Bright yellow with a red push button, an emergency push button/’e’ stop/emergency stop/disconnection is required where there is a risk of an emergency or potentially unsafe condition for the equipment or an operator.
The switch should be continually operable, readily accessible, and initiated via ‘a single human action’ via a mechanical latching mechanism.
The stop should override all other functions, and once the switch has been activated, the equipment should not be able to be re-energized until all stop commands have been reset at the location where the command was initiated.
Resetting the button should only allow restarting of the machinery and not physically start the equipment directly. This is usually achieved by resetting the button, then allowing the equipment to be switched on via another means, usually at the equipment control panel.
Please note that all information contained in this article is one persons interpretation of the NFPA 79 requirements. You should complete your own assessments, investigations and research including specific project risk assessments to understand your own needs to meet local codes etc.
🟩 What different types of E-Stops are allowed?
Although the push-button type is the most common, there are other types of stops that can be used, according to NFPA 79 – Electrical Standard for Industrial Machinery
- Pull-cord–operated switches
- Foot-operated switches without a mechanical guard
- Push-bar–operated switches
- Rod-operated switches
They are not allowed to be:
- Flat switches
- Graphic representation, i.e, a graphic on a digital display.
For this article, we will concentrate on the Push Button Types, as these are mainly seen within a construction project.
🟩 Emergency Stop vs. Emergency Off
There are subtle differences between these two:
🟧 Emergency ‘Off’
‘Emergency off’ focuses on the procedure to quickly and safely shut off power to a machine or system in the event of an emergency.
🟧 Emergency ‘Stop’
‘Emergency stop’ focuses on the procedure to quickly and safely shut down a machine or system in the event of an emergency.
🟩 Where should e-stops be located?
There is no specific requirement relating to the position or distance at an e-stop should be installed to protect the user from a piece of equipment; it is, however noted that it should be readily accessible and be installed where an emergency stop is required.
So we take this as ‘within’ an arm’s length when an operative is working on any equipment part.
🟩 Emergency push button height requirements
There are no specific requirements for the e-stop height requirement, as the equipment the pushbuttons serve can be mounted in various locations and at various heights [above the ceiling, below the floor, wall mounted etc].
In the section above, it’s noted that they should be readily accessible to the operative [within arm’s length].
🟩 Requirements for clearance
There are no specific requirements for clearance around the button, so we need to use our own judgment.
As long as the button can be pushed in one action, under stressful conditions, and is not obstructed, that should be the minimum amount of clearance needed.
🟩 Specification of the push button…
To ensure that the requirements are met, the following lists the minimum requirements for an ’emergency push button device’:
🟧 Push Button shaped like a Mushroom
The shape of the emergency stop button should be ‘mushroom shaped’, so that it is more visible, recognisable, and easily activated by a human palm.
🟧 Push Button to be Coloured ‘Red’
Much like the shape of the button, it should be coloured ‘Red’ to ensure the button is highly visible and recognisable in an emergency situation.
🟧 Yellow Background Colour
The background color immediately surrounding the ‘Red’ mushroom button should be ‘Yellow’, this is usually achieved by the use of color enclosures, colored disc, or adding the color to the stem of the button.
🟧 Self Latching
The emergency stop button once activated and pushed should remain in the ‘pushed’ condition, switching off the equipment and not reset itself until it is intentionally reset.
To do this the stop button will incorporate a spring-loaded mechanism or some other type of latching mechanism that holds the switch in place once it has been activated.
🟧 Unlatching Direction to be Identified
The button should identify and provide clear instructions on how it can be ‘unlatched’ and ‘reset’ after activation, in case needed during the emergency or the button was pushed accidentally.
This information is usually provided by arrows molded into the head of the button.
🟧 Button to be ‘Direct Opening’
Direct opening for the button means that upon activation the power supply to the equipment is immediately disengaged. This is achieved by the push button opening the circuit as soon as it is pressed.
🟧 No Flat or Graphical Representations
Flat or graphical representations based on software should not be used as a emergency stop button, this would cover displays and control panels etc, due to them not meeting the code requirements.
🟧 Immediate Activation
In emergency situations and upon activation, the e-stop button should immediately activate an emergency stop of the equipment/motor shutting it down.
Note: Only for emergency stop applications should the RED/YELLOW colors be used.
🟩 What are the stopping requirements once the button is activated?.
