Clean room filters

Nonwoven wipe categories include products for babies and adults, the food service and electronics industries, medical and clean room appHcations, industrial cleaning, computer diskettes, and household products such as dusters, tea towels, shoe cleaning cloths, towelettes, and hand towels. Nonwoven fabrics are used to filter air, water, petroleum (qv), food, and beverages. Nonwovens loaded with abrasives, cleansers, or finishes can be found in a variety of products used by many industries and in many homes to scour or poHsh. Also, a majority of garments designed to protect industrial workers and consumers from hazardous environments are made from nonwoven fabrics. 

Electrical Hazards. Because carbon fibers are conductive, the airborne filaments can create serious problems shorting out electrical equipment. The best option is to locate sensitive equipment in clean rooms outside of areas where carbon fiber is being processed. If this is not possible, electrical cabinets must be effectively sealed to prevent contact with carbon fibers. A filtered air-positive purge provides additional protection for sensitive equipment. 

HEPA (or absolute) filters provide the greatest degree of air cleaning. These filters, which are akin to paper or felt, will capture particles down to 0.01 pm with efficiencies of up to 99.995 per cent. They are generally used for clean room applications and are expensive. 

For Clean Rooms (rooms of a very high standard) dust count per unit volume will be specified, but other specifications for room cleanliness are usually in terms of filtration performance against a standard test dust. Other important features are resistance to air flow and dustholding capacity, leading to the fan energy required and filter life. 

The shaking and continuous filters are regenerative, but there is a third group usually associated with ventilation work rather than dust and fume. These are throwaway filters, which, as the name implies, means that when they become too caked with dust to operate correctly the filters are removed and replaced with new ones. They will only handle low incoming dust burdens, but their efficiencies are the highest of any filter. Typical applications are fresh air input plants, clean-room filtration and nuclear processes. 

The greatest risk of contamination of a pharmaceutical product comes from its immediate environment. Additional protection from particulate and microbial contamination is therefore essential in both the filling area of the clean room and in the aseptic unit. This can be provided by a protective work station supplied with a unidirectional flow of filtered sterile air. Such a facility is known as a laminar airflow unit in which the displacement of air is either horizontal (i.e. from back to front) or vertical (i.e. from top to bottom) with a minimum homogenous airflow rate of 0.45 ms" at the working position. Thus, airborne contamination is not added to the work space and any generated by manipulations within that area is swept away by the laminar air currents. 

Articles which are to he discharged from the clean room (or elsewhere) to the aseptic area must he sterilized. To achieve this they should be transferred via a double-ended sterilizer (i.e. with a door at each end). If it is not possible, or required, that they be discharged directly to the aseptic area, they should be (i) double-wrapped before sterilization (ii) transferred immediately after sterilization to a clean environment until required and (iii) transferred from this clean environment via a double-doored hatch (where the outer wrapping is removed) to the aseptic area (where the inner wrapper is removed at the workbench). Hatchways and sterilizers should be arranged so that only one side of the entry into an aseptic area may be opened at any one time. Solutions manufactured in the clean room may be brought into the aseptic area through a sterile 0.22-/im bacteria-proof membrane filter. 

Waters Seawater (National Research Council Canada 1992) was collected in the North Atlantic Ocean at a depth of 10 m, 35 km southeast of Hahfax, Nova Scotia, Canada. The water was peristaltically pumped through cleaned polyethylene-hned ethyl vinyl acetate tubing and 0.45-pm acrylic copolymer filters. It was acidified to pH 1.6 with ultrapure nitric acid during its immediate transfer to 50-L acid-leached polypropylene carboys, previously conditioned with ultrapure water acidified to pH 1.6. The seawater was later homogenized in two linked 800-L polyethylene tanks in a clean room and immediately bottled in cleaned 2-L polyethylene bottles. Randomly selected bottles were used for analytical measurements. 

The clean laboratory for trace metals was divided into three areas entrance laboratory (with clothes changing annex), instrument laboratory, and ultraclean sample preparation laboratory, all under positive pressure with active charcoal filtered air. Personnel using the clean rooms were required to wear hair caps, polyethylene gloves, laboratory coats, and designated shoes. These items are worn only in the clean rooms. 

