The "Anatomy & Physiology" Of the Structural Fireground

Past installments of this series introduced the strategic classification of building construction. Ordered strategically, based on perceived fire resistance, the five basic types of building construction were listed as follows: Type I — Fire Resistive...


Past installments of this series introduced the strategic classification of building construction. Ordered strategically, based on perceived fire resistance, the five basic types of building construction were listed as follows: Type I — Fire Resistive Type II — Non-Combustible Type IV...


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Past installments of this series introduced the strategic classification of building construction. Ordered strategically, based on perceived fire resistance, the five basic types of building construction were listed as follows:

Type I — Fire Resistive

Type II — Non-Combustible

Type IV — Heavy Timber

Type III — Ordinary

Type V — Wood Frame

Because a Type IV building is more robust and thus more fire resistive — strategically — than a leaner Type III building, they are listed out of order numerically. The August 2009 installment discussed Types I, II and IV. This month, we finish the strategic classification of building construction with Type III, Ordinary, and Type V, Wood Frame.

Before we get started, fireground decision-makers must keep in mind the fundamental function of building design and building construction. The purpose of a structure's gravity-resistance system — trusses, columns, girders, lintels, cables, purlins, joists, headers, buttresses, etc. — is to deliver the dead load and live load of the building to the earth as compression. That's it, nothing more and nothing less. After ensuring that all dead load and live load will be delivered to the earth as compression, the secondary function of building design and construction is to create a secure and comfortable habitat for human occupation.

Type III Ordinary Construction

Ordinary Construction is a cinch to identify. Just look for some kind of masonry, right? Well, yes — and no.

Remember the Command-O-Quiz at the beginning of the July 2009 article? Buildings such as the one shown in the opening photo feature concrete-block or tilt-up concrete walls. It was impossible to correctly answer the Command-O-Quiz until after you stepped inside and viewed the roof. Let's revisit the Command-O-Quiz: You are standing outside a concrete tilt-up big-box warehouse store. In one hand you hold a pencil, in the other hand a pre-plan form. After entering the date, name of the business, address, contact information and hydrant locations, there is a box that asks: Type of Building Construction? In this blank box you would enter "Type _":

  1. I
  2. II
  3. III
  4. IV
  5. V

If you know building construction, you know that there are two possible correct answers: the big-box warehouse store is either Type II, Non-Combustible, or Type III, Ordinary.

Once inside the building, if you look up toward the ceiling and see a wood roof — say a lightweight panelized roof system (metal plate connected trusses supported by glue-laminated girders that are in turn supported by unprotected steel columns) this structure would be classified strategically as Type III, Ordinary. Don't let the presence of unprotected steel columns throw you; the load-bearing roof structure is combustible, so, to keep it simple, the strategic classification is Type III, Ordinary. On the other hand, if you look up toward the ceiling and see that the roof load is delivered to the columns by unprotected steel girders and steel purlins, it is a Type II, Non-Combustible building.

Thus, we have two simple unifying characteristics for the strategic classification of Type III, Ordinary Construction:

  1. Exterior walls that are made of non-combustible material
  2. Interior load-bearing components (floor and roof structure) that are combustible

It doesn't matter whether the non-combustible exterior walls are made of brick, block, concrete, metal or adobe; if the roof and floor structure is made of combustible material, it is strategically classified as Type III, Ordinary. To keep things simple, there are two strategic categories of Ordinary Construction:

  1. Legacy, unreinforced (usually conventional)
  2. Contemporary, reinforced (usually lightweight)

As mentioned previously, whether legacy or contemporary, all Ordinary Construction features a non-combustible exterior accompanied by a combustible interior.

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