Laboratory hoods are imperative to protecting employees from a variety of dangers in the lab. Their proper use can save workers from serious injury and proper training should be undertaken in this regard.
Many materials used in laboratories can give off hazardous fumes and vapors, and laboratory workers must take suitable precautions to work safely with these materials. Often this means working within a laboratory hood. This article explains some of the different ways in which laboratory hoods protect workers, and how workers should test that the hood is working correctly.
Hoods can provide different kinds of protection for the laboratory worker. Firstly, the "sash" on the hood protects from physical dangers such as chemical splashing, fires and minor explosions. To maximize this protection the sash should be kept at the lowest practical (comfortable) level when working within the hood.
Secondly, the hood prevents airborne contaminants from within the hood from reaching the worker. Airflow should be into the hood, and thus away from the worker, and the contaminants should be captured before being filtered and exhausted from the hood through ducts.
Although a lot of protection is provided by the hood the worker may still need to wear safety glasses, gloves and other equipment while working within the hood.
A laboratory hood will be next to useless if it is not working correctly, and for this reason regular testing and maintenance should be carried out. Testing should occur when the hood is first installed, and at regular intervals thereafter. Retesting should also occur whenever there are changes to the laboratory's ventilation systems.
Testing a hood is a skilled procedure and workers should be trained in the measurements to be taken and in the equipment to be used. Typically the cross-draft (circulation around the hood) is checked first. Then a smoke tube is used inside the hood to make sure that flow leads correctly to the exit ventilation ducts.
Finally the face velocity is measured at several positions. This is the air speed measured through the face (front) of the hood with the sash open. There are specifications for the allowed air-speeds (absolute and relative) across the face, and for the face velocity relative to the cross-draft. Properly calibrated instruments such as anemometers should be used for these measurements.
In the event of problems with some of these specifications then there are some minor adjustments (e. G. Interior hood baffles) which can be made, but if the hood is still failing the specifications then the matter must be reported to a supervisor.
In addition to understanding what the hood does, and how to test the hood, workers should be trained in how to use the hood properly. Activity inside the hood should be arranged so that the airflow remains effective at all times. Experiments should not be right at the edge of the hood, but should be at least six inches inside the hood, and it may be preferable for large items of equipment in the hood to be raised up.
Hoods should not be used as cupboards for extra storage space. The airflow can be restricted by any boxes or jars, and any explosion or fire in the hood may spread to the stored material.
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