As already mentioned, the nature of the agent is the starting point for BL selection. Procedures to be carried out could be considered the final selection criteria.

There are a number of procedures that can increase the risk for personnel as well as environmental contamination potential. These include:

• Work with large quantities of samples
• Work with an agent involving live animals
• Work with concentrated cultures
• Work with large single volumes (i.e. greater than 1 liter) of biologically active materials.

Under these conditions, an increase of the biosafety level assignment or enhancement of practices and techniques may be warranted. These decisions should be made by the primary investigator before work involving infectious agents is undertaken. This process is part of the Biological Risk Assessment.