Next Generation In-Rack Sprinklers
In-rack sprinklers are used when ceiling sprinkler only protection is no longer adequate to protect the rack stored commodities. Well known disadvantages of current in-rack sprinkler designs are (1) additional costs and (2) additional risks of damage of the sprinkler heads during loading and unloading of the racks. Next generation in-rack sprinklers have been UL-tested that are expected to improve on conditions on both fronts.
A new in-rack sprinkler system design1 has been evaluated in a series of fire tests at the Underwriters Laboratories. These next generation in-rack sprinkler designs are based on a k-factor of K-25.2 and are modified with a pendent sprinkler deflector designed to distribute water droplets across the shallow space available in a rack.
The anticipated results are that these modified extended coverage sprinkler heads can be spaced apart further horizontally due to their wider coverage area and vertically due to the modified droplet distribution of the larger K-25.2 heads. This in turn is expected to reduce installation costs, because less sprinkler heads and less (water) piping need to be installed. Also extended coverage in-rack sprinkler configurations eliminate the need for face sprinklers thus significantly reducing the potential for damage of the in-rack sprinkler system. In addition, only in-rack sprinklers in longitudinal flue spaces were installed.
Perhaps most importantly, the required water demand of the resulting in-rack sprinkler system is sharply reduced (up to 60% reduction) when compared to an equivalent ESFR system. In many cases, and usually an issue in older municipalities where city water pressures are low, this will avoid purchasing and maintaining an expensive fire pump to operate an ESFR system.
Fire Testing Of Next Generation In-Rack Sprinklers
A series of full-scale fire tests2 have been performed to evaluate these new in-rack sprinkler system designs. Objectives for these fire tests include:
• Reduce the number of in-rack sprinkler heads for a given scenario – when compared to
the same scenario using conventional in-rack sprinklers (using K-8.0 or K-11.2
quick response sprinklers)
• Reduce overall vulnerability of the sprinkler heads to mechanical damage, as a result of
fewer inracks installed and no face sprinklers being required.
• Confirm lower water demand for proposed sprinkler protection schemes.
The following high-hazard commodities were tested:
• Exposed expanded Group A plastics
• Cartoned unexpanded Group A plastics
Storage Configurations Tested
Table 1. UL Fire Tests – Extended Coverage In-Rack Sprinklers
| Exposed Expanded Group A Plastics | Cartoned Unexpanded Group A Plastics |
|
|---|---|---|
| Storage Height/Ceiling Height | 35 ft/40 ft | 43 ft/48 ft |
| Rack Type | Double Row Racks | Double Row Racks |
| Horizontal Barrier | 20 ft elevation | 30 ft elevation |
| Sprinkler Type (Ceiling/In-Rack) | K-16.8 ESFR/N-252 EC | N-252 EC Pendent/N-252 EC |
| Water Demand (Ceiling/In-Rack) | min. 1428 gpm/min. 414 gpm | min. 828 gpm/min. 414 gpm |
| Total Water Demand | min. 1428 gpm* | min. 828 gpm* |
| Water Pressure (Ceiling/In-Rack) | 50 psi/30 psi | 30 psi/30 psi |
| * The in-rack sprinkler water demand is not added to the water demand of the ceiling sprinklers, because horizontal barriers are applied. Total system water demand is represented by the ceiling water demand only. Hose stream water demands are excluded. For comparison, K-25.2 ESFR, 12 (15) sprinklers at 60 psi, require a water demand of approx. 2340 (2925) gpm. Actual water demands may be higher than calculated due to friction losses. | ||
Figure 1. Test Configuration Exposed Expanded Group A Plastics (Click to Zoom). Image Credit2
All tests2 were set up with in-rack sprinklers installed directly below the horizontal barriers made of 3/8 inch plywood and an 8 ft aisle widths, Table 1. The exposed expanded test configuration used a single level of in-racks at the 20 ft elevation level, Figure 1. Cartoned unexpanded test configurations used a single level of in-racks at the 30 ft elevation level (NFPA 13 2013 prescribes three (four) vertical levels of quick-response in-rack sprinklers with (without) face sprinklers). Additional tests with cartoned unexpanded Group A Plastics on double row racks for a 43 ft storage height and a 48 ft ceiling heights used two levels of horizontal barriers and in-rack sprinklers (at 20 ft and 40 ft elevation levels). No in-rack sprinklers were used in transverse flues of the racks.
Test Results
Despite having fewer levels of in-rack sprinklers applied during these fire tests, it was demonstrated that the fire was contained within the rack bays and few ceiling and in-rack sprinklers activated during the fire tests, see Table 2. No ignition in the target arrays occurred.
Table 2. Fire Test Results – Extended Coverage In-Rack Sprinklers
| Exposed Expanded Group A Plastics | Cartoned Unexpanded Group A Plastics |
|
|---|---|---|
| Ceiling Sprinkler Operated | 1 | 1-3 |
| In-Rack Sprinkler Operated | ||
| * when two horizontal barriers at 20 ft intervals were used, up to 5 in-rack sprinklers activated at 20 ft level and one in-rack sprinkler activated at 40 ft level. | ||
The Codes
The tested or proposed sprinkler configurations based on extended coverage in-rack sprinklers have not been adopted in any of the model codes as of yet. However, if the storage scenario at hand is similar to the successfully tested storage configurations, then these new protection schemes may be reviewed by the AHJ as an ‘alternative means and methods’ to the prescribed regulations.
References
[1] “The Return Of The In-Rack Sprinkler”, Fire Protection Engineering, Steve Wolin P.E., 3rd Quarter/ 2015, SFPE Magazine®, Copyright © 2015, magazine.sfpe.org [2] “Suppression, Detection and Signaling Research and Applications Symposium (SUPDET 2014): Storage Protection Using Horizontal Barriers and Large K-Factor, Extended Coverage In-Rack Sprinklers”, Thomas Multer, Christina Francis, P.E., Reliable Automatic Sprinkler Co. Inc., March 2014, nfpa.org
