Bypassing of protective devices on machinery

Project No. BGIA 5089


completed 01/2006


Accident studies conducted by the BGs for the industrial sector indicate that deliberate bypassing of protective devices clearly occurs in plants. In order to prevent accidents attributable to bypassed protective devices on machinery from occurring in the first place, the reasons for bypassing were to be identified by an empirical study as well as the scale on which protective devices are bypassed. Based upon the results of the empirical study, an interdisciplinary project team drew up possible solutions for prevention, leading ultimately to an action plan.


The first project phase considered in detail the scale on which protective devices are bypassed, and the reasons for tampering. For this purpose, the project team created one general and one special questionnaire. These were employed by labour inspectors on-site in the plants as soon as they discovered cases of tampering or their attention was drawn to them. The results yielded information on the frequency with which protective devices were bypassed, together with possible approaches for dedicated counter-measures. Based upon the results from the first phase of the project, potential solutions for particular disciplines (safety technology, psychology, ergonomics, plant organization) were then developed in a second phase, and documented in a report. Altogether, six company representatives (manufacturers of protective devices and machines; operators of machines) comment in the report on the results of the study. The publication concludes with legal assignment of responsibility and liability in cases of tampering with machines.


The topicality and explosive nature of the study, which was exploratory in its approach, can be shown by a small excerpt from the results: in the opinion of almost 1,000 OH&S experts, bypassing occurs on a considerable scale in plants. In the view of this group, around one-third of all safety devices on machines on average are bypassed either permanently or temporarily. The operators significantly underestimate the increased hazard potential which is created as a result. In many cases, tampering has no repercussions for the individual responsible (tolerance), which combined with aspects reinforcing the behaviour (a faster working pace) tends to encourage tampering. In many cases, the human-machine-protective device interface is not user-friendly in its design, and therefore also not ergonomic. Many protective devices, for example, considerably slow the pace of work when used, thereby favouring the intention to bypass them. Tampering primarily occurs in relation to the following operating modes or essential interventions: set-up, fault remediation, retooling; and also automatic mode. The ease with which the working or machining processes may be observed is a major reason for tampering. Even the latest and most modern machines are tampered with, and their safety solutions are still clearly less than user-friendly. In some cases, protective devices or machinery must be bypassed before maintenance operations, for example, are even possible. The results reveal deficits on all levels of plant activity: personnel, technology and organization. In addition, there appears to be inadequate awareness of the subject of tampering, both in many plants, and within the OH&S community generally.

Last Update:

2 May 2016


Financed by:
  • Hauptverband der gewerblichen Berufsgenossenschaften (HVBG)
Research institution(s):
  • Berufsgenossenschaftliches Institut Arbeit und Gesundheit - BGAG
  • Berufsgenossenschaft Metall Süd
  • Norddeutsche Metall-Berufsgenossenschaft
  • Maschinenbau- und Metall-Berufsgenossenschaft
  • Hauptverband der gewerblichen Berufsgenossenschaften (HVBG)
  • FA MFS

mechanical engineering

Type of hazard:

mechanical hazards, design of work and technology


machine safety, accident prevention, technology design

Description, key words:

bypassing, protective devices, machinery, defeating of protective devices, empirical analysis, document survey, reasons for bypassing, action plan, report