Alarmmanagement

Alarm management refers to the systematic management of alarms in a process control system to ensure the serviceability of the plant operator. An alarm is defined as an event that requires an immediate response of the plant operator. In modern control systems, it is very easy to configure isolated individual alarms. Often, in cases of doubt, an alarm too much than too little is better configured. Already in the undisturbed normal operation produce many processes numerous alarms (average values ​​of over 2,000 alarms per day and plant operators are not uncommon ).

It is easy to see that such a high base load of alarms ( more than one alarm per minute ) investment drivers - in addition to the observation of the alarm system still have many other tasks mostly - leads to desensitization, so that a potentially important alarm in a mass of unimportant alarms can be easily overlooked. The Directive EEMUA 191, which was published in the UK in 1999, has now developed into a globally accepted standard for quasi alarm management. Core concern of EEMUA 191 is to make the alarm system a helpful tool possible for the plant operator. Since human capacity is limited to information that is necessary to ensure that moves the alarm rate of an investment in reasonable areas. EEMUA 191 calls as a rough guide, for example, 1 alarm in 10 minutes in normal operation. Typical symptoms of poor alarm management are:

  • Alarms, without ever having been taken, "blind" acknowledged.
  • Alarm screens are largely ignored.
  • Audible alarms are overridden, otherwise it would be a permanent noise pollution.

Alarm flood

In process disturbances often result in a flood of alarms, since a cause can trigger a variety of causally interconnected alarms. There is a risk that the plant operators, which are often in such situations, under great stress, are overwhelmed by the flood of alarms.

What can cause poor alarm management, the explosion at the refinery of Milford Haven was in 1994. During this accident 26 people were injured, some seriously, there was a loss of about 70 million euros. Defects in the alarm system were a major cause of unhappiness: So the plant operator had in the last eleven minutes before the explosion to 275 different alarms respond. EEMUA 191 recommends that in the first 10 minutes after a process disturbance is not more than 10 alarms should be generated. Such a value is in many installations, however, only at very high cost achievable.

Alarm concept (german alarm philosophy )

There should be a written documented alarm concept for every system, in which is described what happened when as alarmed. The document should contain an allocation rule for alarm priorities, for example, depending on the potential harm to non-compliance and the resources available for a reaction time.

Alarm analysis

An essential first step of alarm management is the logging of all alarms in a database and its statistical analysis. On the basis of the characteristic values ​​obtained ( average alarm rate per plant operators, peak alarm values ​​, etc.) the quality of the alarm system can be assessed and appropriate measures are justified. An alarm analysis is also the basis of an efficient alarm reduction. Experience shows that few, often unimportant configurations are responsible for the majority of reported alarms. Often can be achieved with limited effort a significant improvement of the alarm system.

Alarm reduction

Alarms without value for the plant operator, there are a number of reasons, such as:

  • Defective or dirty sensors generate continuous false alarms;
  • Alarms have been used in the commissioning phase and later never eliminated;
  • Poorly set control loops to periodically exceed the alarm limits;
  • Events that require a response of the plant operator, are reported as an alarm;
  • Too tight set alarm limits;
  • Misplaced alarm parameters (hysteresis, filters).

The elimination of such alarms designed accordingly from very simple to very complex.

Alarm rationalization

A team in which even an experienced plant operator should always be involved, compares alarm for alarm with the alarm concept. To facilitate later change management, every decision should be documented as detailed as possible.

Advanced alerting

The concept of the alarm analysis and reduction as described in EEMUA 191 allows for many plants, with little effort to improve the quality of the alarm system substantially. But to get the problem of flood alarm in case of process disturbances in the handle, more ( and often complex ) measures are required. Thus, causal relationships between alarms and alarms analyzed the current state of the system must be made dependent.

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