E-Stop buttons designed to enhance machine safety

While a risk assessment is a starting point to determine effective safety devices and methodologies, a key risk reduction component is the Emergency Stop

04/25/2013


The Emergency Stop is manually actuated by a single human action, effectively eliminating machine hazards. Courtesy: Banner EngineeringIn any industry, it is critical to produce quality products, fast and efficiently, while ensuring consistent results. To do this, facilities employ a variety of machine-based operations. Though efficient in use, these machines can present significant worker injury risks, ranging from soft-tissue injuries and disfigurement to amputation or even death.

To mitigate these risks, implementing a risk reduction strategy will improve workplace safety, enhance worker morale, and reduce liability. While a risk assessment is the best starting point to determine the most effective safety devices and methodologies, a key risk reduction component is the Emergency Stop. 

Understanding the E-stop 

The primary purpose of an Emergency Stop (E-stop) is to avert or reduce hazards or hazardous situations that could damage machinery/equipment or the work in process, and/or create increased risk of harm to individuals. The E-stop can employ several types of actuation devices, such as pushbuttons, rope/cable-pulls, push-bars/levers, etc., but all are manually actuated by a single human action. 

While E-Stop devices are not considered a true “safeguarding” device since they require a manual action to function, they are used as “complementary” equipment to augment required safeguarding practices and achieve acceptable risk. (See ANSI B11.0 General Requirements and Risk Assessment and ANSI B11.19 Performance Criteria for Safeguarding.) When required by the risk assessment—at a minimum—an E-Stop device must be continuously operable, clearly identified, clearly visible, and readily accessible.

E-Stops are typically located on the operator control panel and at locations around the machine or workcell that are up to 10 ft or less apart. NFPA 79 and IEC 60204-1 mandate that the E-Stop actuators must be red, and that pushbuttons must be on a yellow background and have a self-latching palm or mushroom-head style. The electrical contacts need to be a direct (positive) opening where the force of pushing the button opens the contacts.

Once the E-stop device is actuated, the emergency stop condition signal is sent to the machine control circuit. This immediately halts the dangerous movement/situation and removes power. Manually resetting the pushbutton, typically by twisting or pulling, must not initiate an automatic restart of the machine or other hazardous motion. To provide the minimum performance capabilities, E-stops should be designed to do the following:

  • Be initiated by a single human action
  • Override all other functions and operations in all other modes
  • Remove power to machine actuators quickly and without creating other hazards
  • Function as either a Category 0 or Category 1 stop, depending on the machine

A Category 0 stop immediately removes energy to the machine actuators; a “controlled” Category 1 stop leaves energy to the machine actuators to achieve the stop, at which time the energy is removed.

Innovative E-Stop technology

In an emergency situation, it is crucial that operators and others in the vicinity are able to stop hazardous machine motion or the process as quickly as possible. The swiftness relies on the E-Stop actuator being clearly identified, clearly visible, and readily accessible. The requirement for an E-Stop pushbutton to be red on a yellow background has gone a long way in improving “clearly identified” and “clearly visible.” Recently, identification and visibility have been brought to a new level with LED illumination.

New E-stop button technology combines the practicality of status indication with the safety inherent in emergency stop buttons in one, unique device. Two styles are on the market today: one with illumination in the pushbutton face and another with illumination in the enclosure base. The advantage of the illuminated base is generally more visibility via brighter indication and a 360-degree viewable surface.

Additionally, some illuminated E-stop buttons provide real-time status for workers on the plant floor. This can provide a solution to a common problem with E-Stop pushbuttons—identifying which button was pushed.

Illumination logic, whether provided externally or internally, allows workers to identify at a glance whether a button is armed or has been pushed. A pushed button can simply light up “red” or, in the case of an E-Stop with illuminated base, can indicate whether the button has been pushed (e.g., flashing red), the machine is stopped (e.g., solid red), or if the pushbutton is armed and the machine is ready to operate (e.g., yellow or green indication). Once the emergency situation has been rectified, users can easily identify and reset the button or buttons efficiently with minimal downtime. 

Diverse environments

To address “readily accessible” concerns and accommodate various applications, E-stop buttons are offered in enclosures for mounting remotely from the operator control panel in nearly any location or directly on a machine. With no assembly and quick-disconnect connectors, E-stop pushbuttons can be installed simply, quickly, and cost-effectively.

Machine safety is a cornerstone for productivity, profitability, and worker satisfaction. Taking precautions to minimize machine-related injuries is essential in today’s fast-paced, demanding industries. Therefore, implementing technologies, such as illuminated E-Stop pushbuttons, that deliver more information and enhanced machine performance can “augment” any risk reduction strategy.

Mike Carlson is safety products marketing manager for Banner Engineering.



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