2x4 trusses are a different combustible than the kraft paper. Put a match to the kraft paper when vertical, and a fire will likely grow. Put a match to almost any 2x4 and almost always -- not a problem.
That is why 2x4's are allowed in combustible construction, while paper with del H,c > 1,000 BTU/sq. ft was not intended, generally, to be allowed there. However, kraft paper in the horizontal direction, with blown in insulation over it, won't burn even if it has a heat of combustion greater than 1,000 BTU/lb. There is not enough oxygen. This is a compelling question. The answer to the question involves, if one allows such thing, rational thinking that extends beyond the pure prescriptions and solicits a solution that may not have been originally conceived, but nonetheless a solution in compliance with the intent of the Standard. The Standard is -- to protect to a reasonable degree: life, property and the environment. The word "reasonable" is left undefined, so that "what is reasonable" may be interpreted by us, using judgment, subject to the risk tolerance level at each time and situation of application. A small risk such as we discuss here, may not be tolerable in the MCCA of Boston, but it might well be tolerable in Westwood, CA. I think better decisions are made by "we", we being large samples of stakeholders with moderate-to-in-depth knowledge of the subject. It is realized that there may be prescriptive purists that reason kraft paper should be removed barring del Hc testing. While the AHJ is the final decision, that does not mean we have acquired the best judgment. There is a danger in allowing one individual to make important decisions for several reasons: 1. the individual may hold an "unreasonable" view in a particular subject (where "reasonable" iz determined from the opinions of a crowd of knowledgeable and interested persons, including the building users-- whom normally are externalized to the risks we "experts" impose on them) 2. the individual may be under the influence of coin, 4. the individual may have allegiance to friends 5. the individual may be risk averse, being close to retirement. 6. the individual may be risk friendly, being close to death. 7. the truth may be too messy to be neatly packaged, and an overly simplified decision ensues, I believe most difficult-to-package questions are solved better using group think and open voting, not just because the open debate lifts the curtain enshrouding the Wizards-of-Oz, exposing weaknesses in expert[2] and novice opinions alike, but because open group think is proven to be a highly (if not the most) accurate method [1] of assessing sticky risk assessments where prescribed, answers are all-but-impossible to achieve and where probably *not *everyone will be satisfied with the answer. Also, the very process of an open-debate-and-decision process can sharpen the judgment of curious future decision makers whom are cutting-their-teeth in risk assessment and mitigation. We benefit from open debate; a good critic is a terrible thing to waste. Scot Deal Excelsior Fire/Risk Engineering [email protected] [1] Tetlock, P., Gardner, D,, "Superforecasting: the Art and Science of Prediction. 29 Sept 2015. [2] Voeten,E.; Dart Throwing Chimps and Op-Eds, http://goo.gl/OA4GDm 2nd-to-last and last paragraph. _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org
