Specialized Systems Take Unique Protection & Suppression Paths
While a water mist system has unique advantages in a variety of special applications, the use of a system across a whole building may not be advantageous.
Hello from Stockholm, Sweden. I write this as I have been here to attend the annual meeting of the International Electricaltechnical Commission (IEC) Technical Committee 79 (Alarms), during which the majority of the discussions revolved around intrusion detection, access control and video surveillance. And speaking of industry meetings, this month the International Standards Organization (ISO) will be holding the annual meeting of Technical Committee 21, which covers all aspects of fire protection, detection and suppression. This is being held in Toronto, and I plan on discussing the actions of TC-21 in a column later this year.
For now, however, I would like to go over some specialized water-based and other systems that you may come across. In July’s Fire Side Chat, as you may recall, I reviewed the basic types of fire suppression systems using water. During my time in Europe, I was able to observe two types of systems that are slowly making their way to the U.S. market: water mist systems and hypoxic air systems. Let’s take a look at these so you’ll know what to expect.
Water Mist System Handles Tough Spots
The water mist method of suppression uses water that is placed under high pressure. When it is released, the water comes out in very small droplets, basically microscopic size. This allows the water to get into very small spaces, reduce oxygen consumption and suppress the fire. And if you were wondering, this method has not been found to cause any harm to electronic components that may be reside in server rooms or like spaces. This method is also used where there may be old manuscripts, archives or artwork. Detection for the system would be similar to a pre-action system as described in July’s article. There have been several proposals to both ICC and NFPA codes to allow water mist systems to be used instead of a standard sprinkler system. So far, these proposals have not been accepted. The thought at this time is that while a water mist system has unique advantages in a variety of special applications, the use of a system across a whole building may not be advantageous. The NFPA Standard for these systems is 15, Standard for Water Spray Fixed Systems for Fire Protection.
Hypoxic Air Systems Proactively Prevent Fires
Another type of suppression system that is in use in parts of Europe is hypoxic air systems. This is not a suppression system in the traditional sense, as it is not being induced into the space upon detection of a fire. Rather, the rooms in which the system is being deployed maintain a lower concentration of oxygen – so a fire cannot start, but humans can still breathe. For a fire to start, the oxygen levels must be greater than 15% by volume. The hypoxic air system keeps the oxygen levels below this percentage, but they remain at a percentage high enough so people in the room do not notice the difference. When given a match to light, it will not light. If you walk into the space with a lit candle, the flame will extinguish. As with water mist systems, this is for smaller, more specialized spaces and not an entire building.
Foam Forms Formidable Response on Large Scale
Returning to water-based suppression systems, let’s address aircraft hangers and other like spaces where there will be aqueous film-forming foam (AFFF). Depending on the application, the foam may be low, medium or high expansion. These systems are generally connected to a wet pipe sprinkler system, with a foam concentrator actuated through a solenoid. When the solenoid is tripped, the foam is injected into the piping system. Detection for AFFF systems in most cases is through the use of radiant energy detectors, also referred to as flame detectors. Low-expansion foam will typically be passed through a sprinkler. The medium- and high-expansion foams will be introduced into a space by large foam generators. High-expansion foam can fill a complete hanger to the ceiling within a very short timeframe.
To prevent an unwanted activation, the detection should be cross-zoned so that two detectors need to go into alarm before the solenoid is actuated. Care must also be taken if radiant detection is being used to make certain that it has been selected for the signature of the flame that it aims to detect.
The NFPA standards for these systems are:
- NFPA 11, Standard for Low-, Medium-, and High-Expansion Foam
- NFPA 11A, Standard for Medium- and High-Expansion Foam Systems
- NFPA 16, Standard for the Installation of Foam- Water Sprinkler and Foam-Water Spray Systems
In next month’s column I will extend the discussion and cover clean, dry and wet agent suppression systems.
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