, these also should have an audio-visual alarm if there’s external exhaust fan failure leading to low air flow. The cabinet certifier should test all these different alarms to ensure that failures in the cabinet performance are reported to the user. In this case you can see that the site installation test passed. However, the overall summary for this cabinet is that it failed. 

Optional tests

The optional tests include electrical testing to make sure that the cabinet is grounded and that’s it’s providing the right amount of power. Lighting intensity at the work surface to make sure that you can see clearly inside the biosafety cabinet. A vibration test, to ensure the blower motor is working correctly. An evaluation of the noise level and the UV lamp test, which is no longer an NSF49 required test. 

This video shows the biosafety cabinet maintenance and certification procedures.

Video

Finally, in summary, I just want to remind you of some of the key points. Ensure that you certify your cabinets based upon the risk assessment. Annually is a good measure of time, but you may want to do it more frequently or if the cabinet is not used very often, maybe a little less frequently. Think about your risk assessment and how much assurance you need that your cabinet is performing well. Ensure that you use an accredited certifier. Somebody who actually has been approved by another agency and group to do the work that they’re doing with qualified instruments. Ensure that you confirm that the certifier performs the five mandatory field tests. Remember, the biosafety cabinet will only take care of you as well as you take care of it. So, having it certified on a regular basis is a very important part of the overall process of keeping you, the environment and your product safe.

Thank you for taking this lesson on biosafety cabinet certification. Please take the quiz that follows.