Five ways trapped key interlocks protect tanker loading and unloading

Loading and unloading tankers carries significant risk. Procedures are often complicated, particularly when earth lines and valve systems are involved. Drivers have to consider variables such as load characteristics, the frequency of vehicle movement and the number of products to be loaded or unloaded.

Potential issues include:

• “Drive-aways” while tankers are connected to equipment or damage to extended gantries;
• The wrong substance being loaded or unloaded;
• Shortcuts being taken and steps in safe loading missed, such as earth line connections being made or hoses returned;
• The danger of loading or unloading hazardous or flammable substances;
• Product spillage;
• The environmental impact of product release.

Loading and unloading tankers carries significant risk

Trapped key interlocks (TKIs) provide specific protection and risk control in these types of application. TKIs encode procedures to ensure that systems can only operate one way: the safe way. Depending on the application, TKIs typically control five main risks:

1) They immobilize vehicles while loading and unloading is taking place by using an airline interlock or interlocking existing barriers. This prevents a “drive-away” while equipment is connected.

2) For multi-step processes, they force drivers to always follow the correct procedure and avoid shortcuts.

3) They ensure that valves can only be operated when it is safe to do so.

4) They make sure the correct substance can only be delivered or received by the appropriate tanker.

5) As primarily mechanical devices, they do not pose an ignition-source risk in hazardous areas.

Designing an effective TKI-controlled tanker loading system requires a clear understanding of the procedure involved and the equipment to be included in each stage of the process. This should be carried out in conjunction with a thorough risk assessment of the process itself.

By: David Hughes, Sales Director, Castell Safety International Ltd.

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How trapped key interlocking protects workers at HV substations

Interlocking switchgear within HV substations ensures that personnel operate equipment safely, according to the correct procedures. Using a well-designed trapped key interlocking scheme will prevent personnel accessing potentially dangerous areas before the switchgear system has been put into a safe condition.


Interlocking switchgear within HV substations ensures that personnel operate equipment safely.

A good interlocking scheme will also ensure that the system functions correctly, so that there is no chance of, for example, switching two incoming feeds onto a common bus bar. This protects the equipment from damage and greatly reduces the risk of fire or arc flash.

There are four ways trapped key interlocks (TKIs) protect HV substations and their operators:

  1. Many HV substations are located in remote, unmanned sites which can attract attempted unauthorized access. TKIs help to safeguard this kind of vulnerable equipment.
  2. TKIs intended for HV substations have a proven design life of 45 years, allowing the safety devices to perform through decades of operation.
  3. Trapped key interlocking enforces the correct operation of equipment and therefore protects the continuity of supply.
  4. TKIs ensure that part of a system is isolated and correctly earthed before maintenance can be carried out on that section.

By: Adam Felton, Technical Marketing, Castell Safety International Ltd.

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Switchgear and protection: trapped key interlocking vs LOTO

There are two potential options when considering a mechanical safety system for switchgear applications. The choice is between a trapped key interlocking system or a padlock-based lock-out / tag-out (LOTO) system. Both systems:

  • Provide a method of isolating switchgear.
  • Allow safe personnel access when maintenance of machinery is required.
  • Are available in full stainless steel or brass versions.
  • Offer a comprehensive range of products with different forms and sizes to suit the needs of the equipment concerned.
TKI Switchgear

Trapped key interlocking applied to switchgear protection.

However, in terms of safety, trapped key interlocks (TKIs) offer significantly higher levels of protection compared with LOTO.


LOTO systems don’t provide the same level of protection as trapped key interlocking.

There are four main reasons trapped key interlocking beats out LOTO:

  1. TKIs are durable with a proven track record of withstanding harsh operating environments through decades of operation.
  2. TKI’s force workers to follow a strict process which prevents them from deliberately skipping or inadvertently missing steps. The equipment is interlocked together in such a way that steps cannot be overlooked or ignored.
  3. In an environment where staff may be unfamiliar with operations and speak a range of different languages, the enforced procedure of TKIs negates miscommunication or misunderstanding of operating practice.
  4. When there is a need for full-body access, TKIs provide a personnel key that protects workers from potential danger and puts them in control of the process. Until the personnel key is returned, the switchgear cannot be returned to the live state.

By: Adam Felton, Technical Marketing, Castell Safety International Ltd.


Trapped key interlocks vs light curtains in the food industry

In all industries it is important to balance the demand for safety with the need for fast access to machinery. The latter is vital in the food industry, for several reasons:

  1. The need to easily and hygienically clean the production environment.
  2. The impact on downtime of repetitively cleaning electronic systems.
  3. The requirement to clean all guards and accessories in the immediate location of the food area.

When protecting workers from the dangers of food processing equipment, both light curtains and trapped key interlocks can provide ways to control risk.

Light curtains offer such benefits as:

  1. Immediate access to production areas.
  2. A reduced need for guarding, which in turn reduces the time needed to clean a production area.
  3. Levels of protection ranging from full-body to finger, depending on the light curtain selected.
  4. When programmed appropriately, allowing raw materials to be passed into the production environment without halting processes.

The advantages of trapped key interlocks include:

  1. The ability to isolate the dangerous area until food machinery is made safe through timed or motion-sensing control.
  2. Higher life expectancy thanks to their mechanical (as opposed to electrical) design.
  3. Putting the operator in the hazardous area in full control of restarting the machine through the use of full-bodied interlocks and personnel keys.
  4. Resisting wash-down environments for extended periods due to their mechanical design.


The clear difference between light curtains and trapped key interlocks is most obvious in relation to full-body access

The clear difference between light curtains and trapped key interlocks is most obvious in relation to full-body access. Although light curtains can detect personnel crossing into a full-body zone, they are unable to determine if anybody remains in the danger zone when the machine restarts. This can lead to a dangerous situation if workers are hidden from sight behind equipment.

Trapped key interlocks are able to protect workers while they are in the danger zone through the use of a personnel key. When the operator is in the danger zone, the key is retained with them. This means that the machine cannot be restarted until the personnel key is returned to its original position. If multiple personnel are required to enter the danger zone, several keys can be provided to allow access – the machinery cannot be re-started until all access keys are returned to the exchange point.

In summary

Ensuring that the best solution is applied will depend on:

  • Understanding the hygiene regime requirements for each application.
  • Assessing who needs access to these areas, why and how often.
  • Evaluating access requirements: full- or part-body?
  • Conducting a risk assessment to understand the specific risk around the machinery or equipment.
  • Remembering to assess risk both pre- and post-implementation of a solution.

By: David Hughes, Sales Director, Castell Safety International Ltd.

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