Controlled Environments spoke to Scott Alexander, an Advanced Certification Technician with AGAPE Instruments Service, about why fume hoods are needed in cleanrooms. AGAPE performs independent field testing, certification, and repairs of air filtration and air particulate control devices.
Controlled Environments (CE): What is the importance of fume hood exhaust monitoring in cleanrooms?
Scott Alexander (SA): It is crucial to have calibrated exhaust monitors on fume hoods for personnel protection. If working with hazardous, volatile, or corrosive material without sufficient airflow, the results could be deadly. Most exhaust monitors have an audible and visual alarm. If the air flow has dropped to calibrated levels, this could expose personnel to harmful material.
Another way that the alarm can be used in a cleanroom is to help monitor the pressure. In many cases the pressure in a controlled environment is very important to keep regulated. If inconsistent variation is noticed in the fume hood monitor there may also be a problem with the pressure in the area. This scenario can only be accomplished with monitors that give a digital velocity read out.
CE: What are the different kinds of fume hoods available for cleanrooms?
SA: There are many different kinds of fume hoods available in the market today. For starters, there are two different air flow valve set ups. The first being a variable air volume (VAV), meaning it can be programmed to adjust the air velocity depending on where the sash height is or can regulate the velocity to a set flow no matter what the sash height is. Second is a constant volume valve (CV), meaning the valve is set to a specific velocity at a specific sash height and that is how the hood is designed to be worked in. If the sash is raised past the set point the velocity will then drop. If the sash is lowered the velocity will increase.
Most of the variations consist of size or material. There are many different materials including but not limited to old coated wooden units, stainless (coated or raw), and different polymer materials to be used with acid and other volatile chemicals. I have seen them as small as 2-ft. wide and as large as 10-ft. wide walk-in units.
Fume hoods can also have different kinds of sash opening setups. There are vertical, horizontal, combination, and walk-in sash designs.
In some cases manufacturers have outfitted their fume hoods with supply HEPA filters that are above the work surface and supply the work area with some sterility.
CE: What is the regular maintenance process like for fume hoods?
SA: The regular maintenance process usually consist of an annual or semiannual certification. The certification then consists of a velocity test with a thermal anemometer at predetermined points depending on the size of the sash opening. Followed by calibration of the alarm and smoke visualization test to prove the direction of the air flow and containment of the smoke. On top of the certification there is usually a PM schedule in place to check the blower motor belt. This work is usually done by the facility personal and the frequency is usually determined by the facility procedures.
CE: How often should fume hood exhaust monitoring systems/equipment be replaced?
SA: Replacement of a fume hood monitor is necessary when the system no longer functions or does not calibrate properly.
CE: What do cleanroom facility managers need to keep in mind when selecting a fume hood exhaust monitoring system?
SA: The main things to keep in mind when selecting an exhaust monitoring system is to think about how much data you would like to receive. Some monitors only give an audible and visual light alarm when a set percentage of velocity drop is detected. Others give an actual readout of the velocity. Some customers will require the velocity read out for documentation or trending reasons. I would highly suggest not getting a monitor that does not at least give you an audible and visual alarm of some kind.
CE: Are there any specific standards or resources that facility managers should reference when setting up their cleanroom fume hood exhaust monitoring system?
SA: There are three main standards that we reference when it comes to fume hood monitoring devices.
The first is ANSI/AIHA Z9.5, in which it states that new and remodeled hoods should be fitted with a flow measuring device of some kind.
Second we reference OSHA, which basically states that all fume hoods should be fitted with a monitoring device that should provide convenient confirmation of adequate hood performance before use.
Last is the SEFA-1-2010 standard, which states that all hoods shall have some type of monitor for indicating face velocity or exhaust flow verification.
CE: Are there any common mistakes that are made when dealing with fume hood exhaust monitoring, or anything in particular that facility managers need to watch out for?
SA: One of the most important things to look at when installing a fume hood is the layout of the laboratory. It is not good to have supply vents or filters directly in front of the fume hood. Extra supply air coming down in front of the hood can cause turbulence with the air flow and major issues can be seen in the smoke visualization or tracer gas done during the certification. This can also be true when doors and high traffic areas are close to the unit. This is why it is so important to have a full ASHRAE 110 test at least at the initial certification.
CE: Aside from the fume hood itself, what is the other necessary equipment for a cleanroom exhaust monitoring system?
SA: One last thing I would like to suggest is to make sure the hoods are on dedicated exhaust systems. So often I see clients “gang” their systems and this causes nothing but issues. When one unit within a ganged system requires an adjustment, it often results in an entire rebalance of all hoods within that system. The recommended set up for a ganged system is for each fume hood within the system to have its own dedicated valve.
Scott Alexander is an Advanced Certification Technician with Controlled Environment Certification Services Inc. (a STERIS Corp. Company), doing business as AGAPE Instruments Service, in Cincinnati, Ohio. www.agapeinstruments.com
This article appeared in the January/February 2016 issue of Controlled Environments.