Scene size-up is the immediate, dynamic, and continuous assessment performed by first responders upon arriving at an emergency incident. This process is the foundation for all subsequent actions, ensuring the safety of personnel and guiding the appropriate deployment of resources before any patient care begins. It is an overarching evaluation that starts the moment the emergency call is received and continues throughout the entire duration of the incident. This initial assessment allows responders to form a general impression of the situation and make rapid decisions that can significantly influence the outcome of the emergency.
The Operational Purpose and Timing
Scene size-up serves as the critical moment of transition between dispatch information and on-the-scene reality. The process formally begins the instant the crew is notified of the emergency and continues as they approach the location, using observations from the vehicle to inform early decisions. Patient care cannot commence until this initial size-up is complete and any immediate threats have been addressed or mitigated. This early assessment supports a disciplined decision-making framework, preventing responders from rushing into a chaotic or hazardous environment.
The size-up is not a single, static checklist but a mental process that must be re-evaluated constantly as the situation evolves. It is typically a rapid evaluation, often taking less than a minute upon arrival, yet its findings govern the entire strategy and tactics for the incident. Information gathered during the size-up dictates the level of personal protective equipment needed and whether the crew can safely enter the scene to approach the patient.
Immediate Assessment of Scene Safety
The assessment of scene safety is the first priority in any emergency response, operating under the principle that a rescuer must not become a patient. First responders must visually scan the environment for immediate threats before exiting the vehicle, establishing a safe operational perimeter. Vehicular traffic poses a hazard, requiring responders to position their apparatus to block the scene and create a protected work area. Environmental dangers include unstable ground, severe weather conditions, or structural collapse.
Other significant threats involve potential violence from hostile bystanders, family members, or the patient themselves, demanding situational awareness for signs of aggression or weapons. Chemical and fire risks are identified by clues like strange odors, vapor clouds, or downed electrical wires, which can be spotted by an asymmetry in utility poles as the crew approaches. If the scene is deemed unsafe, responders must not enter and instead focus on mitigating the danger or calling for specialized teams to secure the area.
Determining the Cause and Patient Count
After establishing safety, the size-up shifts focus to gathering information about the incident itself to inform the clinical approach. Responders must quickly determine the reason for the emergency, categorized as either Mechanism of Injury (MOI) for trauma or Nature of Illness (NOI) for medical incidents. MOI involves assessing the forces involved in a traumatic event, such as a high-speed motor vehicle collision, to predict likely injury patterns, like head and neck trauma suggested by a spider-webbed windshield. NOI focuses on identifying the medical condition, using clues like prescription medications, medical devices, or the patient’s general appearance to deduce the disease process.
Responders use observational cues at the scene, such as skid marks, broken glass, or a strong chemical smell, to provide context for the injury or illness. A rapid, accurate count of all patients is simultaneously performed to determine the scope of the incident and whether existing resources can handle the demand. Discovering multiple patients with similar, unexplained symptoms may suggest an environmental hazard, which necessitates an immediate withdrawal and further resource request before patient contact.
Assessing Needs for Additional Resources
The final stage of the size-up involves determining whether the current resources are adequate for the situation identified. This assessment is made quickly, often before patient contact, to ensure that specialized help is en route without delay. Examples of external support that might be requested include heavy rescue teams for extricating a patient trapped in wreckage or Hazardous Materials (HAZMAT) teams for spills or chemical exposures. The need for air medical transport is considered early for patients with severe trauma or those in remote locations.
Additional Fire or Emergency Medical Services (EMS) units are requested if the patient count exceeds the capacity of the initial crew or if the patient’s condition requires advanced life support not available on the first unit. Law enforcement is often requested for traffic control, crowd management, or scenes involving violence. Utility companies may be needed to secure hazards like downed power lines or leaking gas lines. This ensures effective patient treatment once the scene is secured and sufficient personnel are available.