If the analyses are to be performed on board, the room in which the samples are prepared and analysed should, in fact, be built as a clean room. Many modern oceanographic vessels are constructed to accept modular laboratories, which can be removed between voyages. Clean room modules, complete with air conditioning and filtered air supply, have been built for several vessels. It is possible to perform accurate, precise microanalyses on board ship under less favourable conditions, but the analyst is really fighting the odds. 

As already stated, for aseptic BFS, the container is filled in a localized air shower provided with sterile filtered air. However, there is a short period of time between container formation and filling, when the open container is transferred from the par-ison formation position to the filling position and exposed to the clean room environment. During this shuttling period, there is a possibility for contaminants from the room environment to enter the container. The air used to form the parison (parison support air) is typically sterile filtered air. If this is not the case, it is also possible for nonsterile air to enter the parison during parison formation. 

Table 9-1 lists design features of the exposure chambers in the United States that have air-cleaning equipment. The facility at the University of Maryland Hospital, Baltimore, has a chamber with activated-charcoal and high-efficiency particle filters and controlled temperature and humidity. St. Vincent s Hospital and New York University, New York City, each have a clean-room facility. The University of Pennsylvania Hospital, Philadelphia, has a self-contained, reinforced-concrete... 

Dust control is a major problem in corrosion control by silicone polymers. Dust particles which may bridge, or meerly lay upon conductors will absorb moisture diffusing through the silicone and result in a localized site of corrosion. We found this to be the case in a number of our early saunples. Following the results of this study, all of our encapsulated assemblies will be cleaned and encapsulated in a clean room which is serviced by HEPA filters. 

Figure 3.1. Diagrammatic illustration of the flow pattern of HEPA-filtered air through a t5 pical clean room. Air is pumped into the room through HEPA filters (see text) located in the ceiling, and exits via extract units, normally located at floor level. Although the air flow is non-unidirectional (i.e. not true laminar flow), it generates a constant downward sweeping motion, which helps remove air-borne particulate matter from the room...

Commercial standard solutions for flame atomic absorption are not necessarily suitable for plasma and furnace analyses. The latter methods require purer grades of water and acids for standard solutions and, especially, for dilutions. For the most sensitive analyses, solutions are prepared in a dust-free environment (a clean room with a filtered air supply) to reduce background contamination that will be detected by your instruments. 

A study of mercury in Lake Michigan found levels near 1.6 pM (1.6 X 10 12 M), which is two orders of magnitude below concentrations observed in many earlier studies.5 Previous investigators apparently unknowingly contaminated their samples. A study of handling techniques for the analysis of lead in rivers investigated variations in sample collection, sample containers, protection during transportation from the field to the lab, filtration techniques, chemical preservatives, and preconcentration procedures.6 Each individual step that deviated from best practice doubled the apparent concentration of lead in stream water. Clean rooms with filtered air supplies are essential in trace analysis. Even with the best precautions, the precision of trace analysis becomes poorer as the concentration of analyte decreases (Box 5-2). 

Pollution also affects the manufacture of certain materials and products. This is evidenced by the need for clean rooms in metrology standards laboratories and in the production of certain electronics materials and of component assembly operations, In addition to elaborate filtering systems, such rooms are held at a slightly positive pressure (above outside atmospheric pressure) to prevent the entry of raw air from the outside. 

The importance of maintaining air pressure differentials in the enclosures of the aseptic suite within the ranges specified in the design plans cannot be overemphasized. Reversal of airflow, which can occur if the relative room pressures are upset, can allow contaminated air from a noncontrolled region into the clean room, thus defeating the purpose of the HEPA-filtered air supply. 

This kind of contamination was carefully evaluated by using various labware glass and quartz tubes, polytetrafluoroethylene (PTFE) vessels, fluorinated ethylene propylene (FEP) and perfluoroalkoxy (PFA) tubes. Ideally, all trace element determinations should be carried out in clean rooms in which the incoming air is filtered and special clothing is worn. 

The selected samples were sent to the University of Maryland. They were opened in a Class 100 clean room and half of each filter was cut from the holder with a stainless steel scalpel, folded and transferred to an acid-washed polyethylene bag. The bags were placed into pneumatic tube sample carriers ("rabbits") along with standards and flux monitors, and irradiated in the National Bureau of Standards (NBS) reactor at a flux of 5 x 10 n/cm -sec. Gamma-ray spectra of the irradiation products were observed with Ge r-ray detectors using procedures discussed by... 

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