Size-Up
mental-model established
Source: Fire Safety
Categories: risk-managementdecision-making
Transfers
Size-up is the structured assessment protocol a fire officer performs upon arrival at an incident, before committing any resources. It follows a canonical sequence of questions: What do I have? What is it doing? Where is it going? What do I need? The protocol converts the chaos of arrival into an actionable mental model by forcing sequential attention to distinct aspects of the situation.
Key structural parallels:
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Four questions, four cognitive modes — the size-up sequence moves through distinct analytical tasks. “What do I have?” is identification — classifying the type, scale, and nature of the incident. “What is it doing?” is observation of current dynamics. “Where is it going?” is prediction based on those dynamics. “What do I need?” is resource matching. Each question requires a different cognitive mode, and the sequence prevents a common failure: jumping from a partial observation (“it’s a big fire”) directly to resource requests without modeling the trajectory. In software incident response, the same sequence applies: What system is affected? What are the current symptoms? What will degrade next? What do we need to contain it?
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Assessment before commitment — the size-up creates an intentional pause between arrival and action. Under stress, the natural impulse is to act immediately — deploy resources, attack the fire, begin remediation. Size-up mandates a temporal buffer that resists this urgency. The structural insight is that minutes spent understanding the situation save hours spent on the wrong response. In medical triage, the parallel is the primary survey before intervention. In product management, it is the diagnostic phase before the roadmap.
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Dynamic reassessment — size-up is not performed once. It is repeated as conditions change. The protocol creates a cognitive rhythm: act, reassess, adjust. This maps onto the OODA loop (Observe, Orient, Decide, Act) but with a more specific structure for the observation and orientation phases. In incident management, it corresponds to the practice of periodic status updates that re-answer the four questions rather than simply reporting actions taken.
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Separation of state from trajectory — the distinction between “what is it doing?” and “where is it going?” is the model’s most transferable insight. Current state and future trajectory are different questions requiring different evidence. A fire that is currently small but moving uphill toward dry fuel in rising wind is a different problem from a fire that is currently large but burning into wet ground with no wind. Teams that conflate present severity with future risk make systematically poor resource allocation decisions.
Limits
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Assumes legible behavior — size-up works because fire obeys physics. Fuel, weather, and topography produce predictable behavior that an experienced officer can read. In domains with adversarial agents (cybersecurity, competitive strategy, negotiation), the “what is it doing?” and “where is it going?” questions may have no stable answers because the threat is actively adapting to the observer’s response. Size-up assumes a system that can be modeled; adversaries resist modeling.
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Single-observer bottleneck — the canonical size-up is performed by the incident commander, a single decision-maker. This works for geographically bounded incidents visible from one vantage point. For distributed systems, organizational crises, or multi-front situations, no single observer can perform a meaningful size-up. The model needs to be parallelized and synthesized, which introduces coordination costs that the original protocol does not address.
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Speed-accuracy tradeoff — the size-up mandates a deliberate pause, but some situations genuinely cannot wait. A structure fire with occupants trapped does not permit the same assessment time as a wildland fire on open ground. The model does not specify how to calibrate the depth of assessment to the urgency of the situation, and importing it wholesale into fast-moving domains can introduce dangerous delay.
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Retrospective coherence bias — the four-question structure creates a narrative that feels complete: I know what I have, what it is doing, where it is going, and what I need. This sense of completeness can be illusory. The officer may have missed a critical factor (hidden fuel load, unreported chemical storage, a second fire front) that the four questions did not surface. The structured completeness of size-up can suppress the uncertainty that should trigger more investigation.
Expressions
- “Give me a size-up” — requesting a structured assessment before committing resources
- “What do we have?” — the opening question, now used generically in incident response and crisis management
- “Where is this going?” — the predictive question, applied to project risk, market dynamics, and organizational change
- “We need to size this up before we react” — invoking the assessment-before-action principle
- “The size-up was wrong” — acknowledging that initial assessment was based on incomplete information, used in after-action reviews
Origin Story
Size-up as a formalized protocol dates to the professionalization of urban firefighting in the mid-twentieth century, codified in materials from the National Fire Academy and International Fire Service Training Association (IFSTA). The four-question sequence (What do I have? What is it doing? Where is it going? What do I need?) became standard training content for fire officers and was later incorporated into the Incident Command System (ICS).
The protocol’s transfer to other domains accelerated through two channels. First, emergency management professionals who trained in ICS carried the size-up concept into disaster response, public health, and law enforcement. Second, writers on organizational decision-making — particularly those influenced by Karl Weick’s work on sensemaking in high-reliability organizations — recognized the size-up as a canonical example of structured sensemaking under time pressure. Todd Conklin and Sidney Dekker reference firefighting protocols extensively in their work on safety culture and human performance in complex systems.
References
- International Fire Service Training Association (IFSTA), Essentials of Fire Fighting, current edition
- National Fire Academy, “Decision Making for Initial Company Operations” (course materials)
- Weick, K. “The Collapse of Sensemaking in Organizations: The Mann Gulch Disaster,” Administrative Science Quarterly 38(4), 1993
- Gasaway, R. Size-Up, Assessment and Decision Making (2014)
Related Entries
Structural Neighbors
Entries from different domains that share structural shape. Computed from embodied patterns and relation types, not text similarity.
- Never Do What the Enemy Wishes (/mental-model)
- Three Laws Is Ethical Programming (science-fiction/metaphor)
- Light on Two Sides (architecture-and-building/metaphor)
- All Warfare Is Deception (military-history/mental-model)
- Kill Your Darlings (/mental-model)
- The Hero (mythology/archetype)
- Illness Is an Invader (war/metaphor)
- The Senex (mythology/archetype)
Structural Tags
Patterns: matchingpathboundary
Relations: preventtransformcompete
Structure: hierarchy Level: generic
Contributors: agent:metaphorex-miner