Another MIT Incident

Coordinator-Lead Contact MeetingJune 18, 2013

Presented by Dan Herrick

Thanks toKatie Blass, Hans Richter, Emily Ranken,

Jennifer Lynn, Michele Miele

What happened?• A user filled a small hand-held portable liquid

nitrogen (LN2) dewar at a main tank in a hallway, put the cap on, and carried it about 50 feet to the lab.

What happened?• A bystander had just removed his safety glasses and

was leaving the lab as the user was entering.• As the user opened the door to the lab, the cap blew

off the dewar with a loud pop, suddenly and without warning.

• The cap struck the bystander in his right eye, nose and face with sufficient force to cause lacerations.

• The injured bystander was escorted to MIT Medical where he reported that his right eye’s vision was hazy. The doctor advised that his eye would be fine in a couple of days and to make a follow-up appointment.

• The dewar was a 1L, CryPro dewar

available from VWR.• It has a black cap with a Styrofoam

cork and a vent hole. • The caps on these types of dewars:

– prevent LN2 from evaporating too quickly.

– prevent contaminants entering the dewar.

• The cap should fit loosely so the dewar can vent freely.  • The cap is not intended to hold in contents if the dewar

tips; such dewars must be handled carefully and placed in locations where they will not be easily knocked over.

What happened?

Why did it happen?• The probable cause of the cap rocket would seem to

be that the cap was not venting properly, resulting in pressure build-up. This may have been because of:– poor design (cap fits too snuggly onto dewar), or

– poor practices (cap put on too tight).

• The lab reported that the cap was NOT placed on too tight, but rather that the cap’s venting system seems faulty.– “The gas was supposed to vent through a hole in the cork-

like material that made up the cap, but the hole did not go all the way through the cork.”

How can a similar occurrence be avoided?• Check to make sure that LN2 vents through the

indentations inside of the lid. If not venting properly, contact vendor and request a replacement lid.  Stop using dewar until new lid is received.

• Warn lab members that if the cap is pushed all the way down, the dewar may not vent and may allow a buildup of pressure strong enough blow the cap off and possibly injure them or a bystander.

• Labs should examine all handheld dewars (not just this model) to see how the LN2 is designed to vent and to determine that the dewar is venting as designed.

Train lab members to put the lid on, then pull up so it is loose. This will allow LN2 to vent.

Push the lid on then pull up so it is loose

Check to make sure the LN2 vents through indentations inside of the lid

• Wear eye protection when handling LN2 dewars.• Portable dewars filled with LN2 should be placed in

safe locations where they will not tip or be knocked over, and should be carried in a manner that liquid will not spill out, e.g. two hands.

• Labs could consider eliminating small handheld dewars via a modification of their process if possible.

How can a similar occurrence be avoided?

Further follow-up:direct quote from the dewar manufacturer

• The lid they are referring to is believed to be the “VACUUM RELIEF PORT”. It is where we vacuum the dewar out during manufacturing.

• A dewar is made from 2 containers with a vacuum space in between. When there is a crack resulting from external force (like dropping the dewar), the LN2 would leak into the vacuum space.

• When the temp goes up, LN2 evaporates into huge pressure in the vacuum space, and it would blow out the vacuum relief port. So, please return dewar for X-ray check.