What is standard deduction

Use of deductions


Optimal extraction performance

A working fume cupboard only provides effective protection if it is used correctly. The extraction performance is only optimal when the sash is closed and the flow conditions are largely undisturbed. Fume cupboards that are not operated permanently should always be switched on for a few minutes before starting work in order to maintain stable flow conditions. For this reason drafts and other suction effects in the exhaust area should be avoided, e.g. B. Doors and windows are kept closed.

Keep the sash closed

If the closed sash is pulled all the way down, a narrow gap remains between the sash and the work surface, through which air from the laboratory is sucked into the fume cupboard.

The amount of air sucked in per unit of time is basically fixed. The effectiveness of a standard fume cupboard therefore depends directly on the degree of opening of the sash. If the gap opening is small, the air flow speed is significantly higher than when the sash is open. In addition, the following rule applies when the sash is open: the higher the windshield, the higher the emission of pollutants.

With standard fume cupboards, all of the extracted air is sucked in through the gap between the front pane and the worktop. There are also fume cupboards with ejector systems in which additional air is blown into the interior of the fume cupboard via nozzles. These air nozzles are located in the lower and / or side area of ​​the sash frame. In this way, the leakage of pollutants from the inside of the fume cupboard into the laboratory is to be reduced even when the sash is partially open.


To ensure that the flow conditions inside the fume cupboard are largely undisturbed, no fixtures such as shelves, bulky devices or the like should be introduced and work should only be carried out on the designated work surface. Remove unnecessary flow obstacles such as bottles, devices and other objects from the interior of the fume cupboard. Active heat sources can also have a negative impact on the flow conditions.

Do not work in the foremost area of ​​the fume cupboard, as this is where the risk of harmful substances escaping is greatest: Your own movements in front of the fume cupboard, such as quick arm movements or a colleague passing by, can cause an undesirable countercurrent to the air. Of course, you should NEVER lean into an operating fume cupboard.

In fume cupboards with additional air injection, the test setup may only begin 10 cm behind the windscreen, as otherwise the polluted air will be forced out of the fume cupboard.

Limit the amount of substance released

The exhaust air remains unfiltered with standard fume cupboards. Make sure that the release of emissions inside the fume cupboard does not become too great, i.e. harmful gases and vapors at the source, e.g. B are adsorbed.

Safety tips

  1. When working on the equipment, do not open the sash any more than is absolutely necessary.
  2. Front sashes with sliding panes can be kept closed for most work.
  3. When the front sash is open, work may only be carried out in justified exceptional cases, as the emission of pollutants is higher and the user of the fume cupboard is not protected against splashing dangerous substances or flying glass fragments.
  4. Close the sash when the fume cupboard is not in use or the set-up equipment does not need to be operated at the moment.
  5. The experimenter's head should always be protected by the front screen.

If a fume cupboard reports a malfunction, end activities with a risk potential within this fume cupboard immediately and in a controlled manner.