Trapped key interlocks provide fast, safe and reliable access to machinery, prevent shortcuts and enforce procedures. This is achieved through the transfer of keys as the process is stopped or started. The repetitive wash-down procedures common to the food industry can affect the reliability of electrical safety devices, but the rugged, mechanical nature of trapped key systems makes them particularly suited to food processing applications. Here are the five most popular areas in which mechanical interlocks safeguard workers in the food industry.
1) Palletisers, blenders and mixers
These machines present the same risk – that personnel can be exposed to danger without being immediately visible to others – but for different reasons. In the case of palletisers, the large size of the segregated area, the equipment within it and the full pallet itself make it easy for an operator standing outside the machine guarding to miss a colleague’s presence inside. Blenders and mixers, on the other hand, present an impenetrable metal wall at ground-level to external workers.
Electronic methods of detection are sometimes unable to ascertain if individuals remain within a hazardous area. But trapped key interlocks, through the use of a personnel key, and lockout / tagout procedures can ensure that all operators and engineers are safe prior to the machine running. The operator retains the personnel key the whole time they are in the protected area, putting them in control of the machine start-up. Until this key is returned to its original position, there is no way to restart the machine.
The nature of the chemicals used in clean-in-place operations means that any product contamination is extremely hazardous to human health. It is therefore imperative that the correct procedure is followed and completed prior to food production starting. Trapped key interlocks force workers to follow a strict process, without them deliberately skipping or inadvertently missing steps.
3) Product filtration valves
Maintaining and replacing filters in food processing pipework while product flow is present carries two risks. First, removing filters can lead to loss of product and high clean-up costs. Second, operators can be exposed to high-pressure and / or high-temperature product. Interlocking product flow and access to filters ensures that access can only be gained when product flow has ceased i.e. when the valve is closed.
Ensuring the correct dosage of ingredients or additives is administered at the right time can prevent product being spoiled or wrongly formulated, and money being lost. Companies that interlock dosing valves maintain product consistency. Ingredients and additives can only be introduced in the correct order and individual steps cannot be missed or ignored.
5) Ovens and chillers
The risk when maintaining ovens and chillers is that the temperature may not have returned to a safe enough level to allow prolonged exposure by maintenance and operation teams. Having a robust method to guarantee enough time has elapsed before access can be granted means that personnel remain safe while in the danger zone. The access key to the hazardous area is only released once sufficient time has passed to allow the temperature to return to a safe level. The provision of a personnel key that is kept by workers while they are exposed to danger inside the equipment means that they remain in control of the process.
By: David Hughes, Sales Director, Castell Safety International Ltd.
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