Emergency Stops have been required on machinery for a very long time. The current definition for E-Stop is provided in ISO 13850 – Safety of Machinery – Emergency Stop – Principles for Design and NFPA 79, Electrical Standard for Industrial Machinery. The EN standard states that E-Stop is intended to avert arising, or reduce existing hazards and is initiated by a single human action.
E-Stop is not automatic and therefore is not a safeguard such as a guard or interlocked guard. Typically E-Stop is used when something is already going wrong.
E-Stop must not be used as a means of controlling hazardous energy sources. Lockout/Tagout (LOTO) should be used and E-Stop’s and other control devices are not energy isolating devices.
Typical E-Stop devices are pushbuttons and cable pulls. These must be accessible to the operator and unguarded. They require a manual reset. These devices have standard colors and marking requirements.
EN 13850 describes three categories of E-Stop. Category 0 is essentially a coast stop with power removed. Category 1 is a controlled generating stop with power followed by removal of power. Category 3 is a controlled generating stop with power left available to maintain the stopped condition. Mechanical braking may be used if required by the risk assessment.
The standard does not address stopping time. Stopping time must be defined by the risk assessment and affects safe stopping distances.
The E-Stop circuitry often uses the same category, safety integrity level (SIL) or performance level (PL) as the interlocking used on the machine.