Carry on cleaning

As we are all aware, there is increasing concern over the environment in which we live and work, with more emphasis placed on minimising atmospheric pollution. At the same time, engineers within manufacturing and processing industries are continuously being challenged to produce a variety of products in a cleaner and more hygienic environment to protect not only the product, but the operatives as well.

While most readers probably have a high degree of expertise in the subject of cleanrooms, ventilation and air filtration, there are others whose expertise is in the production and processing of products. Some of us are not necessarily familiar with some of the fundamental principles involved in creating a clean environment, while others have forgotten them. Unfortunately, if these are ignored, it could lead to failure. The need to create the correct environment for carrying out any particular process normally falls into at least one of the following categories: • Protection of the employees to ensure their wellbeing • Containment of dangerous materials or fumes • Minimisation of airborne cross contamination • Prevention (for safety reasons) of the accumulation of vapours and gases which may lead to explosive mixtures • Protection of the product during the processing or manufacturing cycle Failure to meet the above criteria may seriously threaten the quality of your product, your productivity, your reputation and your profitability. The creation of a clean environment is generally achieved by means of a ventilation regime within the processing and ancillary areas. Such regimes comprise both supply and extract ventilation systems, combined with the creation of an appropriate air pattern, usually with a cascading air pressure regime. The purpose of such regimes is to ensure pollutants are contained or controlled. We are not going to deal with the requirements of cleaning up and filtering air that is discharged to the atmosphere from a process operation. the aim of this article is to examine the need to "clean" and filter the supply air to maintain the environment within the process area. The "fresh air" that we draw into our supply ventilation plants is often potentially contaminated with a variety of pollutants varying from allergens such as fibres, pollens, varying types of dust through to carbon dioxide and a whole host of atmospheric/industrial contaminants, not to mention viruses and bacteria. The outdoor air quality will vary from location to location and may potentially vary at the same location over a period of years or even on a day to day basis. The assessment of the outdoor air quality in your location may prove beneficial depending upon the process criteria. The amount of fresh air required is governed by a series of factors, including: • The minimum statutory requirements for the operatives, compliance with the Building Regulations • Providing pressurisation to the desired space in order to prevent ingress of potentially contaminated air • Providing replacement air for process extract systems that may be discharged to the atmosphere • Providing, when weather permits, "free" cooling to offset heat gains within the conditioned space The location of the fresh air intakes needs careful positioning to minimise the intake of any undesirable external contaminants into the system. Normally it is acceptable to re-circulate air from the workspace utilising a minimum of fresh air. This offers a more energy friendly solution, but it will depend on the level of any contaminants, which may be gaseous or particulate, that may be entrained within the recirculated air, and the logistics of returning air to the supply ventilation systems. It is essential to examine the quality of the indoor air and hence the environment in which you wish to operate. This may vary from area to area; remember, the cleaner the air requirement, the more expensive it will be to achieve and operate. It will be necessary to consider the requirements of the indoor air quality (IAQ) as part of any risk assessment, including HACCP and HAZOPs analysis, as well as in any value engineering exercise. Having arrived at an idea of the indoor air quality that you require, there are two major steps that need to be considered. a) What type of filtration is required? and b) Do you need a cleanroom to achieve the right air quality? There is a confusing array of international standards for both filter performance and for cleanroom classification. The Committee for European Normalisation (CEN) has issued filter standards EN 779 and EN 1822, which together effectively replaced Eurovent Standards 4/4 and 4/5, ASHRAE 52 – 76, DIN 24 – 184, DIN 24 – 185 and BS 6540. As with filter performance, a new worldwide family of standards for cleanrooms – and the environment within them – is being put into place. These are EN/ISO 14644 and EN/ISO 14698, both of which come under the general title "Cleanrooms and Associated Controlled Environments". These standards are in several parts, some of which have already been published, with the remainder still in development. It is expected that these standards will replace the American Federal Standard FD 209 D (imperial) and FD 209 E (metric), BS 5295, German VDI 2083, Japanese JACA No. 24 and the French AFNOR NFX 44-101. These new standards are being produced through international co-operation and it is expected that they will be universally adopted. If the facility is a pharmaceutical type then it will be necessary to understand the requirements of the Medicines Control Agency (MCA) and the Food and Drugs Agency (FDA).

Filters In terms of filter media, there is a variety of materials available as there is for the frame in which the filters are mounted. It will be necessary to carry out an assessment as to which of those materials available are most suitable for your application. There are several characteristics that should be looked for when selecting a filter media and its mounting frame. They should not shed particles during operation; they should not be subjected to corrosive reactions from airborne contaminants; they should not emit gases or dopants from the filter material; and the filter should have as low a pressure drop as possible to give low energy consumption as well as a longer life expectancy. Other factors for consideration should include its air handling capacity, separation efficiency, service life, capital cost and disposal cost. These factors should be combined to carry out life-cycle cost analysis. It is usually the case that for a higher initial cost of a filter, a longer service life will be achieved, which frequently leads to lower overall operating costs. So the advice is do not consider only initial purchase costs when selecting filters. Once the filter and frame materials have been selected, the next major step is to ensure that the filters are correctly installed and monitored during their operational life. The following guidelines will help prolong filter life and ensure a satisfactory performance: • Make sure the seal between the filter and its mounting frame is effective. There is no point in providing expensive filters to have them by-passed by air leakage between the filter and the mounting frame • Provide weather louvres on air intakes and protect filters from rain penetration. Moisture-laden filters lose their effectiveness • Ensure the pressure drop across the filter is monitored, preferably linked to a building management system, enabling you to identify when the filter needs to be serviced or replaced • Do not exceed the filter's recommended replacement pressure drop. As pressure drop increases through the filter (as it collects the airborne contaminants), then the airflow through the filter will be reduced, which could lead to other problems • Try to ensure a uniform airflow across the filter face and avoid uneven velocities i.e. avoid tight bends in ductwork before the filter • Make sure there is adequate space and access to service and replace the filters • Consider using low cost pre-filters to prolong the service life of more expensive high efficiency filters • Remember that a low-pressure drop gives lower energy consumption by the ventilation fans and also frequently gives a longer service life Air filters are used in a variety of different industries and some, especially the pharmaceutical, biotech and semiconductor industries, have developed excellent ideas and guidelines which can be applied to other industries. One of the most exciting areas of recent innovation is the use of isolation technology and mini-environments. These systems only provide very high quality conditions where they are needed, particularly when the rest of the workspace in which they are contained are at a lower standard or classification. This may lead to both reduced capital cost and operating costs. The draft version of ISO 14644-7 Separation Enclosures has recently been issued for review. I am aware that government sponsored trials have been investigating these technologies, mainly with a view to improving hygiene and reducing potential contamination within the food industry. After all, one of the largest sources of contamination is people and if they can be eliminated from the equation, then processing becomes safer and more cost effective. The use of fan filter units (FFUs) is now becoming widespread in the semiconductor industry. FFUs are used on a decentralised basis reducing the requirements for large central plant and distribution ductwork. This technology is now moving into the pharmaceutical industry. These systems frequently reduce HVAC capital cost, installation time, running costs, lessen the need for plant accommodation and give greater flexibility and increased redundancy. It should never be forgotten that it takes both good design and ongoing facility management to create and maintain a clean environment. Having gone to great lengths to provide a clean facility in which to carry out a process, it is important to ensure that it is properly and fully commissioned and validated. Avoid the temptation to move in early, as it will only lead to heartache in the long run.