The fume hood like other local ventilation devices are designed to address one or more of three main objectives:

1. Protect the user (extraction hoods, biosafety cabinets, glove boxes);

2. Protect the product or experiment inside (biosafety cabinets, glove boxes and especially laminar flow cabinets);

3. Protect the environment (recirculating exhaust hoods, certain biosafety cabinets, and any other type when equipped with appropriate exhaust air filters).

Other secondary functions of these devices include explosion protection, splash protection, spill containment, and other functions necessary for the work performed within the device.

A general, but not specific, term for some of these local ventilation devices is laminar flow cabinet. In this category can be several of the above devices that are characterized simply by the nature of their laminar air flow. The term laminar flow hood, however, is insufficient to identify its actual design and use: some protect the product but not the user, and others protect both. The terminology for local ventilation devices has been and continues to be unclear and non-specific. Attention should be paid to which of the previously specified objectives are covered in each case.

Fume hoods or fume hoods typically protect only the user, and are most commonly used in laboratories where hazardous or harmful chemicals are released during testing, research, development, or teaching.[6] They are also used in industrial applications or other activities where vapors, gases, or dusts that are hazardous or harmful are generated or released.

Because the front of the fume hood is open to the room occupied by the user and therefore the air inside the fume hood is potentially contaminated, adequate air flow from the room to the cabin is essential for proper operation. Much of the fume hood design and mode of operation focuses on maximizing adequate containment of air and vapors within the fume hood.

As most exhaust hoods are designed to connect to exhaust systems that exhaust air directly outside a building, large amounts of energy are required to operate the fans that exhaust the air, and to heat, cool, filter, control and move the air that will replace the exhausted air. Significant recent efforts in the design of fume hoods and other ventilation systems have focused on reducing the energy used to operate these devices.

Contenido

Se emplean principalmente para uso docente, aunque cada vez más se incluyen en proyectos industriales. Estas vitrinas no necesitan conductos para evacuar el aire.[7]​ Poseen generalmente un ventilador montado en la parte superior de la campana, o debajo de la encimera. El aire es aspirado a través de la abertura frontal de la campana y atraviesa un filtro, antes de pasar por el ventilador y de ser retroalimentado en el lugar de trabajo. Con una campana de recirculación de gases, es esencial que el medio filtrante sea capaz de eliminar los materiales peligrosos o nocivos que estén presentes. Como son necesarios diferentes filtros para los diferentes materiales, las campanas de extracción con recirculación sólo deben utilizarse con un estudio previo que certifique el uso seguro según el peligro (productos químicos utilizados, procesos de trabajo, tiempos, concentración, etc.).

Las campanas de extracción con recirculación, con filtros dedicados (específicos para un único producto) pueden no ser adecuadas para aplicaciones de investigación, ya que los materiales utilizados o generados en esta actividad, pueden cambiar o ser desconocidos. En caso de tener interés en este tipo de equipos, con claras ventajas en la instalación y al no afectar a la climatización del laboratorio, se debe estudiar el uso con filtros polivalentes, que permitan de manera segura, tanto el filtrado como el control de la saturación, especialmente crítico en filtros de carbón activo.

Prefiltration

The first stage of filtration consists of a physical barrier, usually an open-cell foam filter, which prevents large particles from passing through. A filter of this type is generally inexpensive, and lasts approximately six months, depending on use.

Main filtration

After pre-filtration, the fumes pass through a layer of activated carbon that absorbs most of the chemicals that pass through it. Ammonia and carbon monoxide, however, pass through most carbon filters. Other specific additional filtration techniques can be added to combat certain chemicals that would otherwise be pumped back into the room. A main filter will usually last about two years, depending on usage.

Most extraction hoods for industrial use have ducts that channel the gases to the outside, which is why there is a wide variety of models. Air is removed from the work area and dispersed into the atmosphere.[8]​.

