The key to achieving contamination control, whether in the hospital operating room or the semiconductor assembly area, is the air filtration system. Such systems are ultimately dependent on hepa (high-efficiency particulate air) filters and in some cases ulpa (ultra-low particulate air) filters. This includes cleanrooms and mini clean filtration "environments" such as biosafety cabinets, clean benches, and fume hoods.

While most hepa filters look the same, they vary widely in quality and high-purity performance. These filters also vary in design, pressure resistance, frame construction, sealant, and temperature capabilities.

Although cleanroom filtration systems are certified to meet initial contamination containment capabilities and regulatory requirements, the effective lifespan of filters may be limited, requiring premature replacement to avoid costly air quality problems. That is, if the user is aware of the problem. Examples of limiting factors include filter design shortcomings, marginal quality of filter material, incomplete or inappropriate filter testing, and insufficient heat resistance in high-temperature applications.

Inadequate filtration in cleanrooms or clean spaces can result in lower production yields and unsatisfactory conditions. It also can mean failure reports, downtime, and frequent replacement or maintenance – all of which can get very expensive.

Given the pivotal impact hepa filters have on cleanrooms and other clean environments, here are five points to consider before replacing your filters or specifying a new cleanroom system:

1. Test according to application. Prior to purchasing, confirm that all hepa (or ulpa) filters are tested individually because batch testing is unacceptable.

2. Use deep pleats to save energy. The lower a filter’s resistance to air flow, the less air handler force is required to push the required amount of air through a filter. Hence, the less energy expended to move the required air via electric fan. The best way to lower resistance is with deep-pleated hepa filters, which are designed to give more surface area and thus dramatically improve filter efficiency.

Deep-pleated filter packs more than double the filter media size of traditional filter packs, and the energy savings are very substantial. Installing deep-pleated filters can allow customers to slow their air handlers by 50% and also shut down a cooling tower. While the initial investment is higher than standard filters, the savings in electric power consumption can save that amount within the first year. Plus, filters won’t have to be changed for years to come.

3. Roomside systems are easiest. The difficulty of changing cleanroom filters is often overlooked by cleanroom designers and engineers. However, when replacement service is required, the cost includes much more than just the filters.

When you change out most individual terminal type filters, which can be time-consuming because they are commonly a difficult replacement, you can tie up a cleanroom for an extended period of time. This will be very expensive in terms of production downtime. It also is a dirty operation, causing contaminants to enter the clean space, and that will require time and labor to clean properly.

However, with a “roomside replaceable” filtration system, you can easily replace filters and minimize downtime. With the HEPA Corp latching system, filters and lights are suspended in a “gridless” double-channel system. The ceiling is constructed and installed completely from the roomside. Filters are self-aligning; there is no need to lift the filters up into the plenum before putting in place, nor time-consuming squaring of a T-bar grid.

Well-designed roomside filtration systems can also improve the laminar flow of air in a cleanroom, making it easier to provide cleanest “first” air to desired areas within the room.

4. Sourcing custom and odd sizes. Some cleanrooms and many mini clean environments (biosafety cabinets, clean benches and fume hoods) require custom, odd-size HEPA filters.

Many distributors don’t stock odd-size filters simply because there are so many shapes and sizes, and orders may be difficult to predict. Some manufacturers evidently find odd sizes difficult to deal with, so they wait for like-size orders to accumulate before making the filters, which can cause extensive delays in turnaround time.

Customers should avoid the backlog that results from filter manufacturers who simply add these special size orders together until they have what they consider a sufficient number to run. Our company makes filters to custom specifications and tests them as part of the normal production flow.

5. Spec'ing high-temperature filters. In the case of high-temperature applications, hepa filters need to have special materials for the frames and seals, allowing them to handle temperatures of up to 750°F. It is essential to specify high-temperature filters according to appropriate filter media, frame, and sealant capabilities.

Some consideration also must be given to filter binders. Since the acrylic binder used in temperature ranges above 500°F will burn off and produce smoke, products should not be introduced to the high-temperature environment until the smoke is exhausted.

Nevertheless, the variables governing the correct choice of high-temperature filters suggest that users confirm their choices. That is, when in doubt about any filter specification, it’s a good idea to talk to a filter manufacturer.