An explosion occurred at a vacuum pump: a rotary vane vacuum pump had been installed in a floor cupboard (ventilated); the operating switches were outside the cupboard, while the switch housing was installed inside the cupboard. The outlet of the pump discharged into the floor cupboard rather than directly into the exhaust system.
Apparently, prior to the incident, the pump had been used to remove diethyl ether under vacuum. In this case sufficient condensation had not been reached in the cold trap, leading to the discharge of diethyl ether into the floor cupboard through the pump outlet. It is not known how effective the floor cupboard’s ventilation system was; however, it is likely that it was not effective enough to keep an explosive atmosphere from forming. When the pump was switched on once again, the atmosphere in the floor cupboard ignited, ripping out the door. Fortunately, the operator was standing beside the cupboard and was not hit directly.
It is very important to learn from accidents. We have to draw appropriate lessons and ask ourselves what led to the accident and which measures can be taken to systematically prevent the same or similar incidents from occurring in the future. This is one of the main objectives of the prevention strategy “VISION ZERO. ZERO HARM – HEALTHY WORK!”
In the present case, one of the contributing factors was that the outlet of the pump did not discharge directly into the exhaust system. Instead, the exhausted vapour accumulated in the cupboard. It was not possible for the operator to determine whether everything was in order; a user cannot be expected to examine the condition of the technical equipment before use. A thorough inspection would have been the only way to determine that the outlet was not discharging into the exhaust system. This would have been discovered if the system had been inspected regularly by qualified staff.
This type of pump cannot be used for solvents removing without a cold trap with sufficient separation efficiency upstream of the pump. Depending on the application, using of dry ice as a cooling agent may not be sufficient. In these cases, liquid nitrogen may be required (however, if applied improperly, the oxygen in the air may condense into oxidizable material in the cold trap, which should be strictly avoided). If the pumping rate is too high or too much air is added while pumping, solvent vapours will be drawn through the trap (or several consecutive traps) even if nitrogen is used as the cooling agent. Likewise, this type of pump is not recommended for operating a rotary evaporator under vacuum, as was the case here; the traps may quickly freeze closed. There are better solutions available, where the separation of solvent vapours without the use of cold traps is achieved.
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