NFPA 13 - Area of Demand 1

[CanuckMiner]

In a question related to my recent thread in regarding Water Demand, can anyone give me an idea about how to select an area of demand?

The project I'm working on has a total area of more than 10,000 sq feet (but less than 25,000 sq ft), laid out in an H-pattern (i.e. resembling the letter H). It is highly unlikely that a fire would engulf the entire area unless the fire suppression system did not work, and even then...not likely.

It is more likely that a fire would be limited to one of the upright branches of the "H" (roughly 3,000 sq ft) or even half of one of the upright branches (1,500 sq ft). I am tempted to use an Area of Demand of 3,000 sq ft, but would like to have a more firm resolution that that is the correct area to use.

The NFPA 13 standard seems rather vague on the issue. I have old (+/- 15 years) Factory Mutual data sheets indicating I should be using 3000-4000 sq ft for my Area of Demand.

Anyone have any experience with this kind of design? I could provide more information if necessary.

Cheers,
CanuckMiner

 

[SooCS]

My interpretation of NFPA defination of fire area, zone, or compartment (depending on which section of NFPA you are refering to)is an area, zone, or compartment when on fire is protected from spreading to other area, zone or compartment either by space (car parks, road, open area, etc)or fire rated barrier (wall, floor, ceiling, deck, etc). Therefore I would treat the H-patern area as a single zone unless H-patern is wide enought to prevent fire from esclating from (shall I say) left to right or right to left and the link between the two sides is protected by a fire rated barrier wall. In this case I would call it 2 zones.

 

[CanuckMiner]

Thank you for your response.

The area is a maintenance shop to be constructed in an underground mine (i.e. located with hard rock walls, ceiling, and floor). The spaces will be mostly open, but could contain vehicles at times. There are limited stockpiles of flammable and/or combustible materials.

I am hesitant to use the entire area of the shop to base my water demand on as this would subsequently require a large, dedicated volume of water to be supplied. If I am going to tell the Owner that he is to provide such a large volume of water (and the facilities to deliver it) I need to be able to back it up (e.g. point to a particular section of a standard or code). Also, in my case, I just can't picture the entire shop engulfed in a fire.

I suppose it is one of those things that must be determined by judgement and experience. Thanks again for sharing yours with me.

Cheers,
CanuckMiner

 

[kieffer]

The area of demand is decided by two things, separation as mentioned by a previous reply and by type of hazard. These hazards are typically Light, Ordinary, Extra hazard, rack storage or a specialized occupancy such as rubber tires, flammable liquids etc. When you have select the occupancy class this select the area of demand from the tables in NFPA 13. For example for Light, Ordinary or Extra Hazard see NFPA 13 -1999, Figure 7-2.3.1.2 and select a point on the area density curve for the Occupancy class you fit. Usually the lower area of demand the more efficient is your sprinkler design. If your fire separations create smaller compartments than given in the above text this may allow you to reduce the area of demand to the size of the compartment.

James D. Kieffer, PE
Kieffer & Associates Inc.

http://www.kiefferassociates.com