Sounds like a crazy idea, right? Research, however, has shown that about half of professional machine operators do not think safety functions are necessary. You know, things like panel limit switches, torque limiters and emergency stop buttons. Who would need that, right? This number comes from a report issued in Germany about 10 years ago, but I am not very optimistic in improvements in these numbers since then. The report can be found here: http://www.dguv.de/ifa/Publikationen/Reports-Download/BGIA-Reports-2005-bis-2006/Report-Manipulation-von-Schutzeinrichtungen/index.jsp (in German).
Researchers have found that the safety functions of machines are frequently manipulated. This is typically done because workers perceive the manipulation as necessary to perform work, or to improve productivity. Everyone from machine builders, to purchasers to operrators should take this into account, to avoid accidents from happening. Consider for example a limit switch. A machine built to conform to the machinery directive (with CE marking) has to satisfy safety standards. Perhaps has a SIL 2 requirement been assigned to the limit switch because operation without it is deemed dangerous and a 100-fold risk reduction is necessary for operation to be acceptable. This means, if the limit switch is put out of function, the risk of operation is 100 times higher than the designer has intended!
What can we do about this? We need to design machine such that safety functions become part of the work flow – not an obstacle to it. If workers have nothing to gain in their own perception from manipulating the machine, they are not likely to do it either. This boils down to something we are aware of, but are not good enough at taking into account in design processes; usability testing is essential not only to make sure operators are happy with the ergonomics – it is also essential for the safety of the people using the machine!