The measurement of air supply volumes and velocities in cleanrooms

Air supply volumes and velocities in cleanrooms are monitored by airflow measuring hoods and anemometers but these measuring methods can be inaccurate if used incorrectly. It is demonstrated in this article that measuring hoods are accurate if the air supply passes evenly out of the hood, as occurs when the air volume is measured from a four-way diffuser or no air supply diffuser. However, when a swirl diffuser was investigated, the measuring hood gave readings more than 50% greater than the true volume. The reasons for the inaccuracy, and methods to correct it were established. Vane anemometers give inaccurate readings at the face of high-efficiency air supply filters, and it was found that the most accurate reading was found about 15 cm from the filter face. The number of readings required across the filter face to obtain an accurate average velocity was investigated, as was a scanning method using overlapping passes

Removal of microbe-carrying particles by high efficiency air filters in cleanrooms

The removal efficiency of high efficiency air filters against microbe-carrying particles (MCPs) in the air supply of occupied rooms, such as cleanrooms, was determined. Knowing the size distribution of MCPs in the air to be filtered, and the removal efficiency of a filter against individual particle diameters, the overall removal efficiency was ascertained. A variety of filters were investigated, and it was found that a filter 90% efficient, when tested against sub-micrometre particles, used in standard classification methods such as EN 1822, was greater than 99.99% efficient in removing MCPs. The effect of filter efficiency on the quality of the air supply, and the concentration of MCPs in cleanroom air was also studied. No practical improvement in airborne concentrations was obtained by filters that had a removal efficiency greater than 99.99% against MCPs. Use of a filter suitable for removing MCPs, rather than sub-micrometre particles, would give a reduction of about 6 to 8-fold in the pressure drop over a filter, and a substantial reduction in the cost of running a cleanroom

Collection efficiency of microbial methods used to monitor cleanrooms

Microbiological sampling methods used in pharmaceutical cleanrooms should efficiently collect and count microorganisms. Methods are described in this paper that allow collection efficiencies to be determined and maximised, and comparisons to be made between sampling methods

Assessing microbial risk to patients from aseptically manufactured pharmaceuticals

The microbial risk to patients from aseptically manufactured pharmaceuticals is dependent on the chance that a product contains sufficient microbes to initiate an infection. This possibility is dependent on risk factors associated with the method of production and product formulation, and can be calculated. An analysis of these risk factors can be used to minimise patient risk and assist in determining the appropriate level of contamination control required for manufacturing

Removal efficiency of high efficiency air filters against microbe-carrying particles (MCPs) in cleanrooms

The removal efficiency of high efficiency air filters was determined against microbe-carrying particles (MCPs) in the air supply to cleanrooms. Knowing the size distribution of MCPs in the air to be filtered, and the filter's removal efficiency against individual particle diameters, the overall removal efficiency was ascertained. The removal efficiency of individual species of microbes with a known size was also obtained. A variety of filters were investigated, and it was found that a filter 90% efficient against the most penetrating particle size (as classified by EN 1822) was greater than 99.99% efficient in removing a MCPs. The effect of filter efficiency on the microbial concentration in both the air supply and the cleanroom air was studied, and no practical improvement in the air quality was obtained by filters that had a removal efficiency greater than 99.99% against MCPs. Use of a filter suitable for removing MCPs, rather than sub-micrometre particles, would give a reduction of about 6 to 8-fold in the pressure differential across the filter, and a substantial reduction in the energy costs of running a cleanroom

The application of the ventilation equations to cleanrooms - Part 2: Decay of contamination

This article is the second of a three-part series that investigates the application of the ventilation equations to designing and testing cleanrooms. This part is concerned with the decay equation. The recovery test, described in ISO 14644-3 (2005) is discussed, and improvements recommended. The application of the decay equation to the ‘clean up’ requirement given in the EU GGMP (2008) is also discussed. Finally, a method is considered that calculates the time needed for airborne contamination in cleanroom areas to decay to acceptable concentrations

Decay of airborne contamination and ventilation effectiveness of cleanrooms

This article reports an investigation into the ability of the air supply in non-unidirectional cleanrooms to aid recovery from episodes of airborne contamination, and minimise airborne contamination at important locations. The ISO 14644-3 (2005) recovery test, which measures the rate of decay of test particles, was assessed and a reinterpretation of the test results suggested. This allowed air change effectiveness indexes to be calculated and used to evaluate the ventilation effectiveness of the cleanroom’s air supply. Air change effectiveness indexes were measured in various designs of cleanrooms, and reasons for deviations in the value of the indexes investigated

Experimental and CFD airflow studies of a cleanroom with special respect to air supply inlets

Investigations were carried out into the airflow in a non-unidirectional airflow cleanroom and its affect on the local airborne particle cleanliness The main influence was the method of air supply A supply inlet with no diffuser gave a pronounced downward jet flow and low levels of contamination below it, but poorer than average conditions in much of the rest of the room A 4-way diffuser gave much better air mixing and a more even airborne particle concentration throughout the cleanroom Other variables such as air inlet supply velocity, temperature difference between air supply and the room, and the release position of contamination also influenced the local airborne cleanliness A CFD analysis of airflow fields in a cleanroom was compared with measured values It was considered that a turbulent intensity of 6%, and a hydraulic diameter based on the actual size of the air inlet, should be used for the inlet boundary conditions and, when combined with a k-epsilon standard turbulence model, a reasonable prediction of the airflow and airborne particle concentration was obtained

Dispersion of microbes from floors when walking in ventilated rooms

The redispersion factor of microbe-carrying particles, which is the ratio of the concentration of floor-derived microbes in room air to those on a floor surface, was determined, as was the percentage of floor-derived microbes in room air. These relationships were shown to vary according to conditions in the room. Equations were derived that allow these relationships to be calculated for a variety of room conditions, including air supply rates, levels of personnel activity, and the effect of gravitational deposition on microbe-carrying particles.<p></p> The redispersion factor in ventilated rooms, such as cleanrooms and operating rooms, when the floor surface concentration was measured by nutrient agar contact dishes, was found to vary from about 1.5 x 10-4 to 7.4 x 10-6, and the percentage of floor-derived microbes in room air from about 0.004% to 10.5%. In a typical cleanroom, the redispersion factor is likely to be about 1.0 x 10-4, and the percentage of floor-derived microbes, 0.7. In a typical operating room, the redispersion factor is likely to be about 5.2 x 10-6 and the percentage of floor-derived microbes, 2.<p></p&gt