An ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis, operating efficiencies and cost savings, as well as all relevant safety standards, such as those from NFPA, ANSI, RIA, IEC, ISO and OSHA. About J.B. Titus.
Machine Safety: System degradation and incidence of injury
February 17, 2012
Since 2002 when integrated safety automation was introduced for machine safety, a growing awareness has emerged questioning the effectiveness over time of a hardwired / hardware safety system versus an integrated safety system. What is the ultimate effectiveness of a safety-related function comparing the date of commissioning to a date several years later given the two approaches?
I’ve been asked this question many times over the past 10 years causing me to do some research. So far I haven’t been successful in finding comparative data for example on the incidence of injuries for:
1) Newly commissioned hardwired / hardware safety systems performing safety-related functions.
2) Versus, (for example) 10-year-old hardwired / hardware safety systems performing safety-related functions.
Nor have I found any convincing data on the incidence of injuries comparing hardwired versus integrated (software / firmware) safety systems. What I have found via research, multiple interviews, and personal experience is that the answer usually boils down to the eventual safety culture discussion. I believe the ultimate answer lies in the “Mean Time To Fail Dangerous” (MTTFD) comparison of the two approaches. Most everyone agrees that both approaches are arguably equal at date of commissioning (new) in their effectiveness and reliability to perform the intended safety-related function. However, the safety culture issue could be the determinate factor to differentiate their comparative effectiveness and reliability over time. This comparison, in my opinion, is represented in the table below.
Comparing older versus newer machine safety systems
Hardwired / Hardware Safety Systems
Integrated Safety Systems
Inflexible – no software
Flexible via software
Few to none
System provided at HMI
Significant un-planned downtime with high trouble shoot time
Minimal un-planned downtime with low trouble shoot time
Broken / loose cables
60 to 80 percent fewer cables
Levels of access security
Increases over time
Constant over time
This discussion is intended to create some cognitive thinking concerning the question of effectiveness and reliability of the intended safety-related function given the two approaches and the lack of supporting incidence data. Additionally, we have abundant supporting testimonials today that report reduced costs and increased productivity with integrated versus hardwired safety systems. This of course depends on the size, complexity, and number of machines on the plant floor.
As a plant manager, you’re the one responsible individual who can evaluate your safety culture and choose the best alternative approach for machine safety for your business.
Are older hardwired safety systems less safe than newer integrated safety systems? Your comments or suggestion are always welcome so please let us know your thoughts. 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: Machine Safety: System degradation and incidence of injury.
Contact: www.jbtitus.com for “Solutions for Machine Safety”.
For more than 30 years, J.B. Titus has advised a wide range of clients on machine functional safety solutions, including Johnson + Johnson, Siemens, General Motors, Disney, Rockwell Automation, Bridgestone Firestone, and Samsung Heavy Industries. He holds a Bachelor of Business Administration degree from Oklahoma University in industrial management and an MBA from Case Western Reserve University in marketing and finance. He is a professional member of the American Society of Safety Engineers and is OSHA-certified in machine guarding. Titus is also TUV-certified as a Functional Safety Expert and serves on several American National Standards Institute, National Fire Protection Association, and National Electrical Manufacturers Association national safety and health standards committees. Reach him at jb(at)jbtitus.com and via www.jbtitus.com.