Classified

The number of clean room certifications are vast and vary tremendously. ISO 14644 is the most used standard when looking at electronics and pharma manufacturing controlled environments. With this popularity, it has also undergone revisions within the past five years.

No matter the standard, each is divided into classes. The classes are rated from 1 to 9. The class identifies the maximum limit for particulate size and quantity per cubic meter of air. The chart below showcases the size and the quantity breakdown.

Cleanroom Classification Allowable Maximums.

ISO 9 as you can see is the loosest standard. This standard is equivalent to air quality within a city environment. These environments can fit a multitude of manufacturing and are some of the easiest to achieve and abide by. The opposite end of the spectrum, ISO 1 is the strictest and hardest to maintain. There are three main factors when designing for a clean room. These are surfaces, airflow, and employee access.

When selecting surfaces that will be within the environment it is best to choose a surface that will hold up to the level of use as well as not be damaged by the cleaners or solvents being used to ensure the surface is clean. This should carry over into part fixturing and even machine materials of construction as well. This is not always easy and should be a design element to the process and environment.

Airflow within the room is what helps maintain the concentration levels of particulates. Generally, a clean room is positively pressurized to where the pressure within the room is higher than that outside of the room. This results in a positive air exchange, generally this is provided by the HVAC system. Having a system that does not recirculate the air from inside of the room and a substantial filtration system is key. Another type of airflow that can be found within these environments is a blowoff operation for the part or process. When installing a blowoff within a clean room environment it should be confirmed that the materials of construction are compatible with the environment and cleaning processes and that the airflow will not be introducing particulate into the environment which can result in contamination.

Lastly, employee access should be limited to those employees who are trained and necessary to be within the environment. Sometimes if an employee wears the wrong type of deodorant it can effect an entire environment. Even the wrong type of clothing or soap can alter the state of an environment, let alone using a blowoff incorrectly or bringing the incorrect cleaner inside the cleanroom. Access to these areas should be limited and individuals should be well trained to meet the demands of the clean room.

If you would like to discuss your production environment or blowoff application within a clean room, please contact us.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF

Per the National Electrical Code (NEC) there are (3) classifications for areas that are defined as hazardous. They are Class I (gases & vapors), Class II (flammable dusts) & Class III (fibers), the focus of today’s Blog is on Class II locations.

Class II locations are those that are hazardous because of the presence of combustible dust. Note that the dust must be present in sufficient quantities for a fire or explosion hazard to exist. The fact that there is some combustible dust present does not mean a Class II hazardous location exists. Dust is defined as a combustible material that must exist as a finely divided solid of 420 microns (0.420 mm) or less. This will allow the dust to pass through a No. 40 sieve. Just as in Class I, Division 1 and 2, the subdivision of Class II into Divisions 1 and 2 identifies the likelihood that there is an explosion hazard.

Division 1 locations are defined as an area where the amount of combustible dust is either suspended in the air or accumulated on surfaces in a sufficient concentration to allow for ignition. The ignition could be caused by a failure or malfunction of the equipment in the classified area. Group E & F dust (see chart below) are considered conductive and could penetrate into electrical equipment such as electric motors, control panels, electrical panels, etc.. and cause an electrical failure.

Group E dusts are metal dusts, such as aluminum and magnesium. In addition to being highly abrasive, and likely to cause overheating of motor bearings if it gets into them. Group E dusts are also electrically conductive and if they are allowed to enter an enclosure can cause an electrical failure.

Group F dusts are carbonaceous, the primary dust in this group is coal dust. Coal dust has a lower ignition temperatures than those in Group E. While Group F dust has a higher thermal insulating value than the layer of Group E. Therefore Group F requires more control of the temperature on the surfaces that the dust settles on. Group E dusts are semi-conductive, however if the voltages are 600 volts or less it is not generally considered a factor.

Group G dusts include plastic dusts, most chemical dusts and food-grain dusts. They are not electrically conductive. Generally these dusts have the highest thermal insulating characteristics and the lowest ignition temperatures. Therefore the equipment used in Group G areas must have the lowest surface temperatures to prevent ignition of a layer.

Lastly, equipment rated for use in Classified Environments have a rating called the Temperature Code or “T-Code”. This is the temperature or temperature range that the rated device will operate normally and/or in a failed or failing state. Consider something as common as a light fixture, electric motors, etc.. as they could become hot enough to cause ignition depending on the type of dust in the area. So be sure to check the “T-Codes” for every piece of equipment that will be used within a Classified Environments.

When you are looking for expert advice on Hazardous Location Cabinet Coolers or safe, quiet and efficient point of use compressed air products give us a call. We would enjoy hearing from you.

Steve Harrison
Application Engineer
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Tag: Classified

Clean Room Certification – ISO 14644

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Explanation of Hazardous Locations – Class II Div. 1, Groups E, F and G

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