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January 2002: ESFR vs. Conventional Sprinklers

ESFR (Early Suppression Fast Response) sprinkler systems are designed to achieve fire suppression for a specific type of storage occupancy before the fire becomes fully developed. ESFR heads vary with K-factors of 11.2, 14.7, 17 and 25.2 with as well as pressures of 50 and 70 psi. In most cases ESFR systems have not been tested for non-storage occupancies.

Conventional sprinkler systems are designed to control a fire and prewet the surrounding area until it can become extinguished by the fire department or trained fire brigade. The sprinkler heads are smaller than ESFR heads and are designed to discharge lower pressures and flows. Conventional systems offer proper protection for manufacturing hazards such as flammable liquid and aerosol operations, injection molding and occupancies with shielded combustibles.

The main advantage of an ESFR system over a Conventional sprinkler system is the possible elimination of the requirement for in-rack sprinklers in rack storage areas. However if suppression mode sprinklers are obstructed or are not designed properly they will fail to suppress a fire and the results can be devestating. Specific detail to sprinkler design and installation is most important. The best ESFR guideline is Property Loss Prevention Data Sheet 2-2 "INSTALLATION RULES FOR SUPPRESSION MODE AUTOMATIC SPRINKLERS," which is published by FM Global and is available for free on their web site at www.fmglobal.com. The data sheet states there are a total of six known fires involving suppression mode sprinkler protection. In all of these incidents, suppression mode protection was successful and no more than four sprinklers operated. In the two incidents for which detailed information was available, the sprinklers involved were not obstructed.

It is critical that exact guidelines from Fata Sheet 2-2 regarding obstructions are followed. Some of the key problems found today in most ESFR systems are that:

- All ESFR sprinkler heads should be located a minimum of 12 in. horizontally from the edge of the bottom chord of open web joists and trusses.

- All ESFR sprinkler heads should be located a minimum of 12 in. horizontally from the edge of all light fixtures located below the sprinklers.

It is critical to provide adequate clearance from obstructions below ESFR sprinklers in order for ESFR sprinkler systems to work properly. One or two obstructed heads over a fire area could lead to an uncontrolled fire.

Another common problem found is that 1 hour fire rated partitions are recommended between areas protected by ESFR and conventional sprinklers.

There has always been the cost factor between ESFR and Conventional sprinkler systems and the following example has been cited many times.

New Building & Rack Storage Specifications:

- Warehouse 240 x 120 ft. (28,800 sq. ft.)

- 9 Double Row Racks (DRR); 13 sections long

- 2 Single Row Racks (SRR); 13 sections long

- 10 aisles
- Sprinkler spacing is 10' x 10', therefore there are 288 ceiling sprinklers
- In-rack Automatic Sprinkler (IRAS) spacing is 8'
- Rack sections are 8' x 4'
- 20' high rack storage
- 25' high building

Estimated Costs

- ESFR Head Installation = $180
- Conventional = $100
- In-rack Sprinkler = $100
- Additional Longitudinal flue sprinklers = $50
- Face Sprinklers = $50 for DRR
- Face Sprinklers = $35 for SRR

Sprinkler Configuration

Total Sprinklers

Conventional Cost ($)

Ceiling (C) only

288

36,000

C + 1 level of IRAS

442

51,400

C + 2 levels of IRAS

585

65,700

C + 3 levels of IRAS

739

81,100

C + 1 level of IRAS + 1 level of Face (F)

722

64,980

C + 2 levels of IRAS + 1 level of Face (F)

865

79,280

C + 2 levels of IRAS + 2 levels of Cube

1,125

91,890

C + 1 level of IRAS + 1 level of Cube

1,125

78,890

C + 2 levels of IRAS + 1 level of Cube +1 level of Intermediate (I)

1,422

100,890

C + 2 levels of IRAS + 1 level of Cube + 1 level of I+ + 1 level of F

1,682

113,500

C + 2 levels of IRAS + 1 level of Cube

1,962

127,080

C + 3 levels of IRAS + 2 levels of Cube + 1 level of I

2,259

143,000

The estimated cost to install the ESFR system is $51,840. Obviously the costs can be more or less depending on many variables (location, contractor, water supply {Pump and Tank}).

There are advantages to both Conventional sprinkler systems and ESFR systems. Conventional control mode sprinkler systems should be used for non-storage occupancies and where the strict guidelines of FM Data Sheet 2-2 do not permit ESFR systems. ESFR systems provide for a more economical and practical suppression mode sprinkler system in storage occupancies.