FIGURE 6.1 Overfilled Pipette Cylinder. Pipettes protruding from a pipette cylinder as a result of attempted insertion of pipettes after the cylinder is full; those protruding from the cylinder will not soakproperly or be disinfected and are prone to breakage (if glass) when other pipettes are added.

FIGURE 6.2 Safely Inserting a Pipette into a Pipetting Device. (a) Wrong position: left hand too far down pipette, risking contamination of the pipette and exerting too much leverage, which might break thepipette; right hand too far over and exposed to end of pipette or splinters should the pipette break atthe neck during insertion. Tip of pipette is also obscured by left hand and arm, risking contaminationby contact with nonsterile surface. (b) Correct position: left hand farther up pipette with lighter grip;right hand clear of top of pipette, with tip of pipette in clear view.

FIGURE 6.3 Cylinder Clamp. Clamps onto edge of bench or rigid shelf and secures gas cylinder with fabric strap. Fits different sizes of cylinder and can be moved from one position to another if necessary; clamp is available from most laboratory suppliers.

FIGURE 6.4 Flask for Alcohol Sterilization of Instruments. The wide base prevents tipping, and the center tube reduces the amount of alcohol required so that spillage, if it occurs, is minimized. (Froman original idea by M. G. Freshney.)

FIGURE 6.5 Microbiological Safety Cabinets. (a) Class II vertical laminar flow, recirculating 80% of theair and exhausting 20% of the air via a filter and ducted out of the room through an optional pathogentrap. Air is taken in at the front of the cabinet to make up the recirculating volume and prevent overspill from the work area. (b) Class II chemical safety cabinet with charcoal filters on extract and recirculating air. (c) Class III nonrecirculating, sealed cabinet with glove pockets; works at negative pressure and with air lock for entry of equipment and direct access to autoclave, either connected or adjacent. (d) Side view of Class III cabinet.