Working with Laboratory Glassware
A safe laboratory work environment can be achieved through an awareness of hazards involved with your equipment. This is no different when it comes to common glassware found in the lab.
A significant part of working safely involves hazard awareness. The most frequent laboratory glassware accidents result in minor cuts. More serious accidents include hazards associated with flying glass, fire, and chemical exposure.
Wear safety goggles when working in the laboratory
Aside from injury reduction, hazard awareness can save you time (ruined reactions) and money (broken glassware and ruined reagents).
Glass contains silica, an element found in sand. There are three primary glass types found in laboratories: soda lime (soft), borosilicate (hard) and pure fused quartz (99% silica). Pyrex™ is a brand of hard glass. Soft, hard and quartz glass have working temperatures of up to 110, 230, and 1000oC, respectively.
A problem with hot glass is that it looks the same as cool glass. Try to establish routines that allow hot glass to cool in out-of-the-way locations. For example, before removing glassware from an autoclave, crack the door and allow the glass to cool for several minutes before handling. The use of gloves and tongs can prevent burns, but they may make handling items awkward.
Heavy gloves should be worn when washing glassware by hand. Glassware cuts are more common than you might expect and can be serious.
Inserting a glass stem into a rubber stopper can be dangerous without proper precautions. The task can be made safer and easier by first lubricating the glass. Laboratory grease works well, but even deionized water is better than nothing.
Protect hands with gloves, rags, or a shield fashioned from wood or plastic. When connecting plastic tubing to the side arm of a flask, condenser, etc., grease or wet the tubing (acetone works well on vinyl tubing). Then, with some type of hand protection, slowly work the tubing onto the glass nipple. When removing tubing from glassware, do not attempt to pull it off. First lay the item on the lab bench, if possible. Cut the tubing near the end of the glass. Always cut away from your body. Next, slice the tubing lengthwise and slide the material off the glass nipple.
Understanding tubing material characteristics can reduce accident incidence and improve laboratory safety.
An alternative to barbed glass nipples are threaded fittings. Plastic tubing is typically connected via a screw cap with a plastic barb fitting and synthetic “rubber” gasket. Several manufacturers also offer “quick-connect” fittings. One piece of the connector is threaded semi-permanently into glass. The other side attaches to tubing.
Another connection option is a threaded compression fitting with a Teflon® seal. O-ring or ferrule-type compression fittings are available in several material types including Viton®, silicone, and Teflon®.
The most common method of connecting laboratory glass apparatus is by ground-glass joints. Typically these are round or tapered. Of the two types, round ground-glass joints are less likely to “freeze.”
Pressure / Vacuum
When glass is used under pressure or vacuum, taking extra precautions is advised. Surface scratches are the most common defect causing weakness and breakage. Be sure to inspect glassware for small defects before applying pressure or vacuum. If possible, mechanically pressurized or vacuum pump systems should be operated in a fume hood with the sash down. Pressure-relief and vacuum-relief devices can reduce hazards and improve research outcomes by reducing the chance of glass breakage.
If an experiment is designed, or has the potential, to generate positive system pressure, check to see that tubing is clamped securely to the apparatus. When working with vacuum systems outside of a fume hood, consider using epoxy-coated apparatus or tape the vessel to help contain glass in the event of failure. Where practical, use a bench-top shield. Keep in mind that round vessels will tolerate more pressure or vacuum than flat-sided vessels of similar construction.
Star cracks and other small defects can be “repaired” by annealing. Annealing is a process of heating glass to a specified temperature followed by slow cooling. The “harder” the glass, the higher the applied temperature.
A more insidious glassware hazard is glass stress. Glass can be stressed when heated unevenly above its strain point. It is difficult to stress quartz glass, but relatively easy to stress borosilicate (Pyrex™) glass, which has a strain point of 510oC. Additionally, thermal strain is most severe in thick glass. If you have borosilicate glass that is routinely heated (e.g., distillation equipment), you may wish to purchase a light polarizer (polariscope) for your laboratory. Annealing (right) removes the stress, making the glassware safer and more reliable.
Chips weaken glassware and may present an injury hazard. Before taking glassware in for repair, be sure to empty and clean each item. If acetone or other flammable solvents are used, rinse glassware with water and allow to dry.
When connecting lab apparatus, it may be necessary to clamp glass to ring stands or other supports. Care should be taken to avoid over-tightening glassware clamps as this may induce mechanical strain.
Used and/or broken glassware should be free of chemical and biological hazards prior to disposal. Place glass in a puncture-resistant box, label “BROKEN GLASS,” and secure with tape. Place box in a trash dumpster.
Finally, open-toed shoes are not allowed in laboratories (not while on feet, that is). Toes in open shoes are more vulnerable to cuts from dropped glassware, chemical attack, and a variety of impact injuries.