Which part of the government is primarily focused on emergency response to hazardous substance releases?

The Environmental Protection Agency (EPA) is primarily responsible for responding to hazardous substance releases and addressing environmental emergencies. This agency implements regulations under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), commonly known as the Superfund Act, which mandates cleanup of hazardous waste sites and oversees responses to such environmental disasters.

The EPA's focus on emergency response includes coordinating with state and local governments, providing technical assistance and resources, and ensuring public safety during incidents involving hazardous substances. They develop guidelines and perform assessments to manage risks associated with hazardous materials, demonstrating their pivotal role in environmental protection and emergency management.

In contrast, other organizations mentioned, such as the Occupational Safety and Health Administration (OSHA), focus on workplace safety and health rather than environmental emergencies. The Department of Energy (DOE) deals primarily with energy policy, nuclear material management, and research related to energy, leaving hazardous substance responses to the EPA. The Federal Bureau of Investigation (FBI) centers its efforts on national security, law enforcement, and criminal investigations, which does not include managing environmental emergencies. Therefore, the EPA's specific mandate and authority in handling hazardous substance releases make it the correct answer in this context.