Less equals more plant safety and efficiency
13 May 2010
New standards and better technology offer some hope to overwhelmed process operators. Patrick Raleigh and Nick Denbow examine
With the advent of digital control rooms, where alarms are available and selectable for every input, there can be up to 2,000 - 4,000 alarms per console, potentially providing thousands of alarm events in an incident which simply cannot be evaluated by the overwhelmed operators.
SCADA installations, for instance, are mostly configured to create an over-abundance of alarms, believes Mike Lamusse, technical director of Adroit Technologies. Operators, therefore, often ignore many alarms as inconsequential, or acknowledge them blindly en-masse, making ’noisy’ alarm viewers redundant.
The only way to solve this problem is through a well planned and executed alarm strategy backed by relevant supporting technology, including the database and management and analysis tools, Lamusse believes.
According to guidelines, an alarm is an event to which an operator must react, respond and acknowledge, and no plant should have more than six such alarm occurrences an hour per operator.
Departure from such guidelines is a primary contributor to unplanned downtime, which can cost hundreds of thousands of pounds, for example when continuous processes are suddenly halted. More important, however, is the impact on safety, as evidenced by accidents such as those at Milford Haven, Texas City Refinery and Buncefield.
Indeed, the link between poor alarm management and process accidents has driven the development of a new standard, International Society of Automation (ISA) ISA-18.2 ’ Management of Alarm Systems for the Process Industries’. Building on the work of other standards and guidelines, such as EEMUA 191, NAMUR NA 102, and ASM, this offers a framework for the design, implementation, operation and management of alarm systems in a process plant.
“ISA-18.2 is a step in the right direction” believes Simon Ellam from Siemens Industry Automation. The standard, he adds, is becoming expected minimum practice by industry, insurance companies and regulatory authorities.
The standard defines an alarm as, ’an audible and/or visible means of indicating to the operator an equipment malfunction, process deviation, or abnormal condition requiring a response’. This means that if the operator does not need to respond - because unacceptable consequences do not occur - then the point should not include an alarm at all.
“The underlying philosophy of the standard is that alarm management is a process that in itself requires continuous attention and so requires a life cycle approach,” added Ellam. “This is based on a staged alarm management framework that covers key stages; alarm philosophy, identification and rationalisation, detailed design, implementation, operation and maintenance, management of change and audit.”
Despite progress with the ISA standard, the overall quality of alarm management is still low in the process industries, according to Ian Nimmo, founder of the User Centered Design Services (UCDS) - a consultancy offering solutions for reducing the frequency and severity of abnormal
“To pursue a policy of safe process plant automation, we must address the big issues affecting the industry and drive ’human error’ out,” Nimmo maintains. “This can only be achieved by having workable standards written by the industry and applied in each country.”
Norwegian field
Nimmo, whose background includes a spell as programme director of the Abnormal Situations Management Consortium in the US, points to developments in the Norwegian sector of the North Sea as showing the way ahead. Norway’s Norsok 1-002 Safety and Automation System (SAS) standard encompasses monitoring, logic control and safeguarding of a whole installation: it considers all control equipment as a total, integral concept, whether from one vendor or from several sources.
The standard brings together automation and safety systems, including ESD, fire & gas, burner management, as well as hard-wired critical alarm systems, independent of the automation system. It encompasses a standardised approach to HMI design and the use of grey-scale graphic standards, using colour only to attract the operator’s attention.
Return to Process Engineering home page
