Size-Up and Risk Benefit for Small Commercial Structures

By Katherine Ridenhour

Do you understand the critical importance of doing size-up thoroughly and properly before committing resources to the firefight?  Are there different size-up factors for commercial structures fires versus house fires? And, are there facts we need to know prior to the alarm before we commit our firefighters inside these types of structures?

Size-up must always include a risk/benefit analysis to truly identify the critical issues on the fireground to allow you to make the most important strategic decision–do we go interior or not? Therefore, we must understand the concepts of fire behavior and how fire behaves in different building types and construction, how high heat and fire conditions affect structural stability, and what our resource levels and equipment capabilities are prior to identifying Go or No Go–offensive or defensive.

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Most principles of size-up will apply to both types of structures; however, fighting fire in a small commercial occupancy is different than fighting fires in single-family dwellings. You have  probably heard of COAL WAS WEALTH, WALLACE WAS HOT or some variation of this size-up model. It’s a good place to start to understand various size-up factors, especially during preplanning, class discussions, or perhaps assessment centers. However, whether you are the incident commander (IC) or the first-due officer or firefighter, you need to understand the differences in building construction, fire behavior, and resource needs prior to committing resources. The size-up factors listed will assist you in making the safest and most effective decisions on small commercial structure fires.

Value, Time, Size (VTS) Model

The absolute best risk benefit analysis model that helps us confidently understand true risk is the Value, Time, Size Model by Assistant Chief (Ret.) Stewart Rose, Seattle (WA) Fire Department. This model has helped thousands of firefighters to become more confident and competent ICs. Your first objective on scene per Chief Rose is to Identify the Problems PRIOR to providing your solutions. It’s the first step before you can forecast the probabilities and determine your real risk benefit.

In a nutshell, VTS involves answering three questions before making entry. If any one of them is answered NO, it dictates a defensive fire until  conditions change. Question 1: Is there Value in sending my firefighters in: Are there lives that are savable or property that can be safely saved? Question 2: Is there Time to send my firefighters inside? Is high heat or fire impinging on structural elements? Question 3. There is a Yes or No answer for the Size of fire: Do we have enough water and enough personnel to apply the water and the right kind of equipment to combat the fire? If all three of these questions can be answered Yes, it’s an offensive fire. If any one of the questions is answered No, it is a defensive fire. You may be thinking that if there is a verified savable life, we will risk everything. But, if the building is in imminent danger of collapsing (no Time) or we do not have the right resources (water or equipment) on scene (no Size), then we cannot and should not GO.

When dealing with small commercial fires (focusing mostly on standalone structures  around 10,000 sq. ft.), first- and subsequent-due personnel must focus on identifying modern fire behavior, commercial construction techniques, and knowing if their resources and equipment match the fire situation.

The most important factor in sizing up small commercial structure fires is this: THIS IS NOT A HOUSE FIRE!  As a student of the fire service and an avid reader of line-of-duty-death reports, it becomes apparent that there are more deaths among firefighters in commercial fires than in house fires. Generally, over the years, firefighter death rates are two times greater in commercial fires, and multiple firefighter deaths are much higher at a single incident in commercial occupancies. When it comes to civilian death rates, according to the National Fire Protection Association, there were 2,640 civilian deaths in residential homes and only 12 civilian deaths in commercial structures. from 2010 to 2014. Do these statistics need to be considered when we perform size-up and risk benefit analysis? Absolutely. They become factors when making fact-based Go or No-Go decisions.

It has been my experience and that of many of the experienced commanders I know that when arriving at commercial buildings on fire, most merchandise has been destroyed by heat or smoke, rarely is there a chance to save someone (only in extreme circumstances is anyone trapped inside), and most of those structures will have to be torn down. In other words, in “most situations in which we find the fire beyond the incipient stage, the merchandise is a total loss and the building will be rebuilt, regardless of our “heroic” efforts. Keep this information in mind: If fire is inside a lightweight truss, it is a defensive fire; if the survivability profile (or Value) changes to No or zero during your ongoing size-up or if Time or Size changes to No, keep and stay defensive; just protect exposures. Zero Value, zero Time, or zero Size means there is no justifiable reason to initiate an “aggressive” offensive attack.

Thorough Size-Up Needed Anyway

However; that does not excuse us from completing a thorough size-up. With the knowledge that (a) the vast majority of small commercial fires do not have anyone inside; (b) we are the people at greatest risk based on statistics; (c) once fire is inside the attic space of especially lightweight engineered wood, we can no longer be under or on top of the roof; and (d) typically regardless of the size of the fire, there is rarely any merchandise that becomes salvageable and any kind of structural damage means the buildings gets torn down anyway, a complete size-up becomes key in evaluating the risk benefit model so that we make factual, realistic, and safe forecasts and decisions.

What to Remember About Small Commercial Structure Fires

So, what is different in a small commercial structure as compared to a single family home? Obviously, the types of construction and building features will pose different challenges, and the internal spaces we are dealing with are larger–much larger. We are generally knowledgeable about small compartment fires–i.e., house and apartment fires. Knowing how fire behaves in larger spaces, in void spaces, and in various attic or cockloft spaces is information we should have before the fire starts. 

