Help! Question on vertical space clearance between sprinkler deflector and AHUs

[jcqa]

Hello everyone, appreciate it greatly if I can hear some opinions. A few years ago, when I was doing a paid student attachment with a HVAC supplier company, I helped to prepare AHU equipment schedules for building projects. In many of the schedules that I prepared for my company, I failed to add the height of AHU base frames(100mm) to the AHU heights since I did not realize at that time that I was supposed to include it. At that time, I did not consider it as important and did not bring it up with my mentor during my time there.

However, now that I'm working in the MEP field, I realize that the NFPA and my country's fire code have a spacing rule whereby there should be minimally an 18 inch vertical clearance between sprinklers and material below it. I'm very worried that this clearance of 100mm could be compromised if the contractors don't notice the mistakes and just install the AHU equipment while blindly following the AHU schedule dimensions without doing final measurements on site. As I'm still new, I'm still not sure how the whole flow of projects go. From what I see, the 18 inch rule is to ensure the sprinkler discharge pattern works the way it's supposed to be and I keep worrying over the scenario that if a fire happens to break out at the AHU room/equipment room/wherever the AHUs are installed, the sprinkler performance will be compromised and might have dire consequences to property and lives.

Can any fire safety experts advice if this is a legit concern or if I'm overworrying? Is there usually a very safe, large clearance between AHUs and sprinklers in the AHU locations? This is for many projects and while I did tell my mentor much later on after leaving the company that I may have missed out on including the base frame heights in some of the projects, I don't think he is aware of the fire requirements as it is a HVAC vendor, and hence not familiar with fire code/NFPA. ANd I am afraid some of the projects might have already been completed. If anyone has the expertise, please help to advice if there are any real dangers and what I should do! This has been stressming me a lot and I don't wish to have my mistakes put anyone in danger.

 

[cda]

Welcome. wait a few days for more answers


My non engineer answer

There are a few variables involved, with fire sprinkler placement.

There is not one general statement, that can be given.

Truthfully, the fire sprinkler installing company should be looking at this, and adjusting.

Now if you are trying to avoid be charged for moving sprinklers, because of your work, get with the fire sprinkler company on the job, and work with them, to avoid obstructions.

 

[ICE]

I encounter missing sprinklers over furnaces quite often. Now and then it's five furnaces in one dwelling. There is usually a job card signed by a fire dept inspector approving the rough sprinklers. I am somewhat surprised that the fire inspector and sprinkler company miss that. Well like the OP, I am not sure of clearances. I tell them to install it/them and get another fire dept inspection....with another signature. I would like to know what the clearance should be but I'll not take responsibility for approving it.

I have gotten push-back from co-workers for challenging the fire dept. That tells me that way too many sprinklers are being missed. And not just any sprinkler....no no no this sprinkler is over an appliance that contains fire.

R313.3.1.2 Required sprinkler locations. Sprinklers shall be installed to protect all areas of a dwelling unit.
Exceptions:
1. Attics, crawl spaces and normally unoccupied concealed spaces that do not contain fuel-fired appliances do not require sprinklers. In attics, crawl spaces and normally unoccupied concealed spaces that contain fuel-fired equipment, a sprinkler shall be installed above the equipment; however, sprinklers shall not be required in the remainder of the space.

 

[FM William Burns]

Sprinkler Obstruction

NFPA 13, [8.5.5.3] Continuous and noncontinuous obstructions less than or equal to 18 in. below the sprinkler deflector that prevent the pattern from fully developing shall comply with 8.5.5.3.

So depending on the obstruction being below or horizontally to the head there are guidelines that need to be followed. Example: In the event HVAC equipment, condensation tray, ductwork etc. creates a greater than 4’ obstruction to the discharge pattern development under a head, another head would be required under that obstruction. Similar obstructions horizontally from the sprinkler deflector that can obstruct the pattern from developing as designed can also require additional protection in accordance with the section 8.5.5.3.

There are some figures that you can view in the section to aid in understanding the obstruction rules and criteria of coverage.