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CastellSafetyAssessing Risk

Risk Assessment and Risk Reduction

A complete risk assessment is recommended to determine whether or not a machine is safe. If it is not safe then a risk reduction analysis followed by the selection of appropriate safety measures is required. Hazards generated by machinery include, amongst others, mechanical (crushing, shearing, entanglement, impact, etc), electrical, thermal, noise, vibration and radiation hazards. Some essential safety requirements can be met by applying the following principles in the order given :

  • eliminate or reduce risks as far as possible by inherently safe machinery design and construction
  • take the necessary protection measures in relation to risks that cannot be eliminated, for example, interlocking
  • inform users of any residual risks due to any shortcomings of the protection methods. Advise if any particular training is required or any personal protection equipment

Selection of Interlocks

One aspect of the risk reduction process is the selection of the correct integrity of interlocks for the machinery. The following factors should be taken into account:

  • the intended use of the machine. This also takes into account conditions of use (e.g.environment).
  • the hazards present at the machine
  • severity of the possible injury
  • probability of failure of the interlock device
  • stopping time and access time
  • frequency of access
  • duration of exposure to the hazard(s)
  • performance considerations of the interlock device

When selecting interlocks, one should consider risk that would occur if the safety function of the interlocking device was not performed.

Upon completion of the risk assessment and risk reduction processes the correct type of interlock can then be selected to achieve the required safety. The integrity of the electrical (or pneumatic / hydraulic, etc) system into which the interlock is fitted is an important consideration. A single channel control system will rely upon the operation of a single components. If the relay / contactor was to become stuck in the CLOSED position the machine would continue to operate regardless of the status of the interlock. A single channel system is only acceptable for very low risk applications. For increased integrity and for applications of greater risk higher classifications of control systems are required. This may include, for example, dual control systems and dual control systems with cross-monitoring.

An interlock of suitable integrity can be used to break the machinery / motor three phase power circuit directly. This is suitable for high risk applications and is termed Power Interlocking. Often, Power Interlocking is also the easiest way to achieve the required safety for lower risk applications.

Download the risk assessment form

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