Machinery Safety 101 » CSA Z432

The Third Level of the Hierarchy: Information for Use

Doug Nix — Mon, 16 Jan 2012 21:06:56 +0000

I’ve written about the Hierarchy of Controls in past posts, but I’ve focused on the ‘engineering’ side of the control equation: Physical changes to machine design to eliminate hazards, and mechanical or electrical control systems that can reduce risk. The …

Interlock Architectures Pt. 6 — Comparing North American and International Systems

Doug Nix — Mon, 03 Oct 2011 12:30:09 +0000

I’ve now written six posts, including this one, on the topic of circuit architectures for the safety–related parts of control systems. In this post, we’ll compare the International and North American systems. This comparison is not intended to draw conclusions …

Interlock Architectures – Pt. 5: Category 4 — Control Reliable

Doug Nix — Mon, 26 Sep 2011 12:30:41 +0000

The most reliable of the five system architectures, Category 4 is the only architecture that uses multiple-fault tolerant techniques to help ensure that component failures do not result in an unacceptable exposure to risk. This post will delve into the …

Interlock Architectures – Pt. 4: Category 3 — Control Reliable

Doug Nix — Mon, 19 Sep 2011 12:30:13 +0000

Category 3 system architecture is the first category that could be considered to have similarity to “Control Reliable” circuits or systems as defined in the North American standards. It is not the same as Control Reliable, but we’ll get to …

Understanding Risk Assessment

Doug Nix — Mon, 31 Jan 2011 13:30:25 +0000

When people discuss ‘Risk’ there are a lot of different assumptions made about what that means. For me, the study of risk and risk assessment techniques started in 1995. As a technologist and controls designer, I had to somehow wrap …

Emergency Stop Categories

Doug Nix — Mon, 27 Sep 2010 12:30:49 +0000

I’ve noticed a lot of people looking for information on Emergency Stop categories recently, so this post is aimed at those readers who want to understand this topic in more depth. Categories The first point to make is that these …

Interlock Architectures – Pt. 3: Category 2

Doug Nix — Tue, 24 Aug 2010 13:23:15 +0000

This article explores the requirements for safety related control systems meeting ISO 13849-1 Category 2 requirements. "Gotcha!" points in the definition are highlighted to help designers avoid this common pitfalls.

Interlock Architectures – Pt. 2: Category 1

Doug Nix — Wed, 28 Jul 2010 12:30:20 +0000

This article expands on the first in the series "Interlock Architectures – Pt. 1: What do those categories really mean?". Learn about the basic circuit architectures that underlie all safety interlock systems under ISO 13849-1, and CSA Z432 and ANSI RIA R15.06.

Interlocked gate testing

Doug Nix — Sun, 18 Jul 2010 00:33:21 +0000

Did you know that interlocked gates require stopping performance testing? Machinery needs to be able to stop in the time it takes a person to open the guard and reach the hazard. If the distance from the guard opening to the hazard is short enough that a person can reach the danger point before the hazard can be controlled, the guard is useless. The resulting situation may be worse

Emergency Stop — What’s so confusing about that?

Doug Nix — Fri, 06 Mar 2009 14:00:54 +0000

I get a lot of calls and emails asking about emergency stops. This is one of those deceptively simple concepts that has managed to get very complicated over time. Not every machine needs or can benefit from an emergency stop. In some cases, it may lead to an unreasonable expectation of safety from the user, which can lead to injury if they don't understand the hazards involved. Some product-specific standards