The document discusses biological safety levels for working with biological agents. It begins with a brief history of biological safety conferences and standards being established in the United States in the 1950s and 1960s. It then provides details on the four biological safety levels (BSL), including standard practices, safety equipment and facility requirements for each level. BSL1 is for agents not known to cause disease, while each increasing level incorporates more containment practices for more dangerous agents, with BSL4 being for dangerous and exotic agents that pose a high risk of life-threatening disease.