Clean air benches

Horizontal laminar flow clean air benches are not BSCs (Section 10.3.4). They discharge HEPA-filtered air across the work surface and toward the user. These devices only provide product protection. They can be used for certain dean activirie.s, such as the dust-free assembly of sterile equipment or electronic devices. These benches should never be used when handling potentially infectious materials. The worker can be exposed to materials on the clean bench. Horizontal clean air benches should never be used as a substitute for, i biological safety cabinet. 

The importance of clean-air rooms, or at least clean areas and benches, is a point often omitted from the earlier literature. 

A small fire (for example, hquid in a beaker or flask, or an oil bath) may usually be extinguished by covering the opening of the vessel with a clean damp cloth or duster the fire usually dies out from lack of air. For larger fires, dry sand may be employed. Buckets of dry sand should be distributed round the laboratory and should be strictly reserved for this purpose. Most fires on the laboratory bench can be smothered by... 

In the laboratory, sodium is best handled in a glove box filled with nitrogen or another inert gas, or in a water-free hood. When sodium is handled on the bench top, water and aqueous solutions must be excluded from the area. Tools for cutting or handling sodium must be clean and dry. Contact of sodium with air should be kept to a minimum because moisture in the air reacts rapidly with sodium. A metal catch pan under the equipment is essential to... 

The purpose of open unidirectional airflow benches is to protect products from particulate contaminants by creating a controlled environment. These benches are used, for example, in electronic, biological, pharmaceutical, and food industries. It should be mentioned that within pharmaceutical production, aseptic sterile processes must be carried out in a Class 100 environment (U.S. Federal Standard 209 E, Airborne Particulate Cleanliness Classes in Cleanrooms and Clean Zones). To avoid particle contamination in the bench, horizontal or vertical airflow with high-efficiency particulate air (HEPA)-filtered air is used. The air velocity is normally 0.4-0.5 ra s". Some examples of typical arrangements of open unidirectional airflow benches are shown in Fig. 10.51. 

In order to achieve a high level of product safety it is well known that good work practices in the bench are necessary, and having a clean environment and proper work clothing are of vital importance. Knowledge about the interaction between air movements and the dispersion of contaminants plays an important role. Wake regions and vortex streets can easily be formed behind obstacles. 

Vertical laminar flow clean benches also are not BSCs. They may be useful, for example, in hospital pharmacies when a clean area is needed. Although these units generally have a sash, the air is usually discharged into the room under the sash, resulting in the same potential problems as the horizontal laminar flow clean benches. 

Exogenous sources such as a person s hair or skin, doorknobs, laboratory benches, dust, reagents, thermal cyclers, and pipet tips are some of the common sources of DNA contamination. Ideally, a laminar air flow bench with filtered air provides a clean, dust-free environment. Sample preparation should be done in a separate room or area. The addition of sample to the PCR reaction mixture in the... 

Consider that if 10 ml of a cell suspension is removed from a vessel it is replaced by 10 ml of air. It is therefore essential to reduce airborne contamination to a minimum. In an undisturbed room bacteria and fungal spores rapidly settle to the floor or the bench, and hence regular cleaning of the floor and bench with antiseptic solutions is required. The floor of the work room should be free of cracks and should be cleaned daily with a disinfectant solution. The work bench should be swabbed down before and after each use with a solution of 70% ethanol. This also serves to kill cultured cells which may have been spilt and hence prevents their transfer to other cultures (see 2.2). 

Chemical preconcentration of the samples (e.g., extraction into chloroform and dithizone) was used in the past by several authors in order to determine the very low concentration of Pb in ancient Antarctic ice (6, 45, 64). Although this method gave reliable results, it needed a huge amount of sample (500-1000 g) and a long period of sample treatment with organic solvents. Another method is based on the preconcentration onto W wire loops that can be placed directly in a graphite furnace of instrument AAS for the atomisation of adsorbed metals for the analysis (44, 65). To minimise the contamination problems from the air of the laboratory the whole preconcentration procedure was carried out inside a vertical laminar flow clean bench. Detection limits of 0.01, 0.47, 0.22 and 0.24 pg/g were obtained for Cd, Cu, Pb and Zn respectively (44). These extremely low detection limits have recently enabled the concentrations of heavy metals in Antarctic ancient ice and recent snow to be determined (28, 72). 

Contamination + + + Low purity reagents Tool or vial material not clean or wrong material Sample exposed to laboratory air Reagents of appropriate purity verification with blank determinations Acid washing as appropriate when contents below Ipg/g to be determined steaming verification by blank determinations Use of clean benches or clean room (class 1 for sub ng/g levels) care in performing methods under cover or in closed systems verification with blank determination... 

Rinse thoroughly with dust-ftee 60°C ddH O and immediately dry the coverslips under the air flow of a clean bench. 

Obtain in a clean, dry beaker about 50. mL of approximately 0.1 M sodium hydroxide, NaOH, solution from the reagent bench. Record the exact concentration of the base in TABLE 16.1C. Rinse your buret with about 10. mL of the standard base. Then add a few milliliters of the standard base to the buret, fill the buret tip completely by manipulating the stopcock or pinch clamp, check to be certain that there are no air bubbles in the buret tip, and add the rest of your standard base to the buret. 

Collection of the dust takes place via extracting walls, roof domes, moveable hoods or extraction work benches. An effective aid when collecting emissions are hot-air curtains which direct additional air into the cabin. The additional air used may be cleaned recycled extraction air, in order to economise on heating energy. However, it should be noted, that a portion of fresh air will still always need to be provided from the outside. 

In safety cabinets of the type partial or total exhaust, the air eventually is collected in a box on top of the bench, coimected via a HEPA-filter with the air in the room (see Fig. 28.If). The box has underpressure due to the exhaust air velocity. In case the safety cabinet has a breakdown, the box construction prevents the ventilator of the exhaust channel to continue while the down flow ventilator in the cabinet stops. Otherwise contaminated air from the room would be sucked under the sash, contaminating the clean side of the HEPA filter in the work area of the safety cabinet. 

In the context of organic trace analysis, appropriate stabilization and storage precautions are a function of the nature of the analyte and its concentration, To avoid contamination by ambient air and dust, all operations should be conducted under clean-room conditions (clean-bench environment). It is of paramount importance to assure that contamination from vessels, covers, septa, and stabilizers is rigorously excluded. 

---