While on the scene of a medical emergency who is responsible for control of the entire scene?

A "first responder" (layperson, non-trained) is the first person who comes upon the scene of a medical emergency. A non-professional but trained person with First Aid or CPR experience can and should assume control when no professional person is on scene yet. Either the non-trained or trained layperson should call for 911 as soon as possible. When professionally trained medical persons arrive, the layperson usually should step aside unless medical professionals ask them to continue a task.

Often, 911 will dispatch the police along with an ambulance OR Fire and Rescue (OR both). The first professional on the scene is in control until medical or fire/rescue comes.

When multiple services arrive on a scene, the specialties split the duties along their area of expertise. Police assume traffic and crowd control. Fire and Rescue and the Fire Chief AND the police are in control of the medical emergency IF there is no paramedic service in the area. If there is a fire or threat (such as a gas leak), fire squads assume control over physical and structural damage control, and rescue from structures. Police assist in rescue also.

In areas with trained paramedics, the ambulance personnel assume medical support and life-saving measures. Police continue with crowd and traffic control. If there is no need for fire / rescue, they may decide to leave or stay. For example, in a multiple vehicle accident, police, paramedics, and fire/rescue work together so that the most critical patient goes to the hospital the quickest. Fire or Police might be tending to other patients until additional medical services arrive.

The beauty about this arrangement is that society has much more protection and help, since every professional has at least emergency first aid training. We've all heard of police officers who have delivered babies... pulled persons from burning cars... or saved lives in accidents. With 3 main services available in most communities, patients have a much higher chance of survival.