generated should be disposed of immediately. The disposal procedure may require
prior autoclaving of the waste, which can be carried out using pressurised steam
at 121C under 105 kPa for a defined period of time. These conditions are required
to destroy microorganisms.
For smooth running of the facilities, daily checks should be made of the tempera-
ture in incubators, and of the gas supply to the incubators by checking the CO 2
cylinder pressure. Water baths should be kept clean at all times and areas under the
work surfaces of the flow cabinets cleaned of any spills.2.2.2 Equipment for cell culture
Several pieces of equipment are essential. These include a tissue culture hood,
incubator(s), autoclave and microscope. A brief description will be given of these
and other essential equipments.Cell culture hoods
The cell culture hood is the central piece of equipment where all the cell handling is
carried out and is designed not only to protect the cultures from the operator but in
some cases to protect the operator from the cultures. These hoods are generally referred
to as laminar flow hoods as they generate a smooth uninterrupted streamlined flow
(laminar flow) of sterile air which has been filtered through ahigh-efficiency particu-
late air(HEPA) filter. There are two types of laminar flow hood classified as either
verticalorhorizontal. The horizontal hoods allow air to flow directly at the operator
and as a result are generally used for media preparation or when one is working with
non-infectious materials, including those derived from plants. The vertical hoods (also
known asbiology safety cabinets) are best for working with hazardous organisms,
since air within the hood is filtered before it passes into the surrounding environment.
Currently, there are at least three different classes of hood used which all offer
various levels of protection to the cultures, the operator or both and these are
described below.Class I hoods
These hoods, as with the class II type, have a screen at the front that provides a barrier
between the operator and the cells but yet allows access into the hood through
an opening at the bottom of the screen (Fig. 2.1). This barrier prevents too much
turbulence to air flow from the outside and, more importantly, provides good protec-
tion for the operator. Cultures are also protected but to a lesser extent when compared
to the class II hoods as the air drawn in from the outside is sucked through the inner
cabinet to the top of the hood. These hoods are suitable for use with low-risk
organisms and when operator protection only is required.Class II hoods
Class II hoods are the most common units found in tissue culture laboratories. These
hoods offer good protection to both the operator and the cell culture. Unlike class
I hoods, air drawn from the outside is passed through the grill in the front of the work
area and filtered through the HEPA filter at the top of the hood before streaming down40 Cell culture techniques