In a recent post, we discussed the history of sprinkler technology. This week, we’ll look at ESFR restrictions and obstructions.

Because of the operating principles around which ESFR technology is based, any delay in sprinkler response, or any interruption or diversion of the flow of water from the ESFR sprinkler, can have a catastrophic impact on the effectiveness of the ESFR system to suppress a fire.

Some restrictions on the use of ESFR sprinklers include:

  • Minimum clearance from sprinkler to top of storage of 36 inches
  • Maximum storage height of 40 feet (with some exceptions)
  • Requirement to maintain proper flue spaces within the storage racks
  • No solid shelving within the storage racks
  • No open top bin boxes within the storage racks

Beyond the above restrictions, “ESFR obstructions” are the Achilles Heel of ESFR sprinklers systems!

In the mid 1990’s, FM Global learned through fire testing that an obstruction as small as ¾ inch (ex: joist bridging member) could disrupt the spray pattern of the ESFR sprinkler enough to make the system ineffective at suppressing the fire.

With obstructions near an ESFR sprinkler, water striking the obstruction forms a mist that cools the air near the roof deck in the vicinity of the operated sprinkler causing skipping of the sprinklers adjacent to the initial sprinkler that operated. This ultimately results in too many sprinklers operating, many of which are not directly above the fire. Due to the large amount of water delivered from each ESFR sprinkler, extra operating sprinklers may overtax the water supply with devastating outcomes.

When water from an ESFR sprinkler strikes an obstruction, the water is deflected and may not reach the seat of the fire with the intended suppressing characteristics. This can delay suppression and result in greater fire and water damage, or prevent suppression altogether, leading to a very significant property loss.

In order to improve the effectiveness and reliability of ESFR sprinkler installations, NFPA 13 and FM Global revised their obstruction guidelines to be more stringent. These guidelines have continued to evolve as more is learned through testing and experience.

New ESFR Installations:

For new installations, a sprinkler designer must refer to the structural steel fabrication drawings for the roof deck to ensure their sprinkler layout is not obstructed by the structural roof support elements.

The designer is constrained by a maximum spacing of 10 feet between sprinklers, a minimum spacing of 8 feet between sprinklers, and a 12-inch horizontal clearance required from every steel member. While there is an exception to the spacing rules to accommodate obstructions, it comes with some onerous restrictions.

For a sprinkler designer, once the structural roof steel is accommodated, there is not much flexibility remaining in the layout to accommodate obstructions formed by other building system components including electrical cables and conduits, plumbing, and light fixtures, to name a few.

This has led to a change in the way buildings have been constructed over the last decade. The designers of plumbing pipes, HVAC ducts and units, electrical conduit runs, light fixtures, and other building service components have been forced to plan for, and avoid the layout of the ESFR sprinkler system in their design and installation.

Existing ESFR Installations:

For obstructions found in existing ESFR installations, there are three choices to mitigate the issue:

  • Remove or move the obstruction to comply with clearance requirements
  • Relocate ESFR sprinklers (within the allowable limits) to eliminate the obstruction
  • Install additional ESFR sprinklers below the obstruction

The potential for sprinkler obstructions does not end when final construction of a facility is completed. Any change to a facility such as the addition of conveyor systems, light fixtures, high-volume low-speed (HVLS) fans, new production equipment, or new storage configurations can create obstructions to the existing ESFR sprinkler system.

To avoid issues, any proposed change that could present an obstruction to the ESFR sprinklers should be to avoid creating an obstruction. If the obstruction cannot be avoided, it must be mitigated following the requirements that are applicable to the situation.

ESFR sprinklers can provide excellent, flexible protection for a facility, but remember the system comes with some “baggage” that must be proactively managed during construction and for the life of the building.

Knowing the limitations and the “Achilles Heel “of ESFR systems is critical to ensuring the system will be able to provide the protection it is designed to provide.

If you would like more information about ESFR systems or need help designing one for your facility, the fire protection engineers at Harrington Group can help. Fill out the contact form below, and one of our experts will contact you today!

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