Fig 445 Types of sprinkler system layouts

4.F.2.a. Sprinkler Heads

Each sprinkler head, in addition to having the proper coverage area and adequate waterflow, must aim an unobstructed spray in the proper direction. Any object more than 4 in. wide and less than 24 in. from any head, or any "shadow" that subtends an angle greater than 9.5° behind which no spray can reach, constitutes an obstruction: this includes beams, truss struts, soffits, ducts, pipes, light fixtures, columns, signs, curtains, etc. Thus proper sprinkler design requires 3-D visualization of the surrounds of each head. Where an obstruction exists, either remove it, relocate the head, or install an extra head to cover the obstructed area.

Sprinkler heads must also be arranged so the spray from one will not cool the thermal fuse of another, they must be away from unit heaters and smoke exhaust outlets, and they must never be field-painted. The spread of each head is determined largely by its deflector design: flat deflectors create conical spreads, small diameters send the water more vertically, large diameters send it more horizontally, slotted edges divide the water into droplets or mist based on the slot size (these reduce temperatures more than quench fires), and sidewall heads (L-shaped deflectors) direct the water horizontally.

4.F.2.b. Types of Installation

The 96 x 140 ft floor area of a furniture factory in High Point, NC, needs a fire sprinkler system. If the furniture is wooden tables and chairs, the ceiling is exposed, and the owner's cousin works for a steel company, what system is best for this facility?

Frame Arm Upright Sprinkler
Fig. 4-46. Sprinkler heads.

Step 1. Determine the occupancy's Hazard Class from below. Where specific conditions merit a more hazardous rating, use it.

Class I, Light Hazard: Schools, offices, most public buildings, museums, theaters including stages, restaurant seating, libraries except large stack areas, nursing homes, residences, and the like.

Class II, Ordinary Hazard: Retail areas, auto parking garages, bakeries, laundries, machine shops, paper mills, restaurant kitchens, wood assembly, piers and wharves, warehouses, and the like.

Class III, Extra Hazard: Airplane hangars, factories of combustibles (lumber, textiles, etc.), areas of great heat (metal extruding, die casting, etc.) or flammable fluids (paints, oils, etc.), and the like.

Class HS, High-Piled Storage: Warehouses containing combustible items that are stored more than 15 ft high.

The occupation most resembling the furniture factory is 'wood assembly' 4 Class II, Ordinary Hazard

Step 2. Select the type of sprinkler head from below:

Small orifice: Orifice diameters are ¡-7/16 in; these are used only in certain hydraulically designed wet systems in light hazard occupancies of small area. Orifices smaller than 3/8 in. require supply-side strainers.

Spray: The standard head, widely available at low cost. Orifice diameter is usually 1/2 or 17/32 in. and head pressure is 15-60 psi.

Large drop (LD): A large-orifice head used where storage is 15-30 ft high. They produce higher flow rates and use more water; thus piping may be larger but the heads cost less. Orifice d iameter is 5g or£ in, head pressure is 25-95 psi, and maximum number of heads is 20 per rack.

Early suppression fast response (ESFR): An extra-large-orifice head that is used in warehouses whose storage is up to 35 ft high. These high-flow heads can protect all hazards, but they require a nearly flat roof (s 1/12 pitch) and no obstructions. Their extreme water demands also require larger piping and use of a fire pump, and their heads are expensive. Orifice diameter is £ in, head pressure is 50-175 psi, and maximum number of heads is 12 per rack.

Water mist: A recently developed sprinkler head that is described in Sec. 4.F.6. Halon Alternatives.

The building is not a warehouse and/or little potential exists for high-hazard fires to spread fast and release much heat in a short time 4 spray heads

Step 3. Select the sprinkler head's orientation, from below:

Upright: Heads rise above the pipes and cast spray over horizontal area. Good above suspended ceilings and where hot gases may be more dangerous than flames.

Pendant: Heads hang down from pipes and cast spray over horizontal area. Good for quenching flames from ordinary combustibles in large open areas, especially ones without suspended ceilings.

Sidewalk Heads aim sideways and spray vertical areas.

Multiple spray: Sprinklers spray up and down at the same time. Good where fire hazards exist above and below ceilings, but expensive.

Large open area and no suspended ceiling 4 pendant orientation

Step 4. Select the type of sprinkler system from below:

Wet-pipe: Water is present in all piping; thus an opened sprinkler head discharges water immediately. The simplest, most economical, most dependable, and fastest-operating system, it requires little maintenance. NG in areas subject to freezing, where water damage is a concern, or where hazards mandate a more effective system.

Antifreeze: A wet-pipe system whose watersupply contains antifreeze to prevent freezing. This is generally limited to small systems, and the supply must be periodically drained, tested, and refilled.

Dry-pipe: Pipes contain a gas which escapes when heads open, then the water follows. Good in areas subject to freezing such as unheated buildings and service docks. Because they respond more slowly than wet-pipe systems, their coverage is limited, but dry-pipe racks can branch from wet-pipe mains. Dry-pipe systems require air compressors, heated main controls, and pitched piping that allows drainage after use.

Preaction: A wet-pipe system that is activated by heat or smoke sensors instead of sprinkler heads. It responds faster than dry-pipe systems, but is expensive and requires more maintenance. These systems may be single interlock (requires only one alarm to activate) or double interlock (requires two alarms, each a fail-safe for the other, to activate).

Deluge: A dry pipe system with open heads; thus when any one sprinkler is activated the whole system area is covered. Used in high-hazard areas and where the potential for rapidly spreading fires (e.g. oil slicks) is possible, but it requires a large water supply. Some buildings have dry pipe preaction deluge systems.

Foam water: A concentrate is mixed with water to produce a foam that discharges through the heads onto a fire. Good for flammable liquid storage areas, aircraft hangers, and other high-hazard areas where water application is inadequate; but it is expensive, creates removal problems afterward, and its piping has high static pressures which could cause leaks and other damage.

Flexible stainless steel hose stem: Single feeds made of flexible stainless steel. Good for mounting in exhaust air ducts and other small spaces where rigid piping is unfeasible or difficult to install. Also good where upgrading or tenancy changes require a small number of new heads.

Building is heated (i.e. temperature is above freezing) and fire is not likely to spread rapidly 4 wet-pipe sprinkler system

Step 5. Select the type of piping from below:

Steel: Stronger, but may degrade in areas of high humidity, salty air, or where harmful gases are present. Thin-walled steel piping should not be used for sprinkler systems.

Copper: Lighter, but more susceptible to damage by high temperatures. All connections must be threaded.

In lieu of more definitive data, assume the owner can buy steel piping at a discount from his cousin at the steel company

Step 6. Select the type of water supply system from below:

Gravity-feed: Water flows down from a roof reservoir. To maintain 25 psi discharge pressure at the sprinkler heads, the reservoir must be mounted on a tower whose lowest level is at least 58 ft above the sprinkler heads. On some sites this is a good idea.

Upfeed: Sprinkler head water is pushed upward by a pump.

Roof structure is light steel and occupants are at ground level where they can escape easily 4 upfeed system

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