Fume Cupboards
Fume Hood
Product Description
If the experimental work undertaken in the cabinet will result in ammonia or carbon monoxide fumes, additional filters can be added to remove these.
The main filter of a fume cupboard will last for about two years, depending on the level of use.
These types of fume cabinets expel a constant volume of air into the atmosphere. However, a six foot constant volume fume hood uses as much energy as three average homes. Therefore the models that reduce the volume of air expelled are more energy efficient.
To improve the energy efficiency (and improve laboratory ventilation costs), fume cabinets with variable air volume systems can be used. These reduce the volume of the air expelled as the fume hood sash is closed. These models often come with an automatic sash closing mechanism, which will close the fume cupboard sash when the worker leaves the hood. This means that the hoods only expel maximum air when the hood is being used.
The location of the ducting is important with a fume cabinet. It should not be positioned so that the discharge outlet is positioned near windows, air supply systems, or near where the public have access.
The purpose of fume hoods:
Fume cabinets are designed to prevent scientific and medical researchers being exposed to dangerous or harmful chemicals. It is important to recognise that they are not designed for use with biological agents such as micro-organisms. If your laboratory is involved in experiments involving micro-organisms, a microbiological safety cabinet or biological safety cabinet must be used instead.
Microbiological safety cabinets (MSC) give protection to the user by means of an inflow air curtain. In additiona, experimental material used in the cabinet is protected from the dirty work room air by a constant stream of HEPA filtered air.
Efficiency:
The efficiency of a fume cupboard in preventing exposure of the laboratory worker to
harmful chemicals depends on the following factors:
harmful chemicals depends on the following factors:
- The basic design of the fume cabinet and meeting of minimum safety standards (e.g. BS 7258 and BS 7989)
- The maintenance and testing of the fume cupboard once it has been installed in a laboratory
- The location of a fume cupboard in a scientific laboratory in relation to other extract equipment being used in the laboratory, local airflows and the number of people who walk through the laboratory
- The amount of chemicals and equipment being stored in the fume hood
- The types of experiments and research performed inside the fume cupboard
The efficiency of re-circulating fume cupboards (ductless fume cabinets) depends on:
- The selection and employment of the correct type of filter for the fume hood
- Regular replacement of the filter using a safe method
- Appropriate and safe disposal of filter
- The volume of dangerous substances being dealt with at any one time
Ductless fume hoods:
Re circulating fume cupboards:
Re circulating fume cupboards:
Re-circulating fume cupboards / fume hoods are used mainly for educational purposes or where the design of a laboratory building does not allow for the fitting of external ducting. They are sometimes known as ductless fume cabinets.
This type of fume cabinet usually has a fan fitted on the top of the hood or sometimes beneath the work area. The principle is simple. Air is drawn in through the front opening of the fume cabinet, circulated through the work area and then passed through a filter. The air this then expelled back into the laboratory environment via the fan.
This type of fume cabinet usually has a fan fitted on the top of the hood or sometimes beneath the work area. The principle is simple. Air is drawn in through the front opening of the fume cabinet, circulated through the work area and then passed through a filter. The air this then expelled back into the laboratory environment via the fan.
Methods of filtration in a fume cabinet:
Pre-filtration:
The air is passed through a filter to remove any noxious chemicals. The first stage of the filter is typically an open cell foam physical barrier, which stops big particles from getting through. Open cell foam filters are generally quite cheap and will last up to six months depending on usage.
Main filtration:
After pre-filtration, the air is drawn through a layer of activated charcoal. Activated charcoal is very efficient at removing most harmful fumes. The exception is Ammonia and carbon monoxide.
If the experimental work undertaken in the cabinet will result in ammonia or carbon monoxide fumes, additional filters can be added to remove these.
The main filter of a fume cupboard will last for about two years, depending on the level of use.
Advantages of re-circulating fume cupboards / fume hoods:
- No ducting is required
- Heated air is not expelled from the laboratory
- Noxious fumes are not expelled into the atmosphere.
Disadvantages of re-circulating fume cupboards / fume hoods:
- The units need regular maintenance – the filters must be checked and replaced
- Filters are not perfect and there is a greater risk of contamination than with ducted version
- The extractor fan can be noisy
Ducted fume cupboards:
Ducted fume hoods are commonly found in industry and in large university research establishments. There is a wide choice of ducted fume cabinets available, but they all operate under the same basic principle – contaminated air is taken out of the workplace and expelled into the atmosphere via a fitted duct.
Constant volume ducted fume hoods:
These types of fume cabinets expel a constant volume of air into the atmosphere. However, a six foot constant volume fume hood uses as much energy as three average homes. Therefore the models that reduce the volume of air expelled are more energy efficient.
Variable volume ducted fume hoods:
To improve the energy efficiency (and improve laboratory ventilation costs), fume cabinets with variable air volume systems can be used. These reduce the volume of the air expelled as the fume hood sash is closed. These models often come with an automatic sash closing mechanism, which will close the fume cupboard sash when the worker leaves the hood. This means that the hoods only expel maximum air when the hood is being used.
Position of fume cabinet ducting:
The location of the ducting is important with a fume cabinet. It should not be positioned so that the discharge outlet is positioned near windows, air supply systems, or near where the public have access.
Advantages of constant volume ducted fume hoods:
- The fumes from chemicals are completely removed from the workplace.
- They require little maintenance.
- The fan is located some distance from the researcher, so there is little noise.
Disadvantages of constant volume ducted fume hoods:
- They require ugly ductwork to remove fumes.
- Heated air is removed from the environment, so they are no energy efficient.
- Fumes are released into the atmosphere untreated.
About Us:
What are fume cupboards?
Fume cupboards, also known as laboratory chemical hoods, fume hoods, fume cabinets or film filtration cabinets are large pieces of scientific equipment very common in chemical, biological and medical laboratories. They are fume extraction systems designed to protect researchers in from toxic fumes.
Lab hoods were invented over one hundred years to protect scientists and lab workers who needed to handle hazardous materials.
Over the years, there have been many refinements to the original Victorian design, but the basic concept of laboratory hoods remains the same. Lab hoods were invented over one hundred years to protect scientists and lab workers who needed to handle hazardous materials.
Fume hoods were originally made from wood, but now epoxy coated mild steel is the favoured main construction material.
Types of fume hood
There rare two main types of fume hood:1. Ductless fume hoods
2. Re-circulating fume hoods (filtered fume hoods)
Historically, the ductless fume hood had a vent pipe made of asbestos but in modern fume extraction installations, the vent pipe is made of PVC or polypropylene.
Specialist hoods:
In recent years, manufacturers have developed specific types of fume cupboards for specialist fume filtration proposes.
Perchloric acid:
These units are designed for use with perchloric acid. They have a water bath system in the ductwork. Note that because perchloric acid fumes settle and create explosive crystals, it is very important that the ducts are cleaned internally using a spray system.
Low flow / high performance:
These are energy-efficient low-flow / high-performance fume cupboards. They have been designed to improve operator protection while reducing expensive HVAC operating costs.
Waterwash fume cupboards:
Waterwash fume cupboards have an internal wash system that cleans the inside of the unit to prevent the build up of dangerous substances.
Scrubber fume cupboards:
Scrubber fume cupboards absorb the fumes through a unit filled with plastic shapes. These shapes are soaked in water. Substances removed are thus washed into a sump, which is often filled with a neutralising liquid. The fumes are then evacuated in the usual manner.
