Editing Vacuum flask (section)

== Safety ==
Vacuum flasks are at risk of  [[Implosion (mechanical process)|implosion]] hazard, and glass vessels under vacuum, in particular, may shatter unexpectedly.  Chips, scratches or cracks can be a starting point for dangerous vessel failure, especially when the vessel temperature changes rapidly (when hot or cold liquid is added). Proper preparation of the Dewar vacuum flask by tempering prior to use is advised to maintain and optimize the functioning of the unit. Glass vacuum flasks are usually fitted into a metal base with the cylinder contained in or coated with mesh, aluminum or plastic to aid in handling, protect it from physical damage, and contain fragments should they break.{{Citation needed|date=November 2018}}

In addition, cryogenic storage dewars are usually pressurized, and they may explode if [[pressure relief valve]]s are not used.

[[Thermal expansion]] has to be taken into account when engineering a vacuum flask. The outer and inner walls are exposed to different temperatures and will expand at different rates. The vacuum flask can rupture due to the differential in thermal expansion between the outer and inner walls. [[Expansion joint]]s are commonly used in tubular vacuum flasks to avoid rupture and maintain vacuum integrity.