Castell Safety InternationalInformationenAssessing Risk

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A complete risk assessment is necessary (as described in pr EN 1050) to ascertain 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. A detailed list of hazards generated by machinery is given in BS EN 292-1 section 4. For example, this includes, amongst others, mechanical (crushing, shearing, entanglement, impact, etc), electrical, thermal, noise, vibration and radiation hazards. The essential safety requirements (SMR) should 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 most important criteria to be considered when selecting interlocks are listed in Section 7 of pr EN 1088 :-

• the intended use of the machine (see BS EN 292-1 Section 3.12). This also takes into account conditions of use e.g. environment
• the hazards present at the machine ( see BS EN 292-1 Section 4)
• 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 "The risk to be assessed is that risk that would occur if the safety function of the interlocking device was not performed." (pr EN 1088 Section 7.2)

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. (See pr EN 954-1 Safety Related Parts of Control Systems).

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 (pr EN 1088 Section 4.1.1). Often, Power Interlocking is also the easiest way to achieve the required safety for lower risk applications.

For full information regarding machinery safety and risk assessment we recommend that you read the relevant regulations. Guidance books are also available from the Health and Safety Executive.

Please do not hesitate to contact us if you would like to discuss the interlocking of your machinery. We would be pleased to offer a free site visit by one of our Engineers, literature and details of an interlocking scheme to suit your safety requirements.