How to Inspect for Clearances?

MeyerFire University | FX103.16

By Franck Orset

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TRANSCRIPT

How do you inspect for sprinkler clearances? 

PROPER CLEARANCES

Today we’re continuing on our series talking about site inspections from the perspective of an insurance carrier, covering how we approach clearances near sprinklers. 

In order for sprinklers to suppress a fire, they need to develop a pre-determined spray pattern.  

The shape of the standard spray sprinkler’s pattern is like a parabolic curve spun around on a vertical axis. The intent is to have water distributed relatively evenly across the area it covers. Think of the curve of the St. Louis arch spun around on a vertical axis, except that water is intentionally thrown in all directions within the curve.  

Different types of sprinklers, like residential, throw more water towards the outside of the pattern where residential combustibles are usually found, but the overall spray premise is similar.  

This distribution of water helps cool the nearby heat source as well as pre-wet any combustibles that are near the edge of the flame. 

What does this have to do with clearances? 

In order for sprinklers to develop their time-tested spray pattern, there can’t be obstructions to that patten immediately next to the sprinkler. We talk about this in terms of clearances. 

TWO CLEARANCE TYPES

When we talk about clearances, there are two different types of clearances that we are usually concerned about in regards to inspections:  

Clearance to ceiling: distance between the sprinkler deflector and the ceiling level  

Clearance to top of storage: distance between the sprinkler deflector and the top of storage level underneath  

CEILING DISTANCES

 As sprinklers operate with a fusible element, its location below the ceiling is a key factor of the response of the sprinkler. If a sprinkler is located too far below the roof or ceiling, then it will take a long time for enough heat to collect above the sprinkler and slowly work its way down until the sprinkler heats up and activates. This time delay would allow a fire to grow larger, create more heat, spread further, and require more sprinklers to suppress.

What height should sprinklers be? This is a good separate topic, but for a cheatsheet see the links below this video.  

Sprinklers should be located at a minimum distance of 1-inch (25 mm) below ceilings, so that they can be easily removed in the future by unthreading or uncoupling the sprinkler, and a maximum distance of 12-inches (300 mm). That’s the general rule.

However, if we have a ceiling that is considered to be “obstructed”, then the height of the sprinkler could be as low as 22-inches (550 mm) below the ceiling. Obstructions could include deep beams or beam pockets, where the spread of smoke will be contained within a pocket. When this happens, the height of the sprinkler can be lower since smoke will be contained in the pocket, and the time it takes for the sprinkler to activate will be similar to a completely flat ceiling with a sprinkler higher up.  

There are also different rules for different sprinklers.  

Specific application sprinklers and ESFR sprinklers may stipulate different requirements for minimum and maximum distances. This information will be found in the product data for the sprinkler, and is based on the testing that the sprinkler underwent in its Listing and Approval stages.  

That’s the general idea when we’re talking about the height of a sprinkler, relative to the ceiling or roof deck above. This is usually documented and inspected when a system is newly installed, but not always. 

STORAGE CLEARANCES

The other clearance we’re concerned about is the clearance to storage below. If storage is stacked too high and is too close to the sprinkler, then the storage can act as an obstruction and block water from getting near the fire source. 

This is one of the important parts of an inspection, because storage arrangements and how things are stored changes all the time. A change in management, a change in supply chain logistics, or many other factors can push employees to store hazards higher and higher which could infringe upon the space the sprinkler needs. 

What is this minimum clearance? 

Some inspectors like to simply say “18-inches” or “3-feet”, but it’s a little more nuanced than that. 

The minimum distance from the sprinkler to the top of the storage below depends on the type of sprinkler that is installed. 

For a standard spray sprinkler, extended coverage sprinkler, or sidewall sprinklers, the minimum clearance between the top of storage and the deflector needs to be 18-inches (450 mm). This comes from Section 20.6.6 of NFPA 13, in the 2019 Edition, or Section 20.9.6 in the 2022 Edition.

One important note is that this doesn’t apply when the storage is against a wall. You won’t properly protect the goods that are stored too high, but this does not present an obstruction to the water discharge. Here, it’s important to check against the allowed height of the storage for the area. Discharge isn’t a concern though. 

For special sprinklers, or where any other standard or product listing dictates more than 18-inches, a minimum of 36-inches (900 mm) must be provided between the deflector and the top of storage. This includes Control Mode Specific Application (CMSA), Early Suppression Fast Response (ESFR) sprinklers, or anywhere where rubber tires are stored. This comes from the same section of NFPA 13. 

EXCESSIVE CLEARANCES

On the opposite end of the spectrum, where clearances are too high, it can also have adverse effects.  

This clearance concern is typically described as excessive clearance.  

A big delta between the top of storage and the sprinkler could mean a delay in activation, which then could result in larger fire growth, more heat to cool, and more sprinklers needed to operate. If there is a large heat plume from the fire with excessive clearances, then it’s difficult for water to penetrate the gases to wet and cool the burning source. Here, droplet size and distribution becomes a concern. Small droplets will vaporize and never reach the heat source, which can cool the plume but not suppress the source.  

Large drop sprinklers are designed with this in mind – but if the plume is already too large because of a huge difference in height, then they could still be compromised. 

Most performance tests are realized with a clearance between 6 to 10 feet (1.8 to 3.0 m), and the ideal target is between 3 ft and 10 ft (0.9 to 3.0 m).  

For that reason, the maximum allowed clearance should be between 10 and 20 ft depending on the type of storage arrangement, type of sprinkler and type of commodity classification. These arrangements and limits can get complex, but they originate from the storage chapters of NFPA 13 and the limitations set forth in insurer criteria, like FM Global. 

If there’s something in question during or after an inspection, that’s the time to open the standards and dig through to find acceptable thresholds on exactly what is being stored. 

STORAGE OCCUPANCY

On an insurer walkthrough, clearances near sprinklers are an important factor in making sure a building and its contents are properly protected. These are the major considerations we’re making when conducting a site visit and evaluating whether clearances are being addressed properly. 

I’m Franck Orset, this is MeyerFire University.