Which of the following describes a biological incident?

A biological incident is specifically characterized by the release of substances, such as pathogens or toxins, that can cause harm to health. This type of incident typically involves biological agents that can lead to illness or injury in humans, animals, or the environment. The focus is on the potential for adverse health effects due to exposure to these harmful biological agents.

In contrast, the other options relate to different types of emergencies. An electrical fire is related to fire hazards, a hazardous chemical spill pertains to chemical incidents, and routine maintenance checks do not involve emergencies or health risks at all. Therefore, the choice indicating a release of harmful substances accurately defines a biological incident.