No Coffee Carafes in Cryogenic Applications
only devices and components designed for cryogenic applica- tions, (c) follow the operating instructions of the respective manufacturer, (d) use appropriate personal protective equipment, (e) obtain regular training and instructions in the handling of the equipment and the gases, and (f) inspect the surface of the Dewar every time before using. T ere should be no scratches, no burst of glass, and no residues of any material on the glass. If a visual check fi nds one of the above-mentioned defects, the Dewar fl ask should be removed from service directly. T e fl ask could implode when the user fi lls it with LN 2 because of the high thermal stress experienced when the glass or metal surface cools down within seconds.
In the article by Dr. Barlow [ 1 ] the following incident involving a glass Dewar with a completely iced and fixed lid was described: “When a user gave the Dewar a slight twist to break the icicle, the twist instead broke the LN-filled glass liner. When the LN hit the metal walls of the Dewar, it vaporized. The rapid expansion of LN within the narrow bore of the Dewar, coupled with the fragmentation of the glass into minute pieces, led to an upward explosion of glass fragments that the user described as a “stream of confetti shooting to the ceiling. For weeks afterward, we found glass “confetti” in and around crevices in the TEM room. Discussions with our service engineers revealed that similar breaks in glass-lined Dewars have occurred in labs around the world.”
For us, authors of the present article, it is hard to say what led to this explosion. We can only guess what could lead to such an incident. One obvious aspect is that the icicle closed the Dewar so completely that there was overpressure inside the Dewar. By twisting the icicle to break it away from the Dewar, the user may have brought too much tension to the glass so that it broke seconds before he could divide the Dewar from the iced lid. So the LN 2 headed up inside the casing of the broken Dewar, pressure rose up rapidly, and then the glass parts and the gas fl ew out the Dewar’s casing.
Conclusion
To prevent dangerous situations when using LN 2 Dewars, we recommend that users stick to the handling procedures described above, especially the following: meet operation- specifi c and country-specifi c requirements in handling liquefi ed gases, use devices and components designed for cryogenic applications, follow all operating instructions, wear personal protective equipment, and perform regular training in the handling of the equipment and the gases. Moreover, when a lid is used, the lid must be loose on top so that pressure can be released. Otherwise a 5 mm hole should be drilled in the lid to release the pressure continuously, or a gas outlet pipe should be installed.
References [1] S Barlow , Microscopy Today 22 ( 1 ) ( 2014 ) 46 – 48 .
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