Do you know your basic fire behavior principles? Understanding fire indicators from an initial size-up is elemental in helping you determine not only your strategy and tactics but also your risk benefit decisions. Observing smoke “push” faster in one location over another generally directs you to the origin of the fire. Observing gray smoke becoming darker indicates more fuel being burned, more incomplete combustion, and a general deterioration of survivable conditions. Dark smoke turning lighter can indicate water is getting on the fire, fuel is becoming consumed, or the fire is going into decay or to an underventilated stage–possibly a very dangerous time to enter because of the potential for delayed flashover, explosive growth stage, or backdraft. Fire exiting a roof or under eaves obviously indicates fire in attic area, and exterior smoke can tell you the fire origin as well as the stage of the fire. Smooth or laminar flowing smoke that becomes turbulent is a warning that ignition is imminent. Remember this: Commercial structure fires have a low life hazard for civilians, yet a high loss hazard for firefighters.   

Building construction techniques are always evolving. Commercial structures are not built with firefighter protection in mind. They are built as cheaply as possible. Generally, there are no fire protection systems that aid in containing fire or smoke or have built-in systems to hold the fire to a manageable size.

A common issue for small commercial occupancies is rapid fire spread, which causes early collapse. Typically, these structures have large open spaces and common attic or cockloft spaces that are generally open and undivided, allowing rapid lateral fire spread above. These structures generally have high ceiling spaces with one or more false or drop ceilings that can hide smoke and fire on entry. They generally have higher fire loads than single-family dwellings, which means hotter and faster fires. The presence of overhangs or facades are common and dangerous in fire conditions. Couple these issues with potential access/egress issues, an irregular and an unfamiliar layout, and aisles of stocked items or highly combustible contents, and it becomes evident why fighting fires in these buildings is dangerous.

Common construction types for small commercial structures are Type 5 (wood frame and usually lightweight), Type 3 (ordinary noncombustible masonry exterior walls with wood floors or roofs members), and Type 2 (unprotected steel structural members).  However, there are many other types that can loosely be placed in the “hybrid construction” category, which will always have its own specific concerns. Fire spread and collapse concerns for various construction types are influenced by the era in which the building was built, but all seem to share some common issues that work against firefighters: long beam/truss spans; heavy roof dead loads (heating, ventilation, air-conditioning); alterations/additions by the occupant; and issues of aging, maintenance, and dubious repairs. To top it all off, most of the roof structures are lightweight construction regardless of the material used, again contributing to early collapse.

How Does Your Department Stand?

Do you know the characteristics of small commercial buildings and, equally as important, how fire behaves in these types of buildings? Do you understand that there are time limits on how long structural members will last before reaching their failure point?  These are questions that must be answered in your size-up phase and risk-benefit evaluation. Often, the signage relating to occupancy type on a commercial building can provide some answers regarding your risk benefit evaluation and the collapse/fire spread potential. For instance, the carpet/flooring showroom is going to burn faster/hotter and collapse more quickly than the insurance agent’s office–all things considered.

When it comes to resource and equipment needs, larger structures necessitate larger resources. Does your department send the same first-alarm complement to a commercial fire as to a house fire? Do you use the exact same equipment (i.e., hoselines, hand tools vs. power tools, and so) on a commercial fire as on a house fire? Most important, do you use the exact same tactics on a commercial fire as a house fire? Though there are many similarities, this isn’t a house fire! 

It’s elemental that you will need more resources on commercial fires than for a single-family dwelling fire.  But do you “preload” your response matrix to more readily implement safe and effective fireground practices early in the game, do you send the right kind of resources and the right kind of equipment for commercial fires?

As far as equipment needs is concerned, hoseline size is an easy difference to point out, but what about the number of personnel to effectively handle larger size handlines? Underwriters Laboratories studies support the use of big water on these buildings, so is it appropriate to pull a 1¾-inch handline when the size of the fire dictates the use of more water? What about the necessary power tools to perform forcible entry or overhaul? Does your rapid intervention crew team stage the same equipment on a commercial fire as a residential fire? Does your IC give the same orders to the crews as they would at a house fire?

The answers to all these questions should be: “We size up and evaluate the problems for each fire situation and make decisions based on our findings.” Unfortunately, that is not what happens; this is especially apparent when reviewing LODD reports or injury statistics. How many departments do you know of that have well-memorized arrival and assignment speeches for every situation instead of evaluating the problems and risk prior to deciding on tactics? Again, “Know your problems before you throw your solutions around” (Chief Stewart Rose) is the only way to justify your decision-making process when deciding strategy and deploying tactics.


KATHERINE T. RIDENHOUR, 30-year veteran of the fire service, is a retired battalion chief from the Aurora (CO) Fire Department. Her career encompassed 25 years in emergency medical services, technical rescue, and FEMA/USAR, battalion commander; past president of Women in the Fire Service; and five years as a volunteer firefighter. Her extensive teaching background includes strategy/tactics, command, conflict solution, leadership, and promotional preparation.


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