More RFIs from engineers and other informed readers.

Deflectors of fire sprinklers installed beneath sloped ceilings shall be installed parallel with the ceiling.

Q. Regarding Chapter 11 in NFPA 13. Assuming we don’t have 50 residual psi available at 850 gpm, if we have an 8,000-sq.-ft. building, and a wet system protects half of it and a dry system the other half, can we pipe-schedule these systems? Or would this be considered (per a new installation exceeding 5,000 square feet?

A. Table in the 2007 edition of NFPA 13 shows 850 gpm as the flow required for ordinary hazard occupancies, where you would need a residual pressure of 50 psi (see at the highest sprinkler in order to use the pipe schedule tables for a system of any size, provided that the duration limit is met. In your case, the 50 psi is not available but each system would only be covering 4,000 square feet. NFPA 13 is concerned here with a single water source, and in the case of multiple risers, only one has to work properly at any time. The code is saying yes, it’s perfectly acceptable to base your design on each 4,000-sq.-ft. system based on the pipe schedule tables. You cannot use the pipe schedule tables for extra hazard occupancies or for situations where storage is expected to be piled higher than 12 feet. Two independent water supplies are not required.

The initial drain discharge of water from this 2” galvanized elbow (near bottom of wall) will be black in color and foul in odor.

Q. We are reviewing plans in which the design density calculated by the contractor was 0.10 gpm/sf over the most remote 1,950 square feet. This is for light hazard, exposed construction. Since the NFPA 13 density curves actually call for a 1,500-sq.- ft. remote area of operation for wet systems, how should we advise the contractor with regard to his submission?

A. Actually, the Density/Area Curves noted in Figure of (2007 edition) NFPA 13 represent minimums, and the contractor’s design technician is certainly allowed to exceed any minimums noted in the standard. Also, I would check these plans for the existence of a sloped ceiling. Section notes that “the system area of operation shall be increased by 30 percent without revising the density when… sprinklers are used on sloped ceilings with a pitch exceeding one in six [2:12]… in non-storage applications.” Adherence to this section, which first appeared in the 2002 edition, was most likely responsible for the decision to utilize a 1,950-sq.-ft. area of sprinkler operation for this project.

This mechanical-tee, installed at the end of a cross-main, supplies one brass upright fire sprinkler.

Q. We had a sprinkler line freeze and a leak came from the sprinkler head. The water was black and had an odor, I am assuming corrosion since it is black metal pipe. My manufacturing manager is worried about mold and wants the water tested. Should I be concerned about the water and should I test it, and what should I test it for?

A. Any pictures or videos displaying pristine potable water being discharged from a fire sprinkler are really a myth. All fire sprinkler water comes out as you described, black and smelly, at least until all the soft black sludge has been flushed out. The water gets that way due to thread-cutting oil, pipe dope, iron filings, and other debris that has been sitting in stagnant water inside the piping system. All fire sprinkler installers are familiar with its distinctive stench. Some of them have reported that after they had placed a system in service for as little as one week, they returned to the job, drained the system, and the discharging water was already black. Since your leak originated by means of a freeze-up as opposed to pipe deterioration, I wouldn’t worry about too much corrosion. However, with water sitting inside piping, bacteria will grow. You could get the water tested - all you have to do is take a sample from the 1" inspector’s test valve. Make sure that you alert the alarm company to your activities prior to flowing any water from the system. Laboratories that test water for signs of corrosion include Vtec (718-542-8248) and Huguenot (800-228-3793).

A double-check detector backflow prevention device has been retrofitted into the supply side of this single 4-inch wet-pipe riser.

Q. Our health care facility has a detached central energy plant, which includes a generator room. This room houses three generators and three 400-gallon day tanks filled with Class 2 diesel fuel. The generators supply essential emergency power to the hospital. NFPA 37: “Combustion Engines and Gas Turbines,” paragraph stipulates that we provide coverage to all areas of the enclosure. Previous fire protection systems for generator rooms have been designed with Ordinary Hazard Group II classifications. Do the generators and day tanks constitute a special hazard?

A. Yes. The generator room is a stand-alone hazard, and you have numerous options for protection. The recommended option for fuel storage is a foam deluge system. CO2 used to be the norm for those applications, but has rarely been utilized since the adoption of numerous regulatory CO2 safeguards. For the room or enclosure itself, remember that the area being protected is to be measured in cubic feet. A safe bet would be to contact a local special hazards specialist and ask him to survey the room in question. He may, after surveying all existing conditions, recommend the installation of a clean agent if the overall area is not too large, or another special hazards system type that will be best for you. My suggestion would be to go with a water mist system.

The potential hazard with which we are concerned is a flammable liquid fire caused by ignition of flammable vapors, ignition of leaked fuel on equipment and floors, or spray fires arising from ruptured suction and return fuel lines. The best remedy will be the most efficiently controlled protection that will provide a fast, reliable response to any fire situation.

Water mist systems were originally conceived to protect jet engines containing highly flammable fuel. These systems are cost-effective and release much less water than conventional fire sprinkler systems. Clean-up following a discharge is very minimal. Any loss of electrical power will impact business operations in a very expensive way, so the total compartment protection afforded by a water mist system is what you’re after.