The fume hood is only one part of the laboratory ventilation system. Since recirculation of air from the laboratory to the rest of the facility is not permitted, the air handling units that serve areas outside the laboratories are kept separate from the laboratory units. As a way to improve indoor air quality, some laboratories also use single-pass air treatment systems, where air is used that is heated or cooled only once before discharge. Many laboratories still use return air systems to laboratory areas to minimize energy and operating costs, while still providing adequate ventilation rates for acceptable working conditions. Fume hoods are used to evacuate air with dangerous levels of contaminants.

To reduce laboratory ventilation costs, variable air volume (VAV) systems are used, which reduces the volume of air evacuated when the fume hood is closed. This product is often reinforced with an automatic closing device, which will close the fume hood door when the user is not operating the fume hood. The result is that the hoods are operating a minimum volume of evacuated air when no one is actually working in front of them.

Reducing or minimizing the volume of gases evacuated is particularly beneficial for reducing energy costs, as well as minimizing the impact on facility infrastructure and the environment. Special attention must be paid to the location of the gas outlet to the outside, in order not to risk public safety, or to prevent the evacuated air from entering the air supply system again.

Low flow/high performance display cases

Conventional extraction cabinets consume a lot of energy. In recent years, manufacturers have developed and introduced more energy-efficient hoods, called low-flow, high-performance hoods, intended to maintain or improve operator protection and reduce costly HVAC operating expenses. Although there is no standardized definition of the terms "low flow" or "high performance", extractor cabinets that operate with less evacuated air flow than is required in a standard solution, less than 300 m/h/ml of sash window opening and with the sash window open to the use opening (some manufacturers have it at 350, 400 or 500 mm), are considered "low flow".[9]​.

Acid vapor extraction showcases

These units are typically constructed of engineered stoneware or polypropylene to resist the corrosive effects of acids at high concentrations. If hydrofluoric acid is used in the hood, the leaf of the glass hood must be made of polycarbonate that resists the aggression of this acid. The hood ducts must be made of polypropylene or internally coated with PTFE (Teflon).

Extraction showcase for perchloric acid

These units have a water washing system in the duct network. Because perchloric acid vapors settle and form explosive crystals, it is vital that the ductwork is cleaned internally with a series of sprays.

Showcases with scrubber and neutralizer

This type of display case absorbs gases into a chamber filled with plastic shapes, which are sprayed with water. The chemicals are drawn into a sump, which is often filled with a neutralizing liquid. The vapors are then dispersed, or will be removed, in the conventional manner.

Radioisotope showcases

This extractor hood has a stainless steel or polypropylene liner and an integral stainless steel/polypropylene countertop that is reinforced to support the weight of bricks or blocks or lead sheet.

To guarantee the occupational safety of the operator, avoid potentially toxic and/or explosive environments and minimize the environmental impact, periodic validation of the display case and control of the correct functioning of the different components is necessary.

The aspects to be evaluated recommended by the different national and international standards are:

Electrical inspection.

Mechanical inspection.

Air flow measurement.

Visualization of air flow through smoke test.

Noise and brightness level.

Environmental conditions.

Layout.

Renewals and flows according to specific use.

Correction of deviations.

A maintenance and certification plan carried out correctly will favor the success of the tests, the prediction and prevention of problems and their solution, minimizing the impact on the area's costs. On the other hand, poor maintenance will have opposite results, increasing uncertainty about the impact on the health of the operators who carry out the work daily.

There are two main types: ducts and recirculation (with filters). The principle is the same for both types: air is sucked in from the front (open) part of the box to dilute and remove the gases with which it is working. This mixed air can be expelled outside the building to a safe place by extractor/fan or recirculated in the laboratory after passing through the filter.

In showcases with ducts, for their correct operation a balance of air intake is required in the laboratory that compensates for the large volume extracted.

Depending on the use, there are different types of display cases identified in EN 14175:

• Showcases for general use (with different heights depending on the effective height of the room where it is installed, minimum 240 cm and maximum 270 cm).

• Direct access or walk-in showcases.

