The introduction of new COMAH regulations in 2015 has once again brought the issue of overfill prevention to the fore. Many smaller firms affected by the rules for the first time and larger companies who are now subject to more comprehensive requirements are taking the opportunity to improve their existing plant.
The Control of Major Accident Hazards (COMAH) 2015 regulations have superseded the legislation that had been in force since 1999. More companies are now required to inform the authorities about the dangerous substances they hold or those that could be generated in the event of an accident. Sites are divided into two categories: top-tier sites (those that hold a greater quantity of dangerous chemicals) and lower-tier sites.
The top-tier sites are dominated by chemical and oil & gas facilities but also include distilleries due to the amount of flammable spirit being held. Overfilling in the distillation process is not only very costly but also dangerous.
As such, systems must be put in place to prevent overfilling the tank. In recent years, industry has moved away from float switches to more reliable devices based on the tuning fork principle, for example the Liquiphant. In its simplest form this device monitors its own condition continually and warns of failure before the level reaches the switch. This self-monitoring has resulted in Liquiphant systems being created to comply with IEC 61508 and to be compatible with SIL systems. The majority of Liquiphant devices conform to SIL 2 (the most common level of SIL required).
In the distilling industry the Liquiphant is usually used in conjunction with a Nivotester mounted in the safe area panel. The Nivotester provides easy-to-use relays which can be hard wired in the panel, a safe power supply to the Liquiphant in the tank, continuous monitoring of the loop and a convenient place to carry out a proof test. Pressing a button on the Nivotester acts as a system test to prove the reliability of the Liquiphant in preventing overfill.
SIL 3 in a single device
Some installations, though, are much higher risk and as such require higher integrity systems to SIL 3. The solution to this in the past has been to use two devices in a redundancy system to reduce the probability of an unsafe condition going unnoticed.
However, this has the disadvantage of requiring two process connections and increases the risk of false alarms.
Now the Liquiphant FTL80 series offers SIL 3 levels of protection with a single device and installation point. The system also includes a Nivotester for easy panel work and proof tests. The device is built to the highest integrity standards with redundant components and continuous self-checking and loop-monitoring capabilities. This results in a system that is reliable and easy to proof test, although it offers such reliability that a proof test is not required within its normal working life.
Reliability decreases with age
IEC 61508 and 61511 define an instrument’s normal working life as 8 to 12 years. Sites with overfill warning systems older than this should be looking for a replacement to avoid unpredictable performance.
Endress+Hauser’s Liquiphant systems provide easy retrofit solutions; in some cases they can even be provided with process connections to replace old float switches.
Of course maintenance of your new system is just as important as its correct installation to ensure continued reliable performance and compliance with regulations, including COMAH. Endress+Hauser offers a range of support throughout your system’s life cycle, from commissioning to regular maintenance and record-keeping, to ensure your instrumentation remains both safe and accurate.
Nivotester FailSafe FTL825 transmitter
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