Abstract

Basing on the results of industrial accident analysis (Dzwiarek, 2004) one can arrive at the conclusion that every year accidents happen because a warning signal is either not heard or not heeded (Haas & Casali 1995). Therefore, one of the important measures to prevent undesired events consists in informing a machine operator about the appearance of hazardous situation quickly and effectively enough. Standard ISO 12100-2:2003 recommends employing warning signals as an additional means for risk reduction, especially in the cases when other safety measures are not effective enough. This additional means plays an especially important role in the courses of machine regulating, maintaining and repair since in those cases the protective devices are usually disconnected and a direct access to dangerous zones is required. One can deal with such a situation also when maintaining an assembly line, where the operator should work during the line standstill and has to leave the dangerous zone before the line moves on. The warning signals are of crucial importance also in the cases when it is impossible for the operator starting a machine for control all the access zones. In such a case there arises the necessity for signaling the intention of starting a machine in the way ensuring that all the persons present nearby will be warned against the danger early enough. Therefore, the warning signals are employed for emergency event alert e.g., in case of unexpected machine start or sudden increase in a tool speed. Those signals can be used for warning the operator before the dangerous situation could have activated the safety devices. Those signals should: (a) be generated before a dangerous event occurs, (b) be unambiguous, (c) be clearly distinguishable from other signals generated within the workplace. Nowadays, visual and acoustic warning signals are most common. However, their main disadvantage consists in the fact that they may be received by many people instead of a person in danger alone. That may distract many people causing disturbances in other workstations. Additionally, visual signals can be seen only when displayed within the visual area of the person in danger. The operator usually focuses the attention and sight on the operations he/she is carrying out, therefore often neglects those signals.

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