In the Lab: Choosing the Right Clean Class and Saving Money

March 04, 2021

interior image of lab

During the design of a laboratory building, the topic of “clean class” makes most people’s eyes glaze over, but it’s important.  Choosing the right clean class can cut cleanroom costs in half – or more.  

What is clean class?  

In many labs – not only in cleanrooms – it matters how clean the air is. Clean class is a way to describe exactly how many particles of dust are in the air.  Each class is ten times cleaner than the last – that is, each class allows one-tenth as much dust as the next, so ISO 6 allows one-tenth the dust of ISO 7.  Smaller ISO numbers mean less dust. 

The usual way to keep the air in the room clean is to constantly suck it out near the floor and blow it in through HEPA filters in the ceiling. Of course, there’s a cost to being cleaner: to achieve one-tenth of the dust usually requires two to five times as much air movement!  Choosing one level cleaner than you need can easily double operating costs, not to mention the construction cost of all those fans and filters. 

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Particles allowed in each clean class. Source: Wikipedia

So why is this complicated?

People have different expectations about what they’ll measure inside a room labeled, for example, ISO 6.  Does the room meet ISO 6 on average (what one scientist might mean)? Is the room never worse than ISO 6 (what industry usually means)? Or does the room meet ISO 6 during research operations, but not during setup (what a different scientist might mean)? 

The first scientist’s “on-average ISO 6” approach is very different from industry standards, which describe a room guaranteed to never, ever be dirtier than ISO 6  – most of the time, it’s much cleaner. The industry would label the space ISO 7 if any of the scientist’s measurements making up the average were beyond ISO 6.

It’s important to make sure everyone in the design process is on the same page about what they mean by “meeting” a clean class because the cost of the operation reduces by half (or more) every time you can be one class “dirtier.”  You can save a lot of money by getting this right.  

How else can you save money?  

In general, the inside of any type of enclosure (like a downdraft hood) is about one class cleaner than the room. Returning to our example of a researcher who measures an average of ISO 6 on their dust meter: we already know that the industry would call that an ISO 7 (meaning “never dirtier than ISO 7”) room.  If that researcher can work inside a downdraft hood that provides that same ISO 7, the room can be run at ISO 8. 

ISO 8 only requires about 10% of the air changes of ISO 6. That’s a 90% reduction in fans and filters upfront and a 90% reduction in operational cost every year the cleanroom operates.  All it took was making sure everyone was using the same definitions and setting up an efficient workspace. 

Choosing the right clean class saves money. 

In some cases, a lot of money.  Moving the work into clean enclosures, if possible, saves even more. 

And all that reduced energy use is good for the world, too!

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