ESFR Protection Of Exposed Expanded Group A Plastics

March 16th, 2015 Print This Post Print This Post

esfrESFR protection of exposed expanded Group A plastics is currently outside the scope of NFPA 13. Attempting to fill this gap, NFPA’s Fire Protection Research Foundation set out to develop experience with these types of commodities and gather data by initiating large-scale fire tests. The goal of these tests was to evaluate the necessary level of protection when ESFR sprinklers in rack storage configurations with no in-rack sprinkler protection are applied.

The effectiveness of vertical barriers installed in rack storage arrays with exposed expanded Group A plastics was studied in six large-scale fire tests1 (see test series summary below). It was expected that the installation of these barriers would enhance the ceiling sprinkler protection, therefore potentially eliminating the need for in-rack sprinklers. It was also expected that the installation of these barriers would stop the fire from traveling horizontally to the extent of the test arrays. In addition, the impact of blocked transverse flue spaces, a common occurrence in the field, was investigated.

The test results demonstrated that the effectiveness of these barriers is rather limited if flue spaces are blocked. During some of these tests the fire jumped the aisle and more than 12 sprinklers opened. NFPA considers the occurrence of either one of these criteria as a fail mark for the system protection. While the vertical barriers clearly have a positive effect on fire propagation, in all of the fire tests the barriers were breached and could not prevent the fire from traveling horizontally, in some of the cases even reaching the ends of the test array.

FIGURE 1.  UL Fire Test (B-1) For Exposed Expanded Group A Plastics With Vertical Barriers, ESFR Sprinkler Protection

FIGURE 1. UL Fire Test Of Exposed Expanded Group A Plastics With Vertical Barriers, ESFR Sprinkler Protection. 20-Foot Storage Height, 40-Foot Ceiling Height, K-25.2.
(Click To Zoom, Image Credit 6)

However, protecting 20-foot rack storage with K-25.2 (60 psi, 1.95 gpm/ft2) and vertical barriers showed surprisingly good results i.e., the fire did not jump the aisle and only six sprinklers opened. Nevertheless, the fire breached one of the (corrugated sheetmetal) vertical barriers and traveled horizontally to the extent of the test array (see Figure 1).

The outcome of this series of fire tests, perhaps, was disappointing, but it did help in the understanding of protection systems for exposed expanded Group A plastics. Most importantly the general feeling was that in-rack sprinklers indeed may not be necessary in a successful ESFR protection scheme.

Exploring this hunch further NFPA’s Fire Protection Research Foundation performed additional fire tests (see test series summary below) building on the experience from the previous test set. It was suspected that the blocked flue spaces may have caused the test failures. Hence the focus for these new sets of tests was on re-evaluating some of the previous protection schemes, but this time with the flue spaces no longer being blocked and maintained as prescribed per NFPA 13.

In each of these additional (four) tests a maximum of seven sprinklers (K-25.2) opened, receiving a pass mark for successful protection. It was confirmed that the vertical barriers delay the horizontal spread of the fire towards the ends of the test arrays and support the sprinkler system to control the fire spread. Furthermore it was concluded that 2-5:

Removal of the (flue space) blocking in the final four tests resulted in significant improvement in sprinkler performance.
8-foot aisle widths were a significant factor in the prevention of aisle jump, a wider aisle width may even have an additional positive effect.
Significant impact on the performance of the protection scheme is determined by sprinkler type, ceiling height and clearance to the commodity thereby influencing water penetration and number of operated sprinklers, and ignition location.

In summary, the final series of tests on ESFR protection schemes for exposed expanded Group A plastics were successful. It was demonstrated that a functional ESFR protection scheme for (open shelfing and) this type of commodity does not require in-rack sprinklers. This in turn will provide greater flexibility in the layout and operation of rack storage configurations. Nevertheless, the test results do highlight the importance of maintaining flue spaces. Blocking them can result in system failure.

The experiences gained and data gathered resulted in the formulation of new protection schemes suggested for adoption and publication in the 2016 edition of NFPA 13.

Fire Test Results For ESFR Protection With Vertical Barriers And No In-Rack Sprinklers

Investigated were double row rack arrangements with storage heights up to 40 feet and ceiling heights up to 45 feet, which are the respective upper limits for ESFR protection in NFPA 13. The commodity used in the fire tests consisted of expanded polystyrene meat trays, stored in plastic bags on hardwood pallets1.

Vertical barriers were installed in the racks with the expectation of inhibiting the horizontal fire travel, while reducing the potential for the fire to reach the extent of the test arrays. The vertical barriers were made of steel or plywood depending on the specific test at hand. Aisle widths were 8 feet.

All tests, with exception of the last four tests, some of the transverse flue spaces were blocked to simulate conditions in the field, where pallet loads of commodities are positioned adjacent to each other, not providing any space for the required transverse flue spaces.

The individual test results 1-5 for each of the test configurations are:

