Video clip 1: Different types of protective equipment used in laboratories

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Introduction & Air Intake The appropriate management of air flow within a laboratory is crucial to the maintenance of a safe and healthy working environment. This video sequence will show the typical ventilation process for laboratories, and will highlight some common problems. Air is drawn from outside and may be passed through any of a variety of filtering media. The air is then conditioned, by either heating or cooling, and then delivered through ducts to the lab.
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Air Intake, Ceiling diffuser
The terminal end of the air supply duct in the lab is typically covered with a diffuser to enhance the distribution of the air.
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Return duct
The air exits the lab via two main pathways. A return air duct may draw some portion of the air into the return air plenum.
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Exhaust, Fume hood
Air can also be removed from the room by exhaust hoods, which are designed to capture and remove gases and vapors from the breathing zone of lab workers.
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Room Changes Per Hour
The rate at which the air is supplied to, and subsequently removed from, a lab is reported in the units of "room changes per hour". This represents the equivalent volume of the room being exchanged over a set period of time. Recommended room changes for labs can range from 4 to 15 per hour, depending upon the work performed in the lab.
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Air Flow Direction
To prevent the accidental release of contaminants into areas of general access, the air pressure in the lab should be lower than that in corridor areas, so that the flow of air is from the corridor into the lab. To verify the proper direction of flow, tracer gases such as smoke tubes can be used.
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Laboratory Fume Hood
Work involving gases and vapors should be performed within exhaust hoods so that emissions are captured and drawn away from the breathing zone of workers. The flow rate of exhaust hood should be routinely verified to ensure appropriate functionality. Although exhaust hoods can provide protection to workers, they do not provide protection to the product or specimen located in the hood, as ambient air is being drawn across the work surface
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Biological safety cabinet
When products or specimens must also be protected, a biological safety cabinet may be used. These devices offer worker protection by drawing air away from the breathing zone, but also offer product protection by filtering the air before it crosses the work surface. These units may stand alone or may be ducted into the lab ventilation system
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Ventilation Considerations
Maintaining appropriate air pressures in a lab is a delicate balance, and malfunctions can result in releases of contaminants. Some common problems to be on the look-out for include:

Modifications to ventilation systems resulting in re-entrainment of exhaust air or the closing off of outside air intakes System alternations or malfunctions that cause the lab air pressure to be higher than the adjoining corridor Failure of exhaust hood fans and Improper work techniques in exhaust hoods – not far enough into the hood or rapid movements disrupting air curtains

Regular monitoring of the work environment can help reduce the instances of such events.
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