ISO Class 0 Compressed Air: Is It Just Another Way of Saying “Oil-Free”?

May 20, 2022
Is Class 0 compressed air really a classification? We recently talked with the experts at Kaeser Compressors about what this designation is and what it means for food and beverage processors.

On today’s special episode, we’re talking with Kaeser Compressors about ISO Class 0 Compressed Air. Join us as we talk with Neil Mehltretter, Technical Director, and Werner Rauer, Product Manager, about what Class ZERO Compressed air really is.

We talk about what a Class 0 label really means as well as what guidelines and specifications there are for class zero air in food and beverage applications. We wrap things up talking about whether there are energy or other cost implications for higher levels of air quality.


Erin: Can we start things off by explaining what does class zero means as it relates to compressed air?

Neil: Sure, it's an interesting term. When you say zero, you think, "Oh, okay, is it good or bad," right? Is zero the best you could do, or is zero the worst you can do. When you apply it to compressed air, there's something that defines air quality, and that's the International Standards Organization, ISO 8573.1, which was updated in 2010. And that describes three different types of contaminants. And those contaminants are solid particulates like dust, then humidity, and then total oil content. And with those three, you can define what class you're in. So each has a class zero, a class one through even nine or greater. So the idea here with class zero is it's less than the definition of class one for each of those three contaminants. And so that gives us an idea on how clean the air might be.

I do want to clarify that class zero is basically user-defined below class one. If the customer has a very specific need or want and it's lower than whatever class one is, we would define whatever that is and then try to deliver that based on what air treatment that you provide. So that's the big-ticket filtration to remove dust (or other particulate), oil, and then how to knock out the water that's in the ambient air, and then whatever oil may be entrained in that air system, either in the ambient air or from the compression stages.

Erin: I know some oil-free compressor models are labeled class zero, is that the same thing?

Neil: When you are defining class zero, we're talking about three contaminants: solids, humidity, and oil. Some compressors whether oil free or oil flooded, include internal refrigeration or heat of compression dryers. To define what that compressor output might be, we could certainly do that, but if it's just a general compressor, with no attached dryer or filtration, then you're subject to whatever you're bringing in with the ambient air.

We've seen systems where questionable placement of compressors; meaning that the compressor is going to ingest something. In a lot of cases, that might be fumes from delivery trucks. And so those fumes are going to have hydrocarbons in it. If there's no air treatment that's downstream of your compressor, then you're going to get those hydrocarbons that are in the ambient air down into your process. To answer the question, are those compressors that are labeled class zero, really class zero? Well, it'll be hard to define that, if there's no additional filtration to ensure that you're getting out whatever is in the ambient air or whatever you might be putting back in from the compression, and/or let's say piping as well.

Werner: However, a compressor that is offered with such a label, as Neil said, it still needs downstream clean air treatment equipment to reduce the water content, the contaminants, and any hydrocarbons that came from the ambient air. Typically, as a minimum, we recommend either a fine coalescing filter or a carbon filter after the dryer. Let me give you an example. You're in the basement of a dairy milk processing and packaging plant. And along with the tanks of cleaning fluids, there's also an ammonia refrigeration equipment right there in the room with a compressor sucking in the air. Any of these contaminants would end up in the milk jugs without further clean air treatment.

Erin: Are there guidelines for class zero air for specific industries or applications?

Kaeser Compressors provides products, services and complete systems for supplying production and work processes with quality compressed air. Learn more about Kaeser Compressors' products and services on their website

Werner: In general, yes, there are tons of guidelines and rules about food safety. And they've been in Europe, worldwide, the Codex Alimentarius; over here, SQF, FDA, just to name a few, but you will have a hard time finding real detailed specifications that are related to ISO 8573 for any particular food application. The guidelines about air quality for food safety worldwide are mostly nonspecific. So food processing companies have to perform a risk assessment for each process they use and they make their own decisions based on industry norms, equipment manufacturer recommendations or requirements, best practices, and past experience, and recommendations from compressed air equipment providers.

Ultimately, the operators are responsible for the products they make and provide any associated product recalls. However, there are some specific in terms of water, particulates and oil for other areas. For example, Grade D breathing air from the OSHA standard 29 CFR 1901.134, they limit the oxygen content, the hydrocarbon, the carbon monoxide, the carbon dioxide, and here they say that the air which the people breathe with the breathing air mask cannot have more than 5 milligrams per cubic meter of oil. So, believe it or not, there are measurement instruments just for that… because there is a specification, there are instruments that measure just exactly that.

