With the number of vacuum implosion accidents that have occurred in laboratory environments, it’s best to operate as though the vacuum glassware could implode at any moment.

Glass vessels under vacuum or pressure can implode or explode, and without the proper protection there is always the risk of being cut from projectiles or splashed by the contents of the flask on the skin or eyes.

The hazards associated with vacuum flasks can be reduced by following the 10 tips below:

1. Inspect glassware for flaws such as cracks, scratches, deep scoring and etching marks before using vacuum apparatus

2. Make sure the vessels are specifically designed for vacuum work. Consider using smaller flasks (less than 1 L)—they are less likely to explode. Thin-walled or round-bottomed flasks larger than 1 L should never be evacuated.

3. Assemble the vacuum apparatus so as to avoid strain. Heavy apparatus should be supported from below as well as by the neck.

4. Tape the glass vacuum apparatus to minimize projectiles due to implosion. Use a criss-cross pattern of filament tape and/or build an enclosure around the flask.

5. Use adequate shielding when conducting pressure and vacuum operations, such as a plexiglas barrier.

6. Know the chemistry of the filter flask’s contents.

7. Do not jar, strike or drop a flask that’s under vacuum pressure. Also, try to avoid exposing the flask to unnecessary vibrations from equipment on the same bench, loud music, etc. The flask should be anchored in place with a ringstand and clamp.

8. Use low-intensity vacuum.

9. Before taking any actions with the flask (removing funnel/stopper, adjusting hoses), make sure to release the vacuum by disconnecting the hose at the vacuum pump end (as opposed to the flask end).

10. Wear eye and face protection when handling vacuum or pressure apparatus.

Sources:
http://www.crscientific.com/article-vacflask-safety.html
http://www.mcgill.ca/ehs/laboratory/labsafety/#cli_12.4