The 13-Point Size-Up Checklist: What to Assess Before You Commit Crews

Size-up is not a single moment. It is a continuous process that starts when the tones drop and does not end until the incident is terminated. But the initial size-up, those critical seconds when you first arrive on scene and evaluate conditions, is where the most important decisions of the entire incident are made. Your initial size-up determines your mode of operation, your attack strategy, your resource allocation, and the level of risk you are willing to accept. Get it right and the incident runs smoothly. Get it wrong and you are chasing problems for the rest of the call.

I have used a 13-point size-up framework throughout my career, and I teach it to every company officer I work with. It is not the only system out there, and you should use whatever system your department trains on. But if your department does not have a structured size-up process, or if you want to sharpen your own, this framework covers the essential elements.

Fire Engineering at fireengineering.com has published decades of tactical articles on size-up methodology, and their archives are one of the best resources available for fire officers who want to study how experienced incident commanders approach decision-making. I recommend spending time there if you want to go deeper on any of these points.

1. Construction Type

What is the building made of? Is it wood frame, ordinary construction with masonry walls and wood floors, heavy timber, non-combustible steel, or fire-resistive concrete? Construction type tells you how the building will perform under fire conditions, how long you have before structural failure becomes a risk, and what collapse patterns to expect.

Wood frame construction is the most common residential type and is the most susceptible to rapid fire spread and early structural compromise. Ordinary construction gives you more time because the masonry walls are non-combustible, but the wood interior components will still burn. Heavy timber is extremely fire-resistant and gives you the most time. Non-combustible and fire-resistive construction types are common in commercial and high-rise buildings and generally provide the longest operational window.

If you cannot identify the construction type from the exterior, assume the worst and operate accordingly.

2. Occupancy and Use

What is the building used for? A single-family home, a multi-family apartment, a school, a warehouse, a church, a restaurant? Occupancy type tells you what to expect inside: the life hazard, the fire load, the contents, the layout, and any special hazards.

A residential structure at 2 AM has a high probability of sleeping occupants. A school during the school day has hundreds of children. A warehouse may have high-piled stock, hazardous materials, and limited access. Each occupancy type demands a different approach, and you need to factor it into your initial plan.

3. Time of Day

This ties directly to occupancy and life hazard. The same building presents a very different risk profile at 3 PM versus 3 AM. A commercial occupancy at 3 AM is likely unoccupied. A residential structure at 3 AM almost certainly has people sleeping inside. A school is empty on weekends but full during weekday hours. Time of day tells you who might be inside, which directly affects your risk tolerance and search priorities.

4. Life Hazard

Are there people in the building? How many? Where are they likely to be? Can they self-evacuate, or do they need rescue? The life hazard assessment is the single most important factor in determining your risk tolerance. If there is a confirmed or high-probability life hazard, you accept more risk. If the building is confirmed empty, your risk calculus shifts dramatically toward firefighter safety.

Look for indicators: cars in the driveway, lights on, occupants at windows, reports from dispatch about trapped persons, neighbors providing information. All of this feeds your life hazard assessment.

5. Fire Location and Extent

Where is the fire? How big is it? Is it in one room, one floor, or multiple floors? Is it in the attic, the basement, an interior room, or an exterior exposure? Fire location tells you where to position your attack and what areas are immediately threatened.

Fire extent tells you whether your resources are adequate. A single room of fire in a residential structure can be handled by a single engine company. A fire that has extended to the attic and is showing from multiple windows may require a second alarm before you can control it. Make an honest assessment of fire extent and request resources early if needed.

6. Building Height and Area

How tall is the building? How large is the footprint? Height determines ladder access and the difficulty of vertical operations. A single-story ranch is manageable with ground ladders. A five-story apartment requires aerial apparatus and significantly more resources.

Area determines whether your water supply and personnel can cover the building. A 1,200 square foot home is one thing. A 10,000 square foot commercial building with fire on one end may require multiple attack lines to control.

7. Exposures

What is around the fire building? Are there other structures close enough to be threatened by radiant heat or direct flame extension? Exposure protection is a key consideration, especially in tight urban settings where buildings are feet apart.

Identify all four sides plus the roof exposure for any taller adjacent buildings. If exposures are threatened, you may need to dedicate resources to exposure protection before or simultaneously with fire attack.

8. Weather and Wind Conditions

Wind speed and direction affect fire behavior, smoke movement, and ventilation operations. A strong wind blowing into the fire building through a window opening can create a wind-driven fire event. High winds make vertical ventilation extremely dangerous. Extreme cold affects water supply and firefighter performance. Extreme heat increases the risk of heat-related illness.

Note the wind direction relative to the fire building and factor it into your attack plan. If possible, approach and attack from the upwind side.

9. Water Supply

Is there a hydrant nearby? How far away? What is the expected flow? Is there a secondary water supply if the first one fails? If you are in a rural area without hydrants, how is your water shuttle going to work?

Water supply must be established early and must be adequate for the fire you are fighting. A working house fire requires 150 to 300 gallons per minute for the attack line alone, plus supply for backup lines and exposure protection. If your water supply cannot sustain that flow, your interior attack is on a clock.

10. Auxiliary Systems and Utilities

Does the building have a sprinkler system? Is it operating? Does it have a fire alarm system? A standpipe? Where are the utility shutoffs for gas, electric, and water? Are there solar panels on the roof that present an electrical hazard even after the power is cut?

Sprinkler systems buy you time. A working sprinkler system may have already controlled or extinguished the fire before you arrive. Do not shut down a working sprinkler system until you have confirmed the fire is out.

Gas utilities need to be controlled early if there is any possibility of gas feeding the fire or creating an explosion hazard. Electric utilities need to be controlled to protect firefighters from electrocution. Solar panel installations create persistent electrical hazards that cannot be fully de-energized by disconnecting the building power.

11. Access and Egress

How are you getting in? How are you getting out if things go bad? Are there multiple entry points? Are there barriers such as security bars, fenced yards, locked gates, or narrow driveways?

Identify at least two means of egress for every crew operating inside the structure. Ladder the building early. Place ground ladders at windows on every floor where crews may be operating. These ladders serve as secondary escape routes if the interior stairway becomes compromised.

12. Resource Status

What do you have on scene right now? What is en route? What additional resources do you need? The first-arriving officer needs to make an honest assessment of whether the resources available can handle the incident. If they cannot, request additional resources immediately. Do not wait until things get worse.

Calling for help early is not a sign of weakness. It is a sign of competence. The worst thing an incident commander can do is try to fight a fire with insufficient resources and get behind the curve.

13. Overall Risk Assessment

After evaluating all twelve preceding points, make a deliberate decision about your mode of operation. Is this an offensive fire where interior attack is justified? Is it a defensive fire where exterior operations are the appropriate strategy? Is it a marginal situation that requires close monitoring and a willingness to transition from offensive to defensive?

This is not a one-time assessment. Conditions change. The fire grows or is knocked down. Resources arrive or are delayed. Structural conditions deteriorate. Your size-up must be continuous, and your strategy must adapt to changing conditions.

The best fire officers I have worked with are the ones who are constantly reassessing, constantly updating their picture of the incident, and never locked into a strategy that the fire has already outgrown. Size-up is not a box you check. It is a discipline you practice on every single call.

First Due Co. was built around realistic size-up practice, giving you scenario after scenario to sharpen your assessment skills before the real thing. Train your size-up at firstdueco.com.