Another one is the NFPA 99 medical gases in healthcare facilities where they say that the compressor chamber where they compress the air cannot contain any oil or hydrocarbons. And that's pretty much all they say. They also say quite a bit about where the ambient air for those compressors should come from. Then we have in the instrument air quality standard, in ANSI/ISA-7.0.01 from 1996, there are pressure dewpoint, particulate size, and here, lubricant content, and they say that for instrument air, they say less than one PPM by weight, which is about 1.2 milligrams per cubic meter. There's one more the Safe Quality Food Institute here located in Alexandria, Virginia, and they basically say that compressed air or other gases, (remember, there's nitrogen and carbon dioxide in food) that contact of food or food contact surfaces shall be clean and present no risk to food safety. And the next note is it shall be maintained and regularly monitored for quality and applicable food safety hazards.

Last but not least, there is a beautiful best practice guide called BPG-102 from the British Compressed Air Society, BCAS, available at the website bcas.org.uk, knowledge base, best practices. Those guidelines, they come the closest in my mind in terms of specific recommendations per ISO 8573. Some may say those are a little bit exaggerated, maybe not, but it's definitely a good read in terms of overall installation, operation, maintenance, and monitoring topics.

Neil: The British Compressed Air Society’s 27-page guideline is a fantastic read and I highly recommend it for plant and process engineers that are trying to design their systems. I think the interesting thing with that too is it provides direct and indirect contact with food recommendations. So that's kind of a really important thing to really dial down and figure out what each point of use may need because the required filtration and or drying type may not be as, let's say, involved for every specific point of use, so something to consider as well.

Erin: Are there any energy or other cost implications for higher levels of air quality?

Werner: We would not have a need for this discussion if the answer would be no. So, yes, in general, oil-free screw compressors are not as efficient as oil-injected units. And we are talking there in the range of about 10% to 15% in specific power, which the oil-free compressors have a higher need for power to produce the same amount of air at the same pressure. The purchase cost of oil-free screw compressors also is higher by about 30% to 50% for the same, again, same amount of flow and the same pressure. If the guideline is to use very low-pressure dewpoints like -40 Fahrenheit or centigrade, there are added costs due to the drying of the compressed air, no matter which principle of compressors you're using, and they range anywhere from 4% to 20% of energy cost, plus the extra cost for the equipment and maintenance of these specific dryers if you compare this to a standard refrigeration dryer. Higher levels of air treatment impact the efficiency, including purge air losses and pressure drop through dryers and extra filters, but this may be a necessary trade-off for the air quality you need.

Like we said earlier, look at the application, and then you treat it as needed, but you're not going to provide the entire building with a certain high-grade-specific air quality if you only need it in one location. The best practice is to identify where do you need this higher air quality and apply, if possible, point-of-use filtration or dryers, and filter the whole plant only for the overall grade of air quality that's required. This saves overall on energy and maintenance cost. In some cases, the plants may run the entire system with the higher quality dryer and filtration. With the higher level of air treatment, we see this quite a bit. Some people want to sleep at night, so it's more like an insurance policy. But they can balance this, the need for sleep with the higher upfront costs, and possibly better long-term insurance. Let's say I just read about another recall on some chocolates with milk chocolate where they had contamination of salmonella, this is something which costs quite a bit of money. So you need to weigh that in terms of "What do I use for my compressed air so I don't have to have a recall because of that, which is very unlikely, but certainly a possibility?"

Neil: In a lot of these food processing facilities, heat recovery is an opportunity to save energy, but you have to decide, how are you going to use that heat recovery? And then what type of cooling are you using for your compressed air system? In a lot of cases, they're air-cooled machines, and in some cases, they're water-cooled. Water cooling compressors can really offer a significant value when it comes to heat recovery. And this is also the case too with air-cooled, but that can certainly be an offsetting cost in regard to your overall operating cost, and not just of your compressed air, but also of your facility.

You see a lot of folks in the food processing world, they're looking at that, "How can I best use the heat of compression or that waste heat that the compressors are putting out?" And you do see that a lot with water cooler compressors, but the offsetting situation too is what's that overall cost like Werner said. The cost to use compressed air can be high, especially when you need very specific pressure dewpoints and/or air quality. That risk assessment, whether you decide to go in oil-free compressor or in oil-flooded compressor, that will significantly increase your overall operating costs. But the nice thing too about oil-free is that there are very high-operating temperatures, and so that gives you a little bit more opportunity to use that waste heat, especially if you're looking at cooling water or using that to preheat some kind of process that you already have.

Erin: Werner and Neil, I want to thank you both so much for joining me for this special bonus episode of the Food For Thought podcast.

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