Within NFPA there are 2 ways of stopping noted:
🟧 Category 0 – Disconnection [preferred solution]
This is completed by ‘disconnecting’ the motor/equipment power/actuators instantly in the event of an emergency.
🟧 Category 1 – Controlled
A ‘controlled stop’ with power to the machine actuators available to achieve the stop then power is removed when the stop is achieved.
The category should be determined from the completion of a risk assessment [usually by the designer].
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🟩 Emergency Stop Reset?
Releasing and resetting the push button should only be achieved by one of the following means:
- turning a key,
- rotation of the button, or
- by pulling the button.
Note: as previously detailed, resetting the button should not directly activate the equipment/machine. This should be via another means.
Resetting the button only provides the ability to switch it back on.
🟩 Alarm requirements.
There are no code requirements relating to sending an alarm upon an emergency stop actuation.
However, this will usually form part of the design to monitor the status of the equipment out in the field.
🟩 Protection from tampering and removal
Tampering and at worse removal of the stop button could increase the risk of accidents, injury, and damage to operatives or equipment that they are protecting.
To deter this they should be designed and installed so as can only be removed by a specific tool and with access gained ideally within a panel.
NFPA 79 [10.8.2.2] notes that it is acceptable to enclose a pushbutton-operated switch within a break-glass enclosure.
🟩 Emergency stop accessories.
Usually supplied as a button only, that can be mounted within a panel or included with an accessory, the following would be available from the supplier:
 Button [Red] |  Contact block |  Disc [Yellow] |  Enclosure for mounting switch [Yellow/Black] |  Signage [Red/White]
🟩 Emergency stop button signage
As can be seen above, some companies manufacture and supply signage to display the position and location of the e-stop. These signs are extremely useful in providing direction.
We do not see anywhere that they are a requirement, so it would generally be up to the designer/installer if want to use them.
🟩 Periodic Testing of Emergency Stops?
Whilst there is no exact requirement for testing an e-stop, they still should be periodically tested due to the wordings used in the NFPA 79 & PUWER 98 documentation.
🟧 Noted in NFPA 79
The functions of electrical equipment, particularly those related to safety and safeguarding, shall be tested and documented.
🟧 Noted in PUWER 98 Section 5
Every employer shall ensure that work equipment is maintained in an efficient state, in efficient working order, and in good repair.
With this in mind, each and every emergency stop button should be periodically tested for operation and to understand if there are any faults.
Depending on the type of equipment and environment the e-stop is installed for/within the period testing should be conducted once a month to once a year.
⬜ Emergency Stop Inspection Checklist Template
Below is an open checklist, in MS Word, that can be used for inspecting Emergency Stop Buttons, click the button to have it sent to you.
🟩 References and Codes
There are many international standards and codes for the manufacture, design, and installation of Emergency Stop Buttons – they are all very similar.
Below provides the most common that can be found in the UK & USA, as with anything to ensure we meet the requirements of the specific location we are working in local requirements should always be checked and adhered to.
- NFPA 79: Electrical Standard for Industrial Machinery [make no follow]
- BS EN ISO 13850: Safety of machinery. Emergency stop function. Principles for design
- BS EN 60947-5-5: Low-voltage switchgear and control gear. Control circuit devices and switching elements. Electrical emergency stop device with mechanical latching function
- BS EN 60204-1: Safety of machinery. Electrical equipment of machines. General requirements
- PUWER 98: The Provision and Use of Work Equipment Regulations 1998
🟩 Frequently Asked Questions
🟧 Is NFPA Mandatory?
No, not on their own the NFPA Codes are not mandatory, but they do become mandatory once adopted and referenced/enforced by governmental organizations such as OSHA and local authorities.
For your own project needs, you would need to understand the local requirements where your projects/works are located.
🟧 How do you Bypass an Emergency Stop Button?
Although possible to bypass, it is not recommended as it would potentially be in contravention of the Code requirements for the installation.
We would suggest you check with a certified electrical contractor/consultant before carrying out this work.
🟧 Can Emergency Stop Buttons be Covered?
No, based upon the NFPA requirement that the stop button should be continually operable, readily accessible and, able to be initiated via ‘a single human action’, it should not be covered as it will mean it is not readily accessible and would require more than one human action to operate.
🟧 Who Manufacturers E-Stops?
One of the largest manufacturers of standard emergency stop buttons is Schneider Electric – they make a series of products under the Harmony range.