Following-up on last month's quick review of the five basic types of building construction, according to National Fire Protection Association (NFPA) 220, Standard on Types of Building Construction (2006 edition), this article looks at Type I, Type II and Type IV building construction from a...
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Following-up on last month's quick review of the five basic types of building construction, according to National Fire Protection Association (NFPA) 220, Standard on Types of Building Construction (2006 edition), this article looks at Type I, Type II and Type IV building construction from a strategic perspective.
Type I, Fire Resistive
Imagine that you are somewhere in North America gazing at a high-rise building. Can you guess what type of building construction it is? It doesn't matter whether you are in Seattle, Miami, Los Angeles, Montreal, Atlanta, Toronto, Honolulu or Chicago; if you are looking at a high-rise building, you are looking at a Type I, fire resistive, structure. Type I is perhaps the easiest of the five types to identify from the street and through the windshield.
Because the structural failure of a high-rise building would be a disaster — as evidenced at the World Trade Center — Type I is the only type of construction where structural failure due to a contents fire is not a strategic concern to fire officers. The structural failure of your house would be unpleasant and may cause a neighborhood fuss, but it would not be a disaster on the scale of a high-rise collapse. There has never been a collapse of a high-rise building due to a contents fire, not even in a Third World country. Thus I can offer you, free of charge, my personal guarantee:
I personally guarantee that your fire department will never experience a structure fire at a high-rise building. The guarantee never expires.
Most of you recognize that this guarantee is completely bogus; most of you know that it is impossible to have a high-rise structure fire. The anatomy of all high-rise gravity-resistance systems is concrete and steel. Concrete and steel do not contribute fuel to a fire, thus it is impossible to have a high-rise "structure fire."' However, there have been numerous and spectacular contents fires within high-rise structures. Recall from Part 1 (April 2009) that columns and load-bearing walls are the most important structural components of a building's "structural hierarchy." (Although they get all the attention, trusses are never number-one in the structural hierarchy.)
Consider a steel column with four hours of fire-resistive protection within a modern high-rise building. The idea behind this four-hour rating is that the stuff burning (contents and combustible finishes) will release its heat energy (be completely consumed) before the fire-resistive material protecting the column will allow heat to transfer to the steel column it is protecting. The basic idea is that furniture will not burn for four hours; the fire-resistive material protecting the structural steel will outlast the rapid oxidation of the contents. (Ever try to keep a sofa free-burning for four hours?)
This is good news for both the building and for the fire department. As mentioned, structural collapse (columns, girders, beams, bar joists, etc.) is not a strategic consideration during a contents fire within a high-rise building. However, the failure of non-load-bearing building components (suspended ceilings, partition walls, exterior curtain walls, interior decorative masonry, etc.) can be a significant strategic concern.
Type II, Non-Combustible
Every Type I, fire resistive, high-rise building starts its life as a Type II, non-combustible, unprotected steel frame building. However, not all Type II, non-combustible, buildings are transformed into Type I, fire resistive, buildings. Thus, we have Type II, non-combustible, construction.
During high-rise construction, as the steel frame climbs, the unprotected Type II hierarchy is transformed into a Type I, fire resistive, structure. This transformation is typically accomplished by spraying the unprotected steel (direct application) with a cementitious, gypsum-based product. Because they are the most important gravity-resistance component in the structural hierarchy, columns receive the thickest coating of fire-resistive material; the thicker the fire resistive coating, the longer the steel will be protected from the heat generated by a contents fire. Other methods of protecting structural steel include encasement in fire-resistive concrete, attaching gypsum sheetrock, suspending a fire-resistive ceiling membrane — or the direct application of a paint-like intumescent coating.