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March/April 2006

Retrofitting Warehouse ESFR Sprinkler Systems
When properly installed, ESFR sprinklers can obtain suppression of a fire in its early stages

By Charlie Bauroth, P.E.

• Warehouse redesign
• The ESFR Sprinkler System
• Warehouse sprinkler compliance
• Project lessons

You installed Early Suppression Fast Response (ESFR) sprinkler systems because they eliminate the need for in-rack sprinklers, allowing free movement of inventory and racks. In addition, when properly installed, ESFR sprinklers can obtain suppression of a fire in its early stages with the activation of usually less than six sprinklers. However, did you know that when not installed properly, or obstructed, ESFR sprinklers could be rendered useless?

For the ESFR system, an obstruction is something as small as one-inch wide straps, cable bundles, or other objects located below and within 12 inches horizontally from the sprinkler. Unlike identifying boxes piled up in front of a fire door, obstructions to ESFR sprinkler heads are not always easy to spot.

To demonstrate the importance of avoiding ESFR sprinkler obstructions, let’s look at a case study of an existing distribution facility in Texas.

Warehouse redesign
In 1989, a distribution company decided that their old warehouse, with its limited ceiling height of 15 feet clear space and concrete bunker construction, no longer met its needs for cost efficient storage and distribution. Therefore, they designed a new building of masonry non-combustible construction with dimensions of 600 feet by 1,000 feet for a total ground floor area of 600,000 square feet. Roof height was a maximum of 30 feet with a slope of less than 2 inches per foot. There were four, small two-story office areas totaling 30,000 square feet with the majority of the building being single- and double-row rack storage of product up to Group A plastic commodity in cardboard cartons with eight picking modules and separate shipping and receiving areas. Orders moved to shipping via a newly installed, sophisticated conveyor system.

The authority having jurisdiction (AHJ) wanted to see a firewall added to break the large open area into two parts. The sprinkler contractor for the job suggested a new technology recently developed in the late 1980s – ESFR sprinklers - that could eliminate the firewall requirement. The AHJ had heard about ESFR sprinklers and that they would actually suppress a fire, so he agreed that the firewall would not be required if the entire distribution center was protected by ESFR sprinklers.

A looped six-inch main at the ceiling that supplied 15 sprinkler risers protected the building. The risers fed 15 gridded wet sprinkler systems that used ESFR14.0 k pendant heads. The design for the sprinkler systems was 12 heads at 50 psi with the greatest system demand being 1,298 gpm @ 154 psi at the pump. The city water supply was originally boosted by a 1,500 gpm at 120-psi electric pump. A second back-up diesel booster pump, also rated for 1,500 gpm at 120 psi, was added in 1995.

Design and construction proceeded and the facility was completed and opened for use in 1991.

The codes in effect during construction of the building included the 1989 edition of NFPA 13, Installation of Sprinkler Systems.

This contained the following provisions on the installation of ESFR sprinkler heads:

• Sprinklers (ESFR) shall be positioned so that the deflectors are a maximum 14 in. and a minimum 6 in. below the ceiling.
• Sprinklers (ESFR) located above bottom of obstructions located at ceiling shall be positioned to meet value specified in Chapter 4 (standard heads)
• Sprinklers (ESFR) shall be positioned with respect to any fluorescent lighting fixtures, ducts, or any other obstruction more than 12 inches wide and located entirely below the sprinklers so that the minimum horizontal distance from the near side of the obstruction to the center of the sprinkler is not less than the value specified in Table 9-3.3.10.2.1 (shown below).

Distance of Deflector Above Bottom of Obstruction	Minimum Distance to Side of Obstruction, ft.
Less than 6 in.	1.5
6 in. to less than 12 in.	3
12 in. to less than 18 in.	4
18 in. to less than 24 in.	5
24 in. to less than 30 in.	6

The ESFR sprinkler system
In 1991, ESFR sprinklers were relatively new and not well understood by many in the fire protection industry. Many people in industry heard of them as a solution to the problem of in-rack sprinklers in storage arrangements, but were not aware that they could not protect all commodities or storage arrangements. Many installers, designers and insurance personnel were not aware of how critical it was to avoid obstructions and adhere to design specifications.

