How to inspect for sprinkler design criteria?
Today we’re continuing on our inspection process from an insurer’s perspective, and we’re talking about reviewing the sprinkler system’s design criteria. While we’re speaking risk here, much of this same process applies for regular fire inspections for the fire service as well.
When we say sprinkler design criteria – what do we mean? We mean the protection level that the sprinkler system was designed to accommodate.
As an example, imagine that these red lines are sprinkler pipe and the dots are sprinklers. A sprinkler system designed for a Light Hazard Occupancy under NFPA 13 would typically provide 0.10 gallons per square foot, over the most remote 1,500 square feet.
This 0.10 gpm per square-foot is a density of water over an area, which makes sense that we call this method the design-area method. Casually we would call the 0.10 over 1,500 our design criteria. In SI, this would be 4.1 millimeter per minute over 140 square meters.
In this example, based on the construction and sprinkler spacing, the design for a light hazard space would involve calculating nine flowing sprinklers in order to achieve a remote area of 1,500 sqft. Our hydraulic placard could read like this. The key takeaways here is the occupancy for the space, which is designated as Light Hazard, the density, which is 0.10 gpm per square feet, and the remote area size, which is 1,500 square feet. In SI these last two would be 4.1 millimeter per minute over 140 square meters.
Storage design criteria can get more complex. Some storage criteria involves a specific number of activated sprinklers at a specific pressure. For example, an ESFR system might have a design criteria of 12, K-25.2 sprinklers at 15 psi. This means that for the design, 12 sprinklers which have a k-factor of 25.2 are flowing at a minimum pressure of 15 psi. In SI, this would be 12 sprinklers with a k-factor of 360 operating at 1 bar.
So our design criteria for a sprinkler system is the level that the system is designed to protect. How do we determine what that is when we’re on site?
For hydraulically calculated systems, NFPA 13 and NFPA 25 require a hydraulic placard on the system. These are usually found at the building riser.
Sometimes, building owners may have a copy of sprinkler plans for their system, digital or printed. The design intent can be pulled from these as well.
While it is not possible to review the hydraulic calculation by a visual field inspection - this would be a lengthy engineering exercise - it is possible to check whether the hazard classification used for the design matches the actual occupancy.
As an example, if the system was designed for a light hazard occupancy to protect offices, but the area is now used for the storage of combustible liquids or racks of plastic storage, we’ve got a big issue. And it needs to be reported and corrected.
A common change in occupancy is found in storage areas because the commodity classification might have changed over the years, as well as the storage arrangement. Warehousing needs change over time. Tenants can change, product materials change, container types change. Even the same owner in the same warehouse can have different appropriations of what they store over time.
Thirty years ago, most warehouses were used to store goods on pile, up to a limited height of 10 to 15 ft with a Class II to Class III commodity. Nowadays, it is not unusual to see the same building contain rack storage of Class IV to Exposed Group A Plastic stored up to 20 ft or more, with no in-rack protection.
Or the provision of carrousel storage units where the combustible load is completely shielded from the ceiling sprinkler protection
The first effort is to see if the commodities have changed. Comparing what the system was designed for to what is actually being stored, is the first step. Again we usually find the design intent by a hydraulic placard on the system or from design documents.
If these don’t match – and the commodity differs from what the system was designed to serve – now we have some additional homework. Is the commodity more or less hazardous than the design intent?
If, for some reason, the storage is now less hazardous than the original design intent, then we’re usually not concerned with this change.
If the storage is more hazardous than the original design intent – or even if it’s unclear – we may have a situation where the suppression system cannot adequately protect the building.
We’ll go into this process in more detail later. Commodity classification and finding the appropriate sprinkler design criteria can be a complex process with an ample amount of engineering judgement and responsibility. It usually involves taking stock of the storage content, the arrangement (or how things are stored), heights, aisle widths, and some other details; taking this information back to the office and doing a code-path out of the storage chapters NFPA 13 or combing through insurance criteria. Then, confirming whether the existing system design meets those needs. If the system can’t handle the appropriate protection criteria, then it might be time to recommend an engineering evaluation or a system upgrade to the owner.
At this stage, in terms of a site walkthrough from an insurance perspective – the important takeaway is that we want to check what the system was designed to protect, and compare that against what the building actually contains.
We want to compare the design criteria to the hazard.
Do we have a clear match, or cause for further investigation?
I’m Franck Orset, this is MeyerFire University
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