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Reducing the risk of operator error

Health & Safety

Lester Millard, Managing Director at Alcatraz Interlocks B.V., takes a look at the use of key interlocks as an effective, safe locking device

While the operation of process equipment is governed by international health and safety protocols, the possibility of human error cannot be ruled out. Mechanical key interlock systems can help operating companies to reduce this risk by preventing process control equipment from being incorrectly operated.

What are mechanical controls and interlock systems?

Mechanical key interlock systems are twin-keyed mechanical locking devices which operate on a 'key transfer' principle to control the sequence in which process equipment may be operated. This system is widely accepted as an effective safety management tool and is being adopted by many of the world’s oil, gas and chemicals majors. Valve mechanical interlocks are also recommended in a number of internationally recognised standards for specific process applications.

Key interlocks date back to 1856 where they were first used in the British railway interlocking control for track switching. Trapped key interlocks are applied to valves, gears, pig launcher closure doors, switches, machine gates, railways or any form of equipment which may be operated manually. The 'open’ or 'closed' position of a locked valve of an interlock can only be changed by inserting a unique coded key, which unlocks the operating mechanism enabling the operation of the valve or other device.

Operating the unlocked equipment immediately traps the initial (i.e. inserted) key; when the operation is complete, a secondary (previously trapped) key may then be released, thereby locking the equipment in the new position. This secondary key will be coded in common with the next lock (item of equipment) in the sequence. By this simple coded key transfer principle a ‘mechanical logic' system is created which prevents operator error.

Standards such as UK Pipeline Safety Regulations recommend interlocks as a suitable safety system in the operation of pig traps and all related valves in a sequence.

Whether a process system is of a simple design, controlled manually, or a complex controlled system like DCS, key interlocks can provide a reliable mechanical assurance of safe operating practice in which the operator's scope for error will be eliminated.

A customised solution

Alcatraz Interlocks provides a full mechanical solution with mechanical key interlocking on all types of valves, gears and switches. Whether adopted as a primary or secondary safety system, key interlocks can be customised to fit any type, make or size of valves, switches or devices. Meeting the relevant API, British and European standards relating to specific process applications, Alcatraz interlocks are recognized as an effective safety management tool and safeguard the most complex operating sequences. They are used in the oil, chemical and gas industries and offshore industry, as well as in the automotive, food and beverage industries.

Applications include numerous critical installations such as changeover of pressure relief valves, loading and unloading of pig traps, sampling devices, industrial mixers and separators, filters and granulators. Alcatraz interlocks also safeguard the coupling and uncoupling of loading arms and hoses on discharge and loading stations. For example, a simple, low-cost system eliminates the risk of human error or negligence in the tanker loading procedure by preventing a vessel leaving the transfer area still connected to the on-shore facilities via a loading arm.