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Aspiration Continued from page 28


ly be tested.” Tests can include blowing sample smoke into the piping system. Ubelhor has designed aspiration systems into air handler


units and claims the systems work well in high air flow environments. “A lot of times, normal smoke detectors are not listed for high air flow and may not be able to catch the smoke in high air flow areas. Aspiration detection systems actually draw the air in and are well designed to situate in high air flow movement areas,” he says. Typically, high air exchange areas have some form of


mechanical ventilation to maintain constant or cyclical air flow for heating, cooling or other special environments.


present a minimum amount of air particles,” he says. Large volume areas and areas with high ceilings, where


a condition called stratification can occur, require special design considerations for the pipe network design. Smoke rises until there is no difference in temperature between the smoke and the surrounding air. Stratification may occur in areas where the air temperature may be elevated at the ceil- ing level, especially where this is a lack of ventilation. In applications where stratification is likely, convention-


al pipe network sampling may not be effective. One way to overcome this problem is to create a vertical sampling pipe, in addition to the horizontal pipe network on the ceiling.


Aspiration detection, which identifies a fire threat at the earliest possible stage, often prevents an actual fire and the asso- ciated damage for critical areas, such as libraries, laboratories, telephone switching centers, computer rooms and muse- ums or other facilities with irreplaceable assets.


Smoke tends to travel with the air flow, hence, positioning sampling pipes near the return of an air handling unit or heating/air conditioning unit ensures early detection of par- ticulate in the area. Ubelhor also uses aspiration systems when designing


fire systems for high-ceiling environments, such as atria or warehouses. “Many times we’ll run air sampling systems across the air intakes in high atrium areas in order to increase the sampling volume. This would be done instead of sampling at the ceiling level where the air flow would


When designing an aspiration smoke system, consider the following:


1. Airflow characteristics and the air change rate


within the room 2. Coverage area per detector or sample point 3. Sensitivity required per sampling point 4. Room size and characteristics: raised floor, tall


ceilings, etc. 5. Annunciation of emergency response systems 6. Activation of mechanical control systems, such as air extraction and sprinkler systems


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The vertical sampling pipe has sampling holes at various heights to sample within any stratification layers in the area. Warehouses with high ceilings are a good example of this type of environment, where having multiple pipe configu- rations at different sampling levels could work well.


Difficult or dangerous installations Scott Golly, senior engineer at Hughes Associates Inc., in


Baltimore, has also designed aspiration detection into fire systems to overcome positioning difficulties. “A good application for aspiration is when it is difficult to get to the smoke detectors for maintenance,” he says. UPS battery rooms, for example, do not require the very


early detection afforded by aspiration technology. Installing and maintaining smoke or heat detectors above high-amperage UPS batteries, however, can be dangerous. “It’s just an unsafe work environment,” states Golly. “Instead, an aspirating smoke detector can be placed on the wall with an array of sample holes and piping installed above the batteries. A remote sample point for each pipe run can then be extended down the wall, positioned to allow testing and maintenance of the system without putting employees at risk.” Golly says that aspirating detection is also being used more frequently for positioning in ambient environments,


February 2011


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