Full-scale fire testing has shown that ESFR sprinkler systems are very effective in extinguishing fires without the use of in-rack sprinklers when they are installed according to the manufacturer’s specifications and the sprinkler’s listing. However, ESFR sprinkler systems cannot protect all commodities and ESFR systems proved far more susceptible to obstructions than conventional time-tested sprinkler systems.

The basic thought process behind ESFR systems is to get as much water as possible as quickly as possible to the seat of the fire. To do this, large orifices are utilized with high-end head pressures to penetrate the fire and quick response links allow the heads to activate quickly.

The very force and volume of the water that makes an ESFR sprinkler so effective can also be its downfall. The water spray hitting seemingly minor obstructions close to the sprinkler creates a void or dry area on the opposite side of the obstruction from where the water spray from the sprinkler is striking it. As no or little water is in this dry area, a fire can grow unimpeded, and quickly, especially in rack storage. See sidebar.

As the concept driving ESFR sprinklers is to extinguish a fire quickly, any dry or shadow areas where water distribution is blocked allows a fire to spread and can quickly grow beyond the design area of the system, resulting in a catastrophic loss to the facility.

The Texas facility was built, sprinklers installed and accepted and insured.

However, in 1998, a routine loss prevention visit by an insurance fire protection engineer, who had recently been educated on the growing awareness of obstruction issues with ESFR sprinkler systems, resulted in a recommendation to identify and resolve observed obstructions in all 15 ESFR sprinkler systems protecting the distribution facility.

There followed a period of research and education for the owners and underwriters, resulting in a joint project to identify the extent of the problem and recommend solutions. During this time, the 1999 Edition of NFPA 13 was adopted and provisions proposed for the 2002 Edition learned. Both of these editions contained much detail on the effect of obstructions on ESFR sprinklers. For the purposes of the remainder of this article, all NFPA 13 references are for the 2002 Edition.

NFPA 13, 2002 edition, utilizes Table 8.12.5.1.1 and Figure 8.12.5.1.1 (both shown below) for positioning of sprinklers to avoid obstructions to discharge.

Distance from Sprinkler to Side of Obstruction (A)	Maximum Allowable Distance of Deflector above Bottom of Obstruction (in.) (B)
Less than 1 ft	0
1 ft to less than 1 ft 6 in.	1.5
1 ft 6 in. to less than 2 ft	3
2 ft to less than 2 ft 6 in.	5.5
2 ft 6 in. to less than 3 ft	8
3 ft to less than 3 ft 6 in.	10
3 ft 6 in. to less than 4 ft	12
4 ft to less than 4 ft 6 in.	15
4 ft 6 in. to less than 5 ft	18
5 ft to less than 5 ft 6 in.	22
5 ft 6 in. to less than 6 ft	26
6 ft	31

 

NFPA 13 addresses two general types of obstructions in section 8.12.5:

Isolated Obstructions – Non-continuous obstructions that restrict only one sprinkler and are located below the elevation of sprinklers such as light fixtures and unit heaters.

Several additional points are made including:

• Additional sprinklers shall not be required where the obstruction is 2 feet or less in width and the sprinkler is located horizontally 1 foot or greater from the nearest edge of the obstruction.
• Additional sprinklers shall not be required where the obstruction is 2 inches or less in width and is located a minimum of 2 feet below the elevation of the sprinkler deflector or is positioned a minimum of 1 foot horizontally from the sprinkler.
• Sprinklers with a special obstruction allowance shall be installed according to their listing.

Continuous Obstructions – Obstructions located below the elevation of the sprinklers that restrict sprinkler discharge pattern for two or more adjacent sprinklers such as ducts, lights, pipes and conveyors.

