Smoke Alarm User Manual

Installation, Operation and Maintenance Manual
Issue 1 Page 5-7
February 2001
5.13 Suction Pressure
Suction pressure is a measure, in inches of water column, of the amount of suction available at each
sampling point. Suction pressures can be measured with a 0 – 25 mm (0 - 1.0 inch) H20 Magnehelic
gauge, and a length of micro tube. Insert one end of the micro-tube into a sampling hole, and connect the
free end to the Magnehelic gauge. The suction pressure at each sampling hole should be taken at the
installation and the subsequent data recorded. Suction pressures should be checked periodically for
maintenance purposes. During the periodic checks if it is found that the suction pressures have
significantly decreased, it is likely that the cause is a blockage, a break in the pipe, or a defective fan. If
suction pressures have remained the same, it can be concluded that there is no difference in the
transport time.
5.14 Zones of Varying Static Pressure
“SNIFF” Version 3.0 software provides the ability to vary static pressure between the Detector and the
piping networks. However, the Detector should be installed in areas where ambient pressure is positive
relative to the ambient pressure surrounding the piping. Detectors may, however be installed in
environments containing static pressures that are negative respective to where the piping is installed.
5.15 Distributed Pipe Network Sampling - Symmetrical and
Non-Symmetrical Balanced Systems
Symmetrically and Non-Symmetrically balanced systems are designed with the “SNIFF” Version 3.0
software. The “SNIFF” Version 3.0 software dynamically balances the piping network to provide equal
sensitivity at each point. All pipe ends are typically capped and the program sizes the sample points.
Where an Open Area Protection listing is required and a 60-second transport time cannot be obtained,
“SNIFF” Version 3.0 software will allow and size an extra hole placed in the end of the pipe. This may
occur in larger applications. The “SNIFF” Version 3.0 software will predict transport times and suction
pressures for each system. For design details refer to the “SNIFF” Version 3.0 Software/User Manual.
5.16 Return Air Grill Sampling
Return air grill sampling systems are designed with the “SNIFF” Version 3.0 software. The sampling
takes place in front of or near the return air grill. Some installations benefit by combining both return air
grill sampling and distributed pipe network sampling to protect a given area. This is often accomplished
without the need for an additional Detector.
5.17 Return Air Duct Sampling
Return air duct sampling systems are designed with the “SNIFF” Version 3.0 software. With return air
duct sampling, the sampled air is drawn directly from inside the return air duct that is servicing the
protected area. The Detector must be located no more than 118 meters (388 feet) from the sampling
points.
The HSSD system is well suited for duct detection. This sampling method provides excellent detection
and minimises installation costs.
5.18 Selecting a Sampling Method
Several considerations must be taken into account when selecting the type of sampling method to be
used in this particular application as the type of application will often dictate the method. The following list
of applications should be considered and used as a guideline to aid in selection of the required sampling
method.