When Do You Apply Machine Guarding Standards in Process Plant?

I am currently in Perth Australia at the IDC Technologies Safety Control Systems conference. As usual with this forum the presentations are good and the question and answer between presentations is even better. Here on the second day of the conference there is a lot of discussion of machine safeguarding standards, analysis techniques, and design practices. Machine guarding standards are currently significantly different from the IEC 61511 style performances based analysis used for safety instrumented functions in the process industry. The machine guarding standards are a lot more prescriptive as to design and stay away from quantitative analysis of risk and reliability. The machine standards are actually quite good as they are. There is currently a push to move toward an IEC 61508 style analysis, as defined in IEC62061, but the end user community is really not much interested, and I personally think the push will fail.

There are quite a few process industry users in the audience here, and it may seem at first look that machine safeguarding standards do not apply to the process industries, but that is not true. Very frequently, the process industries use machines and those machines should be safeguarded using the machine safeguarding standards, not the process functional safety standards.

Let me give you an example. A typical polypropylene plant uses propylene as a raw materials, polymerizes it in a reaction, and then processes the polymer powder that is created. The polymer processing often includes extrusion and the creation of polymer pellets. While most of the interlocks are process related and designed in accordance with the IEC 61511 / ISA 84.01 standard, one is clearly a machine safeguard that should not. The extruded typically has an interlock that will de-energize a motor that turns a cutting blade if the hood of the device is removed to prevent personnel from being exposed to the cutting blade. This is a machine safeguard, and it should be designed according to the appropriate standard, which in the US is the ANSI B11 series, not IEC 61511 / ISA 84.01.