If you arrive here for the first time, you should know that this article takes part in a series of design considerations for cleanroom HVAC calculations. Previous considerations you should have clear to proceed with the cleanroom air balance are the following:
There are a number of best practice guides and benchmarks for cleanroom air change rates (ACR). Many of which reference charts dating back as far as 20+ years. Most commonly referenced are ISO 146144-4 for hourly air changes and air velocity rates, and Federal Standard 209E for fan filter ceiling coverages.
If your employees don’t follow proper gowning techniques, you risk contaminating your cleanroom environment and damaging products in the process. Taking time to periodically review proper garment selection, dressing procedures and expectations of staff members before they enter a cleanroom environment helps prevent unwanted incidents.
If you’re considering a cleanroom, you’re probably trying to gather as much information as possible. What type of cleanroom is right for you? What industry standards do you have to meet? Where will your cleanroom go? You get the picture. Well, one piece of information that might be useful to you is understanding the difference between positive and negative air pressure cleanrooms. As you probably already know, airflow plays a leading role in keeping your cleanroom to standard, but what you may not have known is that air pressure can have a big effect on that as well. So here’s a broken down explanation of each positive and negative air pressure.
Negative air pressure cleanrooms are used for hazardous manufacturing processes using corrosive, flammable and/or potentially explosive chemicals.
Negative air pressure cleanrooms are also used for BSL level P - 2, P - 3, and P - 4 Bio-Safety cleanrooms for production and medical research.
Negative Air Pressure Cleanrooms - Hazardous Process and "Explosion Proof” Facilities
Some cleanrooms are required to be operated at negative air pressure for hazardous processes using chemicals, flammable and potentially explosive liquids and powders, to prevent these chemical or powders from escaping into the surrounding space.
Cleanrooms are classified into 2 categories of air pressurization, positive and negative air pressure cleanroom HVAC (Heating, Ventilating and Air Conditioning) systems. Positive air pressure cleanrooms systems are normally used for Electronics, Aerospace, Optics, Military and Defense applications, and Research, etc., where the air escaping from doors, ceilings, or walls, due to the positive air pressure, is not hazardous and not creating safety or health concerns. The amount of particulate cleanliness required determines the cleanroom design concept, amount of air filtration, CFM (cubic feet per minute) and total HVAC. Our positive pressure cleanroom designs are based on years on experience in air pressurization in a vast variety of applications.
Positive Air Pressure Cleanrooms normally operate in an air pressure range of 0.02 in. to 0.2 in water column (H20). Positive air pressure means the cleanroom or rooms are "pumped up” with more filtered air then the surrounding space outside the cleanroom(s). There are different cascading levels of positive air pressure from the cleanest rooms at the highest pressure down to the gown room/or airlock room.
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