Smoke Alarm User Manual

Installation, Operation and Maintenance Manual
Page 5-10 Issue 1
February 2001
Then using a graphical interface the user will enter an Isometric View of the Pipe Network comprising of:
(1) the length of pipe to the first sampling hole or branch point
(2) the number of pipes in the system
(3) the number of sampling holes
(4) the spacing of the sampling holes
(5) the number and type of system bends
Once entered the software will automatically calculate the system parameters to ensure the transport time
and suction pressures are met. “SNIFF” Version 3.0 will provide a warning to the designer if the pipe
layout is over extended. An optional facility allows a designer to input fixed pipe diameters.
“SNIFF“ Version 3.0 software allows the user to print to save to a file the following:
(1) System data
(2) Isometric Views of the Pipe Network
(3) Sample hole schedule with size, Maximum Transport Time, Suction Pressure, Airflow
Rate, and % of pipe flow through each individual sampling hole
(4) Parts List, Including total pipe lengths
For additional detailed information on applying the “SNIFF” Version 3.0 software, consult the “SNIFF”
Version 3.0 Software User Guide.
5.21 Return Air Duct Detection Design
Duct sampling is the most cost-effective method of air sampling since the pipe runs are minimal and a
single Detector may be used to cover the large area. The speed of response of the Detector to smoke
will be given by the exchange rate in the rooms ventilated by the duct ventilation system. This tends to be
rapid, giving early warning of any smoke present. This type of sampling is particularly suited to high-
sensitivity devices since the smoke content in the air will tend to be diluted to a level below that of point
type detectors. Also, the relatively high airflow in the duct would reduce the effectiveness of point-
detection devices.
The duct sampling method does have one major disadvantage. If the ventilation becomes inoperative,
the airflow through the duct system ceases and the smoke-detection system becomes ineffective.
The Detector is suited for duct applications with an operating air velocity range of 1.52 – 20.32 meters/sec
(300 to 4000 feet/min.).
“SNIFF” Version 3.0 software is used to design duct detection for High Sensitivity Smoke Detector
(HSSD) systems and will calculate hole sizes and transport time according to the following guidelines:
(1) Only one duct can be monitored per Detector.
(2) If the HSSD system is used as the primary smoke-detection system, methods should be
employed to enunciate stoppage of airflow in the duct(s).
(3) The exhaust air from the Detector must be returned back to the duct using an exhaust-
port adapter and associated piping. This requirement assures positive airflow through the
Detector.