Lighting’s vital role in safe HMI

As industry evolves, there is a need for greater interoperability and human-machine interface. Traditional methods for safeguarding need to evolve to allow this safe interaction. Electro-sensitive protective equipment (ESPE), such as light guards, 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, we often visit sites where ESPE inspection and testing is neglected. 

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. 

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 helps machinery end-users to answer this question. It 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. 

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.

We have 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. 

Lee Ray is operations manager for Industrial Products (UK) at TÜV SÜD