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Key interlocks: A safe, effective solution to prevent downtime - says Lester Millard, Alcatraz Interlocks

20th August 2014

Lester Millard, managing director at Alcatraz Interlocks B.V., takes a look at the use of key interlocks as an effective, safe locking device in preventing process control equipment from being incorrectly operated

Key interlocks: A safe, effective solution to prevent process system downtime - Lester Millard, Alcatraz Interlocks
Whether adopted as a primary or secondary safety system, key interlocks can be customised by Alcatraz design team, to fit any type, make or size valves, switches or devices

Operating process equipment as per protocol is safe, however when one does not follow protocol the results could be disastrous.

Petrochemical and chemical processing industries have a disciplined method of design and operating practice, ruled by international standards and enforced by regulators and authorised notified bodies.

But protocols fall unavoidably victim to ‘human error’. The high percentage of reported accidents in the worldwide oil and gas industry may account for its equally high percentage of financial loss.

Probability and Accountabilities

The varying health and safety acts around the world (check your own local act) assign the responsibility on the employees who design, manufacture and or supply equipment for use at work to ensure as far as is reasonably possible that all is safe.

Internationally this methodology places key legal responsibility on owners and operators to adopt ‘best practice’ using best technology to guarantee safety.

When operators rely 100 per cent on written safety procedures (protocols), they are in actual fact relying on the employee to follow the guidelines exactly without failure. How can an operating company reduce this risk and eliminate such possible errors?

Alcatraz Interlocks provides a full mechanical solution with mechanical key interlocking on all types of valves, gears and switches.


What are mechanical controls and interlock systems?

Repetitive procedures are potentially dangerous when carried out incorrectly or in an unsafe modus.

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 and were a British invention where they were first used in railway interlocking controls for track switching.

Trapped key interlocks are applied to valves, gears, pig launcher closure doors, switches, machine gates and still to this day railways or any form of equipment which may be operated by a human. The 'open’ or 'closed' position of a locked valve interlock can only be changed by inserting a unique coded key. Inserting the key unlocks the operating mechanism and enables the operation of the valve or other devices.

Operating the unlocked equipment immediately traps the initially 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 any operator error.

In addition, standards like UK Pipeline Safety Regulations recommend interlocks as a suitable safety system in the operation of pig traps and all the related valves in a sequence.


Primary and secondary safety systems

Whether a process system is of simple design or 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.

Whether adopted as a primary or secondary safety system, key interlocks can be customised by Alcatraz design team, to fit any type, make or size valves, switches or devices.


Alcatraz at critical places

Alcatraz interlocks are successfully in use in the oil, chemical and gas industry, but the automotive, food and beverage industries have also discovered the advantages of the Alcatraz products. Alcatraz Interlocks are recognised and accepted as an effective safety management tool.

Among the standards for specific process applications are:

  • Alcatraz Interlocks are all Fire Safe to API 607 6th Edition
  • EN 1088 (ISO 14119)
  • API RP 520 – Pressure Relieving Systems for Refinery Services.
  • BS EN62061:2005 Safety of machinery – Functional safety of safety-related electrical, electronic and programmable electronic control systems.
  • BS PD 5304:2005 Safe use of machinery.
  • BS EN 954-1 1997 Safety of machinery.
  • BS EN 1037:1996 Safety of machinery: Prevention of unexpected start up.
  • BS EN 60812:2006 Analysis techniques for system reliability. Procedure for failure mode and effects analysis (FMEA).

The applications include numerous critical installations like 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.


A cut and dried solution for each problem

Alcatraz is famous for its innovative and flexible engineering department. In close co-operation with the customer, Alcatraz develops a safety system specially designed for the individual situation. Alcatraz offers effective and reliable safety systems safeguarding the most complex operating sequences, special locks for pneumatic valves, loading and discharge equipment or switches.

To reduce delivery time, Alcatraz maintains a stock of most major parts of its safety systems.

Alcatraz Interlocks simple, low-cost system eliminates the risk of human error or negligence in the tanker loading procedure which could lead to a vessel leaving the transfer area still connected to the on-shore facilities via a loading arm. Only one key is ‘free’ at any time which makes the system simple and operator friendly; the essence of Alcatraz Interlocks are a correct designed key interlock system with full flexibility for Cad-Cam designs for mounting brackets..

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