Why are emergency off and emergency stop often confused?
On the one hand, emergency stop and emergency off devices have a visual similarity and on the other hand, their mode of operation is the same – they are operating devices for emergencies. In an emergency, the energy supply is interrupted with a single movement. However, the main reason for the confusion between the two terms is a translation error.
The English term “emergency stop” was mistakenly translated as “emergency off” in the old Machinery Directive 98/37/EC and the then valid standard DIN EN 418. Because of this, many emergency command devices were labelled with emergency off at that time, which still occurs today in some cases with new machines. Regardless of the correct designation, labelling of emergency stop devices is not permitted according to the standard. Only pictograms may be used to indicate which area is stopped by actuating the emergency stop device.
What is the difference between emergency off and emergency stop?
Put simply, the difference lies in the hazard that occurs and the resulting technical requirements (Figure1). With an emergency stop, a stop command is triggered to bring a hazardous movement or process to a standstill (emergency shutdown). With emergency off, the protection goal is to minimise electrical hazards by disconnecting the power supply to the machine or system when the emergency off device is actuated (switching off in an emergency).
What types of emergency stop devices are there?
In addition to the classic mushroom button, there are other designs for emergency stop that offer additional functions (Table 1).
Are the requirements for used and new machines different?
According to the applicable legal regulations, emergency stop devices are required on machines in order to be able to prevent an imminent or actual danger. It does not matter whether the machine is new or used: Emergency stop devices must be available. Exceptions are made, however, e. g., for hand-held machines or machines with long overrun times.
In the case of process plants, the question of whether and where an emergency stop is necessary cannot be answered in general terms. Equipping machines in process plants with emergency stop devices without exception may conflict with the safety concept of the process plant.
In which areas emergency stop devices make sense must therefore be decided within the framework of a risk assessment or hazard assessment and the safety consideration for process plants, as with a PAAG procedure.
In the information leaflet “Emergency stop and emergency stop devices” of the prevention department “Technical Safety” of the German Social Accident Insurance Institution for the Raw Materials and Chemical Industry (BG RCI), you will find further explanations on the subject of emergency stop and emergency stop in german (www.bgrci.de, page ID: #RSV8 or under the QR code on the right). Additional questions will be answered by the prevention department “Technical Safety” at technische-sicherheit[at]bgrci.de.