In modern processing plants, the issue of functional safety is steadily gaining importance. Alarm annunciators are an integral part of safety planning, especially in processing plants where alarm conditions can be numerous. The introduction of the IEC61508 standard introduced a broad but systemic framework to allow plant engineers to apply functional safety concepts on all modern control equipment. An alarm, or combination of several alarm conditions, requires the reaction of an operator to either investigate the cause of alarms or take the steps required by safety procedures to eliminate the condition.
Alarm annunciators today are seldom included as an integral part of true safety-related shutdown systems, as reliability of the human operator is generally considered insufficient to meet the high reliability requirements. However, with a high level of training and clear procedures in place, it can be accepted that the operator in conjunction with an alarm annunciator will meet (at best) the SIL1 safety loop requirements.
The Omniflex alternative
There is a different use for alarm annunciators in safety-related applications when one considers a purpose-made alarm device such as the two-channel Omni2 annunciator from Omniflex. This type of device is designed for performing a dedicated safety function automatically without operator intervention. There is no requirement for a human operator to undertake any action while the hazardous condition is present. When applied as, for example, a door warning sign in radiological surveillance systems, the device is used to prevent personnel from entering the hazardous area. In this case the main purpose is to provide a highly reliable safety warning.
Because of the obvious safety risk to personnel, it is logical to choose the higher SIL2 level, even if the device is not technically part of an electronic PES (programmable electronic system). There is also the additional benefit of providing automatic output for actuators for locking doors, for example, which then also complies with SIL2 parameters. Such a specialised annunciator function can logically be targeted at SIL2 levels of reliability as it is an entirely electronic system and does not rely on the actions of the human operator.
There is no doubt that with the growing emphasis of functional safety and risk reduction, the alarm annunciator is an important tool in achieving safety objectives. Omniflex is dedicated to providing state-of-the-art products in this field and to promote an understanding of functional-safety issues.
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