Test (A-1): 30-foot storage height, 35-foot ceiling height, K=16.8, pendent ESFR sprinklers, 35-50 psi of water pressure (declining after 6 sprinkler heads opening up), four steel vertical barriers spaced 20 feet apart, 60 transverse flue spaces blocked, 68-foot storage array width.
Test Result: 16 sprinkler heads opened with the fire breaching one of the vertical barriers. The fire did not travel to the end of the test array and did not jump the aisle.
Test (A-2): 20-foot storage height, 40-foot ceiling height, K=22.4, pendent ESFR sprinklers, 50 psi of water pressure, two steel vertical barriers spaced 16 feet apart, 18 transverse flue spaces blocked, 32-foot storage array width.
Test Result: 12 sprinkler heads opened with the fire breaching both vertical barriers. The fire traveled to both ends of the test array. The fire did not jump the aisles.
Test (B-1): 20-foot storage height, 40-foot ceiling height, K=25.2, pendent ESFR sprinklers, 60 psi of water pressure, two steel vertical barriers spaced 16 feet apart, 12 transverse flue spaces blocked, 32-foot storage array width.
Test Result: 6 sprinkler heads opened with the fire breaching both vertical barriers. The fire traveled to both ends of the test array. The fire did not jump the aisles.
Test (B-2): 35-foot storage height, 40-foot ceiling height, K=25.2, pendent ESFR sprinklers, 60 psi of water pressure, four steel vertical barriers spaced 16 feet apart, 72 transverse flue spaces blocked, 56-foot storage array width.
Test Result: 10 sprinkler heads opened with the fire breaching the first two vertical barriers. The fire did not travel to the end of the test array. The fire did not jump the aisles.
Test (C-1): 30-foot storage height, 40-foot ceiling height, K=25.2, pendent ESFR sprinklers, 60 psi of water pressure, four plywood vertical barriers spaced 16 feet apart, 60 transverse flue spaces blocked, 56-foot storage array width.
Test Result: 11 sprinkler heads opened with the fire breaching the central two vertical barriers. The fire did not travel to the end of the test array. The fire jumped the aisle.
Test (C-2): 40-foot storage height, 45-foot ceiling height, K=25.2, pendent ESFR sprinklers, 60 psi of water pressure, four plywood vertical barriers spaced 24 feet apart, 98 transverse flue spaces blocked, 56-foot storage array width.
Test Result: 18 sprinkler heads opened with the fire breaching the central two vertical barriers. The fire did not travel to the end of the test array. The fire jumped the aisle.
Test (D-1): 20-foot storage height, 30-foot ceiling height, K=25.2, pendent ESFR sprinklers, 30 psi of water pressure, plywood vertical barriers spaced 16 feet apart, no transverse flue spaces blocked, 32-foot storage array width.
Test Result: 7 sprinkler heads opened with the fire breaching one of the vertical barriers. The fire did not travel to the end of the test array.
Test (D-2): 25-foot storage height, 30-foot ceiling height, K=25.2, pendent ESFR sprinklers, 30 psi of water pressure, plywood vertical barriers spaced 16 feet apart, no transverse flue spaces blocked, 32-foot storage array width.
Test Result: 7 sprinkler heads opened with the fire not breaching the vertical barriers. The fire did not travel to the end of the test array.
Test (D-3): 30-foot storage height, 40-foot ceiling height, K=25.2, pendent ESFR sprinklers, 60 psi of water pressure, plywood vertical barriers spaced 16 feet apart, no transverse flue spaces blocked, 40-foot storage array width.
Test Result: 7 sprinkler heads opened with the fire breaching the central two vertical barriers. The fire did not travel to the end of the test array.
Test (D-4): 35-foot storage height, 40-foot ceiling height, K=25.2, pendent ESFR sprinklers, 60 psi of water pressure, plywood vertical barriers spaced 16 feet apart, no transverse flue spaces blocked, 56-foot storage array width.
Test Result: 7 sprinkler heads opened with the fire breaching the central two vertical barriers. The fire did not travel to the end of the test array.

Discussion Of First Six Tests

Considering the pass criteria of a maximum of eight open sprinkler heads for successful ESFR sprinkler protection in full-scale testing providing a 50-percent safety factor for a 12-sprinkler head design, the first six fire tests – with the exception of Test B-1 – failed. This test, based on a 20-foot storage height and K-25.2 ESFR sprinklers, passed with a more than 50% safety factor. However, it needs to be noted that the integrity of the vertical barriers was breached in all fire tests. As a result, the barriers could not stop the fire from traveling horizontally (towards the ends of the test arrays), see Tests A-1 to C-2.

Discussion Of Last Four Tests

All four fire tests passed: Tests D-1 to D-4. A maximum of seven K-25.2 ESFR sprinklers heads opened in each of the tests with none of the flue spaces blocked and maintained per NFPA 13. The lower storage heights of less than 25 feet were tested with a water pressures of 30 psi, whereas the higher storage heights, above 25 feet, had 60 psi of water pressure applied. The vertical barriers were breached in three out of four tests – with exception of Test D-2. The fire did not travel to the extent of the test arrays in all four test configurations.

References:

[1] Protection of Rack Stored Exposed Expanded Group A Plastics With ESFR Sprinklers And Vertical Barriers, 1st-6th in a Series of Six Tests, Final Report, The Fire Protection Research Foundation, November 27 2012, One Batterymarch Park, Quincy, MA

[2] Sprinkler Protection Criteria for Exposed Expanded Group A Plastics, Project Summary, 2014, The Fire Protection Research Foundation, One Batterymarch Park, Quincy, MA

[3] Protection of Rack Stored Exposed Expanded Group A Plastics With ESFR Sprinklers and Vertical Barriers, Seventh in a Series of Seven Tests, Final Report, The Fire Protection Research Foundation, June 28 2013, One Batterymarch Park, Quincy, MA

[4] Protection of Rack Stored Exposed Expanded Group A Plastics With ESFR Sprinklers and Vertical Barriers, Eighth in a Series of Eight Tests, Final Report, The Fire Protection Research Foundation, June 22 2014, One Batterymarch Park, Quincy, MA

[5] Protection of Rack Stored Exposed Expanded Group A Plastics With ESFR Sprinklers and Vertical Barriers, 9th-10th in a Series of Ten Tests, Final Report, The Fire Protection Research Foundation, November 11 2014, One Batterymarch Park, Quincy, MA

Image Credit:

[6] Reproduced with permission from “Protection of Rack Stored Exposed Expanded Group A Plastics, with ESFR Sprinkler and Vertical Barriers” Nov. 2012 NFPA Journal® Copyright © 2012. NFPA.

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