Lab equipment under pressure includes any closed container designed to hold gases or liquids at a pressure substantially higher or lower than the ambient pressure. Examples include glassware, compressed gas cylinders, vacuum chambers and custom designed laboratory vessels.
Risks
The pressure differential generated, either positive or negative, is a potential hazard in the event that equipment under such pressure fails. Such failure can produce an explosion (or implosion) generating flying projectiles, gas leaks or spills of hazardous materials causing exposure or injury.
Precautions
When working with pressurized vessels or experimental set-ups, the following steps must be taken to prevent personal injury:
Use vessels that have been certified or at least tested by the manufacturer to withstand the operating pressures, plus a margin of safety.
- Periodically inspect the setup for physical damage or stress.
- Use a shatter proof glass or plastic screen to protect personnel from physical injury.
- Wear safety glasses, lab coat, gloves plus any other PPE needed for protection from the potential hazards of the pressurized system (e.g. face shield).
Vacuum Applications - Glassware
Glassware that is etched, cracked, chipped, nicked or scratched should never be used for vacuum work. Never use an Erlenmeyer flask under vacuum as a filtering flask. Filtering flasks are manufactured with extra thick walls to withstand vacuum applications.
Not all desiccators are designed for vacuum applications; vacuum rated desiccators (PYREX brand) are only rated to one atmosphere of vacuum. Plastic (e.g. polycarbonate) desiccators reduce the risk of implosion and may be preferable but should also be shielded while evacuated. Never heat or move a desiccator under vacuum.
Glassware under vacuum should be kept behind a shield or hood sash, taped, or resin (plastic) coated to minimize flying debris if the glass implodes.
Dewar Flasks
Dewar flasks are under high vacuum and can collapse as a result of thermal shock or a very slight mechanical shock. They should therefore be shielded either by a layer of fiber-reinforced friction tape or by enclosure in a wooden or metal container, to reduce the risk of flying glass in case of collapse.
Pressure Vessels – Glassware
Regular laboratory glassware should not be used as high pressure reaction flasks for air-free procedures. Specially designed heavy-wall tubes/bottles/flasks which are pressure rated (between 60 and 120 psig) and tested must be used instead. This glassware comes with easy-to-use threaded PTFE plugs with O-rings and can be epoxy or plastic coated as an extra safety measure.
When performing reactions in closed vessels, one must think carefully about the solvent level in the flask. It should be based on the volatility of the solvent and the temperature used. If the system is to be heated over the boiling point of the solvent, the flask must never be over half full.
The following table provides a temperature – pressure correlation for different solvents when used in a closed system (data from www.qlabtech.com).
Sealed tube (total volume 35 mL)
|
Pressure (psi) generated at
|
Solvent
|
Solvent BP (°C)
|
Vol solvent used (mL)
|
60°C
|
90°C
|
120°C
|
160°C
|
Diethyl Ether
|
35
|
11
|
10
|
20
|
|
|
Dichloromethane
|
39
|
11
|
5
|
27
|
55
|
70
|
Acetone
|
56
|
11
|
|
15
|
40
|
60
|
Methanol
|
65
|
11
|
|
15
|
30
|
65
|
Tetrahydrofuran
|
66
|
11
|
|
5
|
22
|
46
|
Ethyl Acetate
|
77
|
11
|
|
|
|
45
|
Ethanol
|
78
|
11
|
|
|
25
|
65
|
Acetonitrile
|
82
|
11
|
|
|
20
|
40
|
Water
|
100
|
11
|
|
|
15
|
18
|
Toluene
|
111
|
11
|
|
|
|
20
|
Acetic acid
|
118
|
11
|
|
|
|
15
|
DMF
|
153
|
11
|
|
|
|
< 5
|
Compressed Gas Cylinders
Compressed, liquefied and cryogenic gases are routinely used in laboratories and various other operations at Concordia University. These gases have the potential for creating hazardous working environments as internal cylinder pressures are typically between 2,000 to 3,000 psi.
Environmental Health and Safety (EHS) promotes the safe use of gases by offering information on the proper storage, handling, use, transportation, and disposal of compressed gas cylinders. Please refer to the following Compressed Gas Safety Manual and the Safe Handling and Transportation of Compressed Gas Cylinders Quick Reference Guide for more details.
