Unit 1: Scene Size-Up and Safety
Scene Assessment & Resource Management
Before assessing a patient, an EMT must understand what happened, how many people are injured or ill, and what resources are needed. This NREMT study guide lesson explains the essential steps of scene assessment, including mechanism of injury, nature of illness, and requesting additional assistance. Review these concepts, then test your understanding with five EMT practice questions and answer explanations.
A scene assessment helps Emergency Medical Technicians (EMTs) understand the situation before beginning patient care. Along with identifying safety hazards, EMTs must determine what caused the emergency, how many patients are involved, and whether additional personnel or equipment are needed.
A thorough scene size-up allows EMTs to recognize potential injuries, anticipate complications, and coordinate an effective emergency response.
Mechanism of Injury (MOI)
The mechanism of injury (MOI) describes how a traumatic injury occurred and the forces that may have affected the patient.
Understanding the MOI helps EMTs anticipate injuries that may not be immediately visible.
Common mechanisms of injury include:
- Motor vehicle collisions: High-speed impacts, rollovers, and pedestrian accidents.
- Falls: Injuries caused by falling from heights or onto hard surfaces.
- Blunt trauma: Injuries caused by impacts that do not penetrate the body.
- Penetrating trauma: Injuries involving objects such as bullets or knives.
- Crush injuries: Injuries caused by heavy objects or structures compressing the body.
For example, a patient involved in a high-speed collision may have internal injuries even if there are few visible signs of trauma.
The MOI provides important clues, but EMTs must also assess the patient’s actual condition rather than assuming injuries are present.
Nature of Illness (NOI)
The nature of illness (NOI) describes the medical problem or condition that prompted the emergency response.
Unlike the MOI, which focuses on traumatic injuries, the NOI focuses on medical emergencies.
Examples include:
- Chest pain or suspected cardiac emergencies.
- Difficulty breathing.
- Seizures or altered mental status.
- Diabetic emergencies.
- Suspected stroke.
- Allergic reactions.
Dispatch information, the patient’s chief complaint, and observations at the scene can help EMTs determine the NOI.
For example, a patient experiencing sudden chest pain and shortness of breath may be having a cardiac emergency. However, EMTs must complete an appropriate patient assessment before determining their clinical impression.
Determining the Number of Patients
An important part of the scene size-up is identifying how many patients require medical attention.
A dispatch report may indicate only one patient, but additional patients may be discovered after arriving.
For example, a two-vehicle collision may involve several injured occupants, even if only one person initially called 911.
When the number or severity of patients exceeds the available resources, EMTs should notify dispatch and request additional assistance.
Incidents involving more patients than available resources can manage may require the activation of a mass-casualty incident (MCI) response.
During an MCI, responders use an established triage system to prioritize patients based on their medical needs and the resources available.
Requesting Additional Resources
EMTs must recognize when an emergency requires assistance beyond the personnel or equipment already on scene.
Depending on the situation, additional resources may include:
- Additional ambulances: When multiple patients require treatment or transport.
- Advanced Life Support (ALS): When patients may benefit from advanced assessment or interventions.
- Fire and rescue personnel: For vehicle extrication, technical rescue, or fire-related emergencies.
- Law enforcement: For traffic control, crowd management, or unsafe situations.
- HazMat teams: For incidents involving dangerous chemical substances.
- Air medical transport: When appropriate under local protocols and the patient’s needs.
Requesting resources early helps prevent unnecessary delays in patient care and transportation.
Considering Spinal Injuries
The mechanism of injury may also indicate a potential injury to the spine.
For example, a significant fall, high-energy collision, or direct trauma to the head or neck should prompt EMTs to consider possible spinal injury.
When spinal injury is suspected, use appropriate spinal motion restriction techniques based on the patient’s assessment and local EMS protocols.
Not every trauma patient requires a cervical collar or long backboard. The decision depends on clinical findings, the circumstances of the injury, and applicable protocols.
Communicating Scene Information
After completing the initial scene assessment, EMTs should communicate important findings to dispatch and other responding personnel.
Relevant information includes:
- The nature of the emergency.
- The number of patients.
- Potential or confirmed serious injuries.
- Additional personnel or equipment needed.
- Important changes in scene conditions.
Clear communication helps ensure that appropriate resources are available and responders understand the situation before arriving.
Key Tip
Always identify the mechanism of injury or nature of illness, determine the number of patients, and consider additional resources during your scene size-up. Request assistance early rather than waiting until an emergency becomes more difficult to manage.