Prepared by the Health and Safety Laboratory for the Health and Safety Executive 2013

Health and Safety Executive

Identifying the human factors associated with the defeating of interlocks on Computer Numerical Control (CNC) machines

RR974Research Report

Jane Hopkinson and Chrysanthi Lekka Health and Safety LaboratoryHarpur HillBuxtonDerbyshire SK17 9JN

HSL were commissioned by HSE to carry out research which sought to identify reasons why operatives defeat interlocks on Computer Numerical Control (CNC) machines, and to obtain an understanding of the extent of this behaviour across the UK engineering industry. The findings from this research provided a number of valuable insights about the frequency of defeating interlocks and the influences upon this behaviour.

With regard to frequency of defeating, semi-CNC machines were identified as being commonly defeated in the sample* used in this research. Common activities associated with defeating were setting, proving, swarf removal and deburring. Managers, and operatives / supervisors felt defeating was commonplace (the norm).

With regard to influences, three sets of influences on operative behaviour (Predisposing, Enabling and Reinforcing) were identified as influencing behaviour in relation to defeating interlocks.

Interventions that take into account these influences could be developed to promote behaviour change. Suggestions for such interventions are provided within this report.

This report and the work it describes were funded by the Health and Safety Executive (HSE). Its contents, including any opinions and/or conclusions expressed, are those of the authors alone and do not necessarily reflect HSE policy.

* It must be noted that these findings are taken from small-scale research and may not generalise to CNC machine users in the UK engineering industry.

Identifying the human factors associated with the defeating of interlocks on Computer Numerical Control (CNC) machines

HSE Books

Health and Safety Executive

Crown copyright 2013

First published 2013

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Acknowledgements

The authors would like to acknowledge the contribution made by all those who participated in the research interviews and focus groups. Thanks also go to HSE colleagues who assisted the researchers during the recruitment phase.

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KEY MESSAGES

The current research sought to identify reasons why operatives defeat interlocks on Computer Numerical Control (CNC) machines, and to obtain an understanding of the extent of this behaviour across the UK engineering industry. This research was conducted in two phases. The key messages presented below have been drawn collectively from both Phase 1 (see Annex Report) and Phase 2.

EXTENT OF THE PROBLEM Current research findings imply that defeating safety devices is widespread within the UK engineering industry, involving a variety of machine types and techniques. However there is a lack of robust evidence in general and specifically in relation to CNC machines. Common activities associated with defeating were setting1, proving2, swarf removal3 and deburring4 . Semi-CNC machines5 were identified as being commonly defeated in the sample used in this research. Managers and operatives/supervisors perceived this practice to be the norm. It must be acknowledged however that this finding is drawn from small-scale qualitative research and may not generalise to the larger population of CNC machine users in the UK engineering industry.

FACTORS INFLUENCING OPERATIVE BEHAVIOUR Characteristics of the individual (e.g. risk perception, knowledge of risks), and the environment (e.g. machine design and procurement), as well as the nature of rewards and/or punishment (e.g. lack of disciplinary action) following defeat of safety interlocks appear to exert an important influence on operatives behaviours. The current research explored the following three sets of influences upon operative behaviour in the context of defeating interlocks. Predisposing: characteristics of the individual that motivate behaviour. Key predisposing

factors identified were beliefs about personal susceptibility and negative attitudes about the need for interlocks/guarding.

Enabling: features of the environment that block or promote uptake of controls. Key enabling factors identified were poor machine design and procurement, lack of refresher/specific interlock use training and confusion regarding legislation/regulations.

Reinforcing: rewards or punishments that follow as a consequence of behaviour. Key reinforcing factors identified were lack of visible management commitment, production benefits (e.g. ensure the job is run correctly) and lack of consistent enforcement/disciplinary action.

ISSUES FOR CONSIDERATION Issues for consideration have been drawn from the current research with regard to how to improve health and safety performance and worker involvement (in general and specifically regarding CNC machines/interlocks) within the engineering industry. It is suggested that

1 Setting up a machine to run e.g. selecting the correct programme, ensuring materials are in the right place on the machine. Source: http://en.wikipedia.org/wiki/setting

2 Checking that a programme is running as it should. Source: http://en.wikipedia.org/wiki/proving 3 The removal of swarf (debris e.g. turnings, chips, shavings of meta)l. Source: http://en.wikipedia.org/wiki/swarf

4 Removal of burr (raised edge or small pieces of material remaining attached to a workpiece after machining. Source: http://en.wikipedia.org/wiki/burr

5This is not a term recognised in the current EN ISO standard Machine tools Safety Turning machines 23125:2010. However it does appear to be used by industry (also known as hybrid machines). It is understood that this term refers to manually controlled machines with limited numerically controlled capability.

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http://en.wikipedia.org/wiki/burrhttp://en.wikipedia.org/wiki/swarfhttp://en.wikipedia.org/wiki/provinghttp://en.wikipedia.org/wiki/setting

stakeholders6 should develop pragmatic and cost-effective strategies to help implement such improvements.

6E.g. a collective of machine users, designers, builders, suppliers, employers, employee representatives and regulators.

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EXECUTIVE SUMMARY

BACKGROUND

The defeating of interlocks on Computer Numerical Control (CNC), and other (manual) machines has been identified by HSE (e.g. from COIN7/RIDDOR8 data) as a common problem across small and medium sized engineering enterprises (SMEs). Some anecdotal evidence suggests that despite enforcement action, operatives may continue to defeat interlocks. HSEs experience indicates that the practices often repeat over time within the same organisations. HSE sought a better understanding of operative behaviour regarding the defeating of interlocks to help provide better guidance to inspectors and industry. In turn, this should help improve compliance behaviour and possibly initiate improvements in machinery design and manufacture and machinery procurement by companies.

AIMS AND OBJECTIVES The Health and Safety Laboratory (HSL) was commissioned by HSE to carry out research to identify the reasons why operatives defeat, or are motivated to defeat/by-pass machinery guarding, particularly the safety interlocks on a variety of CNC machines. A further aim was to determine the extent of the problem associated with the defeating of interlocks on CNC machines.

This report represents the second deliverable (the findings of Phase 2 - interviews and focus groups in a small sample of engineering companies identified as having previously defeated interlocks) of the broader research project. The report from phase 1 (literature review, and secondary data analysis) is provided in the Annex Report. Both phases aimed to give an in depth understanding of the nature and extent of the problem regarding the defeating of interlocks on CNC machines, based on analysis of quantitative and qualitative data.

KEY FINDINGS

Links to Phase 1 The current findings support and expand on the findings from phase 1 (see Annex Report). The findings suggest that characteristics of the individual (e.g. risk perception and knowledge of risks), the environment (e.g. machine design and procurement), as well as the nature of rewards and/or punishment (e.g. lack of disciplinary action following the defeating of safety interlocks) exert an important influence on operatives behaviours.

Extent of the problem The current research supports the findings of existing evidence (as described in the Annex Report). It suggests that defeating interlocks on CNC machines is commonplace across the UK engineering industry. This practice was perceived to be the norm within the industry. It must be acknowledged however that this research only collected evidence from a small number of companies and caution should be exercised in generalising this finding to the UK engineering industry. Knowledge of how to defeat interlocks was widespread. Such knowledge was typically acquired from on the job experience operating machines and from peer observation. Int