size-up
The initial evaluation of an incident and how to deal with it.
size-up: reading the scene before you act
A size-up is the structured first look a responder takes at an incident scene to understand what they are facing, what resources they will need, and how much danger exists. It happens in the first seconds or minutes after arrival, before committing personnel to a rescue, fire suppression, or hazmat response. The size-up determines strategy: defensive or offensive operations, evacuation versus shelter-in-place, what equipment to deploy, and whether to call for additional units.
In structural firefighting, the size-up begins at the street before entry. A crew observes the building construction type, number of stories, location and condition of fire (visible flame, smoke color, volume, and location), weather, exposure buildings, access routes, and water supply. They note whether windows are intact, whether the roof appears sound, signs of structural damage or settlement. On arrival at a hazardous materials incident, responders identify the material if possible (placard, label, container shape, odor), wind direction, topography, occupied buildings downwind, and evacuation distances. The size-up directly feeds the incident commander's action plan.
What changes a size-up
Conditions change. A fire may breach a roof that looked solid. A chemical release may spread faster than terrain suggested. An apparently stable building wall may collapse. Responders must reassess continuously, especially before advancing into deep hazard zones. A poor initial size-up, missing a large exposure building, underestimating material quantity, failing to spot structural compromise, can lead to misdirected resources, unnecessary risk, or failure to protect life.
Size-up is distinct from hazard assessment and risk evaluation, though the three overlap. A size-up is primarily observational and factual; it answers what is here. Assessment and evaluation layer in judgment about severity, likelihood of escalation, and acceptable risk given available resources. Size-up is the foundation all three rest on.
The term comes from common speech but has become formal doctrine in emergency services. It reflects the value placed on informed decision-making under time pressure. A thorough size-up takes only seconds but determines whether the next thirty minutes will be successful or catastrophic.