HORIZONS
Jeff Griffiths, CSI
The ancient principles of Yin and Yang have given rise to many philosophies, including those underlying modern passive and active fire protection. Yin and Yang have always been complementary forces, unseen (passive) and seen (active), that interact to form a greater whole as part of a dynamic system. Any attempt to eliminate one element in favor of the other has its risks, giving rise to the inevitable need and emergence of the missing element that restores balance. Such has been the case over the past decade in the effort to maintain a balanced approach to fire protection in all types of buildings.
In October 2003, for example, a U.S. manufacturer of sprinkler heads and fire equipment accessories sought to demonstrate how a solely active fire suppression system could replace the need for passive fire-rated glazing. With the help of Underwriters Laboratories (UL), this manufacturer constructed six test assemblies made up of three 6.4 mm (¼-in.) tempered glass panels butt-glazed together to form a 4 x 4.26-m (13 x 14-ft) wall attached to the face of UL’s test furnace.
Each test assembly used either its vertical pendant or sidewall window sprinkler spaced at various distances from the glass face. The furnace temperature settings followed the time/temperature curve established by ASTM E119, Standard Test Methods for Fire Tests of Building Construction and Materials, and the equivalent UL 263, Fire Tests of Building Construction and Materials. Temperature probes were placed at various locations on the non-fire-side glass surface for monitoring purposes.
At the end of a half-dozen of the two-hour tests, no probe recorded a temperature higher than 70 C (158 F). By relying solely on water dispensed at 76 L/min (20 gpm), the sprinklers seemed to have supplanted the need for passive fire protection. The staff at the UL test laboratory apparently saw no need to conduct the final phase of both the ASTM E119 and UL 263 test requirements—the application of the hose stream.
The next logical step for this manufacturer was to share its invention with code officials and the construction community. It submitted the test documentation to the International Code Council Evaluation Service (ICC-ES) for review. This resulted in the 2007 issuance of Acceptance Criteria (AC) 385, Acceptance Criteria for Special-purpose Sprinkler Heads Used with Fixed Glazed Assemblies to Provide a Fire-resistance-rated Wall Assembly. Not only was this big news among fire-rated glass manufacturers, it was also the first supposed ASTM E119 test conducted and passed while relying solely on an active suppression system. It gave rise to the first assembly deemed a fire-resistive wall without ever passing the hose stream test. The sprinkler head manufacturer had achieved a proverbial ‘twofer.’
Implications for glazing?
The proposed ICC-ES acceptance criteria stated:
Because the sprinkler heads are used to limit the rate of heat transfer through the glazing, the ASTM E119 test method and test assembly are modified to take into account the sprinkler heads and their discharge.
Given the intumescent properties of interlayers contained within the various makeups of fire-resistant glazing, and their demonstrated ability to limit the rate of heat transfer through glazing components, some manufacturers and experts in fire-rated glass circles felt the logical follow-up would be that the ASTM test method should be modified for glazing products as well.
The ‘pass’ for sprinklers was also perplexing given the common knowledge both wet and dry sprinkler systems have a documented rate of failure. In a 2006 study, “An Analysis of Automatic Sprinkler Reliability Using Current Data,” published by the National Fire Protection Association (NFPA), John Hall Jr. states:
The new estimates are that sprinklers failed to operate in 7% of structure fires (reported in NFIRS [National Fire Incident Reporting System] 5.0 in 1999–2002, after adjustment for errors in coding partial systems). The percentage varies from a low of 2% for apartments to a high of 14% for storage properties. The percentage rises to 9% if all types of automatic extinguishing equipment are included. This primarily reflects dry chemical systems used in public assembly properties. Two-thirds (65%) of the sprinkler failures to operate were because the system had been shut off before the fire. Another one-sixth (16%) occurred because manual intervention defeated the system, for example, by shutting off the sprinklers prematurely. Lack of maintenance accounted for 11% of the sprinkler failures to operate and 5% occurred because the wrong type of system was present. Nearly all failures were therefore entirely or primarily problems of human error. Only 3% involved damage to system components.
The same conclusions are supported by numerous other studies prior to those Hall cites. The sprinkler head manufacturer did not demonstrate elimination of human error and equipment failure as part of the modified test procedure, and it was not apparent whether ICC-ES had considered the need for any such evidence.
Hall also points out:
Effectiveness tended to be associated with a small number of sprinklers operating. When only one sprinkler operated, performance was effective 95% of the time. This fell slightly to 94% when two sprinklers operated, to 91% for three sprinklers, 89% for four to 10 sprinklers, and 81% for more than 10 sprinklers.
This should lead to a concern that the longer the run of glass, the greater the risk of the sprinklers failing to properly wet the glass in order to maintain a sufficient barrier to temperature rise and avoid subsequent glass breakage resulting from thermal shock as the fire spreads. This author sees a correlation between the fire spreading and causing more sprinklers to be activated and the amount of water discharged being reduced, increasing the risk of the glass being overheated.
