The Plumis Guidelines limit the ceiling heights to 3.5m for the Automist (Tap and Fixed Heads).
However, for the Smartscan Hydra, this limit can be increased to up to 5m, assuming there is no fire loading mounted above the spray pattern (above 3m). This is because the spray heads are lower down and therefore the biggest impact increase ceiling height has to performance is increased activation time.
The example parameters below illustrate the potential impact:
- Steady-state fire with a heat release rate of 1000 kilowatts
- Fire located at the floor level
- The radial distance between the floor and the heat detector is 4.5m (15ft)
- The activation temperature of the heat detector is 57.2 degrees C (135F)
The radial distance of 4.5m is the maximum distance a fire would be from a detector with a listed spacing of 9.1m. For ceiling heights of 2.4m, 3.5m, 3.8m, and 5.0m the estimated time to detector activation is as follows:
|
Ceiling Height (m) |
Activation Time (s) |
Percent Increase in Time (%) |
|
2.4 |
83.42 |
-- |
|
3.5 |
147.58 |
177% |
|
3.8 |
179.80 |
21.8% |
|
5.0 |
~450 |
>250% |
For these particular parameters, which are representative of a realistic fire scenario, the estimated increase in time to activation between the prescribed 3.5m and the project-specific application of 3.8 is approximately 21.8%. For this scenario, the 21.8% increase equates to approximately 30 seconds of time which is within reasonable expectations for time to detector activation. According to the 2010 edition of the National Fire Alarm and Signaling Code (NFPA 72) section B.3.2.3.1, “where ceiling heights exceed 4.9m (16ft) ceiling height is the dominant factor in the detection system response.” This is supported by the above calculations as the temperature layer in the ceiling becomes less defined without increasing the size of the design fire.
These factors should be considered on a case by case basis.
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