FEATURE Machine Safety y
The importance of light curtain inspections
Light curtains are increasingly becoming an essential bit of kit as they replace physical guards to keep machine operators safe. However, machinery owners remain unsure as to how they should be tested and how often. Here, Lee Ray, operations manager for Industrial Products (UK) at TÜV SÜD, highlights the importance of light curtain inspection
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any employers assume that if they carry out regular inspections of production machines, in line with the
Provision and Use of Work Equipment Regulations (PUWER), that they have done all that is necessary to meet their legal obligations. It would seem reasonable to assume that, provided these PUWER inspections are conducted conscientiously and at appropriate intervals, machinery is safe. Unfortunately, if that machinery incorporates electro-sensitive protective equipment (ESPE), this may not be the case. As technology has moved on, the use of
ESPE has significantly increased. For example, collaborative robots are designed to work alongside human co-workers, performing tasks simultaneously. This means that unlike more traditional machines, they cannot be caged by a physical guarding mechanism. ESPE, such as light guards and laser scanners, are therefore more prevalent than ever before as they provide safe, barrier-free access. However, despite its importance for the safety of machinery end- users, TÜV SÜD often visits sites where ESPE inspection and testing is neglected. This is because many machinery owners are unsure how often their equipment should be assessed and believe the original installation will retain the same parameters throughout its entire period of use. IEC 61496 series specifies requirements for the design, construction and testing of ESPE designed specifically to detect persons as part of a safety-related system, employing active opto-electronic protective devices (AOPDs) for the sensing function. This is then used in conjunction with ISO 13855 to determine the correct installation location for the light guard,to prevent a person making contact with a hazardous moving part of the
20 June 2020 | Automation
equipment. This should be verified after installation. However, there are no specific references to how often these systems should be inspected to ensure that they continue to provide the same level of protection. The Health and Safety Executive’s HSG180 guide (Application of electro-sensitive protective equipment using light curtains and light beam devices to machinery) helps machinery end-users to answer this question of timing. Concerning ESPE and AOPDs that are used to protect people from hazardous parts of machinery, the guide covers installation, use, inspection and test. HSG180 refers to Regulation 6 of the
Provision and Use of Work Equipment Regulations 1998 (PUWER). This covers the extent and nature of inspections, to help ensure that the appropriate systematic checks are done. HSG180 states that: “inspection and testing is only required under Regulation 6 where the safe operation is: critically dependent on work equipment being properly installed or reinstalled and failure to carry this out would lead to a significant risk and where the safe operation is critically dependent on its condition in use and deterioration would lead to a significant risk to the operator or other worker.” Inspection and tests must first be done when the complete ESPE and machine package is installed, and thereafter when modification or repairs have been made. In addition, periodic inspections should be completed. HSG180 defines the recommended maximum period between each periodic inspection and test as being six months for type 4 ESPE and 12 months for type 2 ESPE. However, this is still quite subjective as the guidance then says that the frequency of inspections ultimately depends upon on the equipment that the ESPE is fitted to and the risk as a whole. TÜV SÜD
would always follow the recommendation provided by the HSE in the first instance until a testing plan can be provided. This would depend on the equipment it is installed on, the frequency of use and the environment it is operating in.
The good news for machinery end-users is that HSG180 requires the machine and the ESPE supplier to supply information relating to routine maintenance and inspection requirements. This should help the end-user to develop a robust inspection and set an initial test regime frequency. The guide also requires that the initial inspection and test is carried out by competent persons, such as an in-house inspector, the installer or supplier, or an independent assessor. The results of any inspections must also be
recorded. The HSG180 guide also helps the inspector to ensure that the inspection and test process achieves a good general standard of performance. For example, it should not be possible for the dangerous parts of the machine to be set in operation while any part of a person is in such a position as to actuate the AOPD. TÜV SÜD has seen multiple instances
where the need for light guard testing has not been realised. Whilst functional safety checks are recognised as good practice, they are no substitute for the required periodic testing. The stop time test, performed as part of the periodic test, would detect any deteriorating system parts which no longer offer the required protection. This is something that usually cannot be seen, like in fixed guarding, and therefore can only be proven by testing.
CONTACT:
TÜV SÜD Web:
www.tuv-sud.co.uk
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