Most of your lab work will be carried out inside a fume hood, also known as a fume cupboard. These are spaces which take air from the lab environment and continually exhaust it safely outside, protecting users from being exposed to substances which are being manipulated within them.

Fume hoods play a crucial role in working safely within the laboratory, providing they are used correctly. Fume hoods are designed that the hood can be raised up to a 'safe working height' level, which provides access to the hood along the bottom of the sash.

Most operations in the fume hood should be carried out using the fume hood with the sash at or below this safe level. However, at times it will be nescessary to briefly raise the sash higher in order to be able to safely carry out operations such as clamping at higher levels. It is important to keep these periods to an absolute minimum, closing the hood as soon as possible, and ensuring that there are no operations taking place in the hood from which vapours could escape into the lab.

Containment of noxious chemicals and vapours within a fume hood depends on the correct operation by users and regular servicing and inspection. You will be shown how to safely work within a fume hood, and guided through the controller displays. If at any time you think there may be issues with the fume hood operation or work you are undertaking you should immediately:

• Stop working

• Close the fume hood sash

• Obtain immediate help from a demonstrator or technician 

These same instructions should be followed in the event of mishaps such as a spillage of a chemical, to ensure that any chemicals remain contained within the hood and do not enter the working lab environment.

The air flow in hoods can cause items to be sucked into the ventilation system, which can be detrimental. Try to maintain good hood hygene and avoid bits of paper tissue, weighing boats, wrappers etc being left in hoods which could be drawn up into the extract.

Fume hoods are energy intensive to operate. The more the fume hood sash is opened, the more energy is required to maintain a safe working environment, as larger volumes of air need to be expelled from the lab. The movement of air out of the lab is acheived through the fume hood fans, but air intake is also required, with this air needing to be heated or cooled in the process. To minimise the energy usage:

• Keep the fume hood sash closed whenever you are not actively working in the hood

• Keep the sash as low as possible whilst working, without imparing your abilities to carry out the manipulations safely

An individual fume hood controller is fitted to each fume hood. These measure the air velocity at the fume hood and cause the air volumes being expelled to be adjusted to ensure that air is continually expelled from the lab carrying any vapours in the process. As fume hood sashes are raised or lowered, the fume hood controller automatically adapts the air flows at the hood.

The controllers fitted in Teaching Labs are shown in the images below in various states of operation. It is important you are aware what the different states are, and the actions to take in each scenario.

When coming to use a fume hood, the controller should be powered on and showing a steady green light, indicating the hood is working normally. The LCD panel will show the current face velocity. This is likely to fluctuate, as it is affected by any disturbances in the air.

If the controller is not showing a green light, the unit may have been switched off. The fume hood is not safe to use if the green light is not showing. Consult a senior demonstrator or technician to check that the hood is able to be powered on. When switched off the LCD display will switch between these two messages.

In order to work safely within a hood, it will sometimes be nescessary to briefly raise the fume hood sash above its safe working height in order to carry out certain operations, such as fitting a clamp and boss to the chemframe at height. Before doing this, you must ensure that no work is being undertaken in the hood that could result in chemicals entering the lab environment, such as open bottles of reagents or solvent.

The safety catch can be held to allow the fume hood to pass the safe working height. At this point the fume hood controller will emit an intermittent beep and an amber light will flash on the controller.

In the event that the fume hood is not able to maintain sufficient ventilation to keep the working environment safe, the green light will extinguish and a steady red light will appear. The fume hood controller will indicate 'Alarm Low Air' and a continuous alarm will sound.

Fume hoods have an additional safety feature, which causes the hood to operate at maximum ventilation. This mode is manually triggered by pressing the Vmax button, and is designed for use in the event of a chemical spill within a hood. In the event of a spill you should obtain immediate help from a demonstrator or technician, ensuring the fume hood remains closed. The staff will direct you as to the best course of action in the event of a spill, which could include evacuation of the laboratory.

The Vmax button is an emergency mode, and is indicated by the light next to the button on the right hand side of the controller. This mode may affect other fume hoods, as a hood demanding maximum ventilation may reduce the available ventilation to other hoods. If you notice a hood in Vmax mode, please obtain immediate help from a demonstrator or technician, ensuring the fume hood remains closed.