Background filters in the hazard app

The new background filters have been added to the Hazard Assessment application. The time of day filter can be used to see the effect of removing events during blasting/shift change on the hazard results. You can either view the results in raw or normalised form. The hazard calculations do normalisation for the event rate calcs anyway, to represent hazard in yearly terms. If your analysis period is six months, the number of events is doubled to represent a year’s worth of events. When applying the time-of-day filter though, the actual analysis period is less than six months, because several hours per day have been removed. Without normalisation, the hazard should always drop when applying the time-of-day filter, because you are removing events, and nothing else changes (i.e. still using 6 months). If normalisation is turned on, the time period that has been removed is accounted for in the hazard calculations. The results then represent accurately the state of the hazard during the relevant times of day.

Normalisation also applies to the short-term responses filter, where events can be removed based on a time and distance from a blast or significant event. In this case the normalisation is a bit more complicated. With the time-of-day filter, the effective analysis period is the same for the whole grid. In this case however, there will be an uneven distribution of space and time removed from the analysis. So, each individual cell has its own effective analysis period, based on how many triggers (and responses) are nearby. The idea is still the same though, without normalisation, the hazard will drop due to the removal of events without adjusting the analysis period. With normalisation turned on, the results will represent the hazard state outside of short-term response regions.

A new chart has been added to the Hazard Assessment app that shows the effect of different short-term response filtering on hazard. The chart works in a similar way as the Track Volumes over Time chart, by computing the hazard over and over again, automatically changing variables with each run. The chart and associated control panel can be found in the Hazard Assessment / Hazard ISO’s window, under the Response Analysis menu. To generate the chart, you need to specify a maximum response time, a time delta, and response distances (up to 6). The hazard will be calculated for each response distance and for each response time from zero to the maximum (at delta intervals). The hazard recorded is the probability of exceeding the design magnitude within the chosen grid, which is the value displayed in the footer of the 3D ISO view. It can take some time to calculate, depending on how many iterations you specify. The video below shows the chart being generated for response times up to 72 hours and response distances of 50, 100 and 150 m.