How Do Emergency Stop Buttons Work?

An emergency stop button is a fail-safe control switch installed on most types of machinery to protect people and equipment from harm. Sometimes called a kill or E-stop switch, it ensures that machinery can be instantly turned off in any threatening circumstances. 

They’re fitted in a location that’s easy to access and operate in any emergency, even if you’re wearing gloves. The button is usually required to be red, with a yellow housing, background or bezel to draw attention. Designs that light up in darker environments are also available. Common E-stop buttons come with IP54 ingress protection, but it’s also possible to get a waterproof version that can be certified to IP65 or IP67. 

Emergency stop buttons come in many shapes, sizes and colours, as long as these are highly visible, and conform to international standard ISO 13850. This specifies that an emergency stop switch must be designed in a shape that’s easy to operate in emergencies. They’re often prominently labelled with the words STOP or EMERGENCY. 

Emergency stop buttons are normally red and mushroom-shaped, sometimes with directional indicators if the switch is to be turned. The mushroom head is usually considered the best choice to comply with industrial safety requirements and IEC standards. These state that as well as being safe and reliable, emergency stop buttons must be convenient for operators to use with one hand.

How Do Emergency Stop Buttons Work?

The switch is a safety mechanism specifically designed to protect both the operator and the integrity of the machinery itself in the event of an emergency shutdown. The emergency stop switch can immediately shut off the machinery when it can’t be closed down in the normal way. 

Emergency stop buttons on machinery are wired in series with their control circuit. They function with a direct operation mechanism set in the Normally Closed (NC) position for the electrical contacts. Options are available for switches with one or two NC contacts. When you push the button or mushroom head for an emergency stop, the switch breaks the electrical circuit and prevents electricity from passing through it. This causes the equipment to immediately stop functioning. If the power must be stopped differently, you can connect emergency stop buttons to a controller.

Emergency stop buttons are self-holding switches that stay in place until you release the contacts and allow the machinery to start up again. The release of the button must only take place under strictly authorised procedures when it’s confirmed that the machinery or equipment is entirely safe to operate again. Sometimes, switches are designed for two-hand control, to ensure that both an operator’s hands are safely out of the way during any hazardous procedure. 

The most common emergency stop switches function according to the way the actuator works: 

• Pull release – in this type of button, you push the actuator in to stop the machine and pull the actuator back to release it. 

• Twist release – in this type you push the actuator in to stop the equipment and twist the actuator to release it. 

• Key release – here you push the actuator in to stop the machinery and use a key to release it. You’ll usually insert the key into the head of the button. This type of emergency stop button release is ideal for restricting its operation only to authorised personnel, especially in high-risk environments.

Where Do You Find Emergency Stop Buttons?

You’ll find emergency stop buttons in all sectors of industry, on a wide variety of premises including commercial and public facilities as well as industrial environments. They must be clearly visible to anyone who has to use them as part of their job. You might also find several emergency stop buttons on the same machine if it has several parts that have to be stopped independently. Such instances might include escalators, lifts, lifting equipment, packaging machinery, etc.

Whether machines require an emergency stop button depends on the regulations and standards governing machinery in different industries or countries. Very basic-level machines may not require equipment to have an emergency stop system. In any event, a safety risk assessment must be carried out before installing and using any machine (or part of it). Once such a risk assessment has been carried out and its hazard level (or performance level) determined, you must take the appropriate measures required to reduce the risk.

According to the European machine safety standards ISO 13849 and ISO 12100, there are three categories of standards, labelled A, B and C. The generic safety standards apply to a wide range of machinery from category B. These are further subdivided into four incremental hazard levels: 1, 2, 3, and 4. Each one relates to a particular aspect of safety such as required distances, noise or temperature levels, or types of safeguard. The safety control circuit must also meet these standards, so it will first be put into category B, then subdivided into hazard levels 1, 2, 3 and 4. 

A Key Contribution To Safety

Emergency stop buttons are a crucial component of any automated system, where there may be a hazard to health and safety. Their purpose is to stop machines and equipment instantly if there’s any risk of injury, or a dangerous interruption in the workflow, like jamming. It’s often referred to as a push-button safety switch because it’s there to avert harm to people, equipment or the work processes. 

In the process of risk assessment and compliance, emergency stop buttons also help to reduce or eliminate existing hazards. In this way, they supply a key contribution to machine and employee safety. In most countries, it’s legally required for different types of machinery to provide an emergency stop function. A thorough system assessment is critical to selecting the right emergency stop button for your application.