Laboratory Fume Hoods

In professional laboratories fume hoods are big metal boxes resting on counter tops and are connected by ducts to blower motors on the roof of the facility. The blower motor is constantly sucking the air from the hoods to the outside so that chemists will not be exposed to the vapors of chemicals they are working with inside the hood. The same precautions are taken by non-dead underground chemists. 

Plutonium solutions that have a low activity (<3.7 x 10 Bq (1 mCi) or 10 mg of Pu) and that do not produce aerosols can be handled safely by a trained radiochemist in a laboratory fume hood with face velocity 125—150 linear feet per minute (38—45 m/min). Larger amounts of solutions, solutions that may produce aerosols, and plutonium compounds that are not air-sensitive are handled in glove boxes that ate maintained at a slight negative pressure, ca 0.1 kPa (0.001 atm, more precisely measured as 1.0—1.2 cm (0.35—0.50 in.) differential pressure on a water column) with respect to the surrounding laboratory pressure (176,179—181). This air is exhausted through high efficiency particulate (HEPA) filters. 

Saunders, G.T. (1993) Laboratory Fume Hoods A User s Manual, Wiley. 

This latter equation can also be used for systems without a local exhaust hood by setting the capture efficiency to zero. It could also be used to show the result of recirculation from, e.g., a laboratory fume hood with immediate recirculation. In such a hood all contaminants are generated within the hood and usually also all generated contaminants are captured, so the capture efficiency is 1. The equation demonstrates that if the... 

Fixed systems are those where movement of the hood or other changes to the system, except perhaps opening and closing of lids and doors, is not possible. One example is the hood with a sliding door surrounding a drilling or a milling machine another is the laboratory fume hood and another is the canopy hood above or the enclosure around a paper machine. 

Small versions of downdraft tables (less than approximately 0.5 m-) are used when small-sized chemical work is to be done on rabies instead of in laboratory-fume hoods (see Fig. 10.37). This includes work with low-momentum source (no initial velocity and near room temperature) such as laboratory animal experiments. 

Fume cupboards are frequently referred to as laboratory fume hoods and are a primary method of contaminant control within laboratories. 

The Uniform Fire Code requires that pyrophoric, flammable, or highly toxic gases be within ventilated gas cabinets, laboratory fume hoods, or exhausted enclosures. ... 

J. Melin. Measurements and Analyses of the Performance of Laboratory Fume Hoods, Docu ment D40 l 997. Goteborg, Sweden Chalmers University of Technology, 1997. 

ASHRAE 110-1995. Method of Testing Laboratory Fume Hoods. Atlanta.. American Society of Heating, Refrigeration, and Air-conditioning Engineers, 1995. 

Nordtest. Laboratory Fume Hoods Performance. NT VVS 095. Espoo, Finland, 1993. 

For workbenches or laboratory fume hoods with auxiliary supply it is the working person w ho could break the shielding curtain, and in that way contaminants are transported from the interior of the exhaust hood to the space where the person is situated. 

FIGURE 10.100 Principle for auxiliary air supply to a laboratory fume hood. ... 

For some hood types, measurements usually seen as indirect method, are used to measure the hood s performance to determine regulatory compliance. For example, regulations specify minimum and maximum face velocities for laboratory fume hoods and static pressure (negative) inside enclosed hoods. Continuously monitoring instruments can be connected to alarms that sound when the measurement is outside the specified limits. 

For example, the type test of a laboratory fume hood includes determination of the concentration at various points across the opening of the hodd by using various tracer source locations inside the hood. The commissioning test could concentrate on the measurements taken at one point in the opening with one source location. 

Different protection factors have been defined. One method is to define it as the ratio of the concentration of a contaminant in the exhaust duct (CJ to the concentration in the breathing zone (C[,) of a person standing in front of the enclosure, for example, a laboratory fume hood ... 

In an educational laboratory, fume hood space requirements are substantial, since so many students need a hood at the same time. Many operations that used to be performed on the bench must now be done in a hood for safety reasons. Inadequate hood space has caused many problems even in fairly modem university chemistry buildings. 

Place a small pile of the mixed composition on the fireproof board, insert a section of safety fuse into the base of the pile, and carefully light the end of the fuse with a match. Step back and observe the effect. Because of the generation of smoke by most pyrotechnic compositions, these tests are best conducted outdoors or in a well-ventilated area such as a laboratory fume hood. 3e certain no flammable materials are near the test area, for sparks may be produced. 

Many operations within the laboratory start with weighing. It is difficult to undertake precise weighing in conventional laboratory fume hoods, as the airflow and vibration inside an operating fume hood often disturb the balance. In order to accommodate the need for an engineered control at this scale of operation, dust control systems have evolved known as ventilated weighing safety enclosures or powder weighing hoods. Key characteristics of a ventilated weighing safety enclosure include ... 

Bell, G. Sartor, D. Mills, E. The Berkeley Hood Development and Commercialization of an Innovative High-Performance Laboratory Fume Hood, Lawrence Berkeley National Laboratory Report LBNL-48983 (rev.) Berkeley, CA, September 2003. 

Volatile, flammable, and toxic organic solvents should be handled in a laboratory fume hood and/or other systems designed specifically for these applications... 

Early large-scale applications of activated charcoal were in gas masks in World War I. Various gas-filters including those in cooker extractors and mobile or bench-top laboratory fume-hoods contain activated charcoal filters. About 20% of the activated charcoal that is produced is consumed in the sugar industry, where it is used as a decolouring agent. Water purification uses large amounts of activated charcoal. 

This is a very high velocity, which could hardly be used inside a paint shop. Our practical alternatives are to choose a less toxic solvent, for which the permitted concentration is higher, or to devise some kind of ventilation system, such as a laboratory fume hood, which will prevent the mixing of the benzene with the air that workers breathe. We also need to consider the air pollution consequences of emitting 200 kg/day of benzene to the atmosphere in most U.S. cities that would require a permit and probably some form of capture or destruction of the benzene. 

It is often possible to reduce air-input requirements- by removing the hazardous material at the point of discharge by loccd ventilation. This lowers the ta value in Eq. (8-5), which assumes possible disposal of hazardous material within the entire enclosed volume of the enclosure being ventilated. Hoods and exhaust ducts are placed over such equipment as open filter presses, pulverizers, open tanks, and over laboratory benches and equipment to catch the maximum amount of vapor or dust without interfering with normal operation and maintenance. Local air velocities in the region of pickup will depend on density of the hazardous material or its particle size if a dust or fume. Air velocities greater than 200 fpm are usually employed for industrial operations, while chemical laboratory fume hoods range from 70 to 125 fpm when fully opened. 

Note-. None of the sample preparation methods described here should be attempted without approval, written instructions, and close supervision by your professor or laboratory instructor. The methods described present many potential hazards. Many methods use concentrated acids, flammable solvents, and/or high temperatures and high pressures. Reactions can generate harmful gases. The potential for runaway reactions and even explosions exists with preparation of real samples. Sample preparation should be performed in a laboratory fume hood for safety. Goggles, lab coats or aprons, and gloves resistant to the chemicals in use should be worn at all times in the laboratory. 

Caplan, K.J. and Knutson, G.W., The effect of room air challenge on the efficiency of laboratory fume hoods, mASHRAE Trans., 83, Part 1, 1977. 

Memarzadeh, Farhad, Methodolgy for optimization of laboratory fume hood Containment-... 

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