Responding to an Event…What do I do when I am notified of an alarm? The ultimate goal is to reduce damage to infrastructure and populations. By having access to real-time data this goal of a fast and accurate response is much more likely.

The purpose of drinking water event detection systems that rely upon multi-parameter monitoring is to trigger an alarm if water quality deviations on the sensors become excessive. In some cases these software programs are capable of analyzing these deviations to see if they match an agent fingerprint from a library. It is important to understand that these sorts of systems are only capable of a presumptive classification. Any match is only indicating that the water quality sensors readings have changed in the same manner that they would be expected to if the agent in question were indeed present.

In other words the presence of the agent is being inferred from the changes in sensor readings. The actual agent may or may not be present. Occasionally more than one agent may be indicated. This is simply a signal to investigate further and can act as a guideline to that investigation. If the system were indicating cyanide might be present, it would not be wise to start an investigation on the presence of heavy metals as a first step.

There is a lot of valuable information that can be gleaned from paying attention to the duration and the shape of alarm signals. Spikes or alarms of a few minutes duration are of less concern because they affect only a small quantity of water. See Figure.1. A change that is continuous and persistent is of more concern due to the large volume of water affected. See Figure. 2.

Figure.1 Short duration spikes that exceed the trigger level tend to be of less concern. Figure. 2. Persistent changes that occur for a longer period of time are more of a threat.

An actual agent will usually present a characteristic rise time and a plateau of stabilization. Then a drop off will occur when the contaminated water has moved past the sensors. It is possible that this kind of pattern will produce classification of different agents on the signal rise, plateau, and fall. This is caused by differences in sensor response times. Classifications on the rise and fall are not as reliable as those from the plateau of the response. This should be taken into account during the interpretation of the alarm.

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