Columns

NFPA Journal®, January/February 2005

Another Factor?
The article about the fire in Paraguay listed several aspects that contributed to the high life loss. One aspect that appears to have not been specifically listed as a contributing factor was the exposed foam plastic beneath the roof deck. Exposed foam plastics have been highly regulated in the U.S. for a number of years. Building codes, including NFPA 5000™, Building Construction and Safety Code™, require foam plastics to “be separated from the interior of a building and from plenums by an approved thermal barrier.” Although the article indicated that the burning characteristics of the foam plastic were not available, it would be interesting to learn the extent the exposed foam plastic contributed to fire propagation.

Douglas H. Evans, P.E.
Fire Protection Engineer
Clark County Building
Las Vegas, Nevada

Enclosure system
It was painful to learn of the tragic choices made by some of the store personnel described in the article “No Exit” by Eduardo Alvarez, SFPE and Jaime A. Moncada, P.E., SFPE, (NFPA Journal November/December 2004). I hope that there’s a way that NFPA and other fire protection professionals can assist emerging countries improve the Life Safety requirements in their Building Codes to prevent another tragic incident such as this.

While the article references the potential controlling effect that a sprinkler system would have, I am puzzled as to why there is no reference to the effect a two hour fire-rated enclosure system around the duct would have had. An enclosure system around the duct shown on page 47, is designed to contain the fire within the duct and if utilized, may have provided enough time for the fuel source to be depleted and the fire to extinguish preventing further building damage or more importantly loss of life.

Field-applied, flexible blanket wrap products are well established in the U.S. and are utilized to provide a fire-rated enclosure around kitchen exhaust ducts. These wrap style systems install quickly and are relatively inexpensive. Through independent laboratory testing, wrap systems have demonstrated they can contain a grease fire within the duct itself as well as prevent room fires from entering the ductwork and using it as a conduit to spread to other areas of the building outside the room of origin. Duct enclosure systems comply with nationally recognized fire test standards such as ASTM E1226, specifically for this application and achieve an hourly fire resistance rating along with a specified clearance distance to combustibles which typically is as low as zero.

Christopher E. McPhillips
Fire Protection Specialist
Unifrax Corporation

Explosion in a silo of wood particles
The July/August 2004 issue of the Journal gives (on pages 54-55) an account of how an explosion occurred in a silo containing sawdust and wood chips, and an explanation in terms of a dust explosion is given. I wonder whether the investigators also considered the possibility of a smoke explosion. We are told that the wood had been smoldering “for hours” and it is well known that smoldering is very productive of smoke. Smoke is rich in ignitable substances, partly CO but, more importantly in the case of smoldering combustion of wood, breakdown products of the cellulose broadly describable as “tars and oils.” In the immediate neighborhood of the smoldering, there is too little air for these to ignite: in any case, they might be at a concentration above their upper flammability limit. The cavity described in the incident under discussion might have had the following effects leading to a smoke explosion:

Dilution of the “tars and oils” to a concentration within the flammable range and accompanying enhancement of air supply
Because of the improved air supply, a smoldering-to-flaming transition at the cavity surface providing an ignition source for the “tars and oils.”

The investigators might well be right in concluding dust explosion behavior, but did they consider the alternative? The smoke explosion behavior invoked herein is of course well documented in sources including the monumental 1984 tome by the late P.C. Bowes of the Fire Research Station, UK. He makes the point that if, in a “spontaneous heating test” for a wood or a coal in a laboratory oven, smoke is being released for the operator to open the oven door is dangerous because of a possible smoke explosion; he or she should wait until smoking ceases. In such tests combustion propagation is by smoldering and the similarities with the incident under consideration are obvious.

J.C. Jones
University of Aberdeen, UK

In this Section:

			Buzzwords Quality and reliability of installed systems

			First Word Looking back on 2004: Q&A with James Shannon

			Firewatch Explosion destroys fire station

			Heads Up When sprinklers aren’t there

			In Compliance Code cycle revisions

			Ins & Outs Meeting the research needs of NFPA

			Mail Call Letters to the editor

			Outreach Addressing everyone’s life-safety needs

			Structural Ops Managing overhaul operations

			What's Hot Product spotlight