Understanding machine safety analysis in the U.S. (Part 2)
This trail of breadcrumbs has led us back to ISO 13849-1:2006, Safety of Machinery – Safety-Related Parts of Control Systems. This new standard is the basis for the PL and B10d ratings you see on many safety devices today. The ratings are ranked “a” through “e” in increasing risk to the operator, with “e” being the greatest risk. Within this standard, the EN-954 categories for circuit types survive, but are only part of the implementation. More common-sense approaches are allowed, taking into account variables such as mean time to dangerous failure (MTTFd) for devices, monitoring devices for failure, circuit types (cat.1-4), and even those hazards which cannot be guarded without impeding the work to be done (such as PPE, signage, training, etc.). All of these are on the table if the situation supports them. ISO 13849-1:2006 was developed with the support of ANSI, as this organization supplied representative engineers to help with development of this standard. ANSI is a contributing member of ISO standards development and adoption boards.
All indications point to ISO 13849-1 being adopted in the U.S. in the future, but nothing is official thus far. Many companies are now employing some form of risk/hazard analysis as part of their documentation and development procedures. While this is not a requirement in the U.S., several arguments support adopting such a standardized procedure:
1. Reduced cost—By properly applying a standard such as the one provided by ISO, safety methodologies with appropriate performance criteria can be selected. This avoids overly complex systems in areas where they are not needed, while ensuring a proper level of protection for operators.
2. Defensibility—This is one of the more difficult to discuss, but it bears mentioning. Should it occur that someone is injured by manufacturing equipment in a facility, it would behoove the company(s) and engineers involved to have fully documented the process by which the hazards were identified, quantified, and mitigated. This is the best proof that all reasonably foreseeable hazards and the risks they posed were considered and safeguarded to the best abilities of those involved. Without a documented methodology, each entity involved in the development, construction, and implementation of the equipment leaves itself open to scrutiny in the investigation of personnel injury.
3. Productivity improvement—Where these systems are employed, an improvement in productivity is almost universally reported. The ISO standard does call for input from various sources in the assessment of hazards and their mitigation. These sources come from all levels of interaction on the machine: from operators and supervisors in production, through engineering and purchasing. This creates an environment where the operators and supervisors have a level of buy-in of the final solution through their contribution to its inception. Additionally, their involvement adds to an increased feeling of worth and safety in their work environment. This contributes to a reduction in stress, accidents, and injuries. These reductions lend themselves to improved productivity in the work place.
4. Standardization—The final argument I pose for such safety systems is that of standardization. Standardization in the approach to safety systems allows for a more standardized set of solutions for a production line. Using common documentation, components, and techniques across a production facility allows operators to cross train more easily on equipment, and creates greater flexibility in a production facility. This also shortens the learning curve for maintenance and often reduces the number of replacement parts required to be on hand to maintain production in a facility.
While I have called out ISO 13849-1:2006 as my procedure of choice, it is not the only option out there. I have also mentioned B11-TR3 from ANSI as the procedure from ANSI/RIA, found in r15.06. If you are not currently using a standardized approach to your safety systems, I highly recommend investigating an appropriate solution as your company will see the gains in the near future.
ANSI. (2012). ANSI B11. Machine Tools Safety Package. Retrieved from American National Standards Institute: http://webstore.ansi.org/RecordDetail.aspx?sku=ANSI+B11.+Machine+Tools+Safety+Package#.ULktmYOTqpA
ANSI. (2010). ISO/TR 23849:2010. Retrieved from American National Standards Institute: http://webstore.ansi.org/RecordDetail.aspx?sku=ISO%2fTR+23849%3a2010#.ULkvQ4OTqpA
OSHA. (1991, 5 21). Cooperation between OSHA and ANSI. Retrieved from United States Department of Labor: http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=MOU&p_id=239
OSHA. (2007). Safeguarding Equipment and Protecting Employees from Amputations. Retrieved from United States Department of Labor: http://www.osha.gov/Publications/OSHA3170/3170-02R-2007-English.html
This post was written by Karl Schrader. Karl is a senior engineer at MAVERICK Technologies, a leading system integrator providing industrial automation, operational support, and control systems engineering services in the manufacturing and process industries. MAVERICK delivers expertise and consulting in a wide variety of areas including industrial automation controls, distributed control systems, manufacturing execution systems, operational strategy, and business process optimization. The company provides a full range of automation and controls services – ranging from PID controller tuning and HMI programming to serving as a main automation contractor. Additionally MAVERICK offers industrial and technical staffing services, placing on-site automation, instrumentation and controls engineers.