Chemical hood testing

The phenol used for RNA extraction should be of the highest purity (double distilled), as oxidation products of phenol can cause degradation of RNA. Before use, the phenol is saturated with DEPC-treated water, and the phases are allowed to separate. The pH of the top aqueous layer is tested with pH paper. If phenol is acidic, it is equilibrated with Tris buffer by mixing it with a volume of 1 M Tris-Cl, pH 7.0. After phase separation, the top buffer layer is removed and the phenol is equilibrated twice with water. Additives such as 8-hydroxyquinoline (0.1%) are used in phenol to inhibit the activity of nucleases. Caution should be exercised in the use of phenol, as it is corrosive and a suspected carcinogen. Use in a chemical hood is recommended. Phenol chloroform extraction should be carried out in con-... 

Based on the chemical screening and core hood tests in the laboratory and a numerical simulation study, the following scheme was designed ... 

Each chemical fume hood tested within last year Sash closed when not in active use Chemical-fume hood vents (baffles) unobstructed Chemical-fume hood used with sash in appropriate position Chemical storage limited in actively used hood Chemicals and equipment at least 6 in. firom the sash... 

Finally, hoods should be tested once a year with devices that can measure the airflow to determine if the airflow is adequate. While you may not get involved with this testing, you should be able to locate an inspection sticker that indicates the date and airflow rate at the most recent inspection. A sticker from the inspection should indicate the height of the sash that produces 100 Q)m. This, of course, still does not guarantee that it is working properly today. If you have any doubts about the airflow, you should contact someone who can test the airflow rate. Working at a chemical hood with a faulty fan can be extremely dangerous since the protection that you think you have is absent ... 

For a new process plant, calculations can be carried out using the heat release and plume flow rate equations outlined in Table 13.16 from a paper by Bender. For the theory to he valid, the hood must he more than two source diameters (or widths for line sources) above the source, and the temperature difference must be less than 110 °C. Experimental results have also been obtained for the case of hood plume eccentricity. These results account for cross drafts which occur within most industrial buildings. The physical and chemical characteristics of the fume and the fume loadings are obtained from published or available data of similar installations or established through laboratory or pilot-plant scale tests. - If exhaust volume requirements must he established accurately, small scale modeling can he used to augment and calibrate the analytical approach. 

Other Recirculation or exhaust air from chemical areas is prohibited. No connection between chemical areas and other areas through ventilation system is permitted. Emergency backup power is necessary. Hoods should be tested at least semiannually or after modification or maintenance operations. Operations should be performed 20 centimeters inside hood face. 

Special Chemical laboratory hoods will have an average inward face velocity of 100 linear feet per minute (lfpm) 20% with the velocity at any point not deviating from the average face velocity by more than 20%. Existing laboratory hoods will have an inward face velocity of 150 lfpm 20%. Laboratory hoods will be located such that cross drafts do not exceed 20% of the inward face velocity. A visual performance test using smoke producing devices will be performed in assessing the ability of the hood to contain Lewisite. 

Heat-sealable plastic bags and apparatus Heating blocks, thermostat-controlled metal heating block that holds test tubes and/or microcentrifuge tubes Hoods, chemical and microbiological Hot plates, with or without magnetic stirrer Gloves, plastic and latex, disposable and asbestos... 

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