In American law enforcement (municipal, county, or state), the Emergency Service Unit, or ESU, is a multi-faceted element within a law enforcement agency’s Special Operations Command. Structure The NYPD is credited with establishing the concept of a police emergency squad, as ESU is also synonymous with the term Emergency Services Squad (ESS) and Emergency Service Detail (ESD). An ESU operates at the direction of the command staff and responds to emergency and high-risk situations that occur outside the scope of duties of responding patrol and criminal investigation units. ESU members train continually both in-house, with other local, state, federal and military specialized units and sometimes members of a Federal Emergency Management Agency (FEMA) Urban Search & Rescue (USAR) Team. Duties An ESU often provides services analogous to the functions of a Special Weapons and Tactics (SWAT) team. ESUs respond to high-risk, tactical operations involving barricaded suspects, hostage situations, high-risk warrant service, tactical crowd control and dignitary/VIP protective operations. ESUs also provide operations and technician level response to hazardous materials (HAZMAT) incidents involving the presence of industrial or illicit chemical, biological or radiological agents involving criminals or terrorists. The ESU responds to rescue victims from structural collapse, high-rise structure, confined spaces, trench collapse, vehicle and rail car accident, and machinery accident entrapment. They may also respond to persons having difficulty breathing, heart attacks, and strokes as first respondents, or along with local EMS. Many ESUs also perform both surface and underwater victim rescue, searches and evidence recovery as well as to provide "crisis response" to incidents involving psychologically disturbed individuals. ESU members sometimes provide immediate fire suppression and victim rescue for fires occurring in massive and highly populated structural locations that are under the direct jurisdiction of a state or municipal authority. ESUs' operations are often supported by a Canine (K-9) response capability and members often respond to incidents involving dangerous animals and reptiles. In some jurisdictions, ESU members may provide medical support and team member rescue during tactical operations and sometimes staff a dedicated ambulance. Training Law enforcement agency ESU members must maintain the highest level of physical agility and personal health at all times in order to meet the crisis challenges of tactical situations. ESU officers usually have at least five-(5) years experience as a patrol officer before being appointed to an ESU assignment. Then the candidate usually completes a minimum of eight months of specialized technical rescue training