Safety with Slush Baths

Because the low- melting-point liquid in the slush bath is near its freezing temperature, there is little concern over toxic fumes as when working with some chemicals at room temperature. However, in the beginning, you must work in a fume hood because of the copious amounts of fumes released from the low- melting-point liquid. Once the slush bath is made, it is safe to remove it to the lab. However, it is best to leave the slush bath in the fume hood if at all possible. If the slush bath is used in the lab, move the slush bath to the fume hood immediately after your work is completed. 

Never pour a slush bath down the sink. The low temperatures can destroy plumbing Instead, let the coolant boil off in a Dewar in the fume hood. Later, the low-melting-point liquid can be saved and reused. 

A potentially explosive situation can develop when an acetone slush bath is left sitting for an extended period. Over time, the acetone and dry ice separate and the acetone floats to the surface, whereas the dry ice settles to the bottom of the Dewar. The acetone soon warms up to near room temperature, but the dry ice remains near the slush bath temperature of -77°C. If any agitation causes the warmed acetone to cut into the dry ice slush on the bottom, a flume of boiled off C02 can erupt. This flume will carry the acetone layer that was on the surface in a large spray all around the area.11 If there is a flame or spark (from a motor) in the path of the acetone, this accident could have far greater consequences. This situation can be easily avoided by constantly mixing the solution. A safe alternative to the acetone slush bath is the ethanol slush bath. The ethanol slush bath is somewhat warmer (-72°C) but does not display the same potentially dangerous capabilities. 

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