Netherlocks key transfer stops human error

Industrial plants are designed with the highest accuracy in mind, with several separate safety loops often checking the integrity of process systems. However, can these apparatus also check for human intervention? No, they can’t!

We need to realize that a small human error could cause an enormous catastrophe. Bear in mind that 70% of reported incidents in the oil and gas industry worldwide are attributable to human error and account for in excess of 90% of the financial loss to the industry.
Improving your plant process is normally very complicated and expensive.

However, using Netherlocks ADD-ON devices improves safety and operability in a simple way without taking process equipment out of production.

Why an ADD-ON philosophy?

As mentioned above, most error is caused by humans, not machines. Therefore, in order to control safety, we need to control people.

How do we do this? In cases where process equipment is not actuated and controlled by a PLC or DCS, it can be operated by anyone and at any time. Of course you could guide operators with written procedures or by the use of lock out systems, but this will not eliminate error. The only way to eliminate error is best practice. Operators need step-by-step guidance and the answer to this problem is key interlock systems.

Key interlock systems

Humans are subject to failure. This may sound a little harsh, but people can be ill, distracted, nervous, and so on… So, in every operation involving human intervention there is a chance of failure or error. I won’t go into all of the historical incidents that could have been avoided if proper measurements had initially been taken.

Key interlocking is a “best practice”. Using key interlocks completely eliminates human error. This idea is not new. In fact, it began in the 1980s. Its strength is its simplicity: just mount a key transfer device onto your switch, valve, closure or actuator to guide the operator through every step of the process. This concept is used worldwide and accepted by all major end users, while most of the institutes also add them to their regulations:

1996 No. 825 :(UK) Pipeline safety, section 6.
API RP 14E :Design & Installation pipeline systems, Para. 5.8.b (2)
API RP 520 :Pressure relief systems refineries (part II: section 4)
NFPA12 :National Fire Protection Ass. (1993 edition)
BS 5306 :British Standard (part 4, 1986)
BS 801 :Code & Practice for pipelines (part 2 1992 sect. 2.8.)
BS 8010 :Code & Practice for pipelines (part 3 1993 sect. 6.6.)

How do key interlock systems work

Once mounted on the host equipment, a key interlock is fully integrated and not removable. The lock contains two keys. If one of the keys is not inserted, the system is locked and therefore cannot be operated. Furthermore, a key can only be released in the fully open or closed position.

This is totally different from a chain – padlock type protection. As is well known, a padlock can only block a device; it doesn’t guarantee position and it cannot guide operators through a step-by-step procedure. Therefore, chain – padlock solutions are always subject to failure irrespective of the operator’s knowledge or experience.

So, the position-controlled key release guides the operator through the critical steps that he needs to take. In other words, it doesn’t make his daily work more intensive or complex. On the contrary, it helps him avoid mistakes even when he is distracted or ill.

This locking solution can be mounted onto every imaginable device even if it is controlled by DCS systems. There is no limitation to sequence complexity.

Pigging systems

Pigging sequences can be very complex and, if not done properly, extremely dangerous.

While using a receiver or launcher pressure can easily reach 250 Bar. Imagine what would happen if the closure was opened while there was still pressure in the vessel! You may well be thinking, “Nobody can open a closure with 250 Bar over-pressure”, and you are right, but you need just 1 Bar over-pressure to kill. Interlocks ensure that the closure can only be opened once the pressure has been completely released, but they also guarantee that it can be opened only after the vessel is drained and purged of any H2S gas, if any is present.
Another, never realized, advantages, actuated main- or kicker line valves cannot be opened while the closure is opened. In other words; key interlocks fully controls pig launch- and receiving procedures irrespective the complexity.

Actuated valves

Since the main pigging and kicker line valves are often quite large, they are equipped with actuators. This means that pigging sequences are designed with simple manually-operated valves and actuators. These actuators can be controlled by mainframe distributed logic control (DLC) systems.

Key interlocks in DLC systems?

Yes! Key interlocks can provide a reliable mechanical assurance of safe operating practice in which the operator's scope for error is eliminated.

In DLC-managed systems, key interlocks form a vital link between managed and unmanaged valves. In these circumstances, key interlocks are not intended as the primary safety system but as a secondary back-up system to the primary (DLC) system. Designs have been developed in recent years to provide key interlocking solutions that offer the only total form of interdependent control over the operation of Motor operated Valves (MOVS) and manually operated valves in one fully integrated system. When applied to MOVS, the interlock design ensures that the failsafe function of the valve is never compromised.

Conclusion

The fast speed world leads to an increased risk of accidents through human error. Well designed interlocking systems can mitigate these risks - either by eliminating error or by greatly inhibiting the potential for violations. Well designed key interlock systems are always operator friendly - they require no additional work effort from the operator beyond that required by normal procedures and, most importantly, should never permit more than one key to be free at any one time. The message is, “keep it simple and let’s make it safe”.