The protection challenges for storage commodities have increased with the storage of more plastic commodities, whether cartoned or uncartoned, expanded or unexpanded. Building heights have also increased, particularly with the use of high-bay storage using automated storage and retrieval systems.
The use of ceiling-only sprinklers has not been an effective method for suppression or control of rack storage fires when the ceiling height exceeds certain limits and/or the stored commodities are exposed or expanded plastics. This has concentrated the minds of the fire sprinkler community in search of effective solutions to this challenge.
The concept of using horizontal barriers and large K-factor extended coverage storage sprinklers as in-rack protection came from observations and early results of The Fire Protection Research Foundation’s (FPRF) Exposed Expanded Group A Plastic Test Series. This research was conducted to look at ceiling-only sprinkler protection for rack storage of exposed expanded Group A plastics. Protection schemes for these applications have been outside the scope of the NFPA Standard 13, chapter 17 (see Figure 188.8.131.52 “Exposed Expanded Plastics”). FM Global Data Sheet 8-9 does provide design criteria for ceiling-only protection of exposed expanded plastics with ceiling heights up to 12.2 metres using a specific brand of sprinkler. However, the water demand is extremely high. The FPRF wanted to reduce the water demand and elected to test using vertical barriers on every other rack upright or approximately 4.9 metres apart.
After a series of several tests, the FPRF proposed a suggested design for NFPA Standard 13 using vertical barriers. The basics of the design: 12.2-metre ceiling height, 10.7-metre storage height, 2.45-metre aisle width, vertical barriers at 4.9 metres intervals, K-25.2 Pendent ESFR sprinklers installed at the ceiling, 4.1 bar minimum for each sprinkler, the flow to be calculated for a minimum of 12 sprinklers operating and a hose stream allowance of 946 litres-a-minute for a 60 minute water supply duration.
However, because of water distribution tests that were being conducted on the performance of a K-25.2 extended coverage pendent storage sprinkler as an in-rack sprinkler, a decision was made to conduct a series of fire tests at UL using a horizontal barrier and/or multiple horizontal barriers and not the vertical barriers being used in the FPRF test series. It was postulated that the K-25.2 extended coverage pendent storage sprinkler would provide superior performance because of its extended coverage spray pattern, its ability to flow a large quantity of water at low pressure due to the 25.2 K-factor, and the fast responding characteristics of its low thermal mass solder releasing element.
Subsequent tests produced successful results on both exposed expanded and cartoned unexpanded plastic commodities for various storage and building heights. Test results showed high levels of fire control with very few fire sprinklers opening during the tests resulting in lower overall water demand of the fire sprinkler system compared with current ceiling-only protection schemes. Additional tests have also shown this system as being effective in protection of multiple row racking arrangements, in the case of 1.2-metre narrow aisles and for storage of flammable liquids. The additional tests have also indicated the suitability of this system as an alternative to existing ceiling only protection schemes where water supply is a major issue.
The intent of these tests is to create a pool of data for design professionals to use in a “performance-based design” in order to protect commodities and arrangements beyond the current scope of the NFPA Standard 13 or other International standards.
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