Key Instruction Points
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 Erlenmeyer 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 Erlenmeyer flask rather than a filtering flask for this operation. However, standard Erlenmeyer 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 Erlenmeyer. 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 seamless and is thus not recommended for use under vacuum.