• Showcases for special applications for high temperature work.

• Showcases for special applications for work at high temperatures and concentrated acids.

• Showcases for special applications for work at high temperatures and perchloric acid.

• Showcases for special applications for work at high temperatures and hydrofluoric acid.

• Special application showcases for working with radioisotopes (Currently under regulatory development in part 8 of EN14175).

Other safety devices in the laboratory are: weighing cabinets, localized extraction arms, laminar flow cabinets, sterile cabinets, biosafety cabinets, glove boxes.[5] All of these devices address the need to control dangerous or irritating substances that are usually generated in the air or released within the local ventilation device itself.

The fume hood like other local ventilation devices are designed to address one or more of three main objectives:

1. Protect the user (extraction hoods, biosafety cabinets, glove boxes);

2. Protect the product or experiment inside (biosafety cabinets, glove boxes and especially laminar flow cabinets);

3. Protect the environment (recirculating exhaust hoods, certain biosafety cabinets, and any other type when equipped with appropriate exhaust air filters).

Other secondary functions of these devices include explosion protection, splash protection, spill containment, and other functions necessary for the work performed within the device.

A general, but not specific, term for some of these local ventilation devices is laminar flow cabinet. In this category can be several of the above devices that are characterized simply by the nature of their laminar air flow. The term laminar flow hood, however, is insufficient to identify its actual design and use: some protect the product but not the user, and others protect both. The terminology for local ventilation devices has been and continues to be unclear and non-specific. Attention should be paid to which of the previously specified objectives are covered in each case.

Fume hoods or fume hoods typically protect only the user, and are most commonly used in laboratories where hazardous or harmful chemicals are released during testing, research, development, or teaching.[6] They are also used in industrial applications or other activities where vapors, gases, or dusts that are hazardous or harmful are generated or released.

Because the front of the fume hood is open to the room occupied by the user and therefore the air inside the fume hood is potentially contaminated, adequate air flow from the room to the cabin is essential for proper operation. Much of the fume hood design and mode of operation focuses on maximizing adequate containment of air and vapors within the fume hood.

As most exhaust hoods are designed to connect to exhaust systems that exhaust air directly outside a building, large amounts of energy are required to operate the fans that exhaust the air, and to heat, cool, filter, control and move the air that will replace the exhausted air. Significant recent efforts in the design of fume hoods and other ventilation systems have focused on reducing the energy used to operate these devices.

Contenido

Se emplean principalmente para uso docente, aunque cada vez más se incluyen en proyectos industriales. Estas vitrinas no necesitan conductos para evacuar el aire.[7]​ Poseen generalmente un ventilador montado en la parte superior de la campana, o debajo de la encimera. El aire es aspirado a través de la abertura frontal de la campana y atraviesa un filtro, antes de pasar por el ventilador y de ser retroalimentado en el lugar de trabajo. Con una campana de recirculación de gases, es esencial que el medio filtrante sea capaz de eliminar los materiales peligrosos o nocivos que estén presentes. Como son necesarios diferentes filtros para los diferentes materiales, las campanas de extracción con recirculación sólo deben utilizarse con un estudio previo que certifique el uso seguro según el peligro (productos químicos utilizados, procesos de trabajo, tiempos, concentración, etc.).

Las campanas de extracción con recirculación, con filtros dedicados (específicos para un único producto) pueden no ser adecuadas para aplicaciones de investigación, ya que los materiales utilizados o generados en esta actividad, pueden cambiar o ser desconocidos. En caso de tener interés en este tipo de equipos, con claras ventajas en la instalación y al no afectar a la climatización del laboratorio, se debe estudiar el uso con filtros polivalentes, que permitan de manera segura, tanto el filtrado como el control de la saturación, especialmente crítico en filtros de carbón activo.

Prefiltration

The first stage of filtration consists of a physical barrier, usually an open-cell foam filter, which prevents large particles from passing through. A filter of this type is generally inexpensive, and lasts approximately six months, depending on use.

