Laboratory hoods

For enclosures, velocity measurements, in the plane of the opening, offer a quick check on the design conditions. Fiowever, the opening velocity is not a direct measure of the ability of an enclosure to provide personnel protection. Other measures of efficiency are required and depend on use of the enclosure. In the case of safety cabinets and laboratory hoods, allowance factors for protection and leakage are applied to ensure complete safety when in use. 

Diazomethane In a distillation flask equipped with an distillation funnel and a cooler, place a solution of 5 g of potassium hydroxide in 8mL of water and 25 mL of ethanol. Warm the distillation flask to 65 °C in a water-bath. Add a solution of 21.5g (0.1 mol) of A-methyl-lV-nitroso-p-toluenesulfamide in 130 mL of diethyl ether through the instillation funnel in 5 min. If the distillation funnel becomes empty, pour 20 mL of diethyl ether into the funnel, and distill it gradually. Continue distillation until the distilled ether solution becomes colorless. About 3 g of diazomethane is contained in the whole resultant ether distillate. Caution these procedures should be conducted in a laboratory hood Orbencarb, methyl 2-chlorobenzylsulfone (I), 2-chlorobenzoic acid (II), methyl 2-chlorobenzoate analytical standard materials (Ihara Chemical Industries Co., Ltd) Orbencarb and I standard solution for gas chromatography 1.0 qgmL in acetone Methyl 2-chlorobenzoate standard solution for gas chromatography 0.1 qgmL" in n-hexane... 

The most common example of an enclosed hood is the laboratory hood. A standard laboratory utility hood is shown in Figure 3-6. Fresh air is drawn through the window area of the hood and is removed out the top through a duct. The airflow profiles within the hood are highly dependent on the location of the window sash. It is important to keep the sash open a few inches, minimally, to ensure adequate fresh air. Likewise, the sash should never be fully opened because contaminants might escape. The baffle at the rear of the hood ensures that contaminants are removed from the working surface and the rear lower corner. 

Another type of laboratory hood is the bypass hood, shown in Figure 3-7. For this design bypass air is supplied through a grill at the top of the hood. This ensures the availability of fresh... 

Figure 3-6 Standard utility laboratory hood. Airflow patterns and control velocity are dependent on sash height. Source N. Irving Sax, Dangerous Properties of Industrial Materials, 4th ed. (New York Van Nostrand Reinhold, 1975), p. 74. Reprinted by permission of John Wiley Sons, Inc.

A laboratory hood has an opening 4 ft in length by 3 ft in height. The hood depth is 18 in. This hood will be used for an operation involving trichloroethylene (TCE) (TLV-TWA 50 ppm). The TCE will be used in liquid form at room temperature. Determine an appropriate control velocity for this hood, and calculate the total air flow rate. 

Laboratory hoods will be equipped with audible and visual alarms which will be designed to initiate when the average inward face velocity falls below 90 linear feet per minute. 

Laboratory hoods must be located away from ... 

Laboratory hoods shall have an average inward face velocity of 100 lfpm +/- 10% with the velocity at any point not deviating from the average face velocity by more than 20%... 

Laboratory hoods shall be designed as deep and low in height as practical. Rough wall surfaces and recesses in walls and work surfaces are unacceptable. 

Laboratory hoods will be equipped with a 20 centimeter line taken from the face of the hood. No CSM contaminated equipment should be placed in front of this line during operations. 

Laboratory hoods, ducting and storage rooms where hydrocarbon materials are handled... 

Other Precautions Agent containers will be stored in a single containment system within a laboratory hood or in double containment system. 

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. 

Other Precautions L should be stored in containers made of glass for Research, Development, Test and Evaluation (RDTE) quantities or one-ton steel containers for large quantities. Agent will be stored in a single containment system within a laboratory hood or in a double containment system. 

Solvent collection device with ability to vent to a laboratory hood or elephant trunk. 

Knowledge about the safety devices (e.g., laboratory hood, fire extinguisher, emergency shower, first aid boxes, etc.). 

In a laboratory hood, equip a 500-ml three-necked flask with a sealed stirrer and motor, condenser, thermometer, and an addition funnel. Add 150 ml of a 1% solution of sodium poly (methacrylate) in water and a buffer solution of 0.85 g of disodium phosphate and 0.05 g of monosodium phosphate in 5 ml of water. 

Laboratory ergonomics Laboratory hoods Orientation to laboratory safety Planning for laboratory emergencies Principles of HPLC Principle and practice Principles of IR quantitative Qualitative and quantitative (slide show and discussion)... 

Repellency Tests. To determine the repellency of treated cloth, equal size patches of treated and untreated cloth were suspended in a laboratory hood and given equally timed sprays of emulsified chemical. This treatment was reproducible to plus or minus 10% using the time application at a given pressure. 

Note Regarding Chemical Laboratory Hoods. Industrial hygiene assessment for powder subdivision within chemical laboratory hoods indicates that face velocities should not exceed 100 feet per minute (fpm) with the sash in the lowered position. Personnel exposures at or below 1.0 pg/m3 are achievable for both large-scale and small-scale subdivisions, provided that good work practices are adhered to. When face velocities are maintained between 80 and 100 fpm and the sash is in a lowered position, work practices affect personnel exposure concentration by greater than one order of magnitude. Face velocities above 150 fpm result in excessive turbulence and an inability to weigh accurately, due to air movement, vibration and product loss to exhaust. 

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