Memo 23/08: Explosion risk - sample retrieval from cryogenic storage
A member of staff recently escaped serious injury when a sample vial she was removing from a liquid nitrogen container exploded in her face. During sample storage liquid nitrogen had seeped into the vial and when it was removed from the vessel the rapid expansion of the trapped liquid into gas caused the vial to explode. The researcher was not wearing any face protection and sustained facial abrasions. She was very fortunate indeed to have avoided serious eye injury. Had the vial contained harmful biological agents there was also the potential for the release of infectious aerosols.
The procedure for storing samples in liquid nitrogen is documented in memo M12/01. To reiterate, the memo states that all new samples, or samples being returned to cryo-storage, must be stored in vapour phase nitrogen. Existing samples already stored in liquid phase nitrogen must be placed in a secondary container immediately after retrieval from the storage vessel or, alternatively, the sample vials must be placed in vapour phase nitrogen for at least 24 hours prior to removal. In all cases face shields must be worn when samples are being handled.
All staff using liquid nitrogen storage must be made aware of the potential explosion risks and the control measures to be adopted.
Supervisors and departmental safety officers must ensure that procedures are followed and that appropriate face protection is provided and used.
Workers in non-clinical departments should also consider the circumstances of this accident, take heed and apply the same strict control measures when using cryogens to store their samples/specimens.
October 2009