Question: Are you still experiencing floods of alarms under certain process conditions or during process upsets, despite the fact you have rationalised your alarm population and reduced the number of nuisance alarms to a tolerable level?
If the answer is yes, and these alarm floods are frequent or unacceptably large and mean you are unable to meet the performance targets stated in your Alarm Philosophy, then you should consider the application of one or more advanced alarm handling techniques.
What are advanced alarm handling techniques?
Basic alarm design methods such as the implementation of timers or hysteresis (deadbands) will ensure that your rationalised alarm population is appropriately configured, but may not be sufficient to prevent alarm floods occurring during plant start-ups, shutdowns or process upsets.
Where floods of alarms occur; usually triggered by a single event, more complex methods of suppressing consequential alarms (generally referred to as advanced alarm handling techniques) are required.
Advanced alarm handling is essentially the process of optimizing alarm system performance and minimising alarm floods, by dynamically modifying the behaviour of selected alarms once predetermined conditions have been met; often by the addition of extra layers of logic or programming.
The application of advanced alarm handling techniques requires very careful consideration, and great care must be taken in the design of any suppression logic, as the logic to suppress an alarm can be, and very often is, significantly different to the logic for re-enabling that alarm. There is no magic switch.
Typical examples of advanced alarm handling techniques are:
- Alarm grouping
- Logic based alarming
- Plant state based alarm suppression (Start-up / shutdown etc)
- Dynamic alarm masking
Start small, think BIG
When a pump shuts down, there may be low discharge flow and pressure alarms generated. So if for example, the pump running signal is inverted and used to prevent the low flow & pressure alarms from activating when the pump stops, then there will only be one alarm annunciated to your operator instead of three. (Don’t forget to add a timer to the logic to re-enable the alarms after the pump starts, to allow the flow & pressure to stabilise before un-suppressing those alarms).
If you use remote telemetry units or receive large amounts of data from package units, whenever these links fail, significant floods of alarms can occur which include not only the original failure (perhaps a power or module failure), but also all the alarms transmitted down the communications link. Use the initial failure alarm to mask the tens or even hundreds of consequential alarms from that link.
Now apply the same logic to all similar pumps and communications links to begin reducing alarm floods caused through process trips or power failures. Then move on to other small pieces of equipment with similar consequential alarms and apply similar philosophies.
All of a sudden, by identifying small, repeatable changes and applying them system wide, you can make a huge dent in the number of alarms generated during a process upset or trip.
You can choose to identify further opportunities if necessary at unit level, for example a large compressor or even a whole process train.
Benefits and pitfalls of advanced alarm handling
- Your alarm system is more effective at the times it is most needed
- Reduces alarm numbers during alarm flood conditions due to process upset, meaning your operators are less like to miss important alarms
- Can reduce the number of standing alarms in your system
- Designing and implementing advanced alarm handling techniques is an extremely time consuming and difficult process
- Significant effort is required for each alarm, to assess the potential consequences of masking the alarm in all operating modes
- If not designed correctly to cater for all circumstances, important alarms could be hidden or missed
- Can impose excessive / unnecessary load on the control system, which is highly undesirable and may significantly compromise the performance of your system, especially where mature systems are concerned
- If not appropriately highlighted, the operator may be unaware of suppressed alarms, and therefore unaware of potentially significant hazards
How we can help you
If you find you have a need to consider and implement any advanced alarm handling techniques, we can help you with your challenge.
We will work with you to analyse your alarm and Sequence of Events (SOE) data, to identify opportunities for the application of advanced alarm handling techniques, and help you to design and implement the necessary strategies.
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