Key Instruction Points:
1. Only use
glassware designed to be used under a vacuum for this purpose.
As required by the institutional Hazardous Waste Minimization program , a laboratory
was filtering an aqueous ethidium bromide waste solution through a bed of activated
charcoal to remove the ethidium bromide so that the filtrate could be poured down the
drain.
About 200 ml of a bufffered ethidium bromide was being filtered into a standard
Erlenmyer flask using the house vacuum. During the extraction the flask imploded, causing
broken glass and the solution and to fly into the air. Luckily, the operation was being
conducted inside the lab hood and most of the debris was contained. The extractor being
used was the Schleicher & Schuell (S&S) ethidium bromide waste reduction system.
See S&S
protocol .
What went wrong? The S&S extractors have a side arm which lead lab personnel to use
an Erlenmyer flask rather than a filtering flask for this operation. However, standard
Erlenmyer flasks are not designed to be used under pressure. A filtering flask without a
side arm should be used - these are able to withstand a vacuum. Glass models will be
marked "filtering flask" to avoid being confused with a standard Erlenmyer.
Wider bottoms on the filtering flasks add stability and help prevent tipping over when
connected to vacuum source when filtering products. Pyrex filtering flasks without
side-arms are available from a number of vendors. Nalgene makes a nalgene filtering
flash. However, its nalgene erlenmeyer flask is not seemless and is thus not
recommended for use under vacuum.
S&S ethidium bromide extractor
Glass Flask Rupture During Ozonolysis
(top)
Key Instruction Points:
1. Review risk assessments when
scaling up reactions.
During an early attempt to scale up a procedure, a laboratory worker introduced ozone gas
into a flask containing a small amount of organic material. The flask was set in a fume
hood in a cooling bath designed to lower the experiment temperature to -85° C, 15° C
below that which is normally used for such experiments. The sash of the fume hood was
completely raised. During the procedure, the worker noticed that a deep blue color
had developed in the flask, an indication that the concentration of ozone was increased.
He attributed it to poor mixing and had started to increase the stir rate when the flask
exploded. Flying glass embedded into his face, neck and safety glasses.
The worker did not experience any injuries to his eyes. Many of the cuts on his face and
neck required stitches. Shards of glass were imbedded in the safety glasses.
The sash of the hood might have provided enough of a barrier to avoid injury. However,
most sashes are not designed to protect against explosions. Shielding should be used
around any experiments that might explode. A face shield would have protected the worker
from the cuts on his face and neck. Carefully evaluate the hazards before proceeding with
a scaled-up experiment.
Glass Flask Ruptures, Possibly
Overpressurization by Liquid Nitrogen (top)
Key Instruction Points:
1. Consider shielding for
operations involving vacuum
or pressurization.
2. Be aware of the potential for
pressurization when
working with cryogenic liquids.
A 250 ml glass flask became overpressurized and burst,
spraying two laboratory workers with shards of glass.
Approximately 10 grams of styrene and a minute quantity of a drying agent were immersed in
liquid nitrogen to keep the contents frozen. The laboratory worker then attached the flask
to a vacuum pump to evacuate the flask, without success. Thinking the flask might have
developed a crack, the laboratory worker removed the flask from the vacuum line and was
defrosting it under warm water in the sink, holding it and examining it, when the flask
ruptured.
The best guess as to the cause of the rupture is that a small leak, perhaps a pinhole in
the flask, developed while it was being frozen and that some liquid nitrogen entered the
flask. When the flask was warmed, the liquid nitrogen vaporized (expansion ratio 696:1),
overpressurizing the flask and leading to the explosion.
The laboratory worker holding the flask suffered from several lacerations to the face,
hands, chest and abdomen. The other worker, who was standing across the room, received
lacerations to the abdomen. The worker holding the flask noted shards of glass embedded in
his prescription safety glasses.
The procedure was re-written such that under the same conditions, the stopcock will be
unscrewed and the flask set in a catchbucket in the hood to allow the contents to warm up
and vaporize, if volatile.
Appropriate eye protection helped to avoid a potentially serious eye injury. Consider
shielding for operations involving vacuum or pressurization. Be aware of the potential for
pressurization when working with liquid nitrogen.
Glass Waste Bottle Ruptures, Possible
Reaction of Incompatible Chemical Wastes (top)
Key Instruction Points:
1. Chemical containers should be
triple rinsed and dry
before being used for waste accumulation.
2. Wear safety glasses while in
the laboratory, even
while performing non-laboratory work.
A graduate student sitting at a lab computer was
surprised by a chemical waste bottle which burst and sprayed nitric acid and shards of
glass all over the lab.
Approximately 2L of nitric acid waste had been accumulated in a chemical waste bottle
which originally contained methanol. Over the course of 12-16 hours, it is likely that
some residual methanol reacted with the nitric acid waste and created enough carbon
dioxide to overpressurize the container. Two other waste containers in the hood were
severly damaged and several others were cracked or leaking.
Fortunately, the laboratory worker was not injured.
Chemical containers should be triple rinsed and dry before being used for waste
accumulation. Safety glasses should always be worn while in the laboratory, even while
performing non-laboratory work.
Revision Date: 6/12/2004
url: http://www2.umdnj.edu/eohssweb/aiha/accidents/glass.htm
