Never ignore your instruments
Alan Hunt warns of the danger of ignoring what your instruments are telling you.
While instrument vendors put a huge amount of time, effort and ingenuity into developing new ways to allow their instruments to gather and display information, for many end users many of these capabilities often go unused. Instruments are the frontline for ensuring that processes are running in line with expectations and can provide a valuable source of data for engineers to see what is happening on the plant floor. They can also be a good indicator for warn when things are going wrong. Despite this, incidents continue to occur because instrument readings are either being ignored or misunderstood.
In a recent example, misinterpretation of an alarm reading was found to be the main factor behind the discharge of untreated sewage by a water company. Alarms indicating a potential problem were ignored and not passed on for action as it was considered to be a momentary blip, most likely caused by a probable fault with the instrument. Unfortunately, the alarm was genuine and, as a consequence, untreated sewage spilled into a local waterway.
Luckily, in this example, the outcome of the ignored alarm – though undesirable – was not catastrophic, resulting in just a minimum fine being issued to the company concerned. However, in other situations where there is the potential for serious injury or endangerment to human life, the ramifications of ignoring what an instrument is saying can be far more serious.
Complacency over safety was identified as one of the major contributing factors behind the Buncefield disaster in the UK in 2005, where failure of an automatic tank gauging system led to a fuel storage tank being overfilled. Problems with this system, caused by sticking of the gauge mechanism, had been known for some time, with 14 reported instances having taken place in the four months leading up to the disaster.
There were also problems with an independent high level system on one of the tanks that should have shut off the tank filling process and sounded an alarm. Although the system itself worked properly, a lack of knowledge over how it worked had rendered it ineffective.
The cumulative impact of this was that 250,000 litres of petrol seeped from the overfilled fuel tank, causing a vapour cloud which drifted to other tanks before igniting. The subsequent chain reaction caused other tanks to explode, resulting in a fire that lasted five days and caused extensive damage to the facility and the surrounding areas as well as significant long-term contamination of the surrounding environment. Luckily no-one was killed, but the financial penalties imposed on the companies deemed responsible totalled nearly £10m.
Why are they being ignored?
To tackle the problem, it helps to understand why instruments are being ignored. In many cases it is due to a mismatch between the perception and reality of a problem, where the consequences of a potential failure are not fully considered.
Taking the example of an unreliable instrument, it is understandable that persistent nuisance trips might lead altogether. However, the instrument is there for a reason and the fault may actually be indicative of problems elsewhere, other than within the instrument itself. For this reason, the adage ‘if in doubt, check it out’ should always be applied.
If an instrument is deemed to be unreliable, then good practice dictates that it should either be repaired or replaced, especially if it is in a critical application. If an incentive to do this is needed, then consider that laws are in place that allow both companies and their employees to be punished in the event of a serious failure.
Potential human failings also need to be addressed. You can have the best automated system in place with as many failsafes as you can cram in, but somewhere along the line, someone is going to be needed to perform a particular task, whether it’s initiating an emergency shutdown or carrying out maintenance and checking on the plant. When this needs to happen, the people concerned should be properly trained to do what is required, with the knowledge, skills and motivation to carry out their role. They also need to feel confident enough to question what an instrument is telling them if they have doubts about a reading or an alarm.
Ultimately, taking the time to check and confirm whether an instrument is giving a false reading will always prove to be the smartest and most sensible decision.
Alan Hunt is electromagnetic flow product manager UK & Ireland at ABB Ltd – Measurement & Analytics.>
Source: Control Engineering Europe - All Articles