E-Stops Aren’t Safety Devices

While safety experts say machine safety e-stops are not safety devices, folks in industry pretty much all seem to think e-stops are safety devices because of their function. Ask yourself these three questions.

11/30/2010


Jokab Safety giant E-Stop at Pack Expo 2010; photo by Mark T. Hoske, CFE MediaMachine safety e-stops are not safety devices! That’s at least what the safety experts all say and what the machine safety standards say. However, the folks in industry pretty much all seem to think e-stops are safety devices because of their function.

1. Are you confusing stopping categories and risk categories?

2. Do you wire your e-stops to a standard (non Safety) PLC or controller in order to comply with the mandatory category 0 or 1 stop?

3. And, does your identified hazard require redundant circuits with continuous self checking and automatic diagnostics?

Think twice is my advice! Yes, safety standards such as NFPA 79, clause 9.2.5.4.1.3 requires that an e-stop "shall function as either Category 0 or a Category 1 stop" as determined by the risk assessment. These are stopping functions with categories as defined by NFPA 79, clause 9.2.2. This requirement does not define that e-stops are safety devices!

Furthermore, your required risk analysis may require mitigation of a risk or hazard identified as Cat. 3 or 4. These are categories of risk. If you're wiring direct to a standard PLC your e-stop may only be at best achieving Cat. 2 or less so my advice is to check your risk analysis thoroughly. Then, double check your physical application, design, and the safety ratings on all components including sensors, logic, and actuators. In short, make sure the entire circuit is completely compliant to the level of hazard (Category) and the level of stopping function with its associated category as determined by the risk assessment.

Yes, it’s true that one of the functions of an e-stop could be safety related and therefore a safety function. However, a safety device will always be a safety device and will only be a safety device and will only be intended to accomplish a safety function.   

In my opinion - to be compliant - don’t confuse hazard Categories with stopping functions/categories!

Submit your ideas, experiences, and challenges on this subject in the comments section below. Click on the following text if you don't see a comments box, then scroll down: E-Stops Aren’t Safety Devices.

J.B. TitusRelated articles:

How To Integrate Safety

Machine safety pays off

Contact: www.jbtitus.com for “Solutions for Machine Safety”.



The Engineers' Choice Awards highlight some of the best new control, instrumentation and automation products as chosen by...
The System Integrator Giants program lists the top 100 system integrators among companies listed in CFE Media's Global System Integrator Database.
Each year, a panel of Control Engineering and Plant Engineering editors and industry expert judges select the System Integrator of the Year Award winners in three categories.
This eGuide illustrates solutions, applications and benefits of machine vision systems.
Learn how to increase device reliability in harsh environments and decrease unplanned system downtime.
This eGuide contains a series of articles and videos that considers theoretical and practical; immediate needs and a look into the future.
Robotic integration and cloud connections; SCADA and cybersecurity; Motor efficiency standards; Open- and closed-loop control; Augmented reality
Controller programming; Safety networks; Enclosure design; Power quality; Safety integrity levels; Increasing process efficiency
Additive manufacturing benefits; HMI and sensor tips; System integrator advice; Innovations from the industry
Featured articles highlight technologies that enable the Industrial Internet of Things, IIoT-related products and strategies to get data more easily to the user.
This article collection contains several articles on how automation and controls are helping human-machine interface (HMI) hardware and software advance.
This digital report will explore several aspects of how IIoT will transform manufacturing in the coming years.

Find and connect with the most suitable service provider for your unique application. Start searching the Global System Integrator Database Now!

Cloud, mobility, and remote operations; SCADA and contextual mobility; Custom UPS empowering a secure pipeline
Infrastructure for natural gas expansion; Artificial lift methods; Disruptive technology and fugitive gas emissions
Mobility as the means to offshore innovation; Preventing another Deepwater Horizon; ROVs as subsea robots; SCADA and the radio spectrum
Automation Engineer; Wood Group
System Integrator; Cross Integrated Systems Group
Jose S. Vasquez, Jr.
Fire & Life Safety Engineer; Technip USA Inc.
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.
click me