Plant & Works Engineering
Meeting the grade!
Published:  30 November, 1999

PWE asked domnick hunter's Mark White for advice on how manufacturers can meet the requirements of the Food Grade Compressed Air Code of Practice.

The British Compressed Air Society (BCAS) / British Retail Consortium (BRC) Food Grade Compressed Air Code of Practice is designed to help food manufacturers and processors by providing recommended levels of air quality.

Mark White, filter product manager, at domnick hunter says as with any new Code of Practice, manufacturers will be concerned about existing equipment and may find new product selection a minefield. In reality, he explains, the majority of existing compressed air systems may already comply, or can be easily and cost effectively updated to satisfy this Code with air treatment equipment such as high efficiency compressed air filters and dryers.

PWE: What is the main contaminant in compressed air?

MW: "As air is compressed, large volumes of wet atmospheric air are drawn into the compressed air system, which when cooled in storage vessels and distribution piping, condense into liquid water, making this the major contaminant in the compressed air system. If this bulk water is not removed, it can lead to corrosion of the distribution system, blocked or frozen valves and machinery and can ruin finished products. More importantly is the fact that it provides the ideal environment for the growth of micro-organisms including bacteria.”

PWE: How big is the water problem?

MW: “Up to 99.9% of the total liquid contamination found in a compressed air system is water and the volume of water condensed in the system is staggering. In a typically sized manufacturing unit, a compressor and refrigeration dryer combination can produce over 100,000 litres of liquid condensate per year. Mark adds, “The volume of condensate increases significantly for larger compressor systems, or during operation on hot, humid days.”

PWE: So what about oil?

MW: “Food grade compressed air does not need to be oil free, nor does it need to comply to ISO 8573.1 Class 0 and as it accounts for only 0.1% of liquid contamination, it can easily be removed using filtration.”

PWE: What equipment should be considered to meet the Code of Practice?

MW: “Coalescing filters are probably the most important items of purification equipment in a compressed air system. Designed to remove aerosols (droplets) of water and oil, they also have the additional benefit of removing solid particulate and micro-organisms. Installed in pairs, most users believe one to be an oil removal filter and the other to be a particulate filter, when in fact the first one is a general purpose filter used to protect the high efficiency filter against bulk contamination. This 'dual filter" installation ensures a continuous supply of high quality compressed air with low operational costs and minimal maintenance.”

PWE: Do filters remove all contaminants?

MW: “No, water vapour is water in a gaseous form and is removed from compressed air using a dryer, its performance being measured as pressure dewpoint. A pressure dewpoint of less than

-26°C will not only prevent corrosion, it will also inhibit the growth of micro-organisms within the compressed air system and for this reason, the Code of Practice recommends a pressure dewpoint of -40°C or better for air in direct contact with food, which is only achievable with a desiccant dryer. Refrigeration dryers are also available, however they can only achieve dewpoints down to +3oC and are therefore only used for air that will not come into direct contact with food.”

Mark adds a word of warning, “Desiccant and refrigeration dryers are only designed to remove water vapour, not liquid water, therefore they require coalescing filters to work effectively.”

PWE: How important is the compressor type to air quality?

MW: “No matter what type of compressor is installed, they all draw in large amounts of airborne contamination and therefore the level of air purification equipment is not dependent upon the type of compressor installed. Adequate filtration and separation products will always be required to remove the large volume of dirty contaminated water as well as dust, rust, pipe-scale and microbiological contamination.”

PWE: Should food manufacturers be concerned by ISO standards for air quality?

MW: “The BCAS/BRC code of practice, is aligned with the compressed air purity levels shown in ISO 8573.1 : 2001 and although not directly stated, the purity level for air that is in direct contact with food or could come into contact with food is equivalent to ISO 8573.1 Class 2.2.1, whilst air that will never come in contact with food, is ISO 8573.1 Class 2.4.1. Additionally, test methods in the code refer to the test methods of the ISO standard.”

PWE: Do food manufacturers need to comply with ISO 8573.1 Class 0?

MW: “No, the BCAS/BRC Code of Practice recommends minimum acceptable levels of compressed air quality, which is specific to the food industry and does not require the extra expense required to meet Class 0.”

PWE: How can food manufacturers comply with the Code of Practice?

MW: “It is important to remember, the aim of the Code is to provide air quality recommendations to the food industry that will protect both the manufacturer and the consumer, not to over specify air quality in an attempt to sell plant equipment. Compliance may require little on the part of the food manufacturer as many will find that they already comply with most or all of the Code. A full audit of the compressed air system should be conducted as part of the HACCP process and where required, equipment updated or additional purification added. Remember that additional filters can be installed simply and relatively inexpensively at point of use. Costly compressors do not have to be changed in order to comply.”

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