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Vacuum And Pressure Operations

Some glassware and processes can possess extra safety risks. Therefore, make sure you have had the relevant training prior to working with these kinds of specialized equipments or processes.

Vacuum or pressure operations can damage glassware severely. In such applications, walls of the container must be strong enough to withstand the changes in pressure.  If the container is not able to withstand, the container may be broken.  For those applications, a round bottomed or thick-walled flask must be employed.  Glassware designed for vacuum or pressure operations are able to withstand certain pressure limits.  Do not use glassware under pressure that it is more than it was designed to withstand.

Glassware that has been through repairs or has visible defects, flaw or damage should not be employed for vacuum systems applications.  They are prone to break through thermal shock.  It is important to check the glassware for flaws or defects prior to use.

Protective measures must be taken when setting up a vacuum system include:

  • Put all vacuum apparatus inside a fume hood or behind a blast shield (Remember to use the fume hood in the lowest possible sash level).
  • If possible, use PVC coated glassware.  If not, cover flasks, dewars, and desiccators with a tape or mesh.  
  • Always wear appropriate personal protective equipment (safety goggles, face shield, and gloves).

Heating and Cooling Glassware

To determine safe temperature range of use, check with the manufacturer of glassware. Some glassware is intended to be used in to certain high and low temperatures.  Using this glassware outside of their safe ranges may cause damage or breakage

  • Always keep an eye on evaporation process.  A vessel may easily crack during evaporation.
  • Never place hot glassware on cold or wet surfaces since it may be broken due to rapid temperature change.
  • Never heat etched, cracked, nicked or chipped glassware.
  • Never heat thick-walled glassware (e.g. bottles and jars) over a direct flame.  Do not heat glassware directly on electrical heating elements.  
  • Do not try looking into a vessel being heated as evaporating material can damage your eye/skin.
  • Unless mentioned otherwise, glassware should be cooled down slowly to prevent breakage.
  • Pay extra attention while taking glassware out of low-temperature freezers (-70 to -150 ˚C) to prevent cracking and/or thermal shock.  As a safe method, put the glassware under cold running water until thawing takes place.  Do not transfer from the freezer directly into warm water baths.
  • Remember that the flame of a Bunsen burner should touch the glass only below the liquid level.  A ceramic wire gauze may help diffuse the flame therefore provide a more even heat.
  • Hot plates used to heat the glassware should always be larger than the bottom of the vessel.  Never heat thick-walled glassware (e.g. jars, bottles, cylinders, and filter flasks) on hot plates.
  • Make sure that only the necessary setting is activated when using a hot/stir plates (i.e. if you do not intend to heat, make sure the hot plate is turned off.

References and sources for information from the relevant websites and documentation of different universities, NGOs and government agencies used in the preparation of this website are provided at references.