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New ESFR Obstruction Test Results

FPRFNFPA’s Fire Protection Research Foundation (FPRF) initiated a two-phase study on the effects of obstructions on the ESFR sprinkler system’s ability to suppress fires. Phase one, which was primarily a literature review on the topic, was completed in 2014 and the fire test results from the second phase are now published. The tests were performed on Group A Plastics in rack storage configurations protected by K-17 ESFR sprinklers.

It was shown that steel bar joists and steel bridging members can adversely affect the fire suppression efficacy of ESFR sprinkler systems, especially if obstructions are mounted within 8 inches beneath the discharge nozzles.

Update: The Fire Protection Research Foundation of NFPA published a webinar video discussing the full-scale fire test results on ESFR obstructions.

 

ESFR Sprinkler Obstructions

Early Suppression Fast Response (ESFR) sprinklers are commonplace in the protection of warehouses. The main differences, when compared to standard sprinkler systems, are the large amount of water dispersed (in the event of a fire) and the water discharge patterns. The ESFR sprinkler system’s biggest advantage is that it not only controls the fire, as is the case with standard sprinkler systems, but also suppresses it – often making it unnecessary for the fire department to intervene. However, obstructions impacting the sprinkler discharge pattern can affect the ability of the ESFR sprinkler system to suppress the fires.

Sprinkler system designers and installers have to worry about various types of obstructions consisting of both supporting and non-supporting structural members, with the latter including lights, plumbing, piping, gas lines, cable trays, conduits for electrical wiring and ductwork. Therefore, it is expected that the results from full-scale testing can be used to expand knowledge concerning acceptable thresholds for ESFR sprinkler systems with a variety of obstructions. This will allow for quantifying the effects of obstructions on ESFR performance and ultimately produce safer designs and sprinkler installations.

 

NFPA 13 Requirements For ESFR Installations With Obstructions

Current ESFR obstruction regulations require (with respect to storage height and supporting structural members):1,3

For obstructions based on non-supporting structural members, general rules on obstruction apply (NFPA 13 Sections 8.12.5.1-3). Obstructions are allowed if:3

If the obstruction does not satisfy any one of these requirements, NFPA 13 offers two potential solutions: eliminating the obstruction or adding sprinklers underneath the obstruction.
 

Storage Configurations Tested

All tests were based on a nominal storage height of 30 feet and a ceiling height of 40 feet. Rack storage areas consisted of double-row racks and two single-row racks separated by four-foot aisles on both sides. The tested commodity was cartoned unexpanded Group A Plastics.

K-17 ESFR sprinklers were selected for the fire tests, and were obstructed by (1) bar joists only and (2) a combination of bar joists and bridging members. ESFR sprinklers were spaced 10 feet apart and operated at two discharge pressures, 50 psi and 75 psi.

Dimensions of the bar joists and bridging members applied during these tests are typical for warehouse construction. For spans exceeding 60 feet, the selected joist depth was 36 inches. Smaller spans were represented by joist depths of 22 inches. The most commonly found joist depth that was tested was 30 inches. Joists may also be reinforced with bridging members made from one to two inch angle iron, providing lateral stability. Therefore some of the tests included bridging members, as a secondary obstruction, and in addition to bar joists, as shown in Figure 1.

Figure 1.  Sprinkler setup from bar joist and bridging member

Figure 1. Sprinkler setup from bar joist and bridging member

 

Fire Test Results

The test series results, detailed in Table 1, showed the following:2

– A 3 inch horizontal offset on a 30-inch deep steel bar joist with no secondary
obstruction activated the maximum permissible (12) sprinklers for a pass (Test #2)

– A 6 inch horizontal offset on a 36-inch deep steel bar joist with no secondary
obstruction (bridging member) activated only 3 sprinklers (Test #1)

Table 1. Fire Test Configurations and Results

Fire Test
Test 1
Test 2
Test 3
Test 4
Test 5
Primary Obstruction36 inch deep steel joist, edge of lower
chord 6 inches from centerline of sprinkler
30 inch deep steel joist, edge of lower chord 3 inches from
centerline of sprinkler
36 inch deep steel joist, edge of lower chord 6 inches from
centerline of sprinkler
36 inch deep steel joist, edge of lower chord 6 inches from
centerline of sprinkler
22 inch deep steel joist, edge of lower chord 6 inches from
centerline of sprinkler
Secondary Obstruction
None
None
1.5 inches by 1.5 inches bridging member, 1.5 inches horizontal offset from
sprinkler
1.5 inches by 1.5 inches bridging
member, centered below sprinkler
1.5 inches by 1.5 inches bridging member, 1.5 inches horizontal offset from
sprinkler
Number of Operated Sprinklers
3
12
1
1
23
Result
Pass
Pass
Pass
Pass
Fail
Test Conclusions

From the full-scale fire tests that were conducted, the following conclusions have been drawn:

 

Summary

Information gathered from these tests will be used as a technical basis for the NFPA 13 Technical Committees to develop new requirements and guidelines for ESFR sprinklers. However, given the advanced stage of publication of NFPA 13 2016 Edition, new requirements based on these test results will not be included in the upcoming revision of the standard.
 

References

[1] Obstructions and ESFR Sprinklers – Phase 1, Final Report, The Fire Protection Research Foundation, October 2014, One Batterymarch Park, Quincy, MA

[2] Obstructions and ESFR Sprinklers – Phase 2, Final Report, The Fire Protection Research Foundation, September 2015, One Batterymarch Park, Quincy, MA

[3] NFPA 13, Standard for the Installation of Sprinkler Systems, 2013 Edition, NFPA, One Batterymarch Park, Quincy, MA