Again, several additional points are made including:

• Sprinklers shall be installed below continuous obstructions or arranged to comply with Table 8.12.5.1.1
• Additional sprinklers shall not be required where the obstruction is 2 inches or less in width and is located a minimum of 2 feet below the elevation of the sprinkler deflector or is positioned a minimum of 1 foot horizontally from the sprinkler.
• Additional sprinklers shall not be required where the obstruction is 1 foot or less in width and the sprinkler is located horizontally 1 foot or greater from the nearest edge of the obstruction.
• Additional sprinklers shall not be required where the obstruction is 2 feet or less in width and the sprinkler is located horizontally 2 foot or greater from the nearest edge of the obstruction.
• Ceiling sprinklers shall not be required to comply with Table 8.12.5.1.1 where a row of sprinklers is installed under the obstruction.

Once the facility owners and underwriters gained a clear understanding of what should be considered an obstruction, they performed a survey of obstructions in the facility. Through the survey they identified the following obstructions:

• 828 sprinklers obstructed by bar joists
• 2400 sprinklers obstructed by bridge strapping (about 1.25 inches wide)
• 100 sprinklers obstructed by electrical conduit
• 83 sprinklers obstructed by lighting fixtures
• 155 sprinklers obstructed by ventilation ductwork

The results: of the 5,776 ESFR sprinklers installed in this facility, 3,566 or 61 percent, were obstructed in some manner.

This research and examination also showed that a majority of the ESFR sprinklers had been installed two to five inches beyond the maximum allowable distance of 14 inches from the roof deck to the sprinkler deflector required by the manufacturer.

In essence, this meant that this $200,000,000 distribution warehouse, the largest facility in the company and the sole distributor of several lines of merchandise, was basically unprotected in the event of a fire.

Warehouse sprinkler compliance
To rectify the situation, the company authorized capital budget requests and charged their chief engineer and the insurance account engineer with identifying the most cost effective solution or solutions to bring this critical facility into compliance. The engineers were told to comply with the most up to date NFPA standards and restore the warehouse’s sprinkler protected status for insurance purposes and, more importantly, to protect the retailer and distributor from massive interruptions to their operations in the event of a fire.

The critical reason for proceeding with the project was that the company could not afford to lose this crucial distribution center.

Key provisions in NFPA 13 that would allow this project to succeed included the following changes from the 1989 edition:

• An increased emphasis on the critical nature of obstructions and more and better wording to explain what an obstruction is (8.12.5)
• The allowance to move a branch line or sprinkler head up to a foot so long as maximum or minimum spacing was not violated in order to avoid an obstruction (8.12.2.2.3 & 8.12.3.1)
• That upright ESFR sprinklers would be included in the 2002 edition of NFPA 13 (8.12.5.3.2)

Bids were obtained for raising the branch lines of the sprinkler systems, relocating heads along the branch lines by the bar joists, moving a three inch sprinkler pipe for a mezzanine and relocating the bridge strapping, electrical conduit and lights.

A structural engineer consultant contacted the roof designer/manufacturer to determine if the bridge strapping could be removed or relocated. The results were:

• The bridging is required for roof uplift loading and may not be removed
• The bridging may be moved along the bar joist up to 2 feet
• A letter was obtained from the manufacturer verifying moving the bridging was acceptable
• The bridging should be cut to relocate and replaced by bridging of same configuration
• The bridging should be re-attached with a minimum 1/8 inch by 1 inch weld

The engineer originally thought that relocating the bridge strapping would be less expensive than relocating the sprinkler piping. However, only two bids were received on relocating the bridge strapping and the costs were judged prohibitive.

One bid was for approximately $150,000 but would not utilize the approved weld. The other bid was more than twice as expensive. The manual nature of working at off hours so that the distribution center could continue to operate, working around the rack storage and cutting and re-welding the straps drove up expenses.

A different option was needed.

Not long before, an upright ESFR sprinkler had become readily available commercially. This sprinkler had the advantage of being less susceptible to obstructions than the earlier pendant ESFR sprinklers. See sidebar.

