Understanding machine safety analysis in the U.S. (Part 1)
A few years ago, I was working with an internal integration group for a manufacturing company which had facilities in many domestic and international locations. One of the initiatives I had undertaken was to redevelop procedures for assessing safety hazards on automated equipment.
The existing procedures were based on the aging, but still used, European Standard EN-954. This system of analysis employed a fairly solid hazard analysis, but became extremely rigid in solutions for risk mitigation. This method of risk analysis and mitigation lays out a method of quantifying risk to personnel according to injury, occurrence, and predictability. Once a category level was determined, that category had inflexible minimum requirements for redundancy, monitoring, and safety device design, which defined the necessary control systems mechanically and electrically.
With the planned adoption of the International Standards Organization document ISO:13849-1:2006, the older EN-954 standard was slated for retraction by the European Standards Organization. Anticipating this retraction, we needed to take another look at our own risk analysis and mitigation procedures in order to maintain compliance within the European markets. Moreover, since this updated procedure was to be employed domestically as well, our research grew into an in-depth investigation into the interaction between OSHA, ANSI, and ISO.
Keep in mind that this discussion is my personal interpretation on the relationships and workings of OSHA requirements, along with ANSI and ISO as related to risk analysis and mitigation on automated manufacturing equipment. These interpretations are not published by my current or previous employers as fully authoritative, but are guidelines and should be evaluated before implementing in product development.
To date, OSHA provides no specific direction on how risk is to be assessed, or how risk mitigation is to be implemented in manufacturing environments. However, finding links to organizations to which OSHA defers for standards development and maintenance helps us identify and select methods supported by OSHA. By relying on these organizations, their documentation and associations, we can build a case for identifying which methods we believe will hold the most sway.
In 1991, a memorandum of understanding was published between ANSI and OSHA, where ANSI agrees to “furnish assistance and support, and continue to encourage the development of national consensus standards for occupational safety or health issues for the use of OSHA and others.” (OSHA, 1991) By this understanding between organizations, OSHA establishes ANSI as an authority on health and safety within the operations of OSHA.
Additionally, OSHA calls out several references to the ANSI B11 series of standards, among others, in their standards for machine guarding, OSHA 3170-02N-2007 (OSHA, 2007). This series is titled Machine Tools Safety and refers to several modes of mechanical machining found in manufacturing today (ANSI, 2012). Attached to this series as a technical report are two documents concerning the evaluation of risk: B11.TR3-2000 and ISO/TR 23849:2010. The first of these documents was an early approach to assessing machine safety, but had little direction beyond the assessment. The second provides guidance on applying ISO 13849-1:2006 and IEC 62061 in the design of safety-related control systems on machinery (ANSI, 2010). While neither B11.TR2-2000, nor ISO/TR 23849:2010 are standards, as technical reports they are intended to provide direction on best practices.
The only other risk analysis and mitigation process for industrial machines in the ANSI library is the one found in the ANSI/RIA r15.06:1999, titled Industrial Robots and Robot Systems – Safety Requirements. This standard was developed by the Robotic Industries Association, a participant in ANSI, for the development of standards related to industrial robots. This standard does not provide a risk/hazard analysis as part of the standard, but is provided in the appendix as reference material. This risk/hazard analysis is very similar to the one found in ISO 13849-1:2006. The mitigation section is not as flexible as ISO 13849-1:2006, but it does not need to be as it was developed with a focus on a specific sector of industrial automation.
Next week: Where does all this take us?
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.