All Things Gypsum: Structural Integrity of Stair Towers
These are the outermost points in a debate that the building code creation process has embraced since September 2001, when the World Trade Center Towers in New York City collapsed and the Pentagon, in Arlington, Va., was gashed open; all the result of a coordinated terrorist attack.
After four years of code debate, it appears the real answers to the question lie somewhere in the middle of the discussion, for the debate has shown that while life-safety could be improved by making every building absolutely attack-proof, the practicality of accomplishing that goal is nil and the necessity for doing so in every instance is dubious.
In exploring the myriad facets of the issue, one argument that has repeatedly been made is that high-rise buildings merit a special place in the overall debate. Not only do the buildings have a tempting profile to a terrorist, proponents of the theory proclaim they also contain unique life-safety exposure risks for occupants. Using the Sept. 11 attacks as proof of this theory, this group has pushed building codes to make every high-rise building as attack-resistant as possible.
Final reportTo be fair, the National Institute of Standards and Technology's "Final Report on the Collapse of the World Trade Center Towers" seems to support some of the concepts promoted by this approach. For example, the report contains descriptions of instances where an improved communication response and better coordination between emergency services teams might have saved lives on this day.
But one area where the report does not fully support some high-rise theorists is in the concept of stairway and elevator shaft structural integrity requirements. Nothing in the report supports the notion that high-rise stairways and elevator shafts need to be reinforced to the severe degree proposed by some groups and individuals. And nothing supports the contention that stairs and shafts should be constructed solely of masonry or concrete, as has been occasionally proposed by some interests.
One example of the former is a concept currently being discussed that would require every stair shaft in a high-rise structure to comply with a requirement that it withstand "a 2 psi pressure test."
While that sounds interesting, the theory falls short on a number of levels, not the least of which is that no proponent of the concept has to date explained or described how to conduct the pressure test; and no one has yet explained the relevance or derivation of the 2 psi requirement.
While implementing a 2-psi threshold requirement would likely make stair shafts stronger-it is a criterion that is far in excess of anything currently written into a building code for a shaft or stair wall in any structure-simply making something stronger won't necessarily make the entire building safer. And without a defined test methodology to confirm compliance with the tolerance, the criterion is even less relevant.
Fire test hose stream testAnother approach attempts to equate the ASTM E 119 fire test hose stream methodology with system durability. This old chestnut tries to suggest that a system that passes the optional (full-burn) hose stream test method is inherently superior to a system that has been tested using the primary (dual specimen) test.
"Require all stair enclosures to pass the optional method hose stream test" proponents say, "because only those systems that pass a full-burn test are truly durable."
What this approach ignores is that the ASTM E 119 standard itself doesn't differentiate between the two hose stream choices (each carries equal weight in the eyes of the test method) and the test method makes no claims that the hose stream test has anything whatsoever to do with system durability. Again, what has occurred is an attempt to force more rigorous requirements-requirements that favor one material or system over another-on the code without explaining exactly what benefits compliance with the requirements would provide to society.
So, is the gypsum board industry so curmudgeonly that it is resistant to change when it comes to the issue of stair and shaft structural integrity requirements? Absolutely not. Our industry has shown itself to be adaptive and innovative with proprietary and generic products when building code requirements have changed or when marketing opportunities have arisen. And if contemporary building codes modify life-safety requirements, our industry will certainly adapt.
However, as the debate over stair and shaft structural integrity rages, it would be helpful if a handful of basic concepts were honored by all parties:
The requirements for stair integrity should be equitable to all parties involved. Writing requirements so as to either exclude time-tested systems produced by one industry or to favor systems from another industry is clearly unfair. It also would likely drive up the cost of building construction by eliminating choice.
The threshold requirements should have, at a minimum, some basis in technology. Picking threshold requirements that are either so rigorous that they are unattainable or so vague that they have no basis in research or data serves no purpose. Threshold requirements have to be related to real-world situations; simply mandating a high limit value based on a worse case scenario or a single catastrophic event without realistically relating the limit to relevant previous or potential future events is useless.
The threshold requirements should not be written in a vacuum. Creating structural integrity requirements for stair towers without relating those requirements to other elements of the building could lead to situations where the interior elements of the building are significantly more durable than the floors, roof or exterior skin. What sense is there in constructing a building that could conceivably have its floors or exterior envelope destroyed by an explosive device but have its stair towers remain intact?
Code language for integrity requirements should reflect the use of readily available consensus test methods or standards to the maximum possible extent. Contemporary building codes increasingly use consensus standards as their technical backbone. In keeping with that philosophy, any test methodologies incorporated during the stair tower code language modification process should reference consensus standards or be derived using a consensus process. In addition, the standards should facilitate or be adaptable enough to allow the use of a variety of products or should be written in such a manner as to allow for comparison between standards written specifically for different products.
Like all aspects of the code-creation process, the move toward creating code language that is a derivative of the events of Sept. 11 must be accomplished using a completely transparent process; to do otherwise could potentially place adopting jurisdictions at risk of legal action.
In addition, the process must respect the technologies created by a multitude of industries and the economics of the modern building construction process. Foremost, any code modification must prove that the benefits derived from the change improve a legitimate life-safety issue and that the costs of the change, monetary or otherwise, are fully justified.
If you read this article, please circle number 341.