Main filtration

After pre-filtration, the fumes pass through a layer of activated carbon that absorbs most of the chemicals that pass through it. Ammonia and carbon monoxide, however, pass through most carbon filters. Other specific additional filtration techniques can be added to combat certain chemicals that would otherwise be pumped back into the room. A main filter will usually last about two years, depending on usage.

Most extraction hoods for industrial use have ducts that channel the gases to the outside, which is why there is a wide variety of models. Air is removed from the work area and dispersed into the atmosphere.[8]​.

The fume hood is only one part of the laboratory ventilation system. Since recirculation of air from the laboratory to the rest of the facility is not permitted, the air handling units that serve areas outside the laboratories are kept separate from the laboratory units. As a way to improve indoor air quality, some laboratories also use single-pass air treatment systems, where air is used that is heated or cooled only once before discharge. Many laboratories still use return air systems to laboratory areas to minimize energy and operating costs, while still providing adequate ventilation rates for acceptable working conditions. Fume hoods are used to evacuate air with dangerous levels of contaminants.

To reduce laboratory ventilation costs, variable air volume (VAV) systems are used, which reduces the volume of air evacuated when the fume hood is closed. This product is often reinforced with an automatic closing device, which will close the fume hood door when the user is not operating the fume hood. The result is that the hoods are operating a minimum volume of evacuated air when no one is actually working in front of them.

Reducing or minimizing the volume of gases evacuated is particularly beneficial for reducing energy costs, as well as minimizing the impact on facility infrastructure and the environment. Special attention must be paid to the location of the gas outlet to the outside, in order not to risk public safety, or to prevent the evacuated air from entering the air supply system again.

Low flow/high performance display cases

Conventional extraction cabinets consume a lot of energy. In recent years, manufacturers have developed and introduced more energy-efficient hoods, called low-flow, high-performance hoods, intended to maintain or improve operator protection and reduce costly HVAC operating expenses. Although there is no standardized definition of the terms "low flow" or "high performance", extractor cabinets that operate with less evacuated air flow than is required in a standard solution, less than 300 m/h/ml of sash window opening and with the sash window open to the use opening (some manufacturers have it at 350, 400 or 500 mm), are considered "low flow".[9]​.

Acid vapor extraction showcases

These units are typically constructed of engineered stoneware or polypropylene to resist the corrosive effects of acids at high concentrations. If hydrofluoric acid is used in the hood, the leaf of the glass hood must be made of polycarbonate that resists the aggression of this acid. The hood ducts must be made of polypropylene or internally coated with PTFE (Teflon).

Extraction showcase for perchloric acid

These units have a water washing system in the duct network. Because perchloric acid vapors settle and form explosive crystals, it is vital that the ductwork is cleaned internally with a series of sprays.

Showcases with scrubber and neutralizer

This type of display case absorbs gases into a chamber filled with plastic shapes, which are sprayed with water. The chemicals are drawn into a sump, which is often filled with a neutralizing liquid. The vapors are then dispersed, or will be removed, in the conventional manner.

Radioisotope showcases

This extractor hood has a stainless steel or polypropylene liner and an integral stainless steel/polypropylene countertop that is reinforced to support the weight of bricks or blocks or lead sheet.

To guarantee the occupational safety of the operator, avoid potentially toxic and/or explosive environments and minimize the environmental impact, periodic validation of the display case and control of the correct functioning of the different components is necessary.

The aspects to be evaluated recommended by the different national and international standards are:

Electrical inspection.

Mechanical inspection.

Air flow measurement.

Visualization of air flow through smoke test.

Noise and brightness level.

Environmental conditions.

Layout.

Renewals and flows according to specific use.

Correction of deviations.

A maintenance and certification plan carried out correctly will favor the success of the tests, the prediction and prevention of problems and their solution, minimizing the impact on the area's costs. On the other hand, poor maintenance will have opposite results, increasing uncertainty about the impact on the health of the operators who carry out the work daily.