Whether performing research or providing diagnostic services, infectious materials, organisms and laboratory animals will be encountered by laboratory staff. Proper degree of protection is thus very important for laboratory personnel, the environment and the local community. The protections required by these types of activities are defined as biosafety levels. Biological safety levels are ranked from one to four and are chosen based on the pathogens on which the work is being conducted. Each higher level is built based on the previous level, with the addition of extra barriers and restrictions on top.