‎ Gas Detector Alarm Settings

 

As of version 2.44 users may set varying alarm settings for gas detectors. This will affect both point and open path gas detector coverage calculations based on the high and low alarm distances entered in the Risk Grade properties panel. Contours and isovolumes can be added to display coverage values based on these alarm settings.

 

From the Risk Grades properties panel, under the new Performance Requirements - Gas section, a Gas Cloud Size (High Alarm) and a Gas Cloud Size (Low Alarm) may be entered. The Gas Cloud Size (Low Alarm) has replaced the previous Gas Cloud Size option in the Risk Grade properties.

 

Figure 01 - Updated Risk Grade properties panel with Low and High alarm gas cloud sizes

 

Using entered alarm information, users can choose the Voting Logic they want the coverage calculation to use. The logic can be set to LoLo, LoHi, or HiHi as defined by the figures below.

Figure 02 - Diagram of a single point gas detector and its user defined low alarm (solid blue line) and high alarm (dotted blue line) distances

 

 

 

 

 

Figure 03 - Diagram of two point gas detectors and both of their user defined low alarm (solid blue line) and high alarm (dotted blue line) distances

 

 

 

 

 

Figure 04 - For HiHi alarm settings, the shaded area for 2ooN coverage is the overlapping regions of high alarm distances (left). For LoHi alarm settings, the shaded area is the regions covered by one high alarm and one low alarm (center). For LoLo alarm settings, the shaded area for 2ooN coverage is the overlapping regions of low alarm distances (right).

 

The 1ooN coverage values will vary with the entered alarm distance and voting logic: if HiHi is selected the 1ooN gas cloud size will be based on the High Alarm gas cloud size. If the LoLo or LoHi is selected the 1ooN gas cloud size will be taken from the Low Alarm gas cloud size.

 

You can quickly compare the coverages achieved for the varying alarm levels by changing the Alarm Logic option in the Risk Grade Properties Panel and clicking the Update All button on the toolbar.

 

As an example, six point gas detectors with 5 meter spacing were positioned in a facility. The low alarm distance was set to 12 meters and the high alarm distance was set to 7 meters. A comparison of the coverages achieved for each voting logic is shown below.