Machine Safety: Which safety circuit design is required?

When considering safety circuit designs and compliance requirements, look at B level versus C level safety standards and their approval dates. See levels of machine safety standards graphic.

07/04/2014


Machine safety standards are in levels: A) Basic safety standards apply to industry, B) Group safety standards apply to a defined group or type of machinery, and C) Specialists standards apply to one specific kind of machine, such as mechanical stamping,First of all, is everyone familiar with “B” level and “C” level machine safety standards? Secondly, is everyone familiar with the importance of approval dates of safety standards, particularly when contrasting called out compliance requirements?

Machine safety standards: 3 levels

Let’s begin by looking at the graphic showing example machine safety standards in their respective A, B, and C levels: 

A. Basic safety standards apply to industry.

B. Group safety standards apply to a defined group or type of machinery.

C. Specialists standards apply to one specific kind of machine, such as mechanical stamping, injection molding, converting, etc. 

By looking at the example standards per level, it is easy to understand what is meant by a “B” level versus a “C” level machine safety standard. 

Referenced dates matter

Additionally, when a standard is published, it is also designated via the date it was reviewed and approved. Internal to this process, a standard’s working committee will usually review all content within a standard and either update or not update any specific requirement or miscellaneous information. This can include any normative or informative other referenced standards. These other standards may or may not include a specifically dated version. 

For example, the current NFPA 79 edition is dated 2012. During the update cycle we considered whether to update the Annex J Informational References for ISO 13849-1, 1990 to the more current 2006 edition. The working committee considered this change and voted to keep the 1990 edition reference for ISO 13849-1. This vote was significant because the 2006 edition would have brought into play the newer approach for the SRP/CS (Safety Related Parts of the Control System)—specifically, things like functional safety, performance levels, mean time to fail dangerous, diagnostics coverage, B10 values, and more. This is a major change.

Quite often, when a “B” level standard makes a significant change (like NFPA 79, 2002 adopting safety PLC technology), “C” level standards may or may not be reconciled and/or in sync regarding how safety circuits “shall” be designed. So, the question is asked: Which safety circuit design is required? I understand that in Europe under the Machinery Directive only current editions of standards are “listed” as required for compliance. In the U.S. OSHA is the law and consensus standards are an additional level of compliance requirements. Therefore, and in my experience, most “best-in-class” companies in the U.S. default to a current safety circuit design regardless of “B” versus “C” level standards. How has this question been answered in your experiences?

Add your comments, thoughts, questions, or suggestions about level of machine standards or related topics by submitting your observations, ideas, experiences, and challenges in the comments section below.

www.controleng.com/blogs under Machine Safety has related machine safety explanations. See specific links below.

Related articles:

Machine Safety: what is the value of ISO 13849-1 for U.S. domestic compliance?

How to use ISO functional safety standards

Machine safety standard merger: One global machine safety standard

Machine Safety: Domestic U.S. versus international standards

EHS Today: The Buzz About ISO 13849-1: The Good, the Bad and the Ugly (and a Possible Alternate Solution) by Mike Carlson

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



No comments
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.
The Engineering Leaders Under 40 program identifies and gives recognition to young engineers who...
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.
Save energy with automation; Process control system upgrades; Dispelling controll myths; Time-sensitive networking; Control system integration; Road to IANA
Additive manufacturing advancements; Machine vision enhances robotics; Fieldbus evolution; Process safety; Advice from System Integrators of the Year; Road to IANA
Salary and career survey: Benchmarks and advice; Designing controls; Remote data collection, historians; Control valve advances; Hannover Messe; Control Engineering International
This article collection contains several articles on the Industrial Internet of Things (IIoT) and how it is transforming manufacturing.

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

The digital oilfield: Utilizing Big Data can yield big savings; Virtualization a real solution; Tracking SIS performance
Getting to the bottom of subsea repairs: Older pipelines need more attention, and operators need a repair strategy; OTC preview; Offshore production difficult - and crucial
Digital oilfields: Integrated HMI/SCADA systems enable smarter data acquisition; Real-world impact of simulation; Electric actuator technology prospers in production fields
click me