By Ron Kanterman
Whether you’ve been on the line for one year or 25 years and have not had the time to understand sprinkler systems basics, this article is for you.
Frederick Grinnell, a graduate of Rensselaer Polytechnic Institute, worked in railroad engineering until he retired as chief mechanical engineer and general manager of the Jersey City Locomotive Works. Soon after his retirement, he purchased a controlling interest in the Providence Steam and Gas Pipe Company. Grinnell already knew Henry S. Parmalee, who patented the first automatic fire sprinkler head in 1874. Providence Steam & Gas partnered with Parmalee and manufactured the Parmalee sprinkler. Grinnell also designed and erected the piping installations into which the Parmalee sprinkler heads were fitted. Grinnell improved Parmalee’s first practical automatic sprinkler and patented his own Grinnell sprinkler in 1882.
Continual improvements resulted in the glass disc sprinkler in 1890. With slight modifications, this sprinkler head is still used in modern fire sprinkler systems; sprinklers are even called le Grinnells in France. In 1892, Grinnell organized the General Fire Extinguisher Company, which was renamed the Grinnell Fire Protection Company after his death in 1919.
So, sprinklers have been around and effective in fire control for about 140 years. Yes, those little brass and chrome-plated beauties have been the front line of defense against fire in commercial buildings for quite some time and, more recently, in people’s homes. For many years, it was the insurance industry that advocated for sprinklers in commercial buildings. Sprinklers minimized the loss, minimizing insurance payouts and enhancing their profits at the same time. Although the insurance industry still avidly supports sprinkler system installations, the National Fallen Firefighters Foundation (NFFF) is the current advocate for residential sprinklers, according to Initiative 15 of the NFFF’s 16 Life Safety Initiatives: “Advocacy must be strengthened for the enforcement of codes and the installation of home fire sprinklers.”
Basics
There are two common types of systems, wet and dry pipe systems. In addition, there are two other less common systems, preaction and deluge, used for special hazards and applications. Foam may be used in some systems, particularly when dealing with flammable liquid hazards. All of these systems simply send water or foam (foam is just water with its specific gravity rearranged so it floats on top of hydrocarbons instead of sinking in them) to the fire’s location to control; confine; and, in some cases, extinguish it. Very effective! You still need people to rescue victims and pull them out of harm’s way, so sprinklers only support staffing-they do not replace it. They are a tool to protect property and, in some cases, life (residential) and to assist the fire service with effective, efficient, and safe operations. Sprinklers save firefighters lives, too!
Wet Systems
As implied, they are wet, and the system pipes are full of water up to the sprinkler heads. Because of this, wet systems are the quickest, most reliable sprinklers around. The fire actuates the individual sprinkler heads-this is the only way that water gets on the fire. Sprinkler heads use either a fusible link with a predetermined melting point or a glass bulb filled with a liquid designed to boil, expand, and shatter the bulb. Others use a chemical pellet to retain the water cap, which is released after the pellet melts or bursts, and the water is there immediately. The main riser and related equipment (known as “trim” in the sprinkler business) is where it all starts. The riser is connected to a water supply with a main control valve, a main drain, an alarm check, a retard chamber, a couple of gauges, a fire department connection (FDC), and a water motor gong (photo 1).
1 Photos by Paul Dansbach. |
When one or several sprinkler heads open, water flows though the alarm check, which sends an alarm (that’s why they called it that) possibly to a central station and to the local water motor gong on the outside of the building. That’s the bell that’s ringing when you pull up at 0300 hours and there’s water pouring out from under the door. The exterior gong is there to notify people walking or driving by to call the fire department. The retard chamber is there to take surges in the main. The surge enters the retard chamber so it won’t lift the alarm check clapper, it won’t send a water flow alarm, and you can stay in bed on a 10°F night. It retards the alarm and then automatically drains.
