Calculation procedures - Light Hazard adjacent to Ordinary Group 1

[pipesnpumps]

Example:
A system where the design shall use the area/density method of the occupancy hazard fire control approach, and must be designed for 3,000 sq ft of area.

A mechanical room designed for OH-1 is 1,000 sq ft.
The remainder of the building, is Light Hazard. The building is larger than 3,000 sq ft.

Key point: Room design method is not allowed. Calcs must use area/density method. (Figure 11.2.3.1.1, the design/area curves)

A 35 yr NICET is telling me that he is only required to calculate flow for the sprinklers in the Mechanical Room (OH-1 hazard), and is not required to include adjacent areas into the hydraulic calculations for that design area.

He says that the design areas for different hazards should not be mixed. He says calc 1,000 sq ft Mechanical room for the "Ordinary Hazard Case", and calc the 3,000 sq ft for the "Light Hazard Case".

What do you think? Is he right?

The way I do the estimated calcs on performanced based engineer plans is take an entire 3,000 sf area, with part of it designed for OH-1 and part designed for Light hazard.

I am not a NICET, so I'm sure I could have misunderstood something along the way. Neither NFPA 13 or the handbook notes give any guidance or clear direction.





Real world knowledge doesn't fall out of the sky on a parachute, but rather is gained in small increments during moments of panic or curiosity.

 

[dumor]

Why the 3000 sq ft design area? is there a unsprinklereed comb blind space above?
If not, and the mechanical rooms doors are self closing and 1 hr rated then the calc area culd be limited to the room size.
If you have to calculate 3000 sq. ft because of the un-sprinklered space bove, then the wall/occupancy seperation is not relevent.

 

[TravisMack]

If room design is not allowed, then you have to do the 3000 sq ft, end of story. You flow the heads in the OH1 area at 0.15 gpm / sq ft and the heads in the LH area at 0.10 gpm / sq ft. There is no prohibition in mixing calculation areas that I have ever heard of. If he is fighting it, ask him to provide a reference in NFPA 13 that backs up his case. I would be surprised if he can find one.

The only interesting question would be if you are req'd to use 100 gpm or 250 gpm for outside hose. I think you could use 100 gpm as it is generally a light hazard building, but I would probably do 250 gpm just to be safe. Whenever there is a grey area, I always err on the side of caution or being conservative.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[pipesnpumps]

Thanks Travis, I am a one man island here and he had me doubting myself. I was worried it was one of those things that are so obvious they aren't even written into the standard..

Hose stream I have a good grasp on. I don't have NFPA 13 references, but this is from my review checklist:
---
Where multiple occupancy hazards exist, the hose stream shall meet one of the following: a) hose stream of the highest hazard, b) each hose stream for each hazard class shall be used in the calcs for the design area for that hazard, or c) where higher class is in rooms not greater than 400 sq ft, with no such rooms adjacent, the class of the principal occupancy may be used.


Real world knowledge doesn't fall out of the sky on a parachute, but rather is gained in small increments during moments of panic or curiosity.

 

[pipesnpumps]

dumor, I posed the question that way so as confuse the issue with too many unnecessary details.

The 3,000 sq ft design area is a requirement of UFC 3-600-01 (DoD). Room design method is not allowed, so the design area cannot stop at the mech room walls as allowed by that method.

Real world knowledge doesn't fall out of the sky on a parachute, but rather is gained in small increments during moments of panic or curiosity.

 

[dumor]

What was the verdit on the space above? Why the 3000?

 

[dumor]

Enough said. Albit it's helpfull to know what the design standards are ahead of the question.

 

[TravisMack]

PnP:

UFC 3-600-1 does allow the QR reduction now if applicable per NFPA 13 (QR sprinklers/ LH or OH/ Ceiling less than 20'/ no unprotected pockets/ wet system). So, that may help some, but he is still wrong on just doing the mech room.

I am often on an island here myself. This forum is nice to be able to get help at times like this.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com