With the upright ESFR sprinkler, a continuous ungrouped obstruction located below the sprinkler that was less than 4 inches in width was not considered an obstruction. It was suggested by the sprinkler contractor that using the upright ESFR sprinkler would resolve the bridge strapping obstruction issue. To limit the number of replacement ESFR sprinklers required, the company decided to only install the replacements on the sprinkler lines with bridge strapping obstructions.

According to the manufacturer, having both upright and pendant ESFR sprinklers in the same system would not present any problems with the operation and effectiveness of the sprinkler system with a few caveats. The fusible elements must be installed within the distance below the ceiling allowed by the listings for both types of sprinklers, and the practice of mixing upright and pendant ESFR sprinklers is acceptable to the AHJ.

It was noted that due to the minimum and maximum allowable distances from the roof deck that the upright - 3 inches minimum - and pendant - 14 inches maximum - ESFR sprinklers had to adhere to, that it was impractical to have both types of heads on the same branch line.

Therefore, the company decided to keep the existing pendant heads for all branch lines with unobstructed sprinklers only or with only a few sprinklers in bar joists that could be relocated along a branch line in accordance with 8.12.3.1 of NFPA 13, 2002 Edition.

The branch lines with obstructions formed by the continuous bridge strapping beneath them would have the pendant sprinklers replaced with upright ESFR sprinklers. This was often two branch lines per bay - the lines closest to the side of each bay, which is a common occurrence when obstructions exist.

The sprinkler contractor adhered to strict work rules and cooperated with the company so that the regular work of the distribution center could continue relatively uninterrupted. The work did not begin until early in 2002 so that the critical 4th quarter operations of the company were not affected. Most of the work was conducted during the night hours.

The company utilized its own electricians to relocate any electrical conduit forming obstructions but relocation of lighting occurred after completion of all other work.

For each system, the sprinkler contractor did the following:

• Lines with pendant sprinklers being replaced by upright sprinklers were rotated and the sprinklers changed out
• Pendant sprinklers obstructed by bar joists were relocated in accordance with section 8.12.3.1
• Hangars were shortened to bring deflectors within the allowable distance from roof deck

After the first system was completed, the company conducted a detailed inspection to verify that the system had no remaining obstructions other than some light fixtures which were to be done in the entire facility at one time at the end of the project.

During the inspection, they discovered that adjustments had to be made to the raising of the sprinkler systems so that the combination of the upright and pendant heads throughout the system could both be within the allowable distance from the roof deck.

The sprinkler contractor quickly adjusted to the methods necessary to complete the work. The rotating of lines and replacement of sprinklers went much quicker than expected and the work was completed two months ahead of schedule.

Once the main adjustments, raising of the branch lines and relocating of the pendant heads in the bar joists was accomplished, the company used its regular lighting contractor to relocate the light fixtures that formed the final obstructions. Because they had waited to relocate the lights until after completion of all the sprinkler improvements, the company ended up relocating fewer lights.

The total cost was over $400,000 to complete this retrofit.

Project lessons
Here are the lessons from this example that anyone with ESFR obstructions can use:

• Perform detailed examination of ESFR installation for adherence to manufacturer’s specifications and NFPA 13 requirements.
• Write down all potential obstructions to ESFR sprinklers.
• Utilize NFPA 13 provisions to eliminate potential obstructions from the list. These two are often have the most effect.
  • Items less than 2 inches wide and 24 inches or greater below deflector is allowed
  • Items one foot or less in width and located 12 inches horizontally from sprinkler is allowed
• Contact roof designer/manufacturer if relocation of bridge straps is required and obtain letter detailing procedure to follow in relocation.
• Consider use of upright ESFR sprinklers in place of pendant.
• Do not mix upright and pendant sprinklers on the same branchline.
• Wait until the end of the project to move single isolated obstructions such as light fixtures.
• Check retrofit work early in project to identify any issues.
• Address any special constraints such as operating at night or utilizing hot work procedures over racks before starting retrofit work.

Charlie Bauroth, P.E. is an account engineering manager at Liberty Mutual Property. He is also a member of the Automatic Sprinkler Systems Technical Committee.