You will find wet systems in areas that are heated at all times and not subject to freezing conditions, such as malls, hotels, schools, office buildings, warehouses, factories, hospitals, and industrial processing sites. Wet systems are also found in private homes. Unless there is a reason you shouldn’t have a wet system (e.g., no heat, water-reactive chemical storage) then most codes and standards (and insurance companies) require wet systems.
Dry Systems
A dry pipe sprinkler system has no water in the pipes. A compressor or other source of air or nitrogen holds back the dry pipe valve (a clapper) until the heat of the fire melts the link or bursts the bulb on the sprinkler heads. The air then rushes out of the heads, releasing the pressure on the dry pipe valve, and the water starts to flow. These systems are used in buildings and areas of buildings where there is no heat (e.g., refrigerated warehouses, outdoor sheds, loading docks, multilevel parking structures, and structure attic areas). To reduce response time, some systems use “accelerators” or “exhausters,” also known as quick opening devices (QODs), which help release the air out of the system and more quickly open the dry pipe valve (photo 2).
(2) Photo by Bill Gustin. |
As with the wet system, the riser is connected to a water supply, but there is a dry pipe valve in place of the alarm check. It will also send a water flow signal after it trips. It has a main control valve, a main drain, a couple of gauges, an FDC, and a water motor gong. This system also has a compressor or a nitrogen supply, and an air gauge is on the upstream side of the dry pipe. If it starts to bleed down, a signal will go to the fire alarm panel, reporting a “low air alarm.”
Pre-Action
A pre-action system is also dry, but two distinct actions must occur for water to enter the occupancy. Pre-action sprinkler systems are used in places (e.g., computer rooms, hospital operating rooms, and museums) in which any accidental water discharge is to be avoided. Because two distinct actions must take place to put water in the room, merely snapping off a sprinkler head by accident will not activate the system. Unlike the dry pipe, an opening caused by an accidental break in the piping or a head will not trip the valve. Pre-action valves are electronically tripped through heat or smoke detection (photo 3).
3 Photos by Paul Dansbach. |
Note the following sequence of actuation of a typical pre-action system in a computer room:
- A smoke condition occurs in the room.
- A smoke detector picks up the smoke and signals a small pre-action panel (similar to a fire alarm panel) or the main fire alarm panel for the entire building. In either event, the signal goes to a panel. The smoke detector indicates, “Smoke has been detected in the room. Open the pre-action valve.”
- The panel signals the pre-action valve at the riser, “A smoke condition has been detected in the computer room. Trip and open to flood the piping system and stand by for fire.”
- An electronic solenoid switch on the pre-action valve at the riser activates and electronically “pulls a pin,” which trips the valve. Water flows into the system. At this point, we now have a wet system.
- When the fire grows and reaches the set temperatures of the sprinkler heads (usually 165-175°F in a computer room), the heads will start to open over the fire.
Deluge
The main difference between the deluge system and a dry system is that all sprinkler heads are open with no fusible elements or glass bulbs. It discharges lots of water everywhere and all at once. These systems are usually actuated by heat detection and are mainly found in heavy industrial applications (e.g., around transformers, processing tanks, processing pads with large vessels, small flammable liquid storage tanks). Since the heads are always open, using compressed air to hold a dry pipe valve back won’t work. Activation is similar to that of a pre-action system.
- A heat detector detects fire around a transformer and signals the panel.
- The panel signals the deluge valve at the riser, “A fire condition has been detected. Trip and open to deliver water to all heads and all sides of the transformer.”
- An electronic solenoid switch on the deluge valve at the riser activates and electronically “pulls a pin,” which allows the valve to trip. Water flows into the system and all heads. At this point, we now have a deluge of water surrounding the subject equipment on fire.
- Deluge systems sometimes require an immediate activation pull station at the hazard (in this case, the transformer) and in the riser room, so a person can intervene and manually activate the system even before the detection kicks in (photos 4, 5).
(4-15) Photos courtesy of the